Builders' Forum Archives
Re: Climb on top and plan
Posted by Camper on Dec 4, 2007
I called Professor Science to ask him about all this. Here is what he said, after much muttering and grumbling, and some comments about science teachers and boat magazine editors that I did not hear clearly.
"Camper", he pontificated, "the 'climbing the bow wave' idea has been around longer than the 'alligators in the sewers of New York' myth. Or even the old whopper about 'lift occurs because the air over the top of the wing takes a longer path, so it thinks it has to catch up by moving faster'.
"I'm getting tired of it!
He caught his breath here, and continued in his calmer professorial voice.
"It's much simpler than that. A heavy boat, especially a fat one with a flat run aft, will have a planing speed lower than its hull speed, so it will plane before it exceeds hull speed.
But there's no physical law that says it has to be so. Indeed, many other common boats (rowing shells and light kayaks) have a planing speed HIGHER than their hull speed. These boats will simply exceed their hull speed without planing, and without time moving backward or whatever. Of course, when they DO reach planing speed, they plane.
"If planing speed has nothing to do with hull speed, then what is it? Why, simply the speed at which the hydrodynamic lift force takes over for the buoyancy force, in the gravity-fighting department.
I pass this on without comment, as I am no scientist, just a sometime Sharpie builder who is slowly sealing his garage floor over the years, with drips of a rather expensive two-part garage floor sealer.
In Response to: Climb on top and plane by Doug S on Dec 3, 2007