Subject: Re: [harryproa] Re: Robert versus Doug
From: Michael Gehl
Date: 3/18/2009, 6:49 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

Not sure that unloading the ww hull would result in a loss of speed - remember, it's the *righting moment* that matters, not ww hull mass!

Cut the weight in half but double the beam, and then you have equivalent righting moment *and* less hull in the water, resulting in less skin friction and wavemaking resistance.

Not sure the extended beam option had entered the discussion.

Mike

On Mar 18, 2009, at 4:36 PM, Robert wrote:

Agreed. Windage is the main point rather than weight for driving upwind, and a fast boat is going upwind most of the time.
Going for minimum windage with maximum drive.
Drive depends on righting moment and fore aft stability to avoid loss of flow across the sails.
Righting moment needs a relatively high proportion of the weight in the ww hull. Going for lighter ww hull with the same weight lw hull would not improve the numbers unless you are prepared to go out on a trapeze.
Fore aft stability also means less loss of momentum in a slop.
Fore aft stability depends primarily on length, high prismatic coefficient and good bow shape.
So, long skinny hulls with low windage with at least twice as much weight in the ww hull as the lw hull and as much sail as it can handle in a reasonable breeze.
Robert--- In harryproa@yahoogroups.com.au, Doug Haines <doha720@...> wrote:
>
> OK.
> So you're in your harry and I'm in mine. There is a bet for $10,000 over some 1oonm mil course up the Great Barrier Reef say or say the Brisbane to Gladstone.
>  
> You're cruising style but lightened for the race, so no real water or petrol, ....
>  
> I've swapped the ww hull for something with less windage and weight and much less draft.
> So now its winds ranging from some light 8-12 knots at the start, building up to 10-15, and then last half in say 20-25 from who knows what direction.
>  
> My plans give a 41 knot Relative wind speed for flying a harry. Fully loaded.
>  
> Why not even push it without worrying too much about a capsize? there is no stuff to get ruined on the racing boat.
>  
> Doug


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