Do we want to talk about propellers?
Do we want to talk about propellers?
Hi CTSMBC.
You must excuse me if I couldn't understand everything completely, due to the translation, my fault.
I'm glad you agree with my method on how to attach the propellers.
It was just a suggestion to help those who have never done it and have no other ideas, but there are equally valid methods.
For the moment, after reading all the opinions, my method still convinces me (at least for a certain type of RC models).
As regards propellers in general, a lot has been written in this and other topics, so I understand that not everyone wants to read everything, maybe some messages are skipped.
However, precisely on the propellers I wrote, among other things, that the best method is to do some tests.
I don't disdain calculations in general, but in this case I didn't do any.
I did them when I talked about the immersed volume but that was another matter.
However, I believe that before doing any tests, it is better to have a minimum of basic knowledge about propellers and start from the clearest ideas possible. This was the purpose of this and my other three threads on the subject.
In the last part of your message, I really appreciate your resourcefulness, but I have a completely different philosophy. If I understand correctly, to solve the problem you replaced the double propeller system with a single propeller.
If you have achieved your goal, good for you, but I prefer to solve the problem respecting the original plan.
You must excuse me if I couldn't understand everything completely, due to the translation, my fault.
I'm glad you agree with my method on how to attach the propellers.
It was just a suggestion to help those who have never done it and have no other ideas, but there are equally valid methods.
For the moment, after reading all the opinions, my method still convinces me (at least for a certain type of RC models).
As regards propellers in general, a lot has been written in this and other topics, so I understand that not everyone wants to read everything, maybe some messages are skipped.
However, precisely on the propellers I wrote, among other things, that the best method is to do some tests.
I don't disdain calculations in general, but in this case I didn't do any.
I did them when I talked about the immersed volume but that was another matter.
However, I believe that before doing any tests, it is better to have a minimum of basic knowledge about propellers and start from the clearest ideas possible. This was the purpose of this and my other three threads on the subject.
In the last part of your message, I really appreciate your resourcefulness, but I have a completely different philosophy. If I understand correctly, to solve the problem you replaced the double propeller system with a single propeller.
If you have achieved your goal, good for you, but I prefer to solve the problem respecting the original plan.
Do we want to talk about propellers?
After scrolling all the way back to the original post to find the answer, I realised...YES. All the comments following the questions tells me we want to talk about propellers. But there's another thread on the topic that I'm following.
One thing I do agree with is ASPQR's method of fixing the propellers. While I normally buy the whole drive set from Raboesch, some models I picked up is what I call "butcher built". It's a scratch built where you scratch in dustbins for items you can butcher and use as parts.
I have a Chriscraft that was butcher built. It has 3mm shafts and props with 4mm holes. Now one prop lost a blade in the shallows and I have to replace it. The shaft is smooth ended. It cannot be removed without removing the motor first. And, it has to be counter rotating which means I need to find the exact prop in with the exact same pitch in a CW configuration to match the CCW one that is still in tact.
The solution?
Total rebuilt.
Cheapest option - convert from twin to single
One thing I do agree with is ASPQR's method of fixing the propellers. While I normally buy the whole drive set from Raboesch, some models I picked up is what I call "butcher built". It's a scratch built where you scratch in dustbins for items you can butcher and use as parts.
I have a Chriscraft that was butcher built. It has 3mm shafts and props with 4mm holes. Now one prop lost a blade in the shallows and I have to replace it. The shaft is smooth ended. It cannot be removed without removing the motor first. And, it has to be counter rotating which means I need to find the exact prop in with the exact same pitch in a CW configuration to match the CCW one that is still in tact.
The solution?
Total rebuilt.
Cheapest option - convert from twin to single
Rudy
Do we want to talk about propellers?
Hi Mike, I totally agree with you.
I had already written it in the thirty-first message and in the fortieth message regarding Boatshed and Len's practical tests.
Practice tests are the best thing to do.
With my latest model I did not test various propellers.
I did some evaluations, chose one and pinned it. The tests went well and the result is what I expected.
But if I were to build a motorboat or if I were to give advice I would prefer to follow your method, also because trying different propellers is fun. Your propeller tests and experience may be useful to other modelers.
Your Sylvie is inserted in the following link.
This means that anyone who wants to build a model that is the same or very similar to yours could avoid (if they don't want to) buy a lot of propellers to do the necessary tests.
Looking at your model it already has a very valid starting point.
https://model-boats.com/forum/135991
I had already written it in the thirty-first message and in the fortieth message regarding Boatshed and Len's practical tests.
Practice tests are the best thing to do.
With my latest model I did not test various propellers.
I did some evaluations, chose one and pinned it. The tests went well and the result is what I expected.
But if I were to build a motorboat or if I were to give advice I would prefer to follow your method, also because trying different propellers is fun. Your propeller tests and experience may be useful to other modelers.
Your Sylvie is inserted in the following link.
This means that anyone who wants to build a model that is the same or very similar to yours could avoid (if they don't want to) buy a lot of propellers to do the necessary tests.
Looking at your model it already has a very valid starting point.
https://model-boats.com/forum/135991
Do we want to talk about propellers?
Hello all!
When I read everything like this, the propeller problem really is a closed book!
For me, it's important that the speed and the wave pattern match the model.
I had this problem with the "Sylvie" (ex lotse), but solved it after several attempts with different types of propeller.
Patience, test and test again . . eventually it's right!
Bb Michel-C.
When I read everything like this, the propeller problem really is a closed book!
For me, it's important that the speed and the wave pattern match the model.
I had this problem with the "Sylvie" (ex lotse), but solved it after several attempts with different types of propeller.
Patience, test and test again . . eventually it's right!
Bb Michel-C.
if you don't ask, you won't get an answer!
Do we want to talk about propellers?
I thought that on this topic other impressions, information, anecdotes and problems relating to the world of propellers could be collected but to summarize data that can be useful to everyone it would be better to create a new topic.
In fact, in my opinion, searching for the message of interest among hundreds is very difficult and one can easily give up.
In fact, in my opinion, searching for the message of interest among hundreds is very difficult and one can easily give up.
Liked by Wolle and Mike Stoney and
Do we want to talk about propellers?
using thread lock is a good idea but just be careful on the type you use. They come is various strength from mild that you can easily break the joint all the way up to high strength which is almost impossible to break the joint without damaging the joined parts. There are also other products like vibra-tite but are usually used on threads that are 1/4inch or larger and I have not used them on smaller sizes so I do not know how well they will work.Len
LEN1
Liked by Mike Stoney and GaryLC and
Do we want to talk about propellers?
Hi Wolle,
That's the method that I use when experimenting with different size propellors. Once I have the one I want I then use just a dab of thread lock and tighten the two nuts together.
I have never had a problem if I have ever wanted to remove a propellor at a later date even when using the thread lock. But then I hasten to add I just use a dab just enough to secure not a lot of the stuff.
That's the method that I use when experimenting with different size propellors. Once I have the one I want I then use just a dab of thread lock and tighten the two nuts together.
I have never had a problem if I have ever wanted to remove a propellor at a later date even when using the thread lock. But then I hasten to add I just use a dab just enough to secure not a lot of the stuff.
BOATSHED
Liked by Mike Stoney and Colin H and
Do we want to talk about propellers?
another problem with just using a locknut if you go from full forward to full reverse this puts a tremendous load on the nut and can cause it to loosen if there is not something to prevent the nut from turning. You can install a small set screw (grub screw) into the side of the nut, use a low strength locktite than can be loosened, use a cotter pin thru the nut as Alessandro mentioned, use a double nut.
