Foiling radio control trimarans

[hump101]

Hello UpOnStands
We have considered fixing the rear T foil and having an independent rudder but never got round to designing it. In effect, the rudder could be located behind a skeg that has the T foil on it.

I've done this and it doesn't steer very well at all, it doesn't want to turn with two fixed surfaces in the longitudinal direction (the front foil and the fixed skeg).

 

[PerthMini40man]

I've done this and it doesn't steer very well at all, it doesn't want to turn with two fixed surfaces in the longitudinal direction (the front foil and the fixed skeg).

Thanks for that feedback - useful to know
Rgds

 

[UpOnStands]

I've done this and it doesn't steer very well at all, it doesn't want to turn with two fixed surfaces in the longitudinal direction (the front foil and the fixed skeg).

Very interesting, roughly what was the percentage split of the rear surfaces fixed (skeg)/movable(rudder)

 

[hump101]

Very interesting, roughly what was the percentage split of the rear surfaces fixed (skeg)/movable(rudder)

50:50, as both were made from a section of model helicopter rotor blade. The boat turned so quickly when on foils compared to when on the hulls (it was a catamaran, so slow to turn), but didn't want to turn at all with the skegs. Maybe if they had been smaller, it would have helped, but the lift generated by the skeg to oppose the turn seems to come from the leading edge in the model, more so than at full scale, hence I felt it wasn't worth even trying a small skeg. The helicopter blades are relatively thick sections, which probably didn't help.

 

[UpOnStands]

Thanks for the info
Makes sense. Foilers are much faster than ordinary cats. That makes proportioning the foils critical. One point is -- do you want extremely fast turning speeds when foiling a 46 foot 3500 kg cat at 30 knots?

 

[hump101]

Thanks for the info
Makes sense. Foilers are much faster than ordinary cats. That makes proportioning the foils critical. One point is -- do you want extremely fast turning speeds when foiling a 46 foot 3500 kg cat at 30 knots?

That's a pretty big radio controlled boat!!
Not the right thread, but yes you do, because it is in the transitions where the movement of apparent wind will give all the issues, so if you can turn quickly, you can stay on the foils, maintain speed, and transition the rig when it is relatively lightly loaded. The fastest turn doesn't apply the same accelerations that wave motion will, so it isn't like the forces will be high relative to normal motion.

 

[OzFred]

That's a pretty big radio controlled boat!!
Not the right thread, but yes you do, because it is in the transitions where the movement of apparent wind will give all the issues, so if you can turn quickly, you can stay on the foils, maintain speed, and transition the rig when it is relatively lightly loaded. The fastest turn doesn't apply the same accelerations that wave motion will, so it isn't like the forces will be high relative to normal motion.

While forces on the foils likely aren't an issue for RC boats (and maybe this is getting off topic), but for full-size boats the forces while foiling are hugely greater than in displacement mode. When everything is going to plan, yes, the forces may be reasonable and even "low" in comparison to extremes, but during manoeuvres, they can double.

On the AC 72s the forces on the foils went from 8t to 15t just by turning the boat. Do a crash gybe at 40kn and tell me the forces aren't huge!

 

[hump101]

That's my point, the forces can easily double, but that is nothing compared to the 5g that is seen when the hull is struck by a breaking wave, so if your boat can survive that, it can survive a 2g turn. The foils themselves can't be subjected to more force than they can generate, the extreme of which can be easily calculated (provided you don't hit a rock, obviously).

Back to the original point, if you don't turn quickly, then the apparent will move aft and the boat will drop off the foils, and in any seastate the loads will increase well above the 2g seen in a turn.

 

[PerthMini40man]

A good day today, the wind filled in for some decent sailing, and my latest attempts at sailmaking are an improvement on the past set of sails. The cut-down rudder looks perfect. its 29cm long from base of shaft to T foil. I tried my double foil at the end of the day but tests were inconclusive as I got the receiver wet inside the boat so had to stop. But the S foils are very good. I think it is sailing upwind better than my previous Mini40s in Australia, not sure if this is because of the new foils or the lower rig, or both!

Video is here:

Some pics attached too

 

[UpOnStands]

The stability is very impressive given that you have no in-flight foil adjuster?.

 

[Doug Lord]

Ian, the new foils are just great!

 

[PerthMini40man]

The stability is very impressive given that you have no in-flight foil adjuster?.

Yes that's correct, I can only adjust the foil angles by the screw-adjuster while on the shore - same for the rudder T foil. Once sailing they are fixed. A couple of people are looking at installing gyros, as used in rc helicopters, but I am cautious about adding a lot of electrics. I am constantly looking at wand-controlled configurations and think I am getting close to having another go at this idea

 

[UpOnStands]

I am constantly looking at wand-controlled configurations and think I am getting close to having another go at this idea

Wonder if a wand would work on the rudder/foil rather than the conventional arrangement on the front foils. We steer the boat through the stern. Might provide system damping.
Keep up with the innovations.

 

[OzFred]

Wonder if a wand would work on the rudder/foil rather than the conventional arrangement on the front foils.

The rudder foil adjusts pitch, not altitude so no, that won't work. Wand adjustment of the main foil directly affects height since the main foil carries all the weight, so a much more direct response.

 

[UpOnStands]

pitch of the hull will determine height, pitch down to lower, pitch up to raise. The control wand alternates between pitch up and down and gives you height.
Yes, its possible to directly raise and lower the main foils but that requires far more energy than controlling pitch.
Controlling pitch of the fwd foils directly would seem to yield a twitchy control system.
It might be a possibility, that is all.
At the moment PerthMini40 is getting interesting results with fixed foils, fwd and aft. Controlling just the aft foil - he already has the pitch system built in - would seem to be easiest.