# Monohull Speed: Speed Dream by Vlad Murnikov

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

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### Doug LordFlight Ready

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You can't POSSIBLY understand the potential of a bi-foiler if you don't understand VealHeel-and you most certainly don't! Vealheel moves the CG to windward of the Center of Lift of the hydrofoil by a substantial margin. Nothing like it happens on a sailboard -or on any other non-bifoiler. This is one of the most important design advantages of a bi-foiler over any other boat configuration, period. Study up.

PS- there is another way of looking at it that may help you: visualize a bi-foiler sailing flat with no angle of heel and the crew hiked max out. What Vealheel does is allow that same crew to sail in a stronger wind without moving his position on the boat-simply by heeling the boat to weather he is able to increase his RM a lot because he has increased the RA(righting arm) substantially. Hence Vealheel=RM for "free". Doesn't happen on any other boat configuration. In fact-on a sailboard,with the crew max out, heeled to windward(not fast) it has LESS RM than when it is sailed flat,with crew max out, because the center of lift of the board moves to windward with heel shortening the RA. Draw it out- sailboard flat with crew max out ,sailboard heeled to weather crew max out.
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I made an accidental discovery tonight that more than anything I have yet said illustrates the importance of Vealheel when considerd for a large two foil monofoiler. I hadn't fully understood Vealheel when I first came up with the 60' Moth(see thread) so I picked a figure of 15 degrees. I went back tonight and changed that to 20 degrees and corrected the figures in the spec sheet. I also, for the first time, added up the total RM due just to veal heel on the 60 footer. I was startled, to say the least, to find that it was 42.7% of Total RM! That is an argument for this type of boat beyond any I have yet made since it represents righting moment essentially for "free". I had also never calculated the percentage of RM due just to veal heel for the Moth and was startled, again, to find that it was 31.8%-more proof than I ever understood of how important vealheel is. http://www.boatdesign.net/forums/sa...ng-monofoiler-design-discussion-15143-12.html post 177

Below: picture from Bill Beavers study, sketch of bifoiler using power foils-both show how far the CG moves to windward and the fact that Vealheel results in an RM INCREASE for "free"(independent of altitude). Bill Beavers study, scroll down and read.

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### CheesySenior Member

Im 100% sure that he does get it. It does give me an idea on how to explain the relatively minimal importance of RM with a kite though... From the picture on the left imagine that the lifting foil is the board, now with old technology like a boat the heal to windward is limited by the proximity of the water surface, this is still true for a kite although the angle of 'Veal heal' can approach 90 deg, add to this that the healing moment can actually be bought to zero (not that you would while racing upwind, more to illustrate that the HM is a controllable variable) and it becomes obvious that the rider mass is simply intelligent ballast, with lighter being advantageous...

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### Doug LordFlight Ready

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What in the world are you talking about? A foiler with Vealheel moves the entire CG of the boat to weather of the center of lift without the crew moving its position on the boat. It is NOT the same as the crew hiking out or whatever you call it with a kite or sailboard.

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### CheesySenior Member

How exactly is it not the same?
Board = lifting foil
Veal heel = angle of board to water

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### Doug LordFlight Ready

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Vealheel among other things, is the horizontal movement of the CG of a foiler to weather of the center of lift without requiring the movement of the crew on the foiler. "Angle of the board to the water" is no description of Vealheel! There is no valid comparison to a board of any kind, except maybe a foilboard. Draw it out!
Show me a drawing of any board or monohull boat where the boat CG moves to weather when the board is heeled to weather with the crew in the same position(hiked at the same angle relative to the board flat as with the board heeled to weather-and without moving the CG of the board relative to the CG of the crew). Further, if you please, illustrate how the increase ,if any compares to the 20% increase in RM with a bi-foiler.

pix- sailboard in speed trim: board flat, crew max out with rig and mast near vertical

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### CheesySenior Member

A kite board is a low aspect surface running foil

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### Doug LordFlight Ready

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Yes, a very inefficient foil-how is that relevant to Vealheel?