I prefer not to use lock nuts because the way they look and too easy for them to loosen. I like to secure the prop to the shaft by installing a set screw into a tapped hole in the side of the prop and create a flat along the prop shaft. The flat serves a number of purpose such as preventing the prop from spinning. keeps the set screw for scoring the shaft and making removing the prop very difficult and also allows you to reposition the prop in and out along the shaft Len
I prefer not to use lock nuts because the way they look and too easy for them to loosen. I like to secure the prop to the shaft by installing a set screw into a tapped hole in the side of the prop and create a flat along the prop shaft. The flat serves a number of purpose such as preventing the prop from spinning. keeps the set screw for scoring the shaft and making removing the prop very difficult and also allows you to reposition the prop in and out along the shaft Len
LEN1
Liked by Mike Stoney and RodC and
Do we want to talk about propellers?
Hello, you can also screw a nut onto the shaft first and then the propeller. Then screw the nut and the propeller onto the shaft against each other (locking).
Liked by Mike Stoney and BOATSHED and
Do we want to talk about propellers?
Hi JockScott.
I know that many use nuts and lock nuts. It's probably a great solution.
I've never used it because it wasn't aesthetically coerent to show the nut.
Others use thread locking glue.
If you think you will never have to replace the propeller it may be a good solution.
I preferred not to, I have a plastic propeller that can break.
I might have to replace it and I don't want to go crazy undoing the threads.
I'll tell you the method I used.
First choose the direction of the propeller so that when moving forward it tends to tighten (and not loosen).
In this way, when moving backwards, the propeller will tend to slip out, but you will almost always go forward.
It is not enough.
I also insert a cotter pin.
This I make a hole with a small drill bit and go through the propeller pin and shaft crosswise.
I insert a metal or alloy thread (brass or steel for example).
The cotter pin will hold simply by bending the ends.
Be careful, the hole must not be wider than the cotter pin otherwise the cotter pin (especially if made of steel) will start to cut by dancing in the hole.
I know that many use nuts and lock nuts. It's probably a great solution.
I've never used it because it wasn't aesthetically coerent to show the nut.
Others use thread locking glue.
If you think you will never have to replace the propeller it may be a good solution.
I preferred not to, I have a plastic propeller that can break.
I might have to replace it and I don't want to go crazy undoing the threads.
I'll tell you the method I used.
First choose the direction of the propeller so that when moving forward it tends to tighten (and not loosen).
In this way, when moving backwards, the propeller will tend to slip out, but you will almost always go forward.
It is not enough.
I also insert a cotter pin.
This I make a hole with a small drill bit and go through the propeller pin and shaft crosswise.
I insert a metal or alloy thread (brass or steel for example).
The cotter pin will hold simply by bending the ends.
Be careful, the hole must not be wider than the cotter pin otherwise the cotter pin (especially if made of steel) will start to cut by dancing in the hole.
Do we want to talk about propellers?
How are propellers secured to the shaft? Is it sufficient to tighten it against the nut the shaft came with or, to be sure, does it require other means? I noticed the suggestion to invest in cheap propellers when experimenting....🤔
Do we want to talk about propellers?
Good evening everyone.
Scattered thoughts on the subject.
ChrisF's latest post is interesting and especially his rule of thumb: "the diameter of the propeller must not exceed the diameter of the brush motor if there are no reductions".
Out of curiosity I checked and in my case I always respected this rule.
I would like to include in the next post a summary (updatable) of all your suggestions and links to manufacturers of propellers for ship modeling.
I would also like to include a summary of the proportions between the dimensions of the ship (length and weight) and the characteristics of the propeller.
Most likely, if you do not use an excessively small or excessively large propeller, the model will still sail if it is not a high-speed motorboat.
The latter have more problems and not just propellers; I've seen many people try these cars and walk away angry and disappointed because they couldn't make them navigate at speed, they couldn't make them take turns, they couldn't make them travel a minimum distance without them tipping over.
I forgot that model propellers, unlike real ones, must have the very important indication of the thread.
Scattered thoughts on the subject.
ChrisF's latest post is interesting and especially his rule of thumb: "the diameter of the propeller must not exceed the diameter of the brush motor if there are no reductions".
Out of curiosity I checked and in my case I always respected this rule.
I would like to include in the next post a summary (updatable) of all your suggestions and links to manufacturers of propellers for ship modeling.
I would also like to include a summary of the proportions between the dimensions of the ship (length and weight) and the characteristics of the propeller.
Most likely, if you do not use an excessively small or excessively large propeller, the model will still sail if it is not a high-speed motorboat.
The latter have more problems and not just propellers; I've seen many people try these cars and walk away angry and disappointed because they couldn't make them navigate at speed, they couldn't make them take turns, they couldn't make them travel a minimum distance without them tipping over.
I forgot that model propellers, unlike real ones, must have the very important indication of the thread.
Do we want to talk about propellers?
Obviously prop sizing will be discussed in greater detail as we progress through the subject but I think it worth mentioning at this stage for those with less experience in sizing of props (I include myself in that as only got into the hobby around 7 years ago) that an important consideration is the type and size of motor being used which in turn is dependent on the type, size and weight of model - as mentioned earlier with regard to props, the motor type and size options can usually be obtained from other modellers who have built the same model, from the kit instructions or the plans. For brushed motors there is general information available as well. Less so for brushless.
For brushed motors the rule of thumb/best practice is to have a prop diameter no greater than the diameter of the motor, unless using a reduction system using gears or a belt etc. Brushless can turn bigger props but personally I tend to follow the same rule or maybe a little bigger as I don't use water cooling in my builds and don't want the motor working too hard and getting hot - I tend to oversize my motors anyway.
My RTR (ready to run) plastic raceboats with brushed and brushless motors are a different matter and are water cooled as they are running at constant high speeds.
It is important at an early stage to have a good idea of what motor and hence prop is going to be used so that if using a traditional prop shaft it can be positioned so that there is sufficient clearance between the largest prop that might be used and the hull and for mounting the motor.
Chris
For brushed motors the rule of thumb/best practice is to have a prop diameter no greater than the diameter of the motor, unless using a reduction system using gears or a belt etc. Brushless can turn bigger props but personally I tend to follow the same rule or maybe a little bigger as I don't use water cooling in my builds and don't want the motor working too hard and getting hot - I tend to oversize my motors anyway.
My RTR (ready to run) plastic raceboats with brushed and brushless motors are a different matter and are water cooled as they are running at constant high speeds.
It is important at an early stage to have a good idea of what motor and hence prop is going to be used so that if using a traditional prop shaft it can be positioned so that there is sufficient clearance between the largest prop that might be used and the hull and for mounting the motor.
Chris
Scratch building 7 Faireys at a scale of 1:12
Do we want to talk about propellers?
Boatshed thanks for the info based on your experience. It is a good staring point. Len
LEN1
Liked by Wolle and AlessandroSPQR
Do we want to talk about propellers?
Hi Len1, Ideally you would be buying the cheaper ones off of Ebay, ie plastic, nylon and experiment with them.
The 18" & 21" possibly from 25mm up and the 42" 35 to 40mm up.
That is only going from the models that I have run. But you might get better information to come from others.
Yes brass gets expensive when it comes to testing.
But I don't know what the situation for thing fro Ebay or other dealers are over in the USA.
Good luck in testing. I found it fun.
The 18" & 21" possibly from 25mm up and the 42" 35 to 40mm up.
That is only going from the models that I have run. But you might get better information to come from others.
Yes brass gets expensive when it comes to testing.
But I don't know what the situation for thing fro Ebay or other dealers are over in the USA.
Good luck in testing. I found it fun.
BOATSHED
Do we want to talk about propellers?
