Builders' Forum Archives
Re: fastest kayak?
Posted by Camper on Nov 2, 2006
Hm... Sorry, just googled and could not find any articles, Charlie. They are out there, will post if I run across them.
In the meantime, I remember the physics vaguely, see if it makes sense to you:
1. Every boat has a hull speed (1.34 times LWL). This is the speed at which bow and stern wave constructively interfere, and form drag increases sharply.
2. Every boat has a planing speed. This is the speed at which hydrodynamic lift is sufficient to hold the boat up, rather than buoyancy.
3. In boats of traditional design, planing speed is NOT higher than hull speed. Thus, the boat cannot exceed hull speed WITHOUT planing. To put it another way, in a moderately heavy boat, the power required to overcome the form drag at hull speed is MORE than enough to achieve planing speed.
4. Since that is true of traditional boats, there must be some law of physics stating that it is true of all boats, right?
5. Wrong. In a very light narrow boat, the hull planing speed is HIGHER than hull speed. No speeding laws are violated!
6. Why is this true of ultralight craft? Because in an ultralight, narrow, efficient hull, the bow and stern waves are so small. At hull speed, they constructively interfere. But planing speed has NOT been reached. Above hull speed, they are no longer constructively interfering. So what happens to form drag? It decreases.
7. At some higher speed, planing begins.
In Response to: Re: fastest kayak? by Charlie on Oct 28, 2006