Short Amas and Single Beam ?

MCM, I tried to answer your questions in red below:

 

This all leads me to questions about the geometry of the set-up.

The flight lift-off angle of heel should be less than 15deg. right ? So the two factors here are the desired wind pressure for lift-off, the lifting power of the two foils (vaka and ama), and distance between the two foils.

Is that what determines the best span distance for the beam ?

Then there's the question of foil alignment between main and float foils along the fore and aft line.
And their relationship to center of effort and center of lateral resistance.

Up-tips in the amas and t-foils for main and rudder, but only the main foil needs wand control ?

The t-rudder can be transom mounted and kick-up, but i can't help but wish the other foils could be side mounted and thus kick-up instead of in-hull and crash-boxed.

 

Ama foils can be kick-up.

For a longer displacement ama, they can be mounted just aft of the beam on the inside surface similar to a leeboard.

For a planing ama, they can be easily mounted on the outside like a leeboard (as I did).

It may be possible to mount ama foils on the rear of a short displacement ama similar to a transom hung rudder. The ama to beam connection would need to be near the rear of the ama and the beam would need to be designed for lots of torsion loading.

It may also be possible to mount an uptip ama foil on the outside surface like a leeboard if it is close enough to the back.

For kick up lifting foils and Tee rudders you really need an adjustable solid stop at full forward and you need to make sure it does not kick up unless you hit something solid. The location of the pivot point is part of this puzzle. I put the pivot point near the back edge on my Tee rudder so that it would "lock in place" when lifting. However, on a downwind run it produced enough negative lift to overcome friction and kicked up. I have added a bungee loop that will keep it locked in place better (I hope).

 

Since the boat takes off in around 5mph(4.4knots) of wind it is nearly level-maybe a 5 degree angle of heel. But the angle of heel doesn't matter that much. She is set up at present for about a 10 degree angle of heel when fully foiling.
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Since this is a scale model of a 19.5' boat what determines maximum beam is the strength of the beams. I wanted beams with no waterstays(a diagonal stay between just above the waterline of the main hull out to the beam). Using water stays could allow more beam but this boat doesn't need more beam. A contributing factor in deciding on beam is the designed flying angle if a full flying foiler OR the "just flying angle of heel" -that is the angle of heel when the ama or ama+foil first takes the whole load.
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The quarter chord point of the ama foil is slightly ahead of the daggerboard quarter chord point.
On multies,I generally use the quarter chord point of the rig as a whole with more weight given to the jib than if only its area was considered. Over many years that has worked very well in producing a boat that is well balanced with slight weather helm.
The main foil and ama foils will be retractable on the full size boat and there is a high likelihood that the main foil will be shortened about 2.5' to 3.5' from the present 6'. I didn't want to have any trouble with the main foil popping loose so I made the main and rudder foil deeper than I hoped they would need. And they can definitely be made shorter. The ama foils on the full size boat will be retractable and may be able to be lowered about a foot from where they are now(3.375" if it was done on the model)-that I haven't decided on for sure. All foil controls that need adjustment while sailing will have their controls led to the cockpit.
One of the few disadvantages of most foilers is that retractable foils can't kick up-they have to move vertically.If the rudder was to kick up while the boat was moving something serious would break! Some rudders on A Class cats kick up but they have a very small rudder hydrofoil. Still, I imagine if one of those kicked up at serious speed there might be trouble. If my ama foils kicked up at speed there would be catastrophic failure in the near vicinity of the foil and its mount.......Moths don't even have retractable foils and have to be carried out to deep water on their side! Dr. Sam Bradfield was a pioneer in making his hydrofoils retractable-but you have to retract them before you hit something.
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The main foil is controlled by how the wand is set(length of the wand), and in turn, working with the trailing rudder foil, those two control the pitch angle of the boat and the running angle of the UptiP ama foil.The cool thing about UptiP foils is that they control their own altitude-you can see clear examples of that in the pictures marked "A" and "B" below. "A" shows the main hull in the water but the ama is flying. "B" shows the whole boat flying yet the ama still has the same altitude it had before the main hull flew. The ama foil lift increases due to leeway and speed so as the boat sped up the lift on the ama foil increased as the force on the sail did yet the ama foil maintained its altitude even though its speed and load changed! No other single foil has ever been able to control it's own altitude with no moving parts throughout the speed range of the boat. It's really a breakthru type of foil design whose principle was invented by TNZ in AC34. It is the perfect ama foil for the Fire Arrow configuration.

 

MCM, here are some shots of Dr. Bradfields fairly recent 18'(by 22' wide) foiling trimaran,Osprey, using wands on each ama foil with all foils being retractable:

 

So side mount is possible, that's good news, and your t-rudder kicks up.

That's great as well, but do your side mounted ama foils have any horizontal bend to them.

That could change the picture, and change it even more if there are sailing speeds that would prevent a kick-up without damage.

Most foils around aren't kick-ups, but i don't know if my reaction time is quick enough at those speeds with that wide a span of beam.

 

You blokes need to consider that loads on hydrofoils are very, very high, when sailing at speed - and if you have kick up versions, you had better make sure they don't kick up unintentionally ... because if that occurs on the main foils, you'll be in deep defecation; like lee float/foil twist and bury and definite breakage ... and if the rudder T foil kicks up, the complete assembly plus your transom will also definitely be spat out from the excessive drag like an obese persons' flatulence.

 

Jim Brown's review of Dr. Bradfield's fully flying, foiling tri 'Osprey'. A glowing review that would inspire even the most doubtful.
http://smalltrimarans.com/blog/?p=8890

Thanks again for taking the time and trouble to share all the useful info - i'm saving every word of it.

 

That implies that even intentionally you had better be going slow !

 

The rudder on my boat extends down much more than the ama foils and has hit bottom many times. Probably max speed at ground impact has been close to 8 - 10 kts. So far, kick up at speed has not been fun, but has not caused any real problems. I do worry that a really fast grounding may result in excessive loads on something.

The ama foil groundings have mostly been as I was driving the boat up on shore. However, I have had rotation due to slippage while going faster. The drag at the ama has gone way up, but again, no failures or crashes yet. Ama foil remote retraction and deployment control is still an area I consider "ripe for improvement" on my boat.

The attached photos are from late October and do not reflect several changes. However, they do give you some idea. Remember that this is not intended to be a "finished boat", it is only a constantly evolving "test platform".

 

Those are serious foils !
Where are the amas ?
I didn't notice, did you have a main foil on the main hull ?
That test platform looks life size and it sounds like you've done some valuable real life testing at 10knts +.
Does it fly ?
I know some of us hope you'll let us know all the test results !!


To my mind, a kick-up allows the foil to give way on impact and should cause significantly less damage.
Especially if the kick-up is held in place by a break-away release.
Keep it tied to a lanyard and reel it back in after a break-away.

 

The starboard ama is there, it is just so small that you did not recognize it. It is approx 1' wide, 2' long, with a 3" thick chunk of foam on top for flotation. I will include an early photo of it in the water at low speed.

No "main foil".

"Life size" is pretty close to "minimum usable size", approx 11' main hull. Around 80 lbs with small sail.

Inverted Tee rudders are getting widespread use. I am sure that some have kick up versions that are much better mine. Ideal would be to figure out how to have the tee portion pivot all the way out of the water.

No flying yet. Go read the boat specific thread (link below) for details of my testing. For general questions on my specific boat, posting in that thread would probably be better.

http://www.boatdesign.net/forums/multihulls/small-tri-test-platform-51551.html​