T-foils on small multihulls?

I’m wondering how T-foils would work on a small multihull. Anyone having success using T-foils on a Mini40 or smaller or is the way to go with V-foils?

Siri -

back in early 2000-2001 Dough Lord (Microsail) did extensive work on a large foiler trimaran. He used T-foils controlled by wands that were adjustable and trailed in the water next to the main hull. Doug felt a foiler needed to be wider than long and I did have an opportunity to sail his foiler one weekend. A local fellow has one, and while it was “fun” - it became evident that the practical issues of variable/light winds (no flying) and lake/pond weeds all had an effect which might limit the concept to only big, open water sailing. Since so much of our r/c racing here is done on small ponds or lakes, the weeds were a big factor in buyer interest - along with a rather “steep” purchase price of up around $1800 or so (2001 dollars) when even new IOM boats (with huge international classes) were still less than $1000 at the time.

We are heading off for a weeks vacation, but if interested, I can send you what detail photos I have of the boat when we had it to sail when I return home.

PM me your email address and I’ll gather some and send to you. The idea to use mechanical linkage instead of electronic servos might work on a small trimaran. It was a 3 “T-Foil” concept - Two forward on front cross-beam and one on rear rudder.


Siri - found these - here is are photos of the adjustable side T-Foils from one of Doug’s boats.

In the photo, the T-foils hang down with moveable tabs at the bottom. The “wand” on the left has it’s drag portion (white tube) raised while the wand on the right has the tube extended. This allowed for height adjustment off the surface of the water. Red lines indicated optimum waterline.

If the boat was sitting without wind, the wands were down next to the hull. As the hulls moved forward, the wands dragged in water towards rear of boat, and adjusted the flaps into an “UP” position causing the boat to rise. As less water resistance was on the wand, they would move forward, flaps would level out and the foiler would seeks it correct height. If hulls rose too high, wands would adjust flaps to cause a downward adjustment bringing the hulls back closer to water. The major adjust ment was the amount of tension on each spring on each foil. Once both were adjusted with the proper tension, the boat cruise along. Again, adjustment of the white tube on wand was also critical in setting height off water surface.

The second photo gives an idea of size of the foiler in relationship to it’s owner.

The third photo illustrates quite clearly how even minor lake/pond weeds will effect the boat.

Another view of comparative size.

I really can’t recall if rear rudder flap was fixed level - or if it was servo controlled. Photos go back to August of 2002.

Cheers, Dick

Not sure if a foiler of 65cm size would have room/work - but shuld work on a F-48/Mini40 size boat.

Dear Dick,
thank you for the infos and pics. It seems that guy is the only one so far that managed to build T-foils on a small trimaran.
I found a lot about V-foils on a german language board, also some T-foil build but I think they have given up.

Found this a while back.

It may be of interest to ya.


Hi All,
This is my story !

Probably I’m going OT since the experimental work I have done was for my monohull Marblehead Studio3.

The basic idea was to find a dinamic method to counter act the tendency to produce a nose-down under gusting when running. Every body want to do that !

The winglets were supposes to be radio-controlled, going from a negative incidence when running to zero incidence in all others courses.

Before implementing the radio-control, I used a manual setting mounted coaxially to the rudder stock. The incidence can be varied from +2° to - 4°
What came out from this experiment was that with low wind and low speed, the added wet surface did not produced noticeable effects when running even with -3° setting, instead with wind above 6-7 knt, the system started working properly and getting better with gust above 13-15 knt.

This was remarked beacause others Marblehead sailing at the same time were going nose-down rather often. I had assumed the the winglets were efficients.

The problem was, that not being radiocontrolled yet, I could not change incidence during sailing to restore the 0° when clode-haul.

The winglets negative incidence added to some 25°-30° of hell, acted as a rudder and deviating the boat course and increasing the drifting . This was my impression.

Conclusion : the winglets are still on the rudder but adjusted manually to 0° incidence, one day I will substitute the rudder and put another one free from winglets !

Obviously I did not continued to search for better efficiency changing form and dimensions, further the Class M Rules do not allow a third servo. By the way, one of the possible control system was based upon the use of a ‘memory wire’.

Lesson learn : I will try to anticipate the nose down …uhm , I have to think better !!!


As consequence of the experience made on the Studio3, I have introced a fix winglet on the CD65 rudder. It appears to work well, but i didn’t got yet opportunity to test it under stronger wind conditions.
Soom the above rudder configuration will be used on my next project concerning an RG65 with a Delta Rig.