Just wondering Doug why your foilers are tris (barr the monos of course)? surely a cat could be built lighter?
If its not blowing it sucks!
No way a cat could be built lighter! The two outside hulls can weigh as little as 60%(even less) of the weight of the main hull. The key design decision is how much total reserve buoyanccy is required. Many tris have ama’s that have a total(100% immersion) displacement of around 200% of the boats weight;that is necessary particulary on fast non foiling tri’s so that the flat sides of the ama aren’t immersed too much keeping the wetted surface low when the main hull flies.
On a foiler you just have to have enough total buoyancy so that you are comfortable that in an Xmph gust the boat will accelerate not turn over. That can be less than 75% of total buoyancy depending on overall beam-in other words on a foiler design the outside hulls are not sailed on in stronger winds-they are simply there to prevent capsize while tacking IF the boat doesn’t stay on foils while tacking or is stopped for some other reason; the more beam the smaller the ama, the less the weight.And the tri only needs one torsionally reinforced cross arm to be sufficiently stiff to carry the main foils.
The tri config is without a doubt the best for producing the lightest possible foiler,in my opinion.
But it still requires three hydrofoils and a monohull can have only two…
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
The Europeans didn’t use foils because they didn’t know how to and solve the biggest problem with them which is what to do in lite air. Once a reliable lightweight retractable foil system is available foils will be king in most conditions and small multihulls will be a lot easier to sail in most heavy conditions.
And unless small multihull designers and builders spend a lot of time solving the inherent squirreliness of these small multis people will be doing the same old thing: getting discouraged about sailing these boats.
mini 40’s have shown a big decline in Europe ad I venture to say it is because they are difficult to learn to sail in medium to heavy air. And if mini40’s/F48’s are difficult for beginners to learn to sail where will growth come from? And multiONES will be another order of magnitude harder to sail-as people will find out on their own.
What I am saying is that the pioneers in these two classes need to recognize that there is a serious problem and set out to find solutions not just go on as if this was 1960. We can make these boats exciting reliable speed machines capable of beating any monohull in most conditions but not if these problems are not addressed.
I’ve done as much as possible by putting in writing as much as I know about foils and by being willing to help anyone willing to experiment.
But promoting the sale of boats that do not address the peculier characteristics of this size multihull is just setting customers up for big time discouragement. We have the knowledge of the decline in mini 40 participation in Europe as well as the knowledge of the first AMYA recognized multihull class the Trident to draw from and we really ought to solve these problems once and for all.
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
I think the MultiOne can open up a “whole new type of sailing”. I think it will require a complete change in thinking. What does a 1-1.5lb boat with foils sail like? I don’t think it would ever be possible to sail a bigger boat with similar light loadings. The advantage is that less weight means smaller foils which means less drag. I think there could be a happy medium without retracting foils. Granted it would be a compromise, but would work. So what do you guys think, who will have the first 16 oz foiler?
Kristopher
Doug,
I am familiar with the hydrofoils commanding “full up” problem you aluded to. Here is the boat that I worked on in college: http://lancet.mit.edu/decavitator/ . The pilot had two controls: In the right hand was a rudder which steers the front T-foils. In the left hand was a stick much like a collective stick on a hilocopter that would control the angle of attack of the maoin wings under the fusalage and thereby control the “altitude” above the water.
To get up on the foils, you would start off by pedalling as hard as you could while holding the stick all the way down. Then when you had achieved takeoff speed, you would pull up on the stick and the hulls would pop up out of the water. At this point the boat would accelerate very quickly and you soon had to be pushing the stick back down. If you fly too high, the foils get close to the water’s surface and begin to create some wave drag. But worse than that, you would risk ventalation which would cause the foils to loose all their lift and you would come crashing back down into the water. You wanted to fly as low as possible (2 or 3 inches above the water) without touching the water.
We used a two stage main wing in a ladder configuration with a larger wing for takeoff and a smaller wing for higher speed. The larger wing was hinged so that it would swing forward and up. It was spring loaded to swing up. There was a safety latch to hold it in the down position while you were just puttering around. Once you were flying on the large wing, you would release the safety latch and accelerate to transition speed. Once you were up to speed, you would pull up on the bar and as soon as the large wing cleared the surface, it would swing up out of the way. At which point you would be flying on only the smaller wing. But again, you wanted to fly as low to the surface as possible.
So for your foilers, you may want to consider a mechanism that will allow the foils to neutrallize their lift. You would need to disconnect or slacken the connection between the wands and the flap. When you were ready to foil, you could reconnect or takeup the slack so that the wands were again commanding “takeoff lift” from the foils. This may be a good alternative to retractible foils for lighter winds… It should be as easy to accomplish (mechanically) as the retractible foils.
You may want to think about a way to include both in a retract system. In other words, the first half of the servo movement will deploy the foils. The second half of the servo movement will tighten the connection between the wand and the flaps causing the foils to command “lift off”. This way when you deploy the foils they will not be in the high drag “lift off” position as they enter the water.
I think you should also tune your wand settings so that the boat flys as low as possible. I noticed on the F3 video on your website that it looks like your foils ventilate a couple of times. The boat is flying quite high and then crashes back into the water - classic ventilation. Flying lower will prevent this and will also reduce the drag a bit (I think I see some surface waves from your foils which means they are too close to the surface).
- Will
Will Gorgen
Will, the F3 was flying high mainly because those pixs were taken on the very first day after building was complete and the wands were set for max height(?) which I guestimated might be as little as 1/2 the theoretically correct height(2.5 times the chord). I’m not sure it can be seen in the video but in stills you can see the red lines painted on each vertical fin marking the theoretical flight waterline.
My secretary can’t open the video David posted and I don’t have the original anymore so I won’t be able to look at it again for some time. But as I said off the forum I don’t believe the F3 ever ventillated ; that would show up as a fairly distinct rock to the lee side in the light air of the video or a catastrophic pitchpole capsize in heavier air which never happened . In fact for different reasons the main foils have come completely clear of the water and re-entered with no problem. If a foil was going to ventilate it would probably do it then as it does on the full size Rave sometimes(and why Dr. Bradfield doesn’t think jumping my 16’ foiler will work) But on the model it seems very difficult to cause the foils to ventilate regardless of speed or conditions–as best I can tell it has never happened.Might be because of Reynolds numbers and the flow re-attaching more easily at model size than full size.But flying too high is a problem when going upwind since the boat makes a lot of leeway with just 1.5–2" of vertical fin in the water: ideally the boat should be sailed upwind with the hull relatively close to the water and offwind fairly high. But that takes an adjustable wand length-which Dr. Sam has on the Skat.
The full size Rave has a clutch on the wands for light air sailing that allows the flaps to stay in neutral-could be an improvement to the F3 if I don’t put a retracting system on it. I believe that the F3, X3 and the microMOTH can be made to jump and re-enter safely just for the fun of it- I’ll know shortly since the microMOTH is rigged without a wand and altitude is controlled manually.I use the term controlled loosely because all indications are that the microMOTH will be exceedingly difficult to control in flight. First flight tests any day now.
I think the F3 and X3 can be slightly modified to jump at the whim of the skipper using a servo to bypass both wands…Later for that.
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing