It seems to me that the turns aren't that bad, all things considered.
It actually gives me the impression that it could go faster and there's a lot of air coming out of the back.
It can be improved but it's not a disaster.

One thing is for sure if we send air (due to a possible cavitation problem) instead of water on the rudder, it will definitely have problems even if it is perfect.
It is worth following River Rat's advice, especially because he has gained experience on a model very similar to yours.

Thanks for those comments about the propellor. This is the first time I have had the issue with the only difference being the fact that I moved it forward and replaced the rudder. By doing that I was able to tighten my turns however now have the other issues.
I have not sharpened or tuned the propellor in any way.

Hi Peterd, IMHO that is a propeller issue... In the video it appears to be faster at half throttle... Wow the cavitation is bad. I have this prop on my 1/10 Typhoon ($20 on Amazon) my original prop was shaped like yours and I had the same issue. Octura makes nice props too. I think the propeller is the problem here. Cavitation also affects the rudder performance for sure. You have built a beautiful boat!!! Hope this helps you. RR

Hi and please see the video taken this morning. Back to the drawing board but the resolve should be in sight.

The boat speed was reduced substantially however she turned better than in the past. The problem appears to be 'cavitation' which can be plainly seen and heard in the video. When turning hard you can also see her tend to skip a little sideways.

I cannot remember the format for the video so have posted on a YouTube channel - please let me know if this works - it may be a private channel. Original is MP4

https://youtube.com/shorts/pFKqx6A17SE

Hi Peterd, I'm rooting for you.

In my opinion you will already get some improvements.
At the limit you can always increase the surface of the rudder or create one with an asymmetrical biconvex section.

Hello Mike.
Your system is not useless at all. In my opinion it is effective.
The deflecting surface triples, the water flow is conveyed better and there is no need for three axles.
The only drawback could be (but this is a personal taste) the aesthetic factor.

Interesting concept Mike. I can see where you are coming from.

I am restoring an rc powerboat I was given that was powered by two 11cc aircraft engines.
I am thinking of putting a jet drive on it. No rudder. A long way to go though.

Not such a crazy idea Mike. I have used similar arrangements on boats used for competitive steering courses. 😉

Here is the landlubber from Switzerland,
My idea is totally crazy, but it would be worth a try if the current version doesn't work out.
A bit crazy, but the basic idea could work. I understand Peter, tinkering with an existing fixed drive axle is a horror.
Bb Michel-C.

Version 2 (or is it 3) on the rudder. Will see how it goes this weekend and when happy will rebuild the final edition. I may still take more off the top rear.

Cutouts made - in the sun waiting for the paint to dry.

Thank goodness for some sunshine - we have had our share of rain and wind for the moment. Mind you, a bit of constant wind would be good tomorrow.

Will have a carload, my bootlegger, DF65, Emma and a friend with his Racing Sparrow. I think I need a bus.

Good luck Peter, I think your changes will help. Let us know, pictures and video please 👍👍👍
RR

Hi Alessandro - I will cut back a little this morning to give more room behind the propellor - not happy with that anyhow and also cut a little off the rear of the rudder as well. Unfortunately, cannot do much with the front. Luckily it is hot and dry so the paint will set.

As mentioned in your email, there is no option to alter the location of the rudder shaft. It is a tiny area and I even now struggle just to locate the rudder arm.

I have seen images on larger Baby Bootleggers where the rear of the rudder is quite rounded. Big day tomorrow. Thanks for your interest.

Hi Peterd.

You have definitely improved the situation.

Unfortunately the axis (the vertical pin I mean) of the rudder is too far forward. As already mentioned, it would be better to move it back but it is a fairly invasive and complicated job.
So it's best to see how these changes go first, if they produce the desired effect, nothing else needs to be done, I hope so.

I would have done a different profile, roughly following the red outline. The green outline is optional.

However, I repeat, it could already go well like this, let us know how the tests in the water go.

Terrible photo and a quick build. (Paint is still wet as well.)

Only about 2mm between the rear of the prop and the leading edge of the rudder, however as a trial will see how she goes on Friday, weather permitting.

Yes, I thought that would be half the problem. When at speed she turns reasonably well but at the narrower end very sluggish.
I have reduced my drive shaft forward by 3cm - cannot go any further and have just drawn out a new rudder - about to go and cut it. I am taking the foot of the rudder to just over the level of the propellor base however do not have room to use a fully balanced rudder. A matter of a couple of mm. This rudder will be ply so if I make an error simple to replace.
I use a 40mm propellor.

Hi Peterd.

Yes, just as I was telling you, the rudder responds better to high speeds because currently only a small part is affected by the propeller flow.
If well hit by the flow of the propeller, a good rudder will make you turn the boat even when stationary, if you hold it with one hand.

However, don't expect too sharp curves, even real boats (if they don't have bow thrusters) don't do what many modelers would like to do.

Hi River Rat, thanks for the information.

There is no problem calculating the scale. I enjoy doing this without any software or applications. Simply apply a proportion which is reduced to a simple division, since one of the members is equivalent to one.

What you ask me, however, is not possible if you don't give me the diameter of the real propeller.
I also need to know either the scale of the model or the true length.

Out of curiosity, where did you buy the propeller, do you remember? Otherwise it doesn't matter.

Your model will be a great example to follow because it navigates very well.

