??? ... a boat with 4 retractable legs w/lifting foils

?? You do know that the PHM foil system was highly 'active', right? The vessels could not be flown without it..without the flight control system. As recently as 2003 we delivered the flight controls for a hydrofoil; the actively controlled foilers (Boeing ferry, PHM, etc) were always superior in terms of decoupling from surface wave energy and resulting ride quality. And yet, that very complexity is indeed what drove ther costs and limited their acceptance.

or..were you commenting only on that active suspension concept in particular in Payne's creation? I probably read you wrong. Peter was nothing if not both prolific and 'outside the box' with his naval inventions..

 

But there are SES' in naval combatant service today. No hydrofoils that I'm aware of.

But I'm no partisan by any means; I 'like' and support all AMV types and always have. Each has (or in some cases, 'had') a niche role to play.

 

I understand that fully submerged foil systems need to have active controls. Generally active flaps on the foils. The struts, however, are usually fixed. Payne seems to be taking the addition step of making the entire strut active. I just seems to me we was trying to fix a non-problem. Fixed struts seemed to work fine from what I could see as long as you active flap controls.

Since you have experience with hydrofoils, What do you think of the idea of a outboard powered hydrofoil with three submerged t-foils, one forward and two aft. Instead of a powered electronic control system, each t-foil would have its own height sensing wand and linkage, similar to the main foil on a Moth sailboat. The outboard motor would be on a jacking plate to allow it to be lowered for foilborne operation. The foil struts could be raised and lowered in a daggerboard style. This would allow for full foil and engine retraction for shallow water operation and trailering. I am actually considering building such a thing for my own use. I am curious if you think I am overlooking something with the concept.

I am not sure how turning would work out. I think it would turn pretty flat. The roll would be controlled by the two aft foil assemblies and the height sensing wands/linkages would resist roll in either direction. It would probably be nicer if it banked into turns but I am not looking to run a slalom course with it.

 

100% correct on all accounts. In Payne's 'defense' if there is one, Japanes researchers built a demonstrator that supported the passenger 'cabin' module above the hull on active structs, much like an aircraft simulator cabin.

That didn't work very well except under certain conditions; hard stop motion limits being what they are.

The last hydrofoil demonstrator that we built and tested almost 10 years ago was a 'tail dragger' with the main lifting foil mounted just forward of LCG carrying 80% of the weight and the aft foil (an "H" foil but two "T" foils would accomplish the same thing) carrying 20%. It was propelled by two outboard motors; long shafts modified with the lowered 'racing' water pickups.

But there is where my comments to your query naturally end; our foils were actively controlled (5 flaps on forward main fail, single flap on aft foil) and the entire flight and steering control system was fly-by-wire. A microwave radar unit mounted on a small pylon extending from the bow provided the computer with flying height information.

I cannot imagine how a mechanical surface wand height control scheme would deal with large waves; not well I would guess. With the computerized system, there were algorithms in place to ignore short-term deviations in height of sea surface if that was the desired operating mode (called "platforming") or to follow the surface closely when in very high waves of long period (called "contouring").

 

Actually, the mechanical wand I am thinking of would actually be a rigid bar dragging in the water behind the strut. Because the bar would be relatively heavy for its surface area and move slowly, it would tend to ignore smaller waves and instead find the average water level. Large waves like swells would cause it to move and adjust the foil while short quick waves would be ignored or at least be "averaged". At least, that is what I am envisioning. Reality may have other plans. I will probably build a scale model to tow before committing real money to build an actual boat.

 

I can see that possibly being a true mechanical analog to the computational/controls solution, yes. Add a sliding weight to your rigid bar that could be raised/lowered remotely by a cable or string line so that the average immersion and the response to surface elevation could be 'tuned' underway...and I think you are on to something. Or is that already how the sailing foilers do it anyway?

 

The moth seems to use a very thin, flexible rod as a height sensing wand. I am not sure how it would handle big waves but its length and flexibility probably tend to act as a filter for the small waves. I don't think they have a way to tune it underway. I believe the stern foil is controlled manually on the tiller which is probably one reason why the altitude of the boats seems to vary so much.

http://www.youtube.com/watch?v=MImHbSWKsSk&feature=related

 

The wand does de-bounce the input somewhat. Sessions on the Moth are usually time limited by the person's stamina and strength - so on-the-water tuning isn't as much of an issue as many would think. At my club the Moth sessions are frequently interrupted by shore breaks where any tuning is done.

Moth altitude varies more due to wind strength and point of sail than anything else. The foils are optimized primarily for speed, not maximum lift, so a Moth with maximum lift and highest possible ride would be most likely slower. Also, the helm's weight is a huge variable - two people using the exact same boat will have different ride heights due to weight and trim differences. High ride heights bring ventilation into play.

--
CutOnce