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Old 21st July 2009, 12:24 AM   #11
davide
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Its an iteresting thread and obviuosly drag increases with an increase in weight but its not a proportional increase. In other words doubling the weight will not double the drag. If this were not the case wearing a weight jacket would not increase top speed.The extra weight has to be positioned to also increase the force available but wearing a 20k weight jacket would not increase force available by 20k. (Look at dynamics of weight and forces/vectors)

If heavier sailor did not have better weight/drag ratio how come all top records are held by "heavy" sailors.If Jims expanation re- leverage were only concept involved speed sailors would be tall and light ???
I think you are missing a big part of the equation: strength. Think how much strength it takes to go around a slalom course with a 8.0 sail in 25 knots, or with a 6.0 in 40 knots ...

And of course a 200-230 pound man is going to be way stronger than a 160-180 one, it is not simply a matter of weight, and that is why a weight jacket can only go so far (put 40 pounds on a 160 sailor and he would be dead on the water). It is instead a matter of sheer strength and having legs like trunks and torsos/arms that can keep everything nice and steady. Like in boxing: a middleweight cannot dream to compete with a heavyweight.

PS by the way: all top PWA slalom sailors are more then 200 pounds, Bjorn is actually heavier then Antoine.

Last edited by davide; 21st July 2009 at 01:19 PM.
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Old 21st July 2009, 01:10 AM   #12
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Cool

Found this

Components of planing hull drag

The planing hull equilibrium described above shows us that trim and lift are interrelated. Trim affects lift, and it also affects drag. In fact, trim determines drag, as we will see below.

(Note: This describes the drag on the hull only. A boat in service will have additional drags due to appendages, seas, and shallow water. It might also have devices such as trim tabs that will also affect drag. These are not treated here.)

Planing hull drag is made up of four principle components:

Pressure + Friction + Spray + Windage

Windage drag is the air resistance of the exposed hull that is driven through the air. It has the tendency to increase trim. More windage area means more drag and also more trim.

Spray drag, sometimes called whisker spray, is the drag of the hull driving through the mass of the spray that is produced ahead of the boat. Evaluating the effect of spray is complicated and is often neglected, as well-designed spray rails or strakes can be effective in moving the spray away from the hull rather than leaving it in front of the hull. Like windage drag, spray drag would contribute to greater drag and trim.

This leaves Pressure drag and Friction drag as the two parts of our planing drag analysis. The planing hull analysis that is used here is a modified version of the well-known Savitsky prediction method.

Savitsky prediction method

The Savitsky method poses the bare-hull planing drag as

Bare-hull drag = Pressure + Friction = L tan(τ) + CF ρ S V2 / cos(τ)

where,

L = lift on the planing bottom (nominally the boat weight)

τ = dynamic trim angle

CF = frictional drag coefficient across the wetted planing surface

ρ = mass density of the water

S = wetted planing surface area at the particular dynamic trim angle

V = mean water velocity across the wetted planing surface

The important bit being
Bare-hull drag = Pressure + Friction = L tan(τ) + CF ρ S V2 / cos(τ)


The drag is composed of 2 parts (They are sying Pressure + Friction)
The boat weight (Load L) is only involved in first part consequently increasing load (L) will NOT increase overall drag by same proprtion. (As long as planing is maintained)
I think !!!!
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Old 21st July 2009, 05:29 AM   #13
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moving swiftly on.......if the fastest sailor is doing 40knots to my 33 when the wind is Force x, will I be doing 40 when he is doing 50 in a Force 9 ?
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Old 21st July 2009, 09:25 PM   #14
Farlo
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Deja vu or anyone, the article from Jim Drake on windsurf physics referred in post #7 was very interesting. Unfortunately it seems to have disappeared from the site. Does anyone know where I could find it?
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Old 22nd July 2009, 06:15 AM   #15
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If memory serves me correctly, the Jim Drake piece appeared in the U.S. magazine called Windsurfing about two, maybe three years ago, along with the Robby Naish article.
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Old 22nd July 2009, 12:28 PM   #16
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re: "Dave White says size doesn't matter; why is he 300lb then?"

Because he's a Fat Fu... I mean, because he ate ALL the pies!


(he's fu...in' fast, though!)
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Old 22nd July 2009, 05:43 PM   #17
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Smile Weight!

I have played with my weight for years..... I have been 120 kg and I have been 83 kg.
My personal conclusion is to be around 90 kg, but windsurfing in general I have most fun when I am between 80 kg an 90 kg. When you are lighter it is much easier to stay fit, the accleration is much better. I have been sailing since 1981 the equipment we have now is so much better... The advantage of beeing heavy was much bigger before!

The right set up regardig fins and mast stiffnes and size on board and sail is way more important!

Look at Karin Jaggi doing over 40 knots with the right set up at 63 kg.....
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Old 23rd July 2009, 12:00 AM   #18
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Where are all the light guys in the top professional ranks? Twenty-five years ago the light guys dominated (Robby Naish, Alex Aguera*, and Alan Cadiz). Where are the 170 pound guys now? Along with weight comes strength and the ability to hold down larger sails. Fifteen years ago Dave White weighed a fraction of what he does today and he wore a weight jacket when he competed with little success in speed contests. Today he doesn't need a weight jacket and at 300 pounds he holds production speed records. Robby Naish was able to do 43 knots, but this is a long ways away from AA's 49+. Weight doesn't matter? I've lost nearly 25 pounds and I know it does matter!

* He wrote one of the best articles on "speed technique" I've read, which was published in the April 1988 issue of WindRider magazine, and is still very relevant today.

Last edited by Deja Vu; 23rd July 2009 at 06:51 AM.
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Old 23rd July 2009, 02:11 AM   #19
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But also in marginal winds with this 11 kg less is more easy to take off.
But agree that when you have 25 knots in 10 sqm sail, is better to have it.
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Old 23rd July 2009, 10:58 PM   #20
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Hello Deja Vu, I remember a very informative article of Jim Drake on the Starboard web site. It might be the same than the one published in US Windsurfing magazine. It was also a few years ago (may be a bit more than three but not much). Since it has been removed I was not able to locate it again. Has anyone kept a copy?
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