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post #1 of Old 02-05-2008 Thread Starter
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what is the conversion for

figuring out disp from lbs to cubic feet. I was trying to figure out the SA/disp for my boat, but need this conversion.

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Marty

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post #2 of Old 02-05-2008
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64 lbs/cuft of SW, 62.35lbs/cuft of FW

or
2240lbs(1 ton)=35.84 cu ft FW
2240ibs(1 ton)=35 cu ft of SW

“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.

Last edited by sailaway21; 02-05-2008 at 10:31 PM.
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post #3 of Old 02-05-2008
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One cubic foot of seawater weighs 64 pounds.
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post #4 of Old 02-05-2008 Thread Starter
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Thanks, that is what I needed.

marty

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arrrrg,

so what am I doing wrong?

formula sa/disp

Sail area in sq ft divided [by disp in cu ft times 2/3]

so
626/13448lbs or 626/[13448/64]2/3

626/[210 x 2/3] = 4.47-1?!?!?!?!?!?! Should be closer to 18 or 20-1!

Where did I screw up?

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post #6 of Old 02-06-2008
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hmmm ..... blt2ski ... are you sure that your formula is right?? I would rather use the following:
626 / [(13448/64) ^2/3]
where "^" means power. Your result would be closer to the number you expected ... 17.71.
Have fun,

Chris
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I knew I was screwing up somewhere! Did not know how and why and where!

Thanks Chris!

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post #8 of Old 02-06-2008
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a nice link for this http://www.nwmarinedesign.com/sadscrip.htm

Probably too late but make sure you are using SA as measured with a 100% foretriangle - that is the standard and the only way you can compare to other boats. Also use your real displacement for real numbers, not the factory delivered weight (unless you are just comparing fantasy numbers).

Using the actual SA - say with a 150% genoa might give you and warm and smug feeling, but then you can't compare with other boats.

Note some manufactures/sales people will cheat the numbers to make their boats look better.
As an example my boat (Gemini 105mc)
with 100% foretriangle only has 590 sq ft- 20.5 sa/d
with 150% (670 sq ft) - 23.3 sa/d
with screacher (780 sq ft) - 27.1 sa/d

I'm pretty sure all the sq ft measurements on mine include the roach on the main, so as you can see, it's apples and crab apples.
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post #9 of Old 02-06-2008 Thread Starter
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Chuck,

I know about those fun ways to fool around the numbers, the sq ft I mentioned, is with a 100 jib, no roach main etc, granted factory disp number, as I do not have actual disp number.......I was seeing one that was 23or24-1 for the S/A, but figured that was with a 140'ish or 150'ish genoa. I've seen some rigs in the 60-1 with super huge spinnys...........

nice link, I had not figured there would be a site like this, but in reality, there should be with plug in the numbers and voila, out comes ratio.

Marty

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I drives me dinghy!
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