Rotating Wing Mast – theoretical discussion

[gggGuest]

Originally Posted by petereng

Has anyone seen hydrofoils that are controlled to force down in response to heeling?

This happens on any wand equipped multihull like the Hobie trifoiler, so its been done plenty of times. I think the lack of popularity of such compared to the Moths suggests that it may not be the right approach...

[P Flados]

The current fastest Class B sailboat is Sailrocket at 47.36 kts (http://www.sailrocket.com/). From their web site:

Vestas SailRocket employs a wholly different concept (first documented by Bernard Smith in the 1960s) in which the sail and keel elements are positioned so that there is virtually no overturning moment and no net vertical lift. When used correctly this concept results in a boat which no longer has obvious stability limits and in which the only significant response to gusts is a change in speed!

The Ketterman brothers were the first to use an active control system to pull down on the windward side. This culminated in the Longshot (current Class A record holder at 43.55 kts) and eventually turned into the Hobie trifoiler (http://www.hobiecat.com/sailboats/trifoiler/).

Given that the two examples above are the current world record holders for their respective classes, there is more than a little merit in these concepts.

The other example of nearly ballanced roll moment configuration is the Kite Boards. The overturning moment arm is very small such that overturning moment is not limiting at maximum speed. Rob Douglass holds the current overall speed record at 55.65 kts using this technology (http://www.youtube.com/watch?v=CtFxstw9Zjo)

Over in the "Monohull Speed: Speed Dream by Vlad Murnikov" thread, we have been discussing righting moment (portion of my post #172 copied below). Use of fully balanced systems (Sailrocket) or active control systems (Longshot / Trifoiler / Rave) are actually less efficient than a hybrid system. To the extent possible, all discretionary weight (crew for example) should be to the windward and combined with adjustable ballast (water tank filled via a scoop tube). This is because ballast to windward creates the required down force with no drag. In the post below, I discussed a hybrid where ballast is combined with float actuated active control surfaces (wings).

Originally Posted by P Flados

This is a comment by Tom Speer( and it is a direct quote, not a paraphrase) :

" I asked Mark Pivac why Spitfire had water ballast instead of using dynamic downforce on the windward foil. His answer was, "So it only has to be lifted once." And he was dead right. The leeward foil has to lift both the weight of the boat and the downforce from the windward foil. If either downforce or ballast are used, the load on the leeward foil is the same. However, there is a drag penalty for creating the downforce. There's no drag penalty for the ballast."

For the above point, Tom Speer got it right where so few others have even noticed.

Any force generated by moving fluid over a surface creates drag. The more the force, the more the drag. The one force we can get without a drag penalty is when we use simple ballast for the downforce.

Longshot is a craft that looked capable of so much more with some additional development.

Imagine if all crossbeams on Longshot were round beams shrouded by twist-able airfoils linked to the forward floats such that on each side the airfoils would be the same angle of attack as the J foils. You have to have the crossbeams anyway for structural reasons, they are producing drag as is, so why not get some lift and active control out of them.

Add in the ability to take on water ballast in a windward tank using a scoop tube that can be lowered into the water. Now for a specific one-tack run, remove the windward J foil and start out with the ballast tanks empty. As the boat powers up, you take on ballast into the windward tank as needed to keep the windward side of the twist-able crossbeam airfoil close to a neutral angle of attack. The movement gives some active control at very low AOA's so drag is very small. This would completely eliminate any drag from a windward J foil in the water. The leeward J foil would probably need to be designed to run deeper to let it deliver the required lateral forces, but this would not be a problem.

[Doug Lord]

Originally Posted by P Flados

The Ketterman brothers were the first to use an active control system to pull down on the windward side. This culminated in the Longshot (current Class A record holder at 43.55 kts) and eventually turned into the Hobie trifoiler (http://www.hobiecat.com/sailboats/trifoiler/).

