Skandia and Moth on Foils!!!

See the front page picture on: for an awesome picture of the huge state of the art ocean racer Skandia with a Moth on foils sailing along side-really cool!
Canting keels and hydrofoils in the same picture-I knew it was coming. Now all we need is a picture of them on the same boat!!! Exciting times…

Doug Lord
–High Technology Sailing/Racing

I was showing that picture to one of my full sized sailing friends at work, and he asked the question of the Moth: “how does he balance”.

We thought about it a bit and came to the conclusion that you would use a combination of an inverted pendulum balance technique (steering to keep the foils under the mast) and working the mainsheet (the classic windsurfer balance scenario). I’m not sure which is the more important skill to have or the more intuitive way to sail the boat, bu both require a pretty accurate feel for the boat trying to tip one way or the other.

So, lets translate that into RC boats. The timescale for an inverted pendulum tipping goes like the lenght of the pendulum (it takes longer for a broom handle to fall over than it takes for a pencil to fall over). Thus, the reaction time for an RC sized Moth (dare I say microMoth?) is going to be a lot shorter than the full sized boat require very quick reactions. It might be possible to do this with the rudder, but I’m not sure if sheeting is going to be as intuitive from shore. Now we add the extra degree of freedom which is the moving ballast and that adds a third item to add to the quick reactions list. At that point, we will probably not try adjusting the mainsheet, but do more of the ballancing with ballast. But the question still remains - can the guy on the sticks be quick enough and accurate enough to do it.

Another option would be to put the ballast under the control of a gyro. The gyro would be able to feel the tipping of the boat and react to it by shifting the ballast. The trick would then be what to do when the ballast rack is maxed out…

Now, to digress in the opposite direction - what about the maxi on hydrofoils: Forget about shifting the crew weight to constantly keep the boat in balance. The crew would mutiny after the first 10 minutes if they had to be constantly moving from one side of the boat to the other. Forget about using the main sheet to do it. The time it takes to make major changes in the trim of a fully loaded sail is way to long (plus the muscle men turning the grinders would not be real happy). So what are we left with? The helmsman having to steer the boat to keep the foils under the mast. Hmmmmm. Might be do-able given the longer timescale, but it seems like you would have a hard time in any tactical situation like windward leeward:

L: Keep it up!
W:I can’t, or I will loose my balance!
L: I don’t care, the rules are the rules! Keep clear!
W: (splash) I’ve fallen and I can’t get up!

The only other option would be to shift the ballast (canting keel). Pyewacket has to run their aux diesel to can’t their keel, so now you have to run that full time to keep the boat balanced? Seems like you would run out of diesel fuel in a big hurry. It might be better to put all that diesel fule to a better use and have it turn the screw. Put those pesky sail thingys away and use the motor.

I’m sure someone will figure out how to do it. I would love to take a ride on such a beast if it was ever built just to watch and see how they did it.

  • Will

Will Gorgen

The Moth guys say it’s easier to balance the boat on foils than sailing on the 1’ wide by 11’ LOA hull since the total lift is being developed on a foil significantly wider than the hull.
The microMOTH is a wild thing but off the foils balancing with the movable ballast in a steady breeze is a piece of cake; hasn’t been on foils yet but I expect it will be easer not harder on foils just based on the moth guys and the feel for it I have now-just a guess. But I don’t expect the micro MOTH to EVER be a popular class- too much to learn-time will tell.
One of the key elements you forgot to mention that will have a criical impact on a canting keel foiler(those that pay the royalty any way) is the “power up” flap on the lower part of the cantng keel strut(See Technology" below"). That flap will allow very precise quick adjustments of RM without moving the canting keel!

Doug Lord
–High Technology Sailing/Racing

Why on earth would you want a canting keel and foils on the same boat? The only benefit of foils is going to come from picking the boat up out of the water. When you add keel weight in to the picture it is that much more mass that has to be accelerated and lifted out of the water. Add to it that your going to have an additional keel strut since the foils won’t be mounted to your swinging keel and you have all that extra drag as well. You may fly a dinghy. Your not going to fly a 40 foot displacement monohull.

Unfortunately, Ryan you simply don’t know what you’re talking about!
An ultra light displacement 40 footer is the perfect size; combining a canting keel with a retractable main foil on a daggerboard and a rudder t-foil with a power flap on the canting keel strut and she will fly-no ,ifs ands or buts.
This scenario is one that Bill Lee(“fast is fun”) fully expects to see in the not too distant future-and I agree 100%!

