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Old 30-05-2010, 09:37   #16
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This is a good website to check data and compare boats:
Sail Calculator Pro v3.53 - 2000+ boats

The Tartan 37 is in the list. You can also input the data for your subject boat and make comparisons of data and the assortment of calculated factors and ratios.

Info given there for the T37 includes:
Disp = 16,278
Sail Area = 658
SA/Disp = 16.39
Disp/LWL = 278
Motion Comfort = 28.97

There's plenty of debate about the value of the MC ratio calculation, but there's the data.

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Old 02-06-2010, 00:10   #17
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Thanks Jim D, Is 28.97 good? I use to have a list that compared various boats. Seems to me this is a bit on the low side for comfort. If I recall correctly some were as high as 48. Is that correct? I wish I could find that list.
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Old 02-06-2010, 05:01   #18
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Motion Comfort Ratio was developed by Boat Designer Ted Brewer. The formula predicts the speed of the upward and downward motion of the boat as it encounters waves and swells. The faster the motion the more uncomfortable the passengers. Thus, the formula predicts the overall comfort of a boat when it is underway. Higher values denote a more comfortable ride. As the Displacement increases the motion comfort ratio will increase. As the length and beam increases the motion comfort ratio will decrease.

Here’s what Ted Brewer has to say about CR:

"COMFORT RATIO (CR): This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

Beam does enter into it as as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare the motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch.

The CR is : Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x B1.333).

Ratios will vary from 5.0 for a light daysailer to the high 60s for a super heavy vessel, such as a Colin Archer ketch. Moderate and successful ocean cruisers, such as the Valiant 40 and Whitby 42, will fall into the low-middle 30s range.

Do consider, though, that a sailing yacht heeled by a good breeze will have a much steadier motion than one bobbing up and down in light airs on left over swells from yesterday's blow; also that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet. Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! It is all relative..."


More Here ➥ Ted Brewer Yacht Design
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Old 02-06-2010, 05:59   #19
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Sorry I didn't answer sooner. As I remember it the displacement was about 16000. Also I'm no believer in the comfort ratio figures. But from my experience sailing from the Chesapeake to New England when the wind was light to moderate (10kts or less) the boaty did not have a really smooth motion in the seaway. Hard to describe but it seemed that we wave would pick her up and we'd get a bounce coming down. In heavier winds the modtion was smoother but still not near as smooth as in my previous boat a C&C 40. Wonder if it being a keel/centerboard boat instead of a fixed keel that made the difference.
Enchantress has a much smoother ride, even in chop but she's a much bigger boat with a full keel
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Old 02-06-2010, 17:41   #20
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Quote:
Originally Posted by Jim D View Post

Info given there for the T37 includes:
Disp = 16,278
Sail Area = 658
SA/Disp = 16.39
Disp/LWL = 278
Motion Comfort = 28.97

There's plenty of debate about the value of the MC ratio calculation, but there's the data.

~

I was absolutely NOT kidding when I wrote that the value and application of Motion Comfort ratio was subject to debate. Personally, I think SA/D and D/LWL are much more useful ratios for comparing boats.

However, the MC ratio is out there, and the website for which I provided a link will either provide all the data for a long list of boats, or will calculate the assorted factors if you input the measurements for any boat.

One thing that's fun to explore is doing sensitivity tests of your own using the calculator site, to gain knowledge of what changes have the greater impacts; like you can increase the displacement by 500 pounds and see how all the calculated numbers change.

For me, all the data is interesting, even MC, as it gives you directional indications when comparing two boats against each other. Such relational comparisons are likely more insightful than is the absolute value of any given calculation. For example - I suspect we can all mostly agree that a yacht with SA/D of 12 will be a lot slower and harder to get going in light air than another one with SA/D of 20. That's what I mean. And if I want to think about a boat with which I am completely unfamiliar, then checking these ratios gives me an indication of what I might expect.

Solo mentioned he "used to have a list". Well - such a list is essentially provided right in that calculation website.

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Old 03-06-2010, 22:10   #21
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Well this is all academic at this point. I did more home work last night and the said boat has a Volvo MD11C diesel. I suspect it's NFG at this point so who knows were this sale will go now? But I would like to thank everybody for their input. Buying a good boat at a reasonable or good price in the right place at the right time is difficult. It seems I keep missing the boat so to speak.
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