SailNet Community - View Single Post - SW Florida Boat Choices/Advice
View Single Post
post #19 of Old 12-17-2002
Jeff_H's Avatar
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 7,446
Thanks: 11
Thanked 237 Times in 188 Posts
Rep Power: 10
SW Florida Boat Choices/Advice

The only problem that I have with that site is that almost all of his data is based on designs that are more than 20 years old and many which are over 50 years old. We have learned an enormous amount about the design of boats for comfort, seaworthiness and speed in the past twenty years and in my mind the actual numbers that come out of his ''fuzzy'' logic is only valid if you are into older designs. Unfortunately, many of the designs that he has chosen had artificially short waterline lengths. Since many of the popular ''non-dimensional'' ratios use waterline length as a factor in determining their output, the results within his tables tend to push the resultant output quite high.

Using an example that I have posted her before or two 38 footers which for all intensive purposes are identical (6 foot draft, 6500 lbs ballast, 15000 lb displacement, 685 sf of sail area) except that one has the typical waterline length of a boat designed in the late 1970''s,28 feet and the other has a more typical modern waterline length of 33 feet.

The 1970''s era boat would have the same SA/D ratio (but would have more drag and a lower hull speed) but more significantly the 1970''s boat would have a L/D of 305 compared to the more modern boat''s L/D of 186. The other misleading number is the so called Comfort Factor in which the 1970''s boat would have a CF of 27.42 compared to the more modern design''s 24.5. The reality is that, all other things being equal, the longer waterline and implied finer bow and shallower canoe body of the more modern design would result in a more comfortable motion (less rolly) and in more performance on all points of sail, seastates and wind ranges.

Jeff_H is offline  
Quote Share with Facebook
For the best viewing experience please update your browser to Google Chrome