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### CheesySenior Member

It is providing lift and latteral resistance at a distance to leward of the centre of mass, with increasing heel the distance increases

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### Doug LordFlight Ready

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So, to be clear, you're saying that the distance from the board+crew CG to the center of lift of the board increases with heel to weather? And thats with no change in the distance between the board/rig CG and the crew CG, is that what you're saying?

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### CheesySenior Member

Yes you are right it is nothing like Veal heel

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### cardsinplayda Vinci Group

Maybe more drawings with circles and arrows this time?

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### RHoughRetro Dude

Thank you.

Lets start with some assumptions based on the foiling Moth.

Can we agree that RM = HM? (if it does not the boat will roll)

RM for the Foiling Moth as pictured = 100%
HM for the Foiling Moth as pictured = 100%

Assume that the Moth has 1000# ft of RM, therefore the rig produces 1000# ft of HM.

This places a 165# helm about 6 ft to windward a portion of the hull/wing/rig combo is also displaced to windward so lets say that 75% of 60# (45#) is displaced 2 ft to windward for 90# ft of RM so the 165# helm is only 5.5 ft to windward.

The Moth has 86 ft^2 sail area? So at 1# per sqft the Heeling arm must be 11.6 ft. (86 x 11.6 = 1000)

60# + 165# = 225# 86#/225# = 38% (Sail Carrying Power / Weight)

What would happen if we reduced the heeling arm by 37% to 7.3 ft? You would need 137# of sail force to get the 1000# ft of HM you need to balance the boat. This makes the the SCP/W 137#/225# = 60%

The boat would be much faster.

Suppose this reduction in Helling Arm came at a cost, instead of a 5.5 ft Righting Arm you can only get a 4 ft Righting Arm. This reduces the RM to 165# x 4 ft = 660# ft.

Going back to our 7.3 ft Heeling Arm we can only use 90# of force.

So the SCP/W becomes 90#/225# = 40% only a little better.

What don't we need? We don't need the boat and racks, just the lifting surface, the rig, and the helm. Reduce the 60# to 30# and you have: SCP/W 90#/195# = 46%

Does anyone think that a SCP/W of 38% will be faster than a SCP/W of 46%

Huh?

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### RHoughRetro Dude

Now I've been asked to read the Beaver Moth paper. I have, more than once.

So before I post the diagram and photo, I call your attention to the wind tunnel tests that show:

This wind tunnel test was hull and helm only.
Drag Helm = 42%
Drag Hull and Racks = 58%

Consider now the reduced heeling arm/reduced righting arm boat with only 42% of the aerodynamic drag of the Moth.

SCP/W advantage of 20% (46/38)
Assuming that the helm/hull is 30% of the total aerodynamic drag 42% of 30% is still a 12.6% reduction in aero drag.

20% more powerful and only 88-90% of the aero drag. Which will be faster?

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### Doug LordFlight Ready

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Depends-aussie 18's have SCP/Total weight that is better than the Moth but the Moth is faster.....

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### ancient kayakeraka Terry Haines

Although VealHeel does move the CoG to windward the lift vector of the foil rotates in the same direction, which cancels any increase in moment. However the sideways component of the foil's lift helps to offset leeward force and the lift from the sail supplements foil lift. These two changes result in reduced hydrodynamic drag. See attached vector diagram.

I must admit I was surprised by this, as I expected the offset CoG and resulting increased drive to be the explanation. Vector diagrams have to be done carefully and accurately if they are to be of use.

The heeling moment of a kite compared to its lift is lower because its force acts lower where the line it is held manually and not partway up the mast like a sail. A board has the advantage that it can be heeled independantly of the crew's body to counteract leeway, in this respect it resembles Vealheel in principle. A board doesn't theoretically require a fin to control leeway, although it may be needed for directional stability.

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Last edited: Dec 17, 2010
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