Hi Len.
Thank you for your intervention, I assure you that I will follow your constructions with great interest but above all the experiments with propellers.
I have already learned a lot by listening to the testimonies and following the links of the modelers who have intervened in this forum and I am already very satisfied but I am sure that there is still a lot of information to be discovered.
I hope that everyone can tell me what type of propeller they have installed (diameter, number of blades and, if they know it, the pitch) in relation to their boat (indicating length and displacement), perhaps attaching two photos.
But you will even do some tests.
I really like this approach.
Great.
It's what I would like to do but for now I don't have the time.
Thank you for your intervention, I assure you that I will follow your constructions with great interest but above all the experiments with propellers.
I have already learned a lot by listening to the testimonies and following the links of the modelers who have intervened in this forum and I am already very satisfied but I am sure that there is still a lot of information to be discovered.
I hope that everyone can tell me what type of propeller they have installed (diameter, number of blades and, if they know it, the pitch) in relation to their boat (indicating length and displacement), perhaps attaching two photos.
But you will even do some tests.
I really like this approach.
Great.
It's what I would like to do but for now I don't have the time.
Do we want to talk about propellers?
Alessandro I was asking about the source for model ship propellers. Since I am not sure what I need I was looking for sources of propellers so I could get an assortment with different number of blades, diameters and pitches for some boats I am building. I was thinking about inexpensive plastic ones to experiment with and when I find out witch one work the best for me I will than get brass ones. I have the following boats that I will be experimenting on, 42 inch harbor tug, a 21 inch lobster boat and a 18 inch springer tug.
I will look into the 2 sources as suggested by Chris and Lew.
Len
I will look into the 2 sources as suggested by Chris and Lew.
Len
LEN1
Do we want to talk about propellers?
Hello, I buy my ship propellers from “Modellbau-Kaufhaus”. Here is the link. They're not cheap, but they're great quality and look good. By the way, there is everything possible for building model ships.
https://shop.modellbau-kaufhaus.de/schiffsmodellbau/schiffsschrauben
https://shop.modellbau-kaufhaus.de/schiffsmodellbau/schiffsschrauben
Do we want to talk about propellers?
Hi ChrisF.
I saw the "prop shop" site you mentioned.
It's simply exceptional.
I was wrong. I thought it was difficult to find pitch indications on model-type propellers.
Here they also give a precise indication of the pitch as well as the diameter and the type of metal or alloy is well specified. There is a very wide choice in this too. Spectacular!
How lucky I was to have talked to you!
I saw the "prop shop" site you mentioned.
It's simply exceptional.
I was wrong. I thought it was difficult to find pitch indications on model-type propellers.
Here they also give a precise indication of the pitch as well as the diameter and the type of metal or alloy is well specified. There is a very wide choice in this too. Spectacular!
How lucky I was to have talked to you!
Do we want to talk about propellers?
Hi ChrisF.
As soon as I can I will take a look at the site you pointed out to me "Prop Shop", and the one reported by Roy "Deans Marine", thank you very much for this indication.
I will let you know.
I hope you read message 31 of this topic carefully, as soon as you have time and when you feel like it.
Especially the "Pitch" chapter.
Have a nice day.
As soon as I can I will take a look at the site you pointed out to me "Prop Shop", and the one reported by Roy "Deans Marine", thank you very much for this indication.
I will let you know.
I hope you read message 31 of this topic carefully, as soon as you have time and when you feel like it.
Especially the "Pitch" chapter.
Have a nice day.
Do we want to talk about propellers?
Evening Alessandro
I won't say much at the moment as it's getting a bit late but just wanted to say thanks for your detailed continuation of the subject which I will add to when appropriate and also my problem, model boat related that is! 😊
In the meantime have you heard of Prop Shop (formerly Protean Design)? A lot of us in the UK and elsewhere use them and I'm lucky to live not far away so have collected my props etc., which are lovely. No plastic for my Faireys!
If not see www.prop-shop.uk
I'm sure you will find it fascinating as he gives pitches and materials etc!
Chris
I won't say much at the moment as it's getting a bit late but just wanted to say thanks for your detailed continuation of the subject which I will add to when appropriate and also my problem, model boat related that is! 😊
In the meantime have you heard of Prop Shop (formerly Protean Design)? A lot of us in the UK and elsewhere use them and I'm lucky to live not far away so have collected my props etc., which are lovely. No plastic for my Faireys!
If not see www.prop-shop.uk
I'm sure you will find it fascinating as he gives pitches and materials etc!
Chris
Scratch building 7 Faireys at a scale of 1:12
Do we want to talk about propellers?
Hi Roy, I found your post very interesting.
I'm looking for something about Deans Marine and their matches. Maybe I'll ask you for help.
With all the propellers you have, have you managed to find your own generic rule to match the right propeller to the type of ship (based on its length, its displacement, the type of hull and its intended use)?
I'm looking for something about Deans Marine and their matches. Maybe I'll ask you for help.
With all the propellers you have, have you managed to find your own generic rule to match the right propeller to the type of ship (based on its length, its displacement, the type of hull and its intended use)?
Liked by Wolle
Do we want to talk about propellers?
Good evening to all dynamic modelers.
Hi ChrisF.
This time I think you came very close to what I think.
It would perhaps be better to give a general overview and then tackle the ChrisF problem but it could be boring, so I will immediately state my hypothesis on the matter.
What is important is to compare the notions about real propellers with those in modeling use, highlighting the differences above all.
If what I write about real propellers is consistent with your knowledge, we could move on to modeling ones where your experiences will be decisive, such as that of Boatshed on outboard motors.
Boatshed you do the best thing you can do, you bring lots of propellers and you test them directly in the water observing the differences, very good. Unfortunately I couldn't understand everything you wanted to say. My fault.
I'm very happy that ChrisF analyzed the issue of inertia.
His reasoning immediately leads us to address the parameters that distinguish propellers: diameter, pitch, number of blades, construction material, shape of the blades, surface covered by the blades themselves as a percentage of the circle.
I simplify the discussion a lot because I am not up to the level of in-depth technical discussions, which in any case would not serve our purpose very well.
But what is our purpose? Have fun. Have fun even talking about non-vital issues. A wrong propeller will work more often than not.
DIAMETER
The diameter of the propeller is directly related to the thrust it can provide. The larger the propeller, the more intense the thrust will be but the more powerful the engine that drives the propeller must be.
In practice the diameter of the propeller is usually related to the size of the ship or boat (considering the length and displacement, but also, in part, the destination)
This is true for both real ships and scale models.
Every time I say inaccurate things stop me and correct me.
In reality I have been able to see how this is true in real ships.
For example, in Italian warships, Fincantieri produces propellers with increasingly larger diameters as the size of the ship grows.
There are many more steps if you consider all types of propellers, but I will limit myself to these only:
Aircraft Carriers (Actually Aircraft Carrier Cruisers): diameter 6.4 meters [44 MW for each shaft]
Destroyers and frigates: 4.8 meter diameter [22 MW for each shaft]
Corvettes: 3.1 meters [6.5 MW for each shaft]
Patrol vessels: 3 meters [9 MW for each shaft]
Mega Yacht: 2.0 meters to 3.5 meters [3 to 5 MW per shaft]
Coastguard Patrol Vessels: 1 meter [5 MW for each shaft]
I imagine it's roughly the same thing for English ships, although I haven't checked.
Just a curiosity: the diameter of 4.7 meters is that of the propeller of the battleship Bismark which however had three, the diameter of 6.7 meters was that of the propeller of the transatlantic Queen Elisabeth 2 which had two.
