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post #21 of 23 Old 07-10-2013 Thread Starter
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Re: Boat Buying By The Numbers

Well, the CR on this boat is 59 (according to GoSail) so she should be very comfortable!

And if sailing her doesn't kill us, we'll end up in great shape.
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post #22 of 23 Old 07-11-2013 Thread Starter
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Re: Boat Buying By The Numbers

Originally Posted by ctl411 View Post
Your numbers look high on these, you may have the math wrong???
You're probably right.

When I built the spreadsheet, I compared the numbers the spreadsheet was generating (based on formulas taken from Brewer's primer) to the numbers GoSail was generating and they were right there. So I thought they were good. Yesterday my SO found a post on a naval architect's forum that had motion comfort calculated for about 500-600 boats. Their numbers were much lower than what GoSail or I had.

I rechecked the formulas.

I used CR=Displacement in pounds/.65 x (.7 LWL + .3 LOA) x B1.333.

The NA forum used MCR = Disp / (2/3*((7/10 * LWL)+(1/3 *LOA))*Beam4/3 )

They are almost identical except Brewer calls it Comfort Ratio (CR) and the NA called it Motion Comfort (MCR).

I'll recheck the math Excel is doing. Maybe GoSail did the same thing I did and that's why the similar numbers. But I'm deferring to the NA for his numbers being correct.

Update: I forgot a pair of parenthesis in the Excel formula.

Last edited by JulieMor; 07-11-2013 at 10:25 AM.
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post #23 of 23 Old 07-11-2013
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Re: Boat Buying By The Numbers

Also check to make sure your sail areas are measured the same. Sometimes on cutters or ketches they don't list the stay sail or mizzen area. A place to check sail area is Sailrite web site they have a database of boats and you can also put in your own.
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