Cruisingfoiler -"For a start, it’s not trivial to rotate a rudder through 180 degrees.  At least in the configuration I envisage.  This config sees the foils mounted on stub beams fairly close to the extreme ends of the craft in order to increase pitch stability.  The loads that these foils subject upon hull and stub beam are not trivial.  A finite element analysis demonstrates this.  If you need to rotate thru 180 degrees, the stub beam is longer, increasing the loads.  A symmetrical lifting foil has span.  If kickup is required then the kickup pivot must be angled outward so the foil will kickup outward and clear the hull.  I’m exploring doing all these things but it ain’t trivial.  (Note that you said “trivial to set up)"

Yes, in your configuration it is extremely hard, especially with a kick up rudder at the extremities. Close to impossible, unless weight and money isn't a consideration. What I envision is a cassette in a rotating drum, that does not kick up and is not at the extremities. Like I said, trivial.

Crusingfoiler - "The clarity issue related to pitch stability, not angle through rotation – read what I said.  This depends upon foil config.  I must presume you are referring to T foils without active flap control – a conclusion that depends upon a missing premise in your argument (which is generally a sign that the argument suffers from confirmation bias).  Did you read the links I provided?  Your comments here are at odds with the pitch and heave stability achieved by C-Fly.  Further, although I don’t like the J foils for offshore wave profiling, they are pitch and heave stable (if the rudder angle can be adjusted and wave length is substantially shorter than the foil separation) through leeway modulation (if you don’t know what this is find out what Tom Speer has said on Boat Design forum and watch the Battle of the Bats video link I provided  few days ago).  The asymmetric configuration is not upon first inspection, particularly suited to rotating thru 180 degrees."

I must apologize for not making myself clear. The GOE611 foil configuration without flaps and it doesn't really matter whether it is a T, L, J, C, configuration.

No I didn't bother reading the links you provided, because I have already exchanged a few emails discussing the C-Fly and foiling with Tom Speers and I have been trying to figure out the cavitation and ventilation issues they have. I was kind of waiting for you to bring them up first. You wouldn't happen to be Doug Lord would you? And yes you are correct the C-Fly's asymmetric configuration is not very suitable for shunting, where simply rotating the GOE611 foil is.

Cruisingfoiler - "This statement fails to address the pitch and heave stability of surface piercing foils – again refer to C-Fly.  You cannot directly translate experiences from air planes to foil borne craft.  Foil borne sailing craft are operating at the boundary of two fluids of substantially different density.  Surface piercing foils take advantage of this change in density."

 

I think you have a fundamental misunderstanding of how foils work.  A foil loses lift at the boundary layer and when ventilating or cavitating. C-Fly's trick seems to be using controlled cavitation (stalling) of the front canard to keep the canard submerged and maintain altitude control. Kind of an automatic wand if you will. It is a nice elegant solution without needing a mechanical fix.

Cruisingfoiler - "Again a certain degree of confirmation bias is present.  You are presuming that a canard foiled boat will exhibit the same characteristics – and that this porpoising is a problem.  If a surface piercing canard loses lift it will sink somewhat, decrease its angle of attack and increase its surface area. As the canard pushes through a wave it will lift the bow, correcting the angle of attack of the main foil (initially).  Having broken through the wave the canard reduces lift area and increases attack angle, potentially stalling and sinking before increased area and reducing attack angle, leading to recovery.  While the main foil remains behind the wave crest, the increased angle of attack may precipitate a stall.  So what!  The middle of the hull settles into the wave crest, reducing the angle of attack of the canard (and the likelihood of stall) as it reaches the trough.  Again your assumptions are incorrect in this environment."

I have no actual experience sailing a foil borne boat especially a foiling canard, I would love to have a go on a Moth : ) So you may be correct that my assumptions are wrong. It won't be the first or the last time : ) Also your description is closer to foil assist than flying.

Let me detail the assumptions I am making about your foiled canard.  First of all for an ocean going vessel, looking to foil at 20 knots, you are looking at least 17 knot winds and 2+ meter waves.  That means that the primary lifting foils have to be at least 3 meters below the hull to stay immersed and functioning for the expected conditions. The windward hull needs to be flying at least 3 meters above the wave troughs also.

The C-Fly leading foil has to be able to almost completely submerge as it passes through 2+M waves without increasing lift or drag to keep the boat level.  Call it what you will, pitch control, heaving, altitude control, they are much the same thing. The C-Fly system works by destroying the lift of the upper portion of the lifting foils via cavitation as it passes through the wave ideally without increasing drag too much.  Wands do the same thing except via an aileron or horizontal stabilizer.

I think the reason they haven't gotten the funding for a full scale model is that it may not work very well (It may not scale well). There is a reason flying boats aren't the preferred offshore mode of travel.

If the leading foil broaches the surface it loses lift and increases drag dramatically, pitching the bow downward and raising the aft portion of the boat and the windward hull.  If the speed is great enough the boat will pitchpole. A wave impacting the middle of the hull will just make it pitchpole faster.

On the other hand, my idea of foil assist, relies on the boat hull staying in contact with the water and keeping the foils small enough to prevent completely lifting the hull out of the water. It is trivial to calculate the lift and surface area required to almost lift the leeward hull out of the water at 20 knots and dramatically decrease the coefficient of wave drag at that speed.  Except for situations like surfing down a long steep wave there would be almost no chance of pitchpoling.

If you want to fly, I'll take you for a ride. I love tooling along at 200 knots in ground effect along a coast or up a river.