The largest propeller in the world that I found is 9.6 meters long and weighs over 130 tons and is from the Danish container ship Emma Maersk. (made by Mecklenburger Metallguss GmbH)
If you find any larger ones, tell me.
Oil tankers have only one propeller and it is relatively small (I repeat "relatively" because it is absolutely enormous) because no significant speed performances or maneuverability are required.
It may have happened to someone (lucky him) that he has to choose the propeller for his motorboat or his pleasure sailing boat.
We should hardly choose the propeller for a cruise ship, transport ship or warship if we are not engineers of that field.
It will happen much more frequently that we have to choose the right diameter for our scale RC model, or (if we rely on a kit or a project) observe and memorize this data.
Or not even that, you don't pay attention to it, you don't care and you don't even understand why we are discussing this, ahahahahahahah.
I noticed that this progression of the propeller diameter based on the size of the ship is also respected for the RC models.
I started to peek into the Harbors of this site to see the relationship between propellers and ship dimensions, unfortunately the diameter parameter is not covered but only the number of blades.
So I hope this information comes from you modelers. At most I'll ask you directly, ahahahahahah. Don't report me as a stalker though.
In the modeling world I have seen that the choice of diameters is quite wide.
I've seen that they start from 12 mm and go up to 130 mm with many intermediate sizes.
In short, the choice is certainly not limited (perhaps you will have found some sites that even exceed these ranges).
THE PITCH
Everyone knows that it is the advance (the distance it travels) that the propeller would make in a complete 360° turn if it were screwed into a solid material. In reality, since the propeller moves in water which is a fluid, the actual advancement will always be less than the pitch. The difference between pitch and advancement is called regress.
What does the pitch actually entail?
It is intuitive that a longer pitch will lead to a greater maximum achievable speed.
This is true as long as the pitch is commensurate and suitable for the other characteristics.
A shorter pitch will be better for standing starts or pushing heavier weights (broadly speaking).
Let's make a comparison with the pace of a person.
If this person walks on level ground he will be able to afford to make a wide pitch and therefore proceed quickly.
If the same person encounters a steep climb he will not be able to make the same wide pitch as before, but he will have to take smaller steps to be able to climb.
Motor boats don't have gears and we could compare (allow me with a bit of elasticity) the pitch to the gears of a car.
Therefore, at speed we can shift into fifth or sixth gear, while when going uphill (or starting from a standstill) we should downshift or shift into first gear.
Well, we can compare the sixth gear of a car to the long pitch of the propeller while the low gears to the short pitch of the propeller.
You will agree with me that starting in first gear, if a car does not shift into second, then into third, fourth and so on its maximum speed will be limited.
So just as in a car that goes in first gear the speed is very limited, even a short pitch propeller will have a more limited maximum speed than a long pitch propeller.
To guarantee good performance in acceleration, starting from a standstill but also good maximum speeds, you need to have propellers with variable pitch (or find a compromise situation).
As proof of this we can consider warships which, having to deal with different speeds and continuous acceleration (even switching the propulsion system), have variable pitch propellers.
Oil tankers do not have this need and have fixed pitch propellers.
For example, the D554 "Caio Duilio" missile fighter (defined within NATO as Destroyer) of the Orizzonte class of the Italian Navy has two five-bladed variable pitch propellers.
Its equivalent in the RN should be the Type 45, such as the D35 Dragon, perhaps some of you can tell me if it has variable pitch blades. I don't know but I bet so.
FREMM frigates also have variable pitch blades.
Boats used for water skiing, having to accelerate immediately, have short pitch propellers.
To return to ChrisF's problem, I think he has a pitch that is too long for acceleration and it is normal for him to not perform well in some moments of the race.
Now let's just analyze the causes, let's leave the possible solutions to another post.
In pleasure boats (especially with outboard engines) the choice of pitch is made based on the number of revolutions (rpm) that the engine makes at full throttle (WOT, wide open throttle).
If, for example, an engine has to make 6000 rpm at a certain power and instead makes 5500 (despite being pushed to the maximum) it means that the pitch must be shortened to recover the 500 rpm because the objective is to release all the power to the engine.
If, on the other hand, the motor turns too much, the pitch must be increased.
Again in relation to the diameter, I noticed that for outboard motors and pleasure boats there is not a very wide range of diameters but many pitches available to choose from.
Ok now let's go back to the modeling field.
In my opinion the effects of a longer or shorter pitch also influence RC models.
To avoid misunderstandings I make a clarification:
The variable pitch propeller (Invented by the Italian engineer Corradino D'Ascanio) is different from the tilting propellers and folding propellers.
The adjustable-blade propeller has blades that can be arranged longitudinally with respect to the motion of the water so as to oppose very little advancement in the case of sail propulsion.
The folding blade propeller folds the blades completely backwards so as to offer very little or no forward resistance in the case of sail propulsion.
Let's not forget that in the nineteenth century, during sailing, the propellers were removed so as not to slow down the ship with their resistance. Incredible but true.
NUMBER OF BLADES
The number of blades actually varies from two to seven.
I have never seen one or eight bladed propellers until now.
I have only seen seven blades on submarine propellers.
The lower the number of blades, the higher the speed but at the expense of stability (higher speed but more vibrations).
Each extra blade offers more friction but offers more grip on the water.
This is important.
In reality, the choice of blades is linked to many factors.
Propellers for outboard engines are mostly three- or four-bladed.
In the modeling field the choice is quite wide but not as wide as in reality.
MATERIALS
In reality, the propellers for small pleasure boats and outboard motors are made of steel or aluminium.
The steel ones are better from every point of view but cost at least three times as much as the aluminum ones (that I know of) but still valid.
In larger propellers, mainly two alloys are used: Nickel Aluminum Bronze alloy NiBrAl, and OTS (brass and manganese).
Manganese brass (ZHMn55-3-1), aluminum-manganese brass (ZHAI67-5-2-2) and manganese-aluminum bronze (ZQAI12-8-3-2) are commonly used in China.
In the world of modeling, propellers are either made of plastic or metal or alloy: brass, steel, aluminium, bronze.
I have two that seemed like lead to me, is it possible in your opinion?
There are many differences between plastic and metal propellers in your opinion, has anyone experienced these differences firsthand?
I'll stop here for the moment.
I've clarified my assumptions for Chris's problem.
I hope that what I have written has not bored you, has been useful for someone and above all stimulates further discussion, because surely someone will have had an experience worth sharing, from which to draw valuable information.
Hi ChrisF.
This time I think you came very close to what I think.
It would perhaps be better to give a general overview and then tackle the ChrisF problem but it could be boring, so I will immediately state my hypothesis on the matter.
What is important is to compare the notions about real propellers with those in modeling use, highlighting the differences above all.
If what I write about real propellers is consistent with your knowledge, we could move on to modeling ones where your experiences will be decisive, such as that of Boatshed on outboard motors.
Boatshed you do the best thing you can do, you bring lots of propellers and you test them directly in the water observing the differences, very good. Unfortunately I couldn't understand everything you wanted to say. My fault.
I'm very happy that ChrisF analyzed the issue of inertia.
His reasoning immediately leads us to address the parameters that distinguish propellers: diameter, pitch, number of blades, construction material, shape of the blades, surface covered by the blades themselves as a percentage of the circle.
I simplify the discussion a lot because I am not up to the level of in-depth technical discussions, which in any case would not serve our purpose very well.
But what is our purpose? Have fun. Have fun even talking about non-vital issues. A wrong propeller will work more often than not.
DIAMETER
The diameter of the propeller is directly related to the thrust it can provide. The larger the propeller, the more intense the thrust will be but the more powerful the engine that drives the propeller must be.
