Hi Graham
Now we can see the actual prop shaft and motor it is clear that the shaft is not supported inside the hull close to the coupling. At the high revs your motor achieves I am not surprised you have had problems.
I do agree with all the comments and help you have been offered and agree a 5mm shaft would help as well as a different motor.
I use 3 blade brass props with brushless and have no problems but do keep the prop size to a diameter no greater than the motor diameter, as Mark advises.
It's difficult to see how much space is in the hull to allow the motor coupling and shaft to be closer, but if you are replacing the shaft it may be a good time to reposition the motor and
the shaft with the prop attached to a slightly different angle. This will mean opening the slot and perhaps enlarging the outside skeg but you can easily repair any damage with plastic padding to make good.
Even if you keep the existing arrangement I suggest you provide support for the prop shaft close to the bearing as I suspect this is where you have experienced the problem with the vibration. A simple 2" block of wood attached to the keel and shaft would suffice.
Model looks very good and I look forward to seeing some on water shots.

Hi Mark, all good stuff, as ever from you👍
Just one thing; Prop Shop has ceased production after the fire they had.
Probably only still trading until rest stock is sold and the business then wound up. 🤔

So I would go straight to Raboesch
http://raboeschmodels.com/index.php/en/
(or Krick here in Germany) for cast props and suitable matched shafts.
You can download the whole catalogue from their site to browse at your leisure 😉
This is the announcement on the Prop Shop site
Cheers Doug 😎
http://www.prop-shop.co.uk/
"Welcome to the Prop Shop web site.

AS YOU ARE PROBABLY AWARE A FIRE IN APRIL 2017 SERIOUSLY DAMAGED OUR PRODUCTION FACILITIES. SINCE THEN WE HAVE BEEN NEGOTIATING OUR CLAIM WITH OUR INSURANCE COMPANY.

JUST BEFORE CHRISTMAS A SETTLEMENT WAS REACHED. REGRETTABLY THE AMOUNT WE HAVE BEEN PAID IS NOT SUFFICIENT TO ENABLE US TO FULLY RE-ESTABLISH OUR PRODUCTION CAPABILITY.

WE MUST ADVISE THEREFORE THAT THE DECISION HAS NOW BEEN TAKEN FOR "PROPSHOP" TO CEASE TRADING.

WE WANT TO THANK ALL OUR LOYAL CUSTOMERS FOR THEIR SUPPORT OVER MANY YEARS AND SINCERELY HOPE YOU FIND SUITABLE ALTERNATIVE PRODUCTS THAT MEET YOUR NEED.

REGARDS,

PROPS SHOP TEAM

January 2018" 🤔

Hi Graham, all agreed with you post. But. The last photo looks like the blades are soldered or brazed on, that is a week point, but looking closely the blade appears to have sheared of above the hub.
Your hull is not really a high speed hull, so a racing prop might cause instability, i would suggest a cast prop, (propshop) and possibly 3 blades 40 - 45mm with your 1100kv motor would give good speed combined with good run time.
The 5mm upgrade is also a great idea.
A rule of thumb is don't exceed the diameter of the motor.
Mark

Hi Mark,
i have a 4mm shaft fitted and the boat was out of the water at the time, it happened when i just touched the throttle!
i thinking maybe a 5mm shaft would be good (less whipping)with a racing propeller and a 1100kv motor with a rubber heavy duty coupling, i think that would be a good setup and will be suitable for a 3ft boat. i think the brass propeller is just not built for high revs, or was it a 1 off badly made propeller?
anyway would that setup be good?
thanks
Graham

HI Graham. Every picture tells a story!!! The motor is definitely wrong, its designed for racing, low torque, mega revs, not for scale boats. What diameter is the shaft tube??? looks thin??? did the prop shear in the water?? would explain the vibration and damage to the shaft mountings, try a Raboesch shaft, with a ballrace at the motor end, great quality, also they do a huge range of props, google the name there site will come up.

Mark

Hi All,
a lot of info, i need a complete change to the power train setup.
canabus setup looks good, i think i will follow that. what size in diametre prop shaft did you use, 4 -5 mm?
have uploaded some pictures of the boat, complete with offending motor! and 1 of the resulting damage to the 3 blade brass propeller, which i think was out of balance, so, can't take the speed of rpm? probably need a racing propeller? There is room for 2 lipo's in parallel.
Thanks Again
Graham

This is a Fairey Marine Huntress on a trailer and this rudder has next to no leading edge, These were used for racing way back. I have based some of my rudders on this type of rudder.

