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Old 29-07-2009, 19:21   #1
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Question Not Cruising, Pure Speed

Ok from my read Banque Populaire V has started the record attempt, so my question is what is the best site to follow her on her run?
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Old 30-07-2009, 04:48   #2
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Its in french but its got the maps with winds and stuff
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Old 30-07-2009, 05:25   #3
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I am led to believe that as a displacement hull moves faster and faster its bow wave lengthens until is is the same as the waterline length. If the bow wave created were LONGER than the WL the boat would be trying to sail up the wave as the stern would then be in the trough of the bow wave. Since this appears to "impossible" (not sure why) a hulls speed is constrained by its LWL.

Because a sailboat heels, its hull shape at LWL can change AND lengthen meaning that it hull speed would be greater than the static LWL.

I have observed that my hull will begin to "squat" the stern in the water when "over powered". At anchor the CL of the stern is about 4 - 6" above the water (guess) but at hull speed it appears to be 3+ inches below the water. This is obvious when motoring.

I have made some other observations and would like others to comment.

At speeds LOWER than hull speed, perhaps 85-90% of hull speed the stern ALSO dips a few inches which seems to indicate that the bow wave exceeds the LWL before reaching hull speed. Is this possible?

Which LWL is the one you use to compute hull speed, the windward or the leeward one? I think the windward is shorter. Would this be true and does it matter? Why would the bow wave be symmetrical if the hull shape when heeled is assymetrical...

How much bouyancy is there at the stern of the boat... the very back? Does the buoyancy at the hull vary based on it's area contact with the water?

Can anyone dirert me to a resource for non naval architects which explains this?
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Old 30-07-2009, 06:49   #4
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And meanwhile - the big tris are belting along at 30 plus knots.
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Old 30-07-2009, 08:15   #5
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Quote:
Originally Posted by defjef View Post
I am led to believe that as a displacement hull moves faster and faster - snip -

Because a sailboat heels, - snip - meaning that it hull speed - snip -
Displacement hull, heeling, hull speed - in a thread on BP5 and GRP?
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Old 30-07-2009, 08:21   #6
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The difference in LWL when a boat is heeling versus being upright is so minimal (as a percentage of overall LWL), that I don't think you would even be able to measure the difference, much less notice any difference.
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Old 30-07-2009, 08:38   #7
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Thanks and found 2 great sites:

Groupama 3 • New York - Cap Lizard

Tentative de record - Atlantique Nord - Cartographie et géolocalisation

Wow, they are averaging over 30 knots! and it looks like BP5 is a touch faster (so far)
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