In practice the diameter of the propeller is usually related to the size of the ship or boat (considering the length and displacement, but also, in part, the destination)
This is true for both real ships and scale models.
Every time I say inaccurate things stop me and correct me.
In reality I have been able to see how this is true in real ships.
For example, in Italian warships, Fincantieri produces propellers with increasingly larger diameters as the size of the ship grows.
There are many more steps if you consider all types of propellers, but I will limit myself to these only:
Aircraft Carriers (Actually Aircraft Carrier Cruisers): diameter 6.4 meters [44 MW for each shaft]
Destroyers and frigates: 4.8 meter diameter [22 MW for each shaft]
Corvettes: 3.1 meters [6.5 MW for each shaft]
Patrol vessels: 3 meters [9 MW for each shaft]
Mega Yacht: 2.0 meters to 3.5 meters [3 to 5 MW per shaft]
Coastguard Patrol Vessels: 1 meter [5 MW for each shaft]
I imagine it's roughly the same thing for English ships, although I haven't checked.
Just a curiosity: the diameter of 4.7 meters is that of the propeller of the battleship Bismark which however had three, the diameter of 6.7 meters was that of the propeller of the transatlantic Queen Elisabeth 2 which had two.
The largest propeller in the world that I found is 9.6 meters long and weighs over 130 tons and is from the Danish container ship Emma Maersk. (made by Mecklenburger Metallguss GmbH)
If you find any larger ones, tell me.
Oil tankers have only one propeller and it is relatively small (I repeat "relatively" because it is absolutely enormous) because no significant speed performances or maneuverability are required.
It may have happened to someone (lucky him) that he has to choose the propeller for his motorboat or his pleasure sailing boat.
We should hardly choose the propeller for a cruise ship, transport ship or warship if we are not engineers of that field.
It will happen much more frequently that we have to choose the right diameter for our scale RC model, or (if we rely on a kit or a project) observe and memorize this data.
Or not even that, you don't pay attention to it, you don't care and you don't even understand why we are discussing this, ahahahahahahah.
I noticed that this progression of the propeller diameter based on the size of the ship is also respected for the RC models.
I started to peek into the Harbors of this site to see the relationship between propellers and ship dimensions, unfortunately the diameter parameter is not covered but only the number of blades.
So I hope this information comes from you modelers. At most I'll ask you directly, ahahahahahah. Don't report me as a stalker though.
In the modeling world I have seen that the choice of diameters is quite wide.
I've seen that they start from 12 mm and go up to 130 mm with many intermediate sizes.
In short, the choice is certainly not limited (perhaps you will have found some sites that even exceed these ranges).
THE PITCH
Everyone knows that it is the advance (the distance it travels) that the propeller would make in a complete 360° turn if it were screwed into a solid material. In reality, since the propeller moves in water which is a fluid, the actual advancement will always be less than the pitch. The difference between pitch and advancement is called regress.
What does the pitch actually entail?
It is intuitive that a longer pitch will lead to a greater maximum achievable speed.
This is true as long as the pitch is commensurate and suitable for the other characteristics.
A shorter pitch will be better for standing starts or pushing heavier weights (broadly speaking).
Let's make a comparison with the pace of a person.
If this person walks on level ground he will be able to afford to make a wide pitch and therefore proceed quickly.
If the same person encounters a steep climb he will not be able to make the same wide pitch as before, but he will have to take smaller steps to be able to climb.
Motor boats don't have gears and we could compare (allow me with a bit of elasticity) the pitch to the gears of a car.
Therefore, at speed we can shift into fifth or sixth gear, while when going uphill (or starting from a standstill) we should downshift or shift into first gear.
Well, we can compare the sixth gear of a car to the long pitch of the propeller while the low gears to the short pitch of the propeller.
You will agree with me that starting in first gear, if a car does not shift into second, then into third, fourth and so on its maximum speed will be limited.
So just as in a car that goes in first gear the speed is very limited, even a short pitch propeller will have a more limited maximum speed than a long pitch propeller.
To guarantee good performance in acceleration, starting from a standstill but also good maximum speeds, you need to have propellers with variable pitch (or find a compromise situation).
As proof of this we can consider warships which, having to deal with different speeds and continuous acceleration (even switching the propulsion system), have variable pitch propellers.
Oil tankers do not have this need and have fixed pitch propellers.
For example, the D554 "Caio Duilio" missile fighter (defined within NATO as Destroyer) of the Orizzonte class of the Italian Navy has two five-bladed variable pitch propellers.
Its equivalent in the RN should be the Type 45, such as the D35 Dragon, perhaps some of you can tell me if it has variable pitch blades. I don't know but I bet so.
FREMM frigates also have variable pitch blades.
Boats used for water skiing, having to accelerate immediately, have short pitch propellers.
To return to ChrisF's problem, I think he has a pitch that is too long for acceleration and it is normal for him to not perform well in some moments of the race.
Now let's just analyze the causes, let's leave the possible solutions to another post.
In pleasure boats (especially with outboard engines) the choice of pitch is made based on the number of revolutions (rpm) that the engine makes at full throttle (WOT, wide open throttle).
If, for example, an engine has to make 6000 rpm at a certain power and instead makes 5500 (despite being pushed to the maximum) it means that the pitch must be shortened to recover the 500 rpm because the objective is to release all the power to the engine.
If, on the other hand, the motor turns too much, the pitch must be increased.
Again in relation to the diameter, I noticed that for outboard motors and pleasure boats there is not a very wide range of diameters but many pitches available to choose from.
Ok now let's go back to the modeling field.
In my opinion the effects of a longer or shorter pitch also influence RC models.
To avoid misunderstandings I make a clarification:
The variable pitch propeller (Invented by the Italian engineer Corradino D'Ascanio) is different from the tilting propellers and folding propellers.
The adjustable-blade propeller has blades that can be arranged longitudinally with respect to the motion of the water so as to oppose very little advancement in the case of sail propulsion.
The folding blade propeller folds the blades completely backwards so as to offer very little or no forward resistance in the case of sail propulsion.
Let's not forget that in the nineteenth century, during sailing, the propellers were removed so as not to slow down the ship with their resistance. Incredible but true.
NUMBER OF BLADES
The number of blades actually varies from two to seven.
I have never seen one or eight bladed propellers until now.
I have only seen seven blades on submarine propellers.
The lower the number of blades, the higher the speed but at the expense of stability (higher speed but more vibrations).
Each extra blade offers more friction but offers more grip on the water.
This is important.
In reality, the choice of blades is linked to many factors.
Propellers for outboard engines are mostly three- or four-bladed.
In the modeling field the choice is quite wide but not as wide as in reality.
MATERIALS
In reality, the propellers for small pleasure boats and outboard motors are made of steel or aluminium.
The steel ones are better from every point of view but cost at least three times as much as the aluminum ones (that I know of) but still valid.
In larger propellers, mainly two alloys are used: Nickel Aluminum Bronze alloy NiBrAl, and OTS (brass and manganese).
Manganese brass (ZHMn55-3-1), aluminum-manganese brass (ZHAI67-5-2-2) and manganese-aluminum bronze (ZQAI12-8-3-2) are commonly used in China.
In the world of modeling, propellers are either made of plastic or metal or alloy: brass, steel, aluminium, bronze.
I have two that seemed like lead to me, is it possible in your opinion?
There are many differences between plastic and metal propellers in your opinion, has anyone experienced these differences firsthand?
I'll stop here for the moment.
I've clarified my assumptions for Chris's problem.
I hope that what I have written has not bored you, has been useful for someone and above all stimulates further discussion, because surely someone will have had an experience worth sharing, from which to draw valuable information.
