Kayak Resistance and Speed

[JohnHuth]

Power = Force * velocity. Assuming the paddler has some 'maxed out' power output in the slower kayak at 5 knots, that corresponds to 5.5 knots given Leon's table, which incidentally, gives precisely the same number at 5.5 knots in the faster versus 5 knots in the slower. Or, did someone already answer this and I missed it?

I guess the only issue is that for a 17 ft kayak, the theoretical hull speed is around 5.5 knots, so the drag becomes very large, not linear versus speed in that region.

[leong]

Power = Force * velocity. Assuming the paddler has some 'maxed out' power output in the slower kayak at 5 knots, that corresponds to 5.5 knots given Leon's table, which incidentally, gives precisely the same number at 5.5 knots in the faster versus 5 knots in the slower. Or, did someone already answer this and I missed it?

I guess the only issue is that for a 17 ft kayak, the theoretical hull speed is around 5.5 knots, so the drag becomes very large, not linear versus speed in that region.

Yes, of course, John, the drag is not linear out near hull speed. In fact, even at the lower speeds, where the drag is mostly from frictional resistance, the drag is roughly proportional to the square of velocity. And at higher speeds the drag becomes nearly proportional to the cube of velocity (obviously I’m using the vector “velocity” interchangeably with its magnitude (speed)).

Here are some drag data for the Futura II surfski that I copied from http://files.meetup....akvelocity.html

Spd (knots) -> drag (lbs.)

2 -> 1.04

3 -> 2.12

4 -> 3.88

4.5 -> 4.87

5 -> 6.37

6 -> 10.31

Note that I changed the drag in the link from Kg to pounds … I’ve always hated using the “Kilogram-force” gravitational metric unit of force (weight), … I prefer to use either pounds or newtons when I talk about force.

Dan_f did answer the question earlier.

PS

I always find it puzzling why so many people equate force with effort (the force applied to an object to cause motion). Here’s one way I try to straighten them out. Think of pushing a block as fast as you can at a constant speed on some surface. Why can’t you push it at a higher speed, since the force to push it at a constant speed is independent of speed?

[eidsvolling]

1.21 gigawatts!

But only at the "stroke" of 10:04 p.m.