Most models I see with that type of hull tend to be a bit unstable and flop into turns so I’m not surprised you are getting some torque roll. Whilst the prop can be a factor and 3 blade ones I understand are better in this respect the motor itself can have an influence as well but that is difficult to eradicate unless you go for a twin contra-rotating set up. A smaller 3 blade is definitely worth trying.

Chris

If it makes you feel any better Dave mine flops over and ‘digs in’ when I turn hard to starboard.  I just trimmed a bit off the rudder movement so now if I want to turn sharply I have to slow down.

As Chris says the real solution is two contra rotating props but I’m certainly not going to rip mine apart for the sake of doing that.  It actually handles beautifully at full speed as long as the turns are gentle so I’m quite happy with that.

Dave, that is definitely torque reaction, as suggested.  Basically two approaches, either reduce the torque, which can have performance effects as well, or stabilise the hull.  The challenges there are that you tend to be able to improve the stability for one specific speed, usually the fastest, but the model remains unstable at other speeds.

Always a bit hit and miss but the solution might be a combination of the suggestions made above.  Good luck with the experimenting!  I’ll measure up the prop I have on mine later and let you know the size.  As I said I’m happy with the stability at speed and just have to remember to slow a little for starboard turns.

Adding a wedge is an accepted solution but, as Charles says, you may have to experiment. Simply adding weight on one side will make the boat slump over slightly at rest and low speed. This may or may not matter to you. My SLEC Fairey Huntsman kit model adopts a nose down attitude at rest but is fine once it gets going. Dave Milbourn’s prototype did not exhibit that characteristic and we had a discussion about that. It is possible that I had carved a bit too much away from the bow block to get the Fairey shape which reduced forward buoyancy.

Dave also suggested a 3S LiPo pack to power the model and restrict rudder movement but I still found that the boat turned on its side in a turn so I substituted a 2S pack which made things more civilised. The wider Swordsman was more stable and coped OK with the 3S pack.

In an ideal world, twin screws are the way to go but for practical reasons many boats rely on one and you have to accommodate the consequences of that. Solve one problem and create another! All good fun!

Colin

Glad you got there Dave.  When you get these just right they do put a smile on your face when you put them through their paces.

Hi there Dave

Yes, you are quite correct about the RTTL shafts driving the same direction.  I built my model several years ago.  I used Vic Smeed’s plans as the basics with several other pieces of information I received from Christian Sheppard – he was such a great help in building my model.

Couple of pics to look at.

Going back to where I mentioned the Surfury, what I meant to mention as well (and it completely slipped my mind, as things generally do these days).  Surfury power boat’s engine configuration was 2 engines in line facing each other; driving through a specially adapted gearbox to a single propeller shaft.   The reason for this is that one engine rotates clockwise and the other engine will be rotating anti-clockwise so, in theory, cancelling out a lot of the torque affect.  So that will clear that up.

john