I always use as smaller rudder as I can get away with. I had been running model boats for many years then one day when on Blackheath pond someone was watching my boat and remarked on how it turned. badly, and I replied that's how it had always turned. The guy had a boat the same as mine it was a MFA Spearfish, He asked if he could swap rudders on my boat and try his on my boat so that's what I done and it performed much better on the water. I then tried it on my Vosper RAF Crash Tender and it just stuck to the water on any turn tight or wide. So I have done this ever since. On my Huntsman I had turned it over several times before trying this so I done the same on this and once again it was a lot better turning and didn't turn over. I don't like using large rudders if I cannot get one small enough for what I wan't I will get one and then cut it down. We used to race 5 or 6 boats on the water at a time and always needed to turn tight turns to get round the pond. Even watching Power Boat racing on the telly in the past they make tight turns to get round. I have a Probaot Miss Geico tunnel hull and straight from the box brand new the rudder on that has no leading edge and I can turn that flat out on the water with no roll at all. I suppose I am a speed freak and it has worked fine for me. Even if it is the wrong thing to do. The small avatar picture on my posts is a boat I have in Norfolk. This has a 1960 Volvo Penta outdrive probably one of the earliest one's made and that doesn't like to turn on 3/4 throttle without the engine revs dropping and digging in on a turn. I have tried this when out on open water up there. Don't try it now as got a warning from the Norfolk River Constabulary. Don't want to loose my river licence.

Boatshed - as regards the rudder the part in front of the spindle is to balance part of the force acting on the rudder and take some of the load off the servo or in the case of a full size boat off the wheel.

If a boat is turning too sharply or experiencing "braking" then the rudder is either turning too much or it's too big.

Hi All
I am using Hobbyking 3639-1100 and 3648-1450kv motors
in that size boats(Sea Commander, Precedent Huntsman and SG&K Gentleman's Runabout).
60 Amp ESC with either 3 or 4S Lipo batteries.
Props 2 blade 40mm 1.4 or 1.6 pitch.
The motors are a straight change over and the only change to the ESC is the low voltage setting for the 3S and 4S batteries.
Canabus

Graham - don't tell me you ran the boat at anything like full throttle. if so, it wouldn't just be the prop shaft that you'd have to worry about! if you did it must have been virtually uncontrollable!

I take it you bought the boat with the motor already in it? Whatever, it couldn't really have been a worse choice! With such a high kv and being an inrunner (if I've got the right motor) it's really meant for a lighter, race type boat running on 2S to keep the revs down to a reasonable level.

As you now know, for your type of boat you need a kv around 1000 or even a bit less as torque is what you need and also go for an outrunner. 3S or 4S is fine and if it is too fast limit the amount of throttle.

Without seeing photos it's impossible to say if your existing prop shaft is up to the job but as you've removed it anyway and if you don't mind the expense I'd change it for one of the Raboesch maintenance free ones. I'm using these for my builds and my Fairey Swordsman at 33 inches is a similar size and weight. These are rated for 10k. and 15k. rpm, I've gone for the latter and in 5mm shaft size to be on the safe side.

I doubt that a shorter prop shaft will be feasible as usually the motor is already pretty low in the boat and a shorter shaft will increase the angle and you don't want it too steep. Also you would have to redrill the hole for the different angle. What dia. is the existing prop shaft?

The other thing you need to consider is the prop. What are you running at the moment?

A photo of the boat would be good.

Chris

Very nice but I think our friend's prop tube comes through the keelson .The wedge shaped keel extension piece to which the tube is secured so that support would not suit. However a "U" tube or two could be fabricated and wrapped round tube and secured to keelson with a couple of small screws and a good glue.Ali .copper or brass would do. Brass best to avoid electrolytic corrosion with the brass prop tube. Also brass screws. BTW just looking at shaft is not enough to check if straight. Hold to a known straight edge or rolled on flat surface. This will show up even the slightest curvature by allowing light under the ends when rolling with the fingers in the middle. Or slide a piece of paper (cigarette paper best ) against ends .If it goes under there is a bend in the test piece 👍

What about adding a prop shaft support under the boat I useually add one something like this. I have never had one this strong looking but all ways had one just before the end of the shaft. you could also add one inside the boat or even a shaped wedge under the prop tube inside the boat. This will also help to stop any side whip on the tube.Another thing that I was taught was to do away with the leading edge of the rudder. Only have about one 16th of leading edge as this stops the braking effect when turning the boat at speed. That worked wonders on stopping the boat from digging into the water and doing tight turns as well. I'm not as experienced as a lot of the people on here but these are tip's I have learnt from others. Happy boating.

Hi Graham, are you a member of a local club??? or do you have a local machine shop who could make a couple of plastic bearings for you??? alternatively you could make some with a drill and a couple of files. Most shafts are only held at each end, so a possible remedy would be a thicker shaft, 5 - 6mm but would need replacing the tube

Mark

Hi Mark,
i don't have excess to a lathe, do they sell prop shafts already loaded with bearings? or racing props?

Thanks for your help
Graham

Hi Graham, a 14" shaft is definitely going to whip inside, do you have access to a lathe? if so remove the rear bearing and push a plastic bearing into the tube, move it in about 10" then insert a second about 5" then replace the outer bearing, this will help the shaft to stay central in the tube.
An alternative, fit a shorter tube and shaft closer to the hull exit, this will also lower the motor so beware that you need the space enough to fit it.

