Cheers Mike,

<<At the very least you'll have a platform for experimentation.>>

Yes.  Undoubtedly there'll be plenty of that.  But I hope that the last year has been well spent writing the CAD package, designing the boat and engineering the structure with these foiling loads in mind.

I certainly want the foils to kick up in a collision - but not in advance of it Luc.  If we're about to hit a solid object I don't want the foil to chicken out because a wand has told it to do so.  When it comes to collisions, the foil should act in response not in advance.  When it comes to the amount of damage done: a foil has a thicker skin than a hull.

As to foil configuration, a fully submerged T foil is more likely to foul completely than a ladder or V foil - the latter having reserve foil surface area above the waterline capable of damping the loss of lift.  Mind you, it's one hell of a plastic bag or a fishing net that causes catastrophic loss of lift that could precipitate a nose dive.  Solid objects such as logs and shipping containers, I conjecture, are more likely to support the boat if it has foiled onto the object.  A catastrophic event is perhaps more likely if the boat has sailed into the object.

Another point worth mentioning is that pitch stability requires that the forward foil is more heavily loaded - see Tom Speer's A-Class paper http://www.tspeer.com/Aclass/A-ClassCatamaranFoils.pdf

 and YouTube presentation from Foiling Week TFW Forum day 2

			TFW Forum day 2 July 9th 9.00-9.15 Introduction 9.15-9.45 Key note speech Tom Speer -- Hydrodynamics of A-Class Catamaran Dagger Foils 9.45-10.45 Session 3 -- H...
			View on www.youtube.com	Preview by Yahoo

As a result the angle of attack on rear foil should be lower so that in a pitch down situation, the stern will not simply follow the bow down, but lead or match it.

<<Putting foils on those rudders on the lee hull, particularly if you create stub beams to mount them further towards the ends, could enable the kick-up, and if you rotate them 180 degrees each shunt, would also enable the foils to work in both directions.  The rudders would have to take some big loads, but they already do, and that's something you can design for if needed.>>

The thing that I am most mindful of is that, yes I can design in the features you describe, and they are part of the design brief, but what will they weigh?  And what will this weight contribute to pitching dynamics?  I've toyed with 180 degree rotation with kick-up and to put it mildly: the challenge of designing to a weight limit is enormous.  Firstly how much hull clearance should the foil mounting stub provide?  Only if this foil resembles the rear foil on C-fly would the answer be 'minimal'.  But a canard rudder should be balanced and you couldn't simply rotate this foil through 180 degrees.  Whether the foil resembles the C-fly canard, a T foil or a ladder is not important yet.  Essentially, the answer is: well in excess of a metre long!  The loads are mindboggling.  From my engineering analysis, I'm pleasantly surprised at how light a foil can be - but the supporting structure?  Designing to this brief sees either the weight or the sheer structural volume yielding a white elephant  (more likely a pig as it would probably look and perform like one).

You could design in an off angle kick-up, but this mechanism would possibly be in addition to the foil pitch mechanism which is ideally in line with the direction of travel.

It's time to start thinking outside the box.  In displacement conditions, its better if the foils are out of the water.  So perhaps pivot the foils down over the rudder when conditions suit.  If an object is hit with foils down, the fuse allows the rudder to pivot and releases the foil completely, though perhaps tethered to the craft with a cable. This enables the unit to be placed close to the hull.

Rotating the entire unit through 180 degrees is still particularly challenging from a weight perspective, so I'm toying with using double ended foils along the lines of Speer's proa series foils.  I'm mucking around with Xfoil comparing the proa foils, the H105 and my own designs in order to see if this is possible.

The biggest problem with canard steering is working out the maximum angle of attack, taking into account pitching, sea state and rudder angle.  If the angle of attack is too great, the foil stalls, which is why C-fly is using super-ventilated foils.  A V foil will be subjected to higher attack angles than a T foil when steering, so perhaps it's worth toying with ladder T foils in light of my observations thus far?  All conjecture at this stage.  Hopefully I'll also be able to do some CFD analyses before I commit to building foils.

I must correct some sloppy editorial work in post 10442.  "These attributes are due to raising the Fig. 1, Williwaw sailing at Pacific Multihull Association speed trials, 1975 hulls out of the water and away from wave disturbances, by the increased dampening provided by the hydrofoils, and through the increased stability afforded by widely spaced foil units."

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