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Old 07-26-2012, 06:16 AM   #23
FF
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Hull speed as noted is far from the optimum speed for the lowest fuel cost.

The only folks that frequently operate near "hull speed" are blow boats with a good wind from the after quarter , or a spinnaker.

Since wind is free , why not.the extra hp is free.

For a marine motorist the concept of a hull speed cruise might gain a K or so but at double or triple the fuel cost.

Attempting to climb out of ones wake up and over the bow wave is not cheap.

The simple answer is to measure the LWL of the boat and find the square root of the LWL.

That is known a SL.

.9 to 1.15 x the SL will give most fat boats their cruise speed thru the water.

A really skinny commuter style or CAT or TRI can go a bit faster with the same fuel use..

50 ft boat at best 49 ft LWL the SL is 7 .

SL .9 is 6.3 SL 1.15 is 8.05 somewhere between will be the sweet spot .

The "hull speed is 9.38K , so that extra K or 2 will double to triple the hourly burn, so few actually ever run at hull speed.

FF
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