Monohull Speed: Speed Dream by Vlad Murnikov

Discussion in 'Sailboats' started by Doug Lord, Jan 8, 2010.

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RHoughRetro Dude

Okay folks here it is ...

I used the diagram and photo Doug posted from the Beaver Paper ...

The diagram shows the idea that a windsurfer helm and rig are adding to RM just like the Moth.

The Photo has nifty vectors ... I did not change the scale. I took the helm and stood him on the water (standing on the lifting surface of the board). I took the Moth rig and moved the but of the mast down to the board.

I measured the vertical distance from the foil below the water to the force vector on the Moth sail and measured the vertical distance from the top of the board to the same vector on the sail. This is the 37% reduction in Heeling Arm.

The photo shows the horizontal displacement of the Helm, I did the same with the helm standing on the board. The board helm gets 73% of the righting arm of the Moth helm.

Since the board is the lifting foil, we no longer need the hull and racks so we save some weight. More importantly we lose the drag.

The result?

Moths: Mid 30 knot speeds
Boards: High 40 knot speeds

Lets call it 35 vs 49 it takes about double the power to go from 35 to 49 knots.

After looking at the photo and crunching the numbers, seems pretty obvious why Moths are so slow compared to sailboards.

It is also obvious that the increase in RM from heeling a Moth to windward is more than offset by the increase in the length of the heeling arm. This is simple geometry. Heel the boat 30 deg and for each foot of righting arm you gain you also add 1.73 feet to the heeling arm. This is a net loss in sail carrying ability.

You might be tempted to return to the "Boards are not boats." stance. I have shown that the all the "boat" part of a foiling Moth does is slow it down by more than doubling the aerodynamic drag (again from the source you provided).

Lets take this comment:
A kite board is a low aspect surface running foil.
Yes, a very inefficient foil ...

Really?

35 vs 49 ... Drag goes up with the square of speed.

The estimated drag reduction of 10% due to no "boat" does not account for the speed difference. The rigs are similar, all that is left is the lifting foil drag.

35 vs 49 ... it sure looks like the planing foil is MORE efficient than the Moth foils, not inefficient at all.

This agrees with what we observe, planing boards with sails or kites are faster than foiling Moths. We also observe that other fast watercraft do not use lifting hydrofoils, they use dynamic lift from planing surfaces or aerodynamic lift from a surface effect tunnel or small waterplane hulls or some combination of these.

I think I grasp the concepts pretty well.

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RHoughRetro Dude

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AK, thanks for the effort. As pointed out in the Beaver paper a heeled to weather Moth has an increase in the Righting Arm. Since that is measured from the vertical line representing the lift vector to the boat CG ,RM is also increased-at least as best as I can tell. The vertical fin is unloaded by the horizontal component of lift from the foil and as you point out there is a small amount of lift from the sail.
The increase in righting moment was observed by Rohan Veal years ago when he first discovered it-it is the princible affect of veal heal.

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There is no physical way a board can benefit from Vealheal "just like a Moth".
I talked to a world champion board designer who lives here and the fastest way to sail a board is with the rig nearly straight up(viewd from forward) and raked way back with the board flat.

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RHoughRetro Dude

Then the conclusion is that the difference between 49 knots and 35 knots is that veelheel slows the boat down?

We know the boat part slows the Moth down compared to a board.

If board dynamic are NOT as I showed in the diagrams, then the board has a much lower SCP/W ratio and is still faster. That leads to the conclusion that the "boat" part is slow, and since they do not hike like a Moth, they have much less power available ... so it must be the foils that make the Moth slower.

You can't have it both ways Doug. It is geometry and physics.

Moths are slower than Boards = Fact
Moths have more Aero Drag than Boards = Fact
Boards carry more sail area than Moths = Fact

How can a board carry More Area with Less RM?
How can a board be faster than a Moth with less power?

Foils are slow compared to planing hulls.

R

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RHoughRetro Dude

Want to show this to your world champion?

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Why? A heeled board? It's not remotely comparable to Vealheel. And I'm glad that you're glad a board is faster.

8. CutOncePrevious Member

Jesus, girls. Can you stop fighting about who's cuter, Taylor Lautner or Justin Beiber? You sound like bitchy 12 year old premenstrual princesses. Just sayin.

--
CutOnce

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RHoughRetro Dude

The physics are the same. The CG of the board/helm/rig is displaced to windward EXACTLY like the Moth. To deny that obvious fact requires a logical argument that allows the board to carry more sail with less RM.

The heeled board is a heeled lifting surface just as the Moth foils are a heeled lifting surface. The heeling arm in both cases is from the CE in the water to the CE of the rig. The righting arm in both cases is from the CE in the water to the CG to windward.

How can the two NOT be the same? (other than the foiler is slower)

Being glad implies emotion. It does not make me glad or sad. I don't care which is faster. I know the boards are. I am mildly interested in why they are.

R

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RHoughRetro Dude

Not fighting, just learning.

I have no vested interest in the outcome. I'm just doodling and thinking out loud. I keep coming to conclusions that must be wrong if hydrofoils are lower drag than planing surfaces and I'm trying to find the error.