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Do we want to talk about propellers?
I've been listening in the background, seems you hit a vain of knowledge.
Phil UK 👍
Phil UK 👍
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As we will probably find out a lot of what applies to full-size may not transfer to models and may well be difficult to calculate and is usually unnecessary anyway as reference can be made to what others have used in their builds or similar. And if it doesn't work from the off then alternatives can usually be tried without any great expense unlike with full-size! Not many builds are unique so in most cases a satisfactory solution can be readily found and if say more speed is required then this can often be achieved with a different motor or more volts. And as said if built from a kit or plans then usually details of suitable motors and propellers are given.
Model race boats are by their nature more sensitive as I've found out with mine. It could be caused by cavitation or sucking air from the surface as the prop is very close or a combination of both or something else. When moving off I didn't give it full throttle but gently increased it but still had the issues with gaining speed.
The model is as manufactured and well tested and performs well for other owners (but maybe on bigger lakes?) so maybe it's just set-up? From the photo you can see there is height adjustment for the prop but it looks as though it's as low as it can go? Though it has a flex drive I think the adjustment is mainly for alignment as the exit hole in the hull for the drive isn't far away. It's been well over a year since I tried the boat but it will be nice to give it another try at some point.
Model race boats are by their nature more sensitive as I've found out with mine. It could be caused by cavitation or sucking air from the surface as the prop is very close or a combination of both or something else. When moving off I didn't give it full throttle but gently increased it but still had the issues with gaining speed.
The model is as manufactured and well tested and performs well for other owners (but maybe on bigger lakes?) so maybe it's just set-up? From the photo you can see there is height adjustment for the prop but it looks as though it's as low as it can go? Though it has a flex drive I think the adjustment is mainly for alignment as the exit hole in the hull for the drive isn't far away. It's been well over a year since I tried the boat but it will be nice to give it another try at some point.
Scratch building 7 Faireys at a scale of 1:12
Do we want to talk about propellers?
What is a good source of propellers shipping to the States?Len
LEN1
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Hi Boatshed, you make some good points. I know Allessandro likes the technical analysis of rpm, speed and performance set against efficiency. Interesting as it is that should not make a new or old builder, who perhaps finds that part difficult to calculate from just having a go.
There are so many start options that it is almost a black art. How heavy is the boat, what voltage batteries do you have, which motor to use, it goes on. I had a count a while back I have over 100 props in a couple of boxes, one marked Large, the other Small and quite often I still need a different one.
I have about the same number of electric motors or though a few are collectors items. Most of my battery packs are 4, 6 or10 cell ones and then there is the right charger for the job!
Although I do not agree with all of the Deans Marine philosophies he details you the right size prop and motor recommended for each model. When you know better then so much the better. Experience gives you options, my own mantra is the minimum power needed to get the boat to perform, only one other factor sometimes happens and that is what about the others on the lake and can I stop quickly!
Talking about cavitation is interesting but make sure that you (anyone) know how to recognise it, i.e. that you are not sucking down air because the prop is too near the surface.
If you do see cavitation then maybe your expectations of prop speed is in question.
We do get some very basic questions which might come as a surprise to the well informed but they are often from people who would like to join in but have no idea how to start. So the forum and the Mayhem one are happy to help and hopefully induct a new modeller.
I am in a club where I fight for attention with yachts and am about accepted for model boats but vie with live steam locos which also interest me. Frequently we find there is a lot of cross over in our hobbies.
So the choices are all personal, read what you want, respond if interested, a 'like' for a bit of interesting information and make sure there is a handy cup of coffee. Do not be bothered by ranks, it is like when we all collected Green shield stamps!
regards to all respondants,
Roy
There are so many start options that it is almost a black art. How heavy is the boat, what voltage batteries do you have, which motor to use, it goes on. I had a count a while back I have over 100 props in a couple of boxes, one marked Large, the other Small and quite often I still need a different one.
I have about the same number of electric motors or though a few are collectors items. Most of my battery packs are 4, 6 or10 cell ones and then there is the right charger for the job!
Although I do not agree with all of the Deans Marine philosophies he details you the right size prop and motor recommended for each model. When you know better then so much the better. Experience gives you options, my own mantra is the minimum power needed to get the boat to perform, only one other factor sometimes happens and that is what about the others on the lake and can I stop quickly!
Talking about cavitation is interesting but make sure that you (anyone) know how to recognise it, i.e. that you are not sucking down air because the prop is too near the surface.
If you do see cavitation then maybe your expectations of prop speed is in question.
We do get some very basic questions which might come as a surprise to the well informed but they are often from people who would like to join in but have no idea how to start. So the forum and the Mayhem one are happy to help and hopefully induct a new modeller.
I am in a club where I fight for attention with yachts and am about accepted for model boats but vie with live steam locos which also interest me. Frequently we find there is a lot of cross over in our hobbies.
So the choices are all personal, read what you want, respond if interested, a 'like' for a bit of interesting information and make sure there is a handy cup of coffee. Do not be bothered by ranks, it is like when we all collected Green shield stamps!
regards to all respondants,
Roy
Do we want to talk about propellers?
Wow, I find this all very confusing regarding the propellors. I have only ever gone to the pond with a bag of assorted propellors and played big time. Swapped from standard sized say 35 or 40mm prop to a 35x or 40x. or if I could get them 35.5x. I have them both smaller and larger than those, those are just a for a reference. I can see no one has mentioned a cavitation plate anywhere, outboard motors have them fitted just above the propeller. I had tried that on a model outdrive that I had on one model boat, it did help a little but for that outdrive there were not enough propellors available to fit when I bought it. That was way back in the early eighties, it was a copy of a Volvo Outdrive. I quickly sold it on as I wasn't happy with it. I didn't really give it a good enough trial. The market for propellors have come on a lot since then. I have since then bought another outdrive. The first picture was the Volvo copy outdrive from the eighties I had and the second picture is my present outdrive on the same hull but in white fibreglass. I bought 2 of those hulls back in the eighties from a company called Hydrofibre in Bungay In Norfolk. I only have the white one left now 51" long. It will have a Brushless powering it now it was going to have that 26cc electric start blinged up Zenoah running it. But I have now sold off all of my IC engines to go Brushless.
BOATSHED
Do we want to talk about propellers?
Someone else has mentioned it might be due to inertia, it's quite a big boat at 730mm, though not too heavy, but there are two 2S 4000mAh LiPos on board, and the prop is relatively small so it might be reluctant to get moving?
Also I think a 3 blade prop is quite unusual for this type of boat and in a review for a different fast electric someone said that they changed to a 2 blade because of "cavitation" though as we are surmising that might not be the reason as such.
In another review of the same boat as mine it stated that it accelerated well and got onto the plane easily which mine certainly doesn't. Maybe a change of prop is the answer given the restrictions due to the size of the lake as high speed isn't really attainable or important.
Also I think a 3 blade prop is quite unusual for this type of boat and in a review for a different fast electric someone said that they changed to a 2 blade because of "cavitation" though as we are surmising that might not be the reason as such.
In another review of the same boat as mine it stated that it accelerated well and got onto the plane easily which mine certainly doesn't. Maybe a change of prop is the answer given the restrictions due to the size of the lake as high speed isn't really attainable or important.
Scratch building 7 Faireys at a scale of 1:12
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Hi ChrisF.
I like your tidy way of looking at things.
When I can, I also prefer to proceed in logical and chronological order but this is a forum.
In the forum it is right that spontaneity reigns, the discussions follow a natural and not preordained interest, therefore in my opinion your intervention was not untimely, but rather very apt and interesting.
In the forum, doing theory without referring to our practical problems on naval models, thinking without playing, would be very sterile.