Hi AlessandroSPQR. I will chase that link however will try and get some video this Friday. In the meantime I am going to build a new rudder and when finished will give that a try. I seem to have less issue when at speed, it is when i have to slow down for a tight area. The video i will be looking for will be in that area of the waterway which leads to a weir.
These boats are built for straight line. Our waterway is pear shaped and my turning point is right at the narrow end.

Thanks for that info on your battery esc setup. I would be getting a similar time on my nimh battery with the brushed battery though have never taken the time to work it out due to sail activities/racing. Prior when using the larger 750 brushed motor it was quite a different story - 10 mins max.

Hi Alessandro, the prop is 37 mm bronze with a 4.76 mm shaft size. I sharpened and balanced. I'm not sure if it's scale or not, maybe you can calculate the percentage... The boat is 1066 mm long, prop 37 mm, rudder is 76 mm tall and 32 mm at it's widest point. You have my curiosity about how much they are oversize. Thanks, Dave

https://youtube.com/shorts/IF1oJDFlnfo?si=oW0lElxDSEcFn7Ou

Hi River Rat, a question:
In addition to the rudder, did you also oversize the propeller or is it to scale?

Hi Peter, I am running a brushless 3660 motor, 60A speed control and a 2s 7.4v Lipo. I get about 25 minutes of run time.
RR

Good morning everyone.

Hi Peterd.
I was hoping that River Rat would intervene, because he made a splendid model similar to yours and has experience on this type of motorboat.
I almost brought it up.

In the first attached image the area outlined in red is (in my opinion) the one that influences the turn the most.
The area outlined in blue is the missing one.
In reality, as he rightly says, the rudder could be slightly oversized.

Many model makers, who make RC galleons or ancient vessels, are forced to use rudders ten (or more) times larger than the scale one because, not having the propeller, the scale rudder would be so small as to be irrelevant. That's not your case.
Regarding the scale dimensions of the rudders, if you want, you can read the forty-sixth and forty-eighth messages in the link at the end.

The configuration in the first image you posted is fine, and a balanced rudder could also be fine.
In addition to shortening the propeller axis, you could move the rudder axis (the pin) back, but I understand that this is a much more invasive job.

Could you show us a navigation video?

forum/128542

(River Rat) Just watching a video of a mahogony typhoon on you tube. Quite an impressive vessel.

What motor are you using? I am now running with a 550 brushed and a single 7200 nicad. (I originally had two batteries and a 750 motor but not really required.

Thanks Mike - unfortunately there is no room for twin rudders as the stern is very narrow (quite an effort to simply just mount the rudder arm). I appreciate all comments and am looking very seriously at the other option of rebuilding the rudder.
It is a simple matter to just move or shorten the shaft for the prop which will allow me to move approx 1.25 inches forward. New rudder and that should do the trick. I had also been looking at the assembly on the boat (image attached) whereby the propellor shaft is fitted to the rudder - this is a more direct drive distance to the propellor but similar principal.

I agree with Alessandro about the balanced rudder.
To achieve this the prop tube will need to be shorter with the prop positioned forward of its present position. A balanced rudder has a similar area forward of the pivot point as aft of it. This design puts least stress on the rudder servo because the pressure exerted on the rudder shaft is almost zero.
I love the shape of this boat.
Good luck with finding a solution. 😉

Hi Peter, Here's a picture of my Typhoon. The rudder is approximately 60mm from the propeller. The rudder is a little larger than scale. With this setup it turned to good, I had to slow down the steering servo rate to better control it. Included a picture (sorry for the poor photography) and a short video. I hope this helps you. I agree with Allessandro on shorten the prop shaft and tube and rework the rudder.

Oops, I overlooked the most important thing. 🙈🙈🙈
Alessandro, you're right. The best thing to do would be to put the screw back to the base of the shaft, then fit a completely new rudder without the recess. At that time I couldn't change the drive shaft, so I had fitted 2 rudders.
Good luck Peter!
Best wishes, Michel-C.

Hi Peterd

I have never built a boat like this and I am not a nautical expert (much less of fast motorboats).
There will certainly be better advice, I'll write to you what I think is wrong and how you could solve the problem.

There is something wrong with the project or subsequent modifications.
The vertical rudder pin is forward of the propeller.
It's an unusual situation, it's the first time I've seen it. The problem is that it's a very inconvenient situation.
The propeller must be forward of the rudder.

A very efficient rudder (perhaps the most effective of all) is the balanced rudder; it is the rudder with the central pivot.
In your situation you couldn't use it.

The rudder works best when it is hit by the propeller flow.
In general, a rudder affected by the flow of the moving propeller is much more effective than a rudder that only has the boat's forward motion.
If you look at your photo, you will see that the part of the rudder that is in front of the propeller flow is a small part of the entire surface area of the rudder.

The first solution would be to shorten the propeller axis, put the propeller forward of the rudder if possible and completely redesign the rudder (even better if with a symmetrical biconvex section).

The second solution is to redesign the rudder by increasing the surface area, especially that affected by the propeller flow.

I can't now, but this afternoon I will insert some drawings to help me understand better.
If I haven't explained myself well, just tell me.

Hello Peter!
I'm a landlubber, but I experienced this on one of my boats, which now "lives" with my son. I will ask him to send a few photos.
I had simply removed one rudder and fitted two to the left and right of the propeller so that the propulsion was diverted by one rudder each.
Is it correct? I'll leave the comments to the experts on this homepage!
Everyone, someone here needs help!
Who has better experience with this than me?
Servus Zamˋ
Michel-C.