# Thread: Ted Brewer & Comfort Ratio

1. Junior Member
Join Date
Jun 2003
Location
Great Lakes
Posts
20
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. Junior Member
Join Date
Jul 2003
Location
New Zealand
Posts
15
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

3. Junior Member
Join Date
Jun 2003
Location
Great Lakes
Posts
20
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. Senior Mumbler
Join Date
Mar 2002
Location
Duncan, Vancouver Island
Posts
28,131
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

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