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post #9 of Old 08-02-2002
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Hull Speed

Greetings, Dean.

I did a quick google search on the topic and the best I could find was the snippet (from you''ll find below.

Please keep in mind that I''m not in a position to debate the subject on too technical a level since my fluid mechanics courses were long ago and not of much use here anyway. Since I have not read Gerr''s book, I can''t say what assumptions were used to derive the formula.

Fair winds,

[start snippet]
But just how fast can a monohull boat be expected to go? It all depends on displacement -- more specifically on the D/L ratio (i.e., how heavy the boat is compared to the LWL). Naval architect Dave Gerr worked out the relationship, one of the great accomplishments in modern naval engineering. (David Gerr: Nature of Boats, McGraw-Hill; Offshore, Dec. 94, pp 29-33)

D/L ratio = D[in long tons, 2240 pounds]/(0.01 x LWL)^3.

S/L ratio = 8.26 /(D/L ratio)^0.311

The formulas show that lower displacements permit higher speeds without actually planing. Everyone is familiar with Anthony Deane''s original formula for heavy displacment hulls, and people are slow to catch that non-planing boats go faster than Deane''s formula predicts, despite our observations that boats sometimes do go faster than they''re supposed to.
[end snippet]
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