Minuet Yachts: a 2m fun boat-can the design be improved?

May get broken: the one in the pic is protected.

 

L60

On a small boat? But the crew could grab it and slide it from the outside.

 

L60

Here is a picture of the Quant 28 sailing upwind on stb tack-- take a close look at the DSS foil:

click on image-

 

L60

Unless I hear a really good argument against it soon the 12' will be my choice for a small "Open 60" for the reasons I mentioned below. No question that for the max crew weight(250) the 12 is better at the performance level being designed for. Still a big question on the viability of DSS on this small a boat which I hope to learn more about after the first. Still shorter than the 2.4 meter and much lighter, much easier to transport etc. Much larger than the Minuet that inspired all this, but there is a lot more to the 12 as well. Long time off for me but a really neat way to sail.

 

On a small boat the DSS foil could simply be pulled out before storing on land or car-topping the hull; it would not likely be kept in a marina, so the risk of foil breakage is minimal . . .

 

http://www.youtube.com/watch?v=XJodKrSYgWE

 

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Cool little boat! One of the ones that have pioneered "foil assist"....

 

L 60----Deep DSS-telescoping foils

I've become convinced that there is a real problem in deploying DSS on a small planing hull sailboat. Getting the chine deep enough so that the foil is 2-2.5 chords below the surface is one thing, but even if you do that when the boat planes it will, of course, lift up vertically particularly at the point along the hull that the DSS foil would be deployed. On a 12 footer(or any smaller) the problem is serious enough to perhaps preclude the use of DSS. DSS, and the RM it can generate, is critical in order for the L 60 to achieve its performance goals and so I've wracked my brain for a solution and I may have found it. There is much to understand and research about this potential solution, but here is a rough ,preliminary, sketch.
Deep DSS features:
-- the system allows proper submergence of the DSS foil without interference from surface proximty drag on a fast planing hull sailboat designed to be sailed flat or nearly flat with no compromise to the planing hull shape while ,at the same time, facilitating additional vertical lift above and beyond what would be possible with a DSS foil alone. It allows for a (mostly,at this point) retractable system that should allow off the beach sailing,
-- the horizontal DSS foil trunk is retractable up to the bottom of the boat, and maybe further by using a flexible membrane or some other solution. The foil trunk is foil shaped and will act as a lifting foil for "Foil Assist" reducing the boats displacement along with the extended DSS foil and abrogating the need for curved lifting daggerboards,
-- the weather daggerboard is deployed when the DSS foil is extended to leeward or, with "bulb" attachment of the horizontal foil/trunk, the typical lee foil could be deployed. Some work has shown that a bulb attachment system reduces drag(see third picture below),
-- The "stub daggerboard trunks" in the rough sketch allow the horizontal trunk/foil to retract,
-- Adjustment of the angle of incidence of the DSS foil and foil trunk can be accomplished simultaneously by angling the "stub daggerboard trunks" fore and aft at the top. A problem keeping the bulb correctly oriented to the flow could develop in the use of a bulb attachment system with this kind of incidence control.
-- design for an angle of heel other than 0 degrees can be facillitated by making the horizontal foil/trunk curved.
-- target would be for the horizontal foil +DSS foil to lift 50-80% of the boats weight(angle of incidence adjusted as required). Possible problem could occur with this system providing too much vertical lift. Downside, for sure, is that horizontal foil/trunk will be deployed in conditions where it would produce more drag than benefit but that would be in light air conditions and, maybe to some extent upwind in light to moderate conditions. Much more research required here.


Pictures: telescoping foils on the Pi28 foiler, "bulb" attachment of horizontal foils(see Multihulls)-
click on images--

 

As you have noted a horizontal DSS must be deployed from an immersed portion of hull and therefore cannot extend horizontally from a planing hull.

Referring to you sketch, it seems to me to be difficult or impossible to come up with a DSS deployment system that will fit within the required envelope of the horizontal lifting foil, without some feature such as a rack on the external surface of the DSS that a drive mechanism could engage. That would likely disturb the hydrodynamics of the foil.

