>> One point three four times the square root of waterline length(in
>> feet) gives hull speed in knots.
>> (Not many people know that) :o)
>This has gotta be a boat rule - no way it can be true for a board - I can
>change the waterline and still keep the same planing surface - or change
>it cant work for planing boards - Boats dont really plane like boards do...
>they get into a SUPER displacement mode - not real planing like a rock
>skipping over water
The formula given above by RobSm is, indeed, approximately correct. Simply
stated, the tern "hull speed" refers to the approximate speed at which a
hull starts to climb its bow wave. A nine-foot board has a "hull speed" of
about 4 knots.
The formula's limitations: while it does apply to planing hulls, it's not
very useful in connection with them -- not even longboards, which exceed
hull speed even when going upwind in moderate conditions. You're right to
think the formula is most useful in connection with high-displacement