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max hull speed
You calculate the theoretical maximum hull speed (in knots) using the formula 1.34 x SQRT(waterline length in ft). So, for a C30, that would be 1.34 x SQRT(25), or 1.34 x 5, or 6.7 kts. The number is not dependant on the type of rig (tall vs. standard) nor type of keel.
You calculate the theoretical maximum hull speed (in knots) using the formula 1.34 x SQRT(waterline length in ft). So, for a C30, that would be 1.34 x SQRT(25), or 1.34 x 5, or 6.7 kts. The number is not dependant on the type of rig (tall vs. standard) nor type of keel.
Thank you! So can she go faster than her
theoretical hull speed or is my knotmeter off?
We've had her up to 7.6kts according to the knotmeter. Yee Haw!
theoretical hull speed or is my knotmeter off?
We've had her up to 7.6kts according to the knotmeter. Yee Haw!Surfing
It's possible when surfing waves to exceed the max hull speed for short periods of time. Or the knotmeter could be off. If you display 7.6 kts for extended periods of time, I'd question the knotmeter's accuracy (try motoring along a measured mile to determine that, or confirm with a gps in an area with no current).
It's possible when surfing waves to exceed the max hull speed for short periods of time. Or the knotmeter could be off. If you display 7.6 kts for extended periods of time, I'd question the knotmeter's accuracy (try motoring along a measured mile to determine that, or confirm with a gps in an area with no current).
Exceeding theoretical hull speed.
You can exceed theoretical hull speed by heeling the boat over, which will increase its waterline length by a foot or so. A GPS measures speed over ground, not through water. I have had GPS speeds up to 8 knots with my 27 footer.(6.25 Theoretical) As a result of current or wave action.
You can exceed theoretical hull speed by heeling the boat over, which will increase its waterline length by a foot or so. A GPS measures speed over ground, not through water. I have had GPS speeds up to 8 knots with my 27 footer.(6.25 Theoretical) As a result of current or wave action.
Theory
The "theoretical maximum hull speed" is a good approximation for a sailing vessel with a "slippery" displacement hull form. It isn't a wall that cannot be exceeded, however. Since it's based upon the propulsion energy supplied by sails (or an auxiliary engine), the limit factor dominating will be when the standing wave crest-to-crest created by your forward motion is about equal to your waterline length. To "punch through" that standing wave, much more propulsion energy is needed. That energy can come from very high winds and/or wave action. There are many cases when boats caught in storms are surfing along in excess of hull speed under bare poles! (hence using drogues to slow things down). This max hull speed phenomena is analogeous to the "sound barrier" for an aircraft. Lot's of extra energy needed (and a different hull shape) to punch through. Power boats with semi-displacement hulls and lots of horsepower under the hood can get into a planing mode fairly quickly. Ditto for inflatable dinghies -- flat bottom, low weight, and a big engine. I suppose if you strapped a few 275 HP outboards on the tail of your C30, you might get into a planing mode, too. Might alter your trim a tad though ...
The "theoretical maximum hull speed" is a good approximation for a sailing vessel with a "slippery" displacement hull form. It isn't a wall that cannot be exceeded, however. Since it's based upon the propulsion energy supplied by sails (or an auxiliary engine), the limit factor dominating will be when the standing wave crest-to-crest created by your forward motion is about equal to your waterline length. To "punch through" that standing wave, much more propulsion energy is needed. That energy can come from very high winds and/or wave action. There are many cases when boats caught in storms are surfing along in excess of hull speed under bare poles! (hence using drogues to slow things down). This max hull speed phenomena is analogeous to the "sound barrier" for an aircraft. Lot's of extra energy needed (and a different hull shape) to punch through. Power boats with semi-displacement hulls and lots of horsepower under the hood can get into a planing mode fairly quickly. Ditto for inflatable dinghies -- flat bottom, low weight, and a big engine. I suppose if you strapped a few 275 HP outboards on the tail of your C30, you might get into a planing mode, too. Might alter your trim a tad though ...
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