I do not see any provision for extending a DSS horizontally in the picture of the Pi28 foil assembly; rather it appears that the entire assembly of foils and struts can be moved sideways relative to the hull. I may be wrong about that but that is what I think I am seeing. This would be incompatible with a fixed trunk within the width of the hull.

This seems to me to leave four options. Either a DSS can be deployed at a downward angle to achieve the necessary depth, which would require a DSS on each side, or a curved DSS inside a similarly curved horizontal trunk.

The third option would be to have a DSS on each side mounted on a strut that could be raised until it is just under the bottom of the hull then rotated about a vertical axis to retract it, perhaps fitting into a slot. This might be the best performance option but timing might be critical for safe deployment at speed.

The fourth and last option I can think of is a foil on struts underneath the hull per your sketch, which would provide the necessary counter-heeling moment not by moving sideways but by twisting, or perhaps with a flap or slot to change lift so one side is lifting up and the other side is pulling down. This could extend beyond the struts per your sketch to have greater span in order to increase the "aileron" effect.

 

L60-Deep DSS

Deploying the DSS foil within the horizontal trunk/foil is a problem I haven't solved yet but compared with the original problem ,probably minor. But I'm just not sure yet. Here is how a "normal" DSS foil is moved:

click on image--

 

L60-Deep DSS 2

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Got it! Using a thin cable or line attached to the center of the DSS foil inside the trunk and run as a continuous loop up the struts("stub,retracting,trunk foils") on each side will probably do it. The line could be set up to move when the daggerboards are deployed/retracted. Need to look into it more.
Thanks for your suggestions, AK....
Note: a simplified version could eliminate the stub trunks and just deploy twin daggerboards. A control line would deploy and retract the DSS foil.

Click on image--Deep DSS 2 & 3 DeepDSS3 can be offset forward as well but doesn't need to be-I don't think. The twin foils can be easily retracted and there seems to be less complication by eliminating the "stub trunks".....

 

That should work. Wish I'd thought of that! I kinda liked the downward curving DSS but I realized it would have increased leeway unless it curved in 2-dimensions, which would have been hard enough to design, let alone build.

 

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Thanks, AK. If you haven't already take a look at this:
http://www.boatdesign.net/forums/sailboats/dinghy-design-open-60-influence-36401.html pages1-4
I thought I had a "brilliant" idea using a curved foil that pointed outboard because it would(I thought) increase RM and lift. Greg Ketterman and a few others proved that would be a bad idea. Before Gregs post I had discovered that the foil would have high and low pressure on the same side but I didn't fully understand what that meant-Ketterman straightened me out.( post 54 of the above thread)
Interesting how all this stuff is so interrelated!( DSS, DeepDSS, Sailrocket, T-foils, curved foils etc)
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Using an effective DSS foil on the L60 absolutely changes the character of the boat, increasing power to carry sail immensely-probably better than almost any other form of movable ballast.

 

My related experience is limited to a coupe of years playing around with Bruce Foils. My rule of thumb for a curved Bruce Foil - which seems close to the few images I have seen - is to have the surface of the foil normal to the vector between it and the sail's center of effort. I haven't tried it but I believe that works best with the foil on the windward side (as is the case for SailRocket) where the lift would be negative; I have always suspected that the tip vortex would be worse and cause a lot of drag with the foil to leeward for lift. I prefer the simpler flat foil to leeward, but I am not looking for lift. For this discussion I am, of course, ignoring the non-flat foil profile.

 

Hi, Doug.

Just thought of another possibility.

Why not make the hull narrower and deeper, like a double ended sharpie with canoe proportions.

The DSS will be wider than the boat, but it can be cranked over to the opposite side when docking.

The reason for the pointed stern is to get away with a completely flat run aft.

The bow would slope upward, so the but of the stem just touches the water at design load.

A 2.0 foot wide hull would sink close to 6.0 inches deep at the displacement you're talking about.

The foil's lift become more and more effective as the boat heels, even though there will be a very slight leeward lift vector.

A foil that curve upwards at its ends would mitigate that, but may have less effective righting moment.

Even at rest, the boat would behave like a bicycle with training wheels, with the foil extended only half way.

Just a thought.