R

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Paul ScottSenior Member

Actually, you can get the 'veal heal' with a keel- Gedankenexperiment!- make sure the shrouds are above the CE of the mainsail, have a curved track (curved up, like Newick did) to attach the bottom of the mast to a car, like a mainsheet car, attach the top of the keel to the bottom of the mast (it will have to slide a bit in and out of the track car to have movement), with the keel pivoting laterally at the bottom of the hull- the usual place. As the bottom of the mast moves to leeward, the bottom of the keel (the bulb, if you will) moves to windward. I believe you could do a RC scale boat that might do this, Doug, and see if the theory works. i suppose you would have to add some foils to suit your own philosophy. You could also arrange for the track to pivot at the ends for and aft, which would move the keel in the opposite direction, so you could rake the mast aft, and the keel would swing aft (although a bulb would play havoc here), which would mimic a windsurfer standing in the back straps. Since minis have already messed with 2 degrees (lateral, longitudinal) of freedom with their keels, and Newick has messed with 1 degree of freedom (lateral) with a mast this would be an evolutionary move, not a revolutionary move, since windsurfers already do it. Now this wouldn't be moving the CE to windward, but it has already proved more stable for control, at least on multihulls than swinging the CE to windward. Although the french swing their masts to windward on the ORMA tris. When I saw the BMW/O tri on her first trials, she was canting her mast all over the place with a staionary mast step. Not much though, and boy did those guys look nervous about it. But that really begs the question- once you have tri on one hull, with a curved lifting foil, or straight canted foil, with the mast canted to windward, aren't you doing the Veal heel?

Paul

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Bistros, don't understand a word of it do you?

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Not even close. Vealheel moves the CG of boat(hull), the rig and the crew to windward. The CG of the board remains in nearly the same position, relative to the center of lift the board flat or heeled though it might be possible for the Center of lift of a heeled wide board to move slightly to windward with heel, shortening the RA.
With Veel heel, the CG of the hull of a Moth moves over 1' to windward-this does NOT happen on any other type of boat, period. On a 60 foot Moth with Vealheel
the hull moves 6' to windward!

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Paul ScottSenior Member

1) Well, if part of the argument revolves around friction drag, a foil has two surfaces in the water. If you have a transom with 2' laterally immersed by 4" longitudinally immersed vs a foil 2' laterally and 4" longitudinally immersed, the foil has 2 sides of friction, while the planing surface only has 1. Foil = 192 sq in Hull= 96sq in.

What size of contact patch with the water does a windsurfer have when planing anyway? And a 2' span foil is kind of small, at least for Moths. Foiling Kayaks have gone that span, but with a chunkier AR. Windsurfers also have air lift under the hull, like an airboat. Rolling on marbles.

Assume one vertical foil for both of the same area to make things simple.

2) If another part of the argument revolves around induced drag, then add lift induced drag for the foil, and whatever drag the hull induces while planing.

add wand drag for the foil

add 2 tip vortices for the foil, and one for the planing hull.

Plus you have surface piercing effects for the vertical foil of the foiler, vs an endplate for the foil coming up to the windsurfer hull, at least some of the time, although there are flow consequences at the foil/hull interface. There will be less lift induced drag on the vertical foil of the foiler because of Veal heel, and more lift induced drag on the windsurfer skeg, as it will be taking more of the leeway resistance role, unless the hull is helping (and usually it is- a little).

Then add a rudder/foil system for the foiler, where you don't need one for, say a windsurfer.

And judging by the weight of the aluminum Bradford Foils I have in my garage, and the weight of a Moth compared to a windsurfer, foilers have to be heavier.

The reverse spiral has to be at work here, to some extent, although you have to admit foilers are efficient.

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cardsinplayda Vinci Group

Who is this claimed reference, what World Championship does this person hold and when was it achieved?

Perhaps, you, with your overwhelming desire to massage your argument and adjust same with some less than dandy wordsmithing, can define that angle from vertical, when a sailboard rig is "nearly straight up" at max speed? Is it 0 degrees, 15 degrees, 30 degrees? What is this magical and all-too nebulous angle of which you speak?

Doug, we all know you are desperate to make some points in this argument because so far, you are losing very badly. So, how about you come clean and stop with the nonsensical, absurdly hair-splitting definitons and simply admit that you've been unceremoniously bested, so that the thread can get on with other business?

Failing that bit of grace.... If you are speaking of Tinho Dornellas as your World Champion board designer, then I'm very curious as to this claim of yours, as Tinho doesn't mention a World Championship for board design in any of his literature on line and neither do his board sponsors.

I do see that Tinho is a Master Windsurf Instructor and that he has a very interesting and extremely varied resume as a Waterman and I'm sure that I'd like to meet him away from your Lordly ground effect, but there's no claimed World Championship. Please let us know who this World Champion person might be who is giving you advice as to a sailboard rig that is fastest when it does not heel to weather?

Are we going to have to email Tinho to get to the bottom of this kind of stuff, or is there another individual with whom we can do a follow-up to solidify the claims made on these pages?

A non-answer to the major questions above would indicate that you are decidedly less than forthright about your justification, so please... lay it on us, Mr. Lord.

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