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Originally Posted by gggGuest

This happens on any wand equipped multihull like the Hobie trifoiler, so its been done plenty of times. I think the lack of popularity of such compared to the Moths suggests that it may not be the right approach...

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According to James Grogono in "Icarus The boat that Flies", the first foiler design to use dual "feelers" similar to what Ketterman used(incidence controlled foils-whole foil moves) was Force 8 by the Pattison brothers in the UK about 1979. The first dual "wand" system used to control just a flap on the main foils(like the Rave, Osprey, Skat and F3 RC model) was developed by Philip Hansford on Philfly in the 80's. Both these systems have the "advantage" of developing 100% all the RM required (up to the structural limit of the boat) with the windward foil pulling down automatically when required and the lee foil increasing lift automatically as necessary. Both modern versions of these systems have exceeded the top recorded speed of a Moth in heavy air but the Moth is far superior in light to moderate air. Both the Rave and Trifoiler were build to the requirements of production boats that resulted in fairly heavy boats severely impacting their light air takeoff capability. The new all carbon Osprey by Dr. Sam Bradfield(who invented the modern planing wand) will be very interesting-and very light.

Click on image:

[P Flados]

Originally Posted by Doug Lord

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===================
According to James Grogono in "Icarus The boat that Flies", the first foiler design to use dual "feelers" similar to what Ketterman used(incidence controlled foils-whole foil moves) was Force 8 by the Pattison brothers in the UK about 1979. The first dual "wand" system used to control just a flap on the main foils(like the Rave, Osprey, Skat and F3 RC model) was developed by Philip Hansford on Philfly in the 80's. Both these systems have the "advantage" of developing 100% all the RM required (up to the structural limit of the boat) with the windward foil pulling down automatically when required and the lee foil increasing lift automatically as necessary. Both modern versions of these systems have exceeded the top recorded speed of a Moth in heavy air but the Moth is far superior in light to moderate air. Both the Rave and Trifoiler were build to the requirements of production boats that resulted in fairly heavy boats severely impacting their light air takeoff capability. The new all carbon Osprey by Dr. Sam Bradfield(who invented the modern planing wand) will be very interesting-and very light.

Click on image:

You are probably right.

Greg Ketterman (http://members.cox.net/gkettermanb/Home%20TriFoiler.shtml) indicates he was just at the model stage in 1981. The part I find neat is that they did their first full scale homebuilt prototype in 1987 and then progressed to a world record by 1991.

[yojamey]

A couple of pages of fotos and video on Longshot coming out of mothballs for a
day of play in the SF Bay at the end of 2010

http://www.pressure-drop.us/forums/c...ot-Rides-Again

http://www.pressure-drop.us/forums/s...ck-in-the-game!


One of the captions reads for the "last time" making it sound like Namibia is
not in the cards... Rumour has it that Longshot was sold to the Makani Power Kiteboat folks http://project.kiteboat.com/page/project


Foils tend to cavitate at high speed
PBS-Scientific American Frontiers Date: 1994-02-16, Episode: Science and Sports: Speed Sailing: Windsurfer vs. Trofoiler vs. Planning Hull...Also shows foil cavitation in an MIT water tunnel
http://vsx.onstreammedia.com/vsx/pbs...f405&entire=No

[Doug Lord]

Originally Posted by yojamey

A couple of pages of fotos and video on Longshot coming out of mothballs for a
day of play in the SF Bay at the end of 2010

Scientific American....

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Good stuff, thanks!

[Jan2]

I know, this is supposed to be a theoretical thread, but one practical example could be enlightening. I have been trying to figure out the optimum camber for a square head full batten mainsail to be used in conjunction with approx. 4.5 x 9" tear drop wing mast section (Ballenger), extended about 3/4" by Tides Marine track. This is to be used on a fast tri. The dimensions of the sail are: luff 40.5', leach 42.25', foot 14.3', head 38", roach 34". I am more interested in close-hauled performance than, say, broad reach.
Would anybody know the answer or could point me the right direction to help me to find out for myself? Thank you.
Jan