What is the formula for hull speed? I can''t remember.

duffer1960 · #1 05-07-2003

Help.

928frenzy · #2 05-07-2003

For a displacement hull, it''s: 1.34 X the square root of the waterline length (LWL).

Happy sails to you ~ _/) ~

capnjim02 · #3 05-08-2003

One thing to remember is that the water line length for calculation should be for the boat under sail or power. depending on the design of the stern its length can be extended considerably. remember the old rule beaters with 6'' of stern hanging out of the water when they were at the dock.

Jeff_H · #4 05-08-2003

There has been a lot of research on so called hull speed in recent years. While there has been a lot of conjecture about the phenomina as modern boats have routinely exceeded thier calculated hull speeds. The current research seems to suggest that having longer length when heeled can add to a boats overall speed and push the hull speed limit upward a little, having a longer heeled waterline length really does not add as much as the traditional formula using a constant of 1.34 times the waterline length would suggest for this longer heeled waterline. So, for example,if you look at a 32 CCA era boat which might typically have had a 24 waterline when static and a 28 foot waterline when heeled down and moving at speed, this boat would neither have the 6.5 knot hull speed suggested by its static waterline nor the 7.1 knot hullspeed suggested by its heeled wateline, but perhaps something in between. Current theory suggests that the reason that these CCA era boats were able to achieve speed in excess of the hull speed suggested by their static waterline was in part due to overdriving the hull with the sail plan, which also resulted in larger heel angles, as much as by the increase in waterline length when heeled.

The current increases in hull speed over the traditional formulas currently concentrate on reducing the size of the bow wave by making the bow finer. This of course is the opposite of the bow shapes used during the CCA era when bows were made fuller in order to pull the bow wave as far forward as possible.

Jeff