Ever since you represented your problem I have been passionate about it and I'm thinking about it. Although fast motorboats are not my passion, I am developing my own thoughts.
I haven't written anything yet because I don't want to monopolize the discussion and I prefer to learn about other people's experiences; However, while I do not discard the cavitation hypothesis, I also have other ideas in mind regarding the causes of your problem but I will wait for the interventions of other modelers with more experience.
I like your tidy way of looking at things.
When I can, I also prefer to proceed in logical and chronological order but this is a forum.
In the forum it is right that spontaneity reigns, the discussions follow a natural and not preordained interest, therefore in my opinion your intervention was not untimely, but rather very apt and interesting.
In the forum, doing theory without referring to our practical problems on naval models, thinking without playing, would be very sterile.
Ever since you represented your problem I have been passionate about it and I'm thinking about it. Although fast motorboats are not my passion, I am developing my own thoughts.
I haven't written anything yet because I don't want to monopolize the discussion and I prefer to learn about other people's experiences; However, while I do not discard the cavitation hypothesis, I also have other ideas in mind regarding the causes of your problem but I will wait for the interventions of other modelers with more experience.
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I completely agree with you Wolle.
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Hello Alessandro
Discussions and lessons are almost the same in my opinion. My father always said...If you don't ask, you're stupid...if you don't listen, you're stupid...even the oldest and the smartest can still learn something. Everything that is written here in this super nice, respectful forum deserves recognition and the greatest respect from me. And I am happy to be part of this society.
Discussions and lessons are almost the same in my opinion. My father always said...If you don't ask, you're stupid...if you don't listen, you're stupid...even the oldest and the smartest can still learn something. Everything that is written here in this super nice, respectful forum deserves recognition and the greatest respect from me. And I am happy to be part of this society.
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As others have said, thanks for the potted history. I've come across parts of it before but not all of it.
The whole subject is being tackled in the right order now and my problem of cavitation, if it is that, may I suggest be left to later once the different types of full-size propeller have been covered with those for model boats and their size being left to last. There will invariably be some overlapping once we get onto model boats no doubt but at least the subject will be tackled in a logical order rather than us jumping all over the place like I did!
Chris
The whole subject is being tackled in the right order now and my problem of cavitation, if it is that, may I suggest be left to later once the different types of full-size propeller have been covered with those for model boats and their size being left to last. There will invariably be some overlapping once we get onto model boats no doubt but at least the subject will be tackled in a logical order rather than us jumping all over the place like I did!
Chris
Scratch building 7 Faireys at a scale of 1:12
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Thank you so much Mike for your more than kind, flattering words.
Sorry, but when I wrote the message for Wolle I hadn't read yours yet.
Sorry, but when I wrote the message for Wolle I hadn't read yours yet.
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Thank you very much Wolle.
Mine was intended as a starting point for discussion, certainly not a lesson, I am not capable of giving lessons, especially to expert model makers like you.
I don't know if it happens to you, when you read some stories, there are anecdotes that stick in your memory more than others.
It happened to me with some anecdotes related to the evolution of the propeller.
Of course I had to reread the texts where I had acquired these notions, I didn't remember everything by heart because a lot of time had passed.
Mine was intended as a starting point for discussion, certainly not a lesson, I am not capable of giving lessons, especially to expert model makers like you.
I don't know if it happens to you, when you read some stories, there are anecdotes that stick in your memory more than others.
It happened to me with some anecdotes related to the evolution of the propeller.
Of course I had to reread the texts where I had acquired these notions, I didn't remember everything by heart because a lot of time had passed.
Do we want to talk about propellers?
Hallo Alessandro
Thank you for the detailed and very interesting history lesson.👍👍👍
Thank you for the detailed and very interesting history lesson.👍👍👍
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Hello to all naval modelers.
In the absence of other interventions, I wanted to stimulate the discussion by returning to the discussion on cavitation, variable pitch propellers and ChrisF's very interesting problem, but then I remembered that we had left the historical part arising from Roy's anecdote pending.
I like talking with you about the historical part because it's not always as boring as you think. Sometimes some episodes are very unique and stimulate curiosity.
Roy told us how an accident caused a propeller blade to break and the boat started to go faster.
This episode immediately reminded me of what happened to the British inventor Francis Pettit Smith in 1837.
But let's take a step back.
The latest studies on the propeller dated back to Archimedes and Leonardo.
The interest and real development occurred in 1800 after the industrial revolution and the invention of the steam engine.
Some attempts had also been made without a steam engine, such as on the "Turtle", the first submarine created in 1775 by the American David Bushnell.
Propulsion was entrusted to Archimedes' screw, because it started from there. The mechanical movement was given by human strength alone.
With the steam engine they sought more effective thrusters than the paddle wheel, which is vulnerable in war, increases the width or length of the ship, is affected by wave motion, and is much less efficient than the propeller, but at that time no one knew.
In reality, it was the Bohemian inventor Josef Ressel who firmly believed that a propeller placed at the stern of the ship was the best solution, certainly better than the paddle wheel, who carried out independent studies in Trieste (at that time under Austrian domination) where there 'is now a statue of him.
He started from Archimedes' screw and patented the propeller in 1827, he also had a ship built but his merits were recognized much later.
Even before that, already in 1810, the British Samuel Owen supported and tested the superiority of propeller propulsion compared to the paddle wheel in Stockholm.
The other great advocate of the superiority of the propeller over the wheel as a propulsion system for steam engines was Francis Pettit Smith. He also started from Archimedes' screw for his propeller which he patented in 1836.
And here comes the best part:
In 1837 I tested his wooden propeller which had two complete spirals on a boat.
Well during the test the propeller (or rather the screw) broke in half by chance and the boat immediately started to go faster.
What a fantastic story.
It still had a helical shape but then they gradually understood what the best shape was until arriving at the technological masterpieces that are the current propellers.
If we look at the first propellers we would be amazed at the strange and archaic shapes they had (such as that of the Great Britain of 1841).
The tests between Rattler and Alecto in 1845 definitively established the superiority of the propeller, as already written.
The anecdotes related to the experiments of the unfortunate and, for a long time, ignored Ressel, should be reported in more detail but I have already written too much for the moment.
Attached are:
1. Turtle submarine
2. Archimedes' screw
3. Smith spiral
4. Lyttleton helix
5. Shorter Propeller
6. Sauvage Propeller
7. Propeller Mangin
8. Ericsson propeller
9. Ericsson propeller
10. Propeller Great Britain
11. Sketch by Ressel.
In the absence of other interventions, I wanted to stimulate the discussion by returning to the discussion on cavitation, variable pitch propellers and ChrisF's very interesting problem, but then I remembered that we had left the historical part arising from Roy's anecdote pending.
I like talking with you about the historical part because it's not always as boring as you think. Sometimes some episodes are very unique and stimulate curiosity.
Roy told us how an accident caused a propeller blade to break and the boat started to go faster.
This episode immediately reminded me of what happened to the British inventor Francis Pettit Smith in 1837.
But let's take a step back.
The latest studies on the propeller dated back to Archimedes and Leonardo.
The interest and real development occurred in 1800 after the industrial revolution and the invention of the steam engine.
Some attempts had also been made without a steam engine, such as on the "Turtle", the first submarine created in 1775 by the American David Bushnell.
Propulsion was entrusted to Archimedes' screw, because it started from there. The mechanical movement was given by human strength alone.
With the steam engine they sought more effective thrusters than the paddle wheel, which is vulnerable in war, increases the width or length of the ship, is affected by wave motion, and is much less efficient than the propeller, but at that time no one knew.
