Mini40 / F48 Class Trimaran foiling trials

My FireDragon with new laminar foils and a new wing on the rudder;



with the new wing on the rudder and my old turbulent foils




Nice videos Ronaldo. There are moments, when your tri is mainly on one foil, that seem to be nice examples of the lack of heave stability for angle boards (eg at 50 seconds in Clip #3), as described in the link Alan pointed us to in a recent post:

“Angle Boards - Every part of the foil span contributes evenly to vertical lift so, assuming enough foil angle is possible to lift the boat clear of the water, there is no stability in heave (ride height).”

I’ve been wondering if acute L foils could be used on a trimaran such as yours, and prevent this sort of instability. If the boards were quite short their height could be set so that they were out of the water when that float was out of the water (this might require the floats to be quite high, and hence may need a canting mast). Does this sound feasible?

Hi Roland - boat exhibits a nice “attitude” while sailing on the foils. Looks good. Not sure if it was the video playback speed or not, but a few of your tacks look to be “snap” tacks which will stall a lightweight multihull - unlike a monohull with a lead keel and some inertia behind it.

I am curious how well it points to windward with your foils, as the videos all seem to be reaching - or close to it.

Regards, Dick

Hi Mij,
the boat is built to mini40 rules, the foils are intended to provide foiling in ideal conditions. The boat is not built as a specific foiler which would have to be much wider and thus outside the class rules. The boat is sailing on one hull on a close reach which is like it should be. I might try l-foils if I have the spare time to do some to see the difference.
@Dick, as you know like all multis the boat is best on between a close reach and a broad reach , close hauled or running will slow it down. The FireDragon points about 45 deg to the wind without slowing down, I do not have much footage of going upwinds because looking at the stern is boring. You’re right I’m doing snap tacks when the boat is fast enough, that’s some extra fun.



Your boat foils really nicely for a Mini 40 trimaran. I was just interested to see theory in action, with the stability being lost when only one angled board was in the water. I hope you do get a chance to try L foils on your Fire Dragon, it would be really interesting to see how they compare.

By the way, I also reckon you should try a wing sail on one of your boats. I think that the Ninja would be particularly fast.


Hi Jim,
I will try L-foils on my Ninja Catamaran first because I have a second hull set I have set aside for foil trials. The foils are in the make already. A wing sail is the next on the list, but there is still the 2m project and like Dick I recently got entangled in off topic projects like building a smoker and do some sausage making - one must eat too :D.
I will post here when I have some news regarding my boats.