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  #1  
Old 07-09-2013
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Boat Buying By The Numbers

I read Ted Brewer's Primer on Yacht Design and found it very educational. In it he discusses numerous factors of boat design and includes formulas he uses. Two of those formulas I had never heard of before: Comfort Ratio (CR) and Capsize Screening Formula (CSF). The first is to gauge crew comfort and the second to gauge how a boat will do in open water (basically).

For grins, I built an Excel spreadsheet that would determine those factors, as well as other factors, and took a sampling of 37'-40' sailboats and used Sailboat Data figures to plug in the numbers. Here's what I came up with:

Of course you shouldn't buy a boat based solely on these numbers but they can provide a different perspective that one may or may not want to consider.

If you want a very seaworthy boat that can handle heavy weather and speed doesn't matter, the CR38 could be the boat. For all around, the Swan and the Sabre 38-1 seem to be the better choices. For pure speed, it could be the Jeanneau or the Ericson.

Of course there's so many factors involved when buying a boat, but I thought it might be interesting to take a look at boats from a numbers perspective.

FWIW, the three boats on the right are recent models, the rest are designs from the 80's.
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Old 07-09-2013
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Re: Boat Buying By The Numbers

the numbers can make you crazy Julie. Where and how you will use the boat you find is a big factor too.
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Old 07-09-2013
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Re: Boat Buying By The Numbers

Check out Sail Calculator. You'll have hours of fun.
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Old 07-10-2013
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Re: Boat Buying By The Numbers

Do some searching here, especially some of Bob Perry and Jeff_H's comments. You'll see that the numbers are just that - numbers. They can be indicative, but that's about it, because they don't take enough variables into account.
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Old 07-10-2013
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Re: Boat Buying By The Numbers

Quote:
Originally Posted by deniseO30 View Post
the numbers can make you crazy Julie.
I like numbers.
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Old 07-10-2013
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Re: Boat Buying By The Numbers

I like numbers too. In fact, I have a spreadsheet that I created, very similar to yours. But you do need to remember that they are just numbers.

Is a boat with a comfort rating of 35 and a capsize ratio of 1.85 better for offshore cruising than a boat with a comfort rating of 32 and a capsize ratio of 1.93? The numbers might lead you to an answer of "yes," but that answer might be completely wrong.

Will a boat with an SA/D of 14.5 be slower than a boat with an SA/D of 15.2? Again, the numbers might lead you to think the answer is "yes," but that answer might be completely wrong.

In general, among boats of similar design, these differences mean almost nothing of any importance. Obviously there is a big difference between a Cabo Rico 38 and a Jeanneau 379, and the numbers reflect that. Using these numbers to choose which of those types you prefer makes some sense. But the differences between the Jeanneau and the Beneteau are insignificant. Using these numbers to choose between them does not make sense. It would make more sense to choose between those two boats based on which one looks prettier to you, or which one has nicer color coordination in the interior.
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Re: Boat Buying By The Numbers

You should determine what you will use the boat for 90% of the time and get a boat suited to it. For us, it's coastal cruising. We like several destinations that are 30 to 50 miles away and would like to get there and back on long weekends, often with guests. Speed rules, followed by liveaboard comfort. We found the exact boat for the job.

Any boat can go anywhere the other 10% of the time, if you plan and outfit properly.

p.s. the validity of many of these numbers is hotly debated. Don't obsess.
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Old 07-10-2013
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Re: Boat Buying By The Numbers

WHAT!! No STIX ratings.
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Old 07-10-2013
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Re: Boat Buying By The Numbers

The numbers are a narrow and limited way of looking at boats, but I found this kind of an analysis useful in the very early stages of my search. When I was completely new to the boat game (10 years ago) I used these databases as a means of matching my aesthetic desires and perceived needs with certain types of boats. Later, once I really knew what I needed and liked (which only came with time and experience), I used this kind of analysis to compare my narrowed group of boats.

It's one of many tools.
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Re: Boat Buying By The Numbers

I'm a believe in the motion comfort ratings. Sailed on lake Michigan you will feel the differance. Your numbers look high on these, you may have the math wrong???
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