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Thread: Ted Brewer & Comfort Ratio

  1. #1
    Join Date
    Jun 2003
    Location
    Great Lakes
    Posts
    20

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    I read an article in the recent Good Old Boat magazine where Ted Brewer floated a formula to describe a boat's comfort at sea. I've seen something similar in a formula for "heave" where heave = displacement/water plane area.

    The problem here is obtaining/determining the water plane area for a number of boats that you're comparing & considering for purchase. Brewer stated that the WPA is roughly equivalent to [0.65 * (length @ water line, LWL) * (beam @ water line, BWL)], where the beam(B) is used to approximate the BWL. To account for hull overhang the LWL is further broken down into weighted components of LOA + LWL. He further weights the beam (B) in the final formula to account for wider boats increased form stability & associated acceleration.

    Brewer's "Comfort Ratio" formula in its final from becomes:

    Comfort Ratio = Displacement(lbs)/ [0.65 * (0.3LOA + 0.7LWL) * B^1.333]

    Where higher CR's are more desirable.

    I'm familiar with a number of the typical ratios that describe hulls and their performance. They can help in sorting through various boats, but this comfort ratio seems to add quite a bit of clarity to the sorting task. In my rather simple mind the CR has pretty much replaced the D/L ratio as the CR is not only considers the D/L, but also the overall comfort(motion) of the boat in a seaway.

    Brewer gave a number of example boats & their CRs in the article. I have calculated out another 30-40 CRs for other boats & it's interesting to see how some boats have quite high D/L ratios (300+) while actually having (according to their CRs) quite uncomfortable motion.

    From what I've seen there are a good number of folks here that are quite skilled in the design area. Is the 'comfort ratio' as useful as it seems to be?

  2. #2
    Join Date
    Jul 2003
    Location
    New Zealand
    Posts
    15

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    Hi,
    it depends on what aspect of comfort you want .
    boat at rest anchored calm seas
    boat at rest anchored medium to very rough seas
    boat underway low and high speeds in calm seas
    boat underway low to high speeds in medium to very rough seas.
    very few desigers have been able to achieve all of these, as there is a trade off somewhere along the line.. Albert Hickman was probably one of the very few who came close.
    don
    [URL=http://invertedvboats.bravepages.com/]<br />[URL=http://invertedvboats.20m.com/]

  3. #3
    Join Date
    Jun 2003
    Location
    Great Lakes
    Posts
    20

    Post

    Badge,
    Sorry, maybe I should have narrowed things down a bit. I'm thinking displacement speeds & primarily sailboats or maybe a motor vessel with auxiliary sails...at rest or underway.

  4. #4
    Join Date
    Mar 2002
    Location
    Duncan, Vancouver Island
    Posts
    28,131

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    I think Ted just kinda made up the comfort ratio one day many years ago. I hadn't even realized he'd turned it into an actual formula
    There is no rational, logical, or physical description of how free will could exist. It therefore makes no sense to praise or condemn anyone on the grounds they are a free willed self that made one choice but could have chosen something else. There is no evidence that such a situation is possible in our Universe. Demonstrate otherwise and I will be thrilled.

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