In reality, it was the Bohemian inventor Josef Ressel who firmly believed that a propeller placed at the stern of the ship was the best solution, certainly better than the paddle wheel, who carried out independent studies in Trieste (at that time under Austrian domination) where there 'is now a statue of him.
He started from Archimedes' screw and patented the propeller in 1827, he also had a ship built but his merits were recognized much later.
Even before that, already in 1810, the British Samuel Owen supported and tested the superiority of propeller propulsion compared to the paddle wheel in Stockholm.
The other great advocate of the superiority of the propeller over the wheel as a propulsion system for steam engines was Francis Pettit Smith. He also started from Archimedes' screw for his propeller which he patented in 1836.
And here comes the best part:
In 1837 I tested his wooden propeller which had two complete spirals on a boat.
Well during the test the propeller (or rather the screw) broke in half by chance and the boat immediately started to go faster.
What a fantastic story.
It still had a helical shape but then they gradually understood what the best shape was until arriving at the technological masterpieces that are the current propellers.
If we look at the first propellers we would be amazed at the strange and archaic shapes they had (such as that of the Great Britain of 1841).
The tests between Rattler and Alecto in 1845 definitively established the superiority of the propeller, as already written.
The anecdotes related to the experiments of the unfortunate and, for a long time, ignored Ressel, should be reported in more detail but I have already written too much for the moment.
Attached are:
1. Turtle submarine
2. Archimedes' screw
3. Smith spiral
4. Lyttleton helix
5. Shorter Propeller
6. Sauvage Propeller
7. Propeller Mangin
8. Ericsson propeller
9. Ericsson propeller
10. Propeller Great Britain
11. Sketch by Ressel.
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Of course Doug, the phenomenon of cavitation is well known in the nautical field because it manifests itself with its deleterious effects on propellers.
We know that due to high speeds, low pressure areas are created in some areas of the propeller.
Low pressure lowers the vapor pressure (i.e. the temperature at which there is a change of state from liquid to gas).
This causes water to turn into steam in some limited areas (although there is no increase in temperature).
Bubbles of steam (water in a gaseous state) continually implode as they pass through a high-pressure area.
The traumatic impact of the implosion causes damage to the blades.
I'm interested in knowing your opinion on the modeling field.
Have you also encountered the cavitation phenomenon on scale RC models?
I don't mean just the damage (that could only manifest itself in the long run) but the phenomenon itself.
What symptoms do you think are irrefutable (apart from damage to the propeller) to suspect the presence of cavitation?
What do you think about ChrisF's specific problem?
Do you think it could be attributed to cavitation?
We know that due to high speeds, low pressure areas are created in some areas of the propeller.
Low pressure lowers the vapor pressure (i.e. the temperature at which there is a change of state from liquid to gas).
This causes water to turn into steam in some limited areas (although there is no increase in temperature).
Bubbles of steam (water in a gaseous state) continually implode as they pass through a high-pressure area.
The traumatic impact of the implosion causes damage to the blades.
I'm interested in knowing your opinion on the modeling field.
Have you also encountered the cavitation phenomenon on scale RC models?
I don't mean just the damage (that could only manifest itself in the long run) but the phenomenon itself.
What symptoms do you think are irrefutable (apart from damage to the propeller) to suspect the presence of cavitation?
What do you think about ChrisF's specific problem?
Do you think it could be attributed to cavitation?
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Alessandro, as you found that microcosm site interesting although I fully agree rather on the expensive side, may I suggest that you do what I do which is go on to eBay every now and again and check out microcosm, as he often has boilers, steam engines, and various bits and pieces up for auction, and I have been lucky once or twice. my last bargain was an automatic pressure-controlled gas valve, normally sold for £70 and mine for the knockdown price of £40 plus postage. Regards, Gary.
Gary Steam Marine, the only way to go.
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CAVITATION.☹️
😎
Pic 1. Cavitating propeller, model in a water tunnel experiment.
Pic 2. Cavitation damage.
Pic 3. Cavitation bubble implosion (what does the damage.😠)
https://www.miwheel.com/propeller-cavitation-explained/
😎
Pic 1. Cavitating propeller, model in a water tunnel experiment.
Pic 2. Cavitation damage.
Pic 3. Cavitation bubble implosion (what does the damage.😠)
https://www.miwheel.com/propeller-cavitation-explained/
Young at heart 😉 Slightly older in other places.😊 Cheers Doug
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Hi Gary, I saw the site you pointed out to me.
Exceptional!
I also saw the variable pitch propeller. Of course the prices are a little too high in my opinion.
Exceptional!
I also saw the variable pitch propeller. Of course the prices are a little too high in my opinion.
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This is my fast electric. Well it is once it gets going! Problem I have is that our lake is quite small and even slowing for the the turn buoys means that it starts to cavitate again, if that is the problem, and is slow to get on the plane again.
it needs a much bigger lake where higher speeds can be achieved with sweeping corners.
I thought it was a good idea at the time for club racing! But totally unsuitable.
Chris
it needs a much bigger lake where higher speeds can be achieved with sweeping corners.
I thought it was a good idea at the time for club racing! But totally unsuitable.
Chris
Scratch building 7 Faireys at a scale of 1:12
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This was the post I saw last year which mentions variable pitch props. One of the guys found some Raboesch NOS (new old stock).
I think this is going to be a long but interesting thread on propellers as there is so much to say!
https://www.modelboatmayhem.co.uk/forum/index.php/topic,69666.0.html
I think this is going to be a long but interesting thread on propellers as there is so much to say!
https://www.modelboatmayhem.co.uk/forum/index.php/topic,69666.0.html
Scratch building 7 Faireys at a scale of 1:12
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Hi Gary.
The length of the name is a matter of tactic.
When the enemies of the Macedonians, like the Persians for example, warned of Alexander's arrival, before they finished pronouncing his name, he was already upon them with his cavalry, ahahahahahaha.
I can't wait to see the site you recommended.
I'll let you know what I think as soon as possible, thank you in the meantime.
I'll open a parenthesis on the Chinese. The cliché that their products are poor is now (alas) outdated.
Once upon a time, Germany and the United States were mentioned in order to be guaranteed the quality of a technological product; it was said that the Chinese only know how to copy and do it badly.
Today the Chinese are able to produce cutting-edge technology in all fields.
There are still many substandard products but they are substandard not because they are backwards or because they don't have the capabilities, but because they purposely want to save on copper and other raw materials.
Today they have surpassed the Europeans and Americans in many fields and are absolutely competitive on prices.
I don't express what I think about their institutional form and their government because this is not a political site; I'm just saying that the respect I have for the Chinese people, culture and history has nothing to do with their leadership.
The length of the name is a matter of tactic.
When the enemies of the Macedonians, like the Persians for example, warned of Alexander's arrival, before they finished pronouncing his name, he was already upon them with his cavalry, ahahahahahaha.
I can't wait to see the site you recommended.
I'll let you know what I think as soon as possible, thank you in the meantime.
I'll open a parenthesis on the Chinese. The cliché that their products are poor is now (alas) outdated.
Once upon a time, Germany and the United States were mentioned in order to be guaranteed the quality of a technological product; it was said that the Chinese only know how to copy and do it badly.
Today the Chinese are able to produce cutting-edge technology in all fields.
There are still many substandard products but they are substandard not because they are backwards or because they don't have the capabilities, but because they purposely want to save on copper and other raw materials.
Today they have surpassed the Europeans and Americans in many fields and are absolutely competitive on prices.
I don't express what I think about their institutional form and their government because this is not a political site; I'm just saying that the respect I have for the Chinese people, culture and history has nothing to do with their leadership.
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