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How to Calculate Hull Speed

by Will Charpentier
A ship's speed equals the square root of its bow wave, multiplied by 1.34.

A ship's speed equals the square root of its bow wave, multiplied by 1.34.

Your boat length determines its hull speed, simply because you boat's hull produces a wake -- a bow wave -- whose length is determined by the boat's length. The only time your boat can exceed its design speed is when it's surfing down the face of a following sea. In that situation, you're moving at the speed the wave's energy is moving forward and your boat creates no bow wake.

Length Translates to Hull Speed

Your boat's hull speed is the speed at which its length equals the wavelength of its bow wave. Determine your boat's length at the waterline, based on its state or federal documents. Determine the square root of the length at its waterline, using a calculator or slide rule, or -- if you know the procedure for mathematically extracting a square root -- by calculation. If your boat's 98 feet long at the waterline, take the square root of 98. Multiply the result, 9.9, by 1.34. The resulting figure, 13.27, is the hull speed of your boat in knots.

References

About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.

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