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 Catalina/Capri 25/250 Sailor's Forums
 Catalina 25 Specific Forum
 Sail Area/Displacement		  New Topic  Topic Locked
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Jonathan Cuff
Navigator

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Cayman Island
173 Posts
Initially Posted - 08/20/2004 :  09:53:33  Show Profile
Hi guys

I've been checking out various comparisons between boats looking at the Sail Area/Displacement ratio. This is probably a really stupid question, but how is this figure arrived at? It seems that the higher the figure the more sail area per displacement.

Cheers Jonathan
Pie Sees 2 C25 #5686 1987 SR/WK
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Bill Holcomb
Admiral

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USA
769 Posts
Response Posted - 08/20/2004 :  14:20:05  Show Profile
Hi Jonathan,

Sail area to displacement ratio is a measure of relative power for a boat. The formula is: SA/D = (Sail area of the mainsail plus forward triangle) divided by the displacement of the boat in cubic feet to the 2/3 power. It's easier to figure than you might think....especially with a calculater.

For a C25 FK/SR you'd have: SA/D = 270/(4550/64)2/3 or 15.7
For a C25 FK/TR you'd have: SA/D = 295/(4550/64)2/3 or 17.2

Thereby giving an idea as to the relative "power to weight" difference. The tall rig is about 16% more powerful than the standard rig.

BTW: Dividing the displacement by 64 is for salt water to give equivalent cubic feet. For fresh water divide by 62.2

Bill Holcomb - C25 Snickerdoodle #4839
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Jonathan Cuff
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Cayman Island
173 Posts
Response Posted - 08/20/2004 :  15:10:20  Show Profile
Many thanks Bill. I'll get cracking with the calculator later!!

Cheers Jonathan
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Dave Laux
Captain

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318 Posts
Response Posted - 08/20/2004 :  18:57:29  Show Profile
You might consider that your actual SA/D is probably lower than the calculation would indicate because the boat is heavier than the advertised weight. This is true of most boats so the comparison is still usefull. Dave
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Jonathan Cuff
Navigator

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Cayman Island
173 Posts
Response Posted - 08/21/2004 :  12:50:28  Show Profile
Hi

Sorry to be a dummy, but I can't get it to work out to those figures. Can someone better at math than me explain the equation in terms that an 8 year old could understand please?

Cheers Jonathan
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.