Mark

Hi Boatshed,
i have just ordered today, an aligner tool for when i rebuild the prop shaft, i didn't know they exsisted when i installed the prop shaft the first time! But the prop-shaft does seem to be inline to the motor spindle..... and the prop shaft is straight, so i think maybe the propellor was out of balance.
but i think i will reduce, the next motor KV size to about 1100kv - 1300kv.
Thank everyone for their help, very much appreciated!
Graham

Do you not use a solid metal motor to shaft aligner to be sure every thing is in line ??

HI there

With that setup you are trying to make a boat fly :-)

Several members of my local modelboat club is running the same setup as I do with my Classic. And that is a Graupner Compact 260Z 1380KV for the Classic 2S is more than enough and 3S will still make the Queen fly over the water. So a 1100KV on 3S with a 3 blade semi racing prop will do a great job.

You could also cut down on amount of "S" on your existing setup and program the ESC to slow start.

Hi Mark,
The Prop shaft is 14.5 " long.i don't know the make but it's the normal prop they sell with brass bushes. i have just taken the shaft out of the prop Tube to see how bent it might be but it looks very straight to me and if push it through the tube it buts up to the middle of the motor spindle and seems inline to the motor spindle.
i can't see how i could fit an extra bush into the tube.
can you recommend a prop with bearings that would do and where to order from?
Thanks
Graham

Hi Traiderman, How long is the propshaft and tube???? The reason for asking is that if the shaft is more than 6 - 8" and of small diameter, 4mm, it is likely that the shaft is whipping inside the tube, a 1000kv, ish, motor with if needed some support bearings inside the tube, what model is being fitted???

Mark

hi Richard,
Thanks for the info, i have decided to remove the Prop and check it for straitness, before i start again with rebuilding using a heavy duty coupling and a slower motor, as i think the existing motor is just too fast at 47000 rpm for the propshaft and coupling and if the propellor is slightly out of balance then the prop will come off again!
Thank you Richard and all other contributors that have helped!
Graham

By the way the Araldite is very good glue but is brittle and as you have found cracks off with vibration. The other glues mentioned all have flexibility so will absorb any vibration.

Hi traderman I suspect something is bent.Shaft,tube or both. Take them out and roll them on a flat surface to check. You can try to straighten them but better to buy new. When installing roughen the tube a bit and use one of the glues already mentioned or go on Master Bond site and ask them.Or use Gorilla original with the tube well clamped or taped in place. Also check if the mounting is dead straight too or you could end up bending the new assembly too as you press it into place👍

Hi traiderman
I am no expert.
dont forget, as pmdent highlights, you you multiply the KV by the volts of the supply to get the RPM of the prop. so you can play with the volts supplied or the Kv of the motor or both.
regarding the vibration, have you supported the outer end of the shaft? if the shaft leaves the hull and has a good amount of unsupported shaft the end of the shaft effectively will scribe a circle. At the speed the shaft is turning and with the pressure on the prop this may cause your vibration.
Richard

Hi,
Thanks for the info Peter and Dave, very much appreciated!
The hull is all wood. I will order an 1100kv motor and make sure there is Thrust Washer's on the Propsharft.
Thanks again
Graham

I have to agree with Peter's comments.

I would also suggest that you look at the coupling and fitment of your prop shaft. it could be that the whole unit is seizing together. You also need to check it is true and free running.

You need a prop and locknut followed by a thrust washer then at the inboard end a thrust washer locknut and coupling. There should be a gap between the thrust washer and bearing of a few thou', we used to use a Rizla paper, Make sure all joint are tight and that the shaft turns freely and smoothly.

The motor need to be securely mounted to a good solid base and 100% aligned with the coupling and prop shaft. Personal experience tells me you don't get a second chance with brushless, you have been fortunate if it is only the prop tube has suffered.

Is your hull wood, plastic, fibreglass? Whilst Araldite is a fine adhesive you may need to use Stabliz Express or UHU Acrylit Plus which provide an exceptionally strong joint. E-bay have sellers of UHU in the UK.

Good luck and please keep us posted

Traderman - whilst I am not an expert ( I am currently trying to decide what brushless combo to fit to a 34" RAF Crash tender) - clearly your motor is turing your prop shaft way to fast. With your motor spec of 3180 kV and a 14.7 V Lipo - your motor will be trying to turn your shaft at a speed of somewhere in the order of 45,000 RPM !! Firstly your prop shaft may not be rated for anything like this speed and secondly any slight mis alignment will likely be generating significant vibration - enough to cause your problem- have you noticed any?
As to motor power - the motor may not be too powerful - but certainly dropping to a lower kV motor say 1100 and reducing the Lipo voltage to a 11 or even 7 volt system might be the right answer......but as I am finding its all a bit suck it and see...
Peter