Nice model, though.
Do you have a video or YouTube link?

Allesandro yes, sticking to the OEM is first prize. However, when it's a kit build it doesn't really matter to me. This particular kit is old and was damaged a few times in its life.

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.

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

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.

forum/135991

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.

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.

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

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.

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