Doug Lord
–High Technology Sailing/Racing

There will be “no ,ifs ands or buts” when it gets built and we see evidence of it flying. Even more so when you actually build a model with a keel and make it fly. One more thing we’ll be hearing about for years and then it will quietly dissappear when it doesn’t work.

lol now i have heard it all. Doug knows everything about big boats two.


Are you guys having a contest for the greatest lack of imagination?

Doug Lord
–High Technology Sailing/Racing

Another quote from Australian Sailing November 2003."Veal arrived at the venue,with his new 9.5kg Prowler hull (yes,9.5kg; with rig totalling 28kg) and hydrofoils, which required some getting used to on the Atlantic before racing started.
The hydrofoil setup, manufactured by John Ilett at Fastacraft in Perth, consists of a fully submerged t-foil rudder, made from a mold using pre-preg carbon fibre. The centreboard is a very thin, straight-section blade(120mm x 14.5mm), angled forward from the case towards the bow to stop air travelling down the blade. On the bottom of the centreboard is an 800mm NACA 63412 hydrofoil wing (120mm x 14mm).
The rudder is also a symmetrical straight blade which sits on the back of a large moulded carbon-fibre outrigger, to increase the distance between the two foils underwater and improve ride stability.
The two foils each have an adjustable flap at the trailing edge. The centreboard is automatically adjusted by a ride height sensor arm mounted at the bow on a moulded carbon-fibre bracket. The arm is actually a tapered fibreglass batten that is inserted into a slightly bent alloy tube.
This tube then attaches to a hinge on the bow bracket and allows the arm to swing up and down so that it just touches the water’s surface.
The constant touching of the water is maintained by some 2mm Spectra line passing through a micro pulley on the bow and attached to shock cord that leads back into the boat for adjustment. An adjustable cable then attaches to the top end of the alloy section on the control arm and leads back into the cockpit where it mounts onto a block just in front of the centreboard case. The end of this cable then attaches to a pivoting arm poking through the top of the centreboard.
Also attached to this arm is a thin fibre-glass rod that travels down to the bottom of the centreboard, where it attaches to the adjustable flap. Therefore, as the hull rests in the water when travelling at low speeds, the control arm is pushed back and up, which in turn adjusts the trailing edge flap so that it induces maximum lift on the centreboard hydrofoil to make the boat fly.
Once the boat is airborne, the control arm drops down to the water’s surface, retracted by shock cord, therefore adjusting the trailing edge flap and reducing the amount of lift created.
If it did not do this, the boat would simply want to keep on lifting until the foil lost pressure as it breaks the water’s surface. This would then be followed by a spectacular crash landing of the boat back down to the water’s surface.
If the foil does break the water’s surface, the moment is usually followed by a rather loud underwater explosion, like a bomb going off underneath the boat. The effect is increased when travelling at high speeds due to the increase in pressure around the foil.
From Veal’s experience, hydrofoil cavitation on the Moth is only caused when he is sitting too far back on the wing bar or when sailing into a big wave. However, this is easily counteracted by doing one or all of the following, Firstly, more tension can be applied to the shock cord which forces the end of the control arm to dig deeper in the water and hence reduce the lift force earlier. Secondly, move body weight forward once the boat is airborne to reduce the angle of attack and hence reduce lift, on both hydrofoil sections. Or finally, the rudder also has an adjustable trailing edge flap that can be manually controlled by means of twisting the tiller extension in either direction to induce lift or reduce lift.
If you can’t understand this, don’t blame me, it was the easiest way to answer some of the posts in this forum. Everything said here is as I have stated at the top of this post taken directly(quoted) from an article in the November 2003 edition of Australian Sailing.

The MOTH wand system is the same system used on he Rave multifoiler and is virtually identical to the one used on the F3 hydrofoil model. In both the multi examples the altitude control system using a wand on each ama allows the boat to develop its own righting moment getting more stable as the wind blows. In fact the limiting factor on a multi like the Rave or F3 is structural strength since the wands /foils generate so much power.
On the Moth the primary purpose of the wand is simply altitude control…

Doug Lord
–High Technology Sailing/Racing