Originally Posted by irwin1951
Peddling for two years and love the engineering of the Mirage Drive - Outback, Turbo fins/Sail rudder - this year got a Cuda 350 GPS/Fishfinder trying to figure out more features on this thing every time I go out. GPS speed shows on a easy to moderate pace a 3.5MPH. Heavy pace pedal can sprint 5.+MPH. What do ya think - slow - average - fast ? My son wasnt impressed at all with it's speed - hull design is the main factor of the speed of a water craft - what kind of speed are you guys getting in your rides - peddle or paddle???? - Thanks -
I'm a kayaker, not a sailor but looking through a book on sailing (to learn about weather & tides etc) I came across a sailing term I found very interesting which is refered to a "max hull speed".
Apparently all displacement boats ( i.e. those that go through the water rather than plane, or skip over the waves ) have a theoretical maximum speed.
I dont remember the exact details but basically displacement boats push a wave in front of them. Obviously the faster the boat goes the faster the wave, and faster waves have longer wavelengths. For some reason once the wave length is the same length as the water line length of the boat, then the wave can't be pushed along any faster. Pushing harder then just makes the wave in front of the boat higher and higher, hence harder to push.
At this speed ( the Max Hull Speed ) the only way to go faster is to push so hard that the boat climbs over the wave, and leaves it behind and skips over the waves ( starts to plane ).
So as a boat speeds up and starts to approach this "max hull speed" limit the effort needed starts to rapidly increase out of all proportion to the extra speed obtained.
Once the boat is up "on plane" then less effort is needed. But to get a boat on plane and keep it there requires a powerful engine or big sails, a good wind and a light boat.
Kayaks are really displacement boats , so the same affect applies.
The formula for max hull speed is simple:-
Max Hull Speed knots = 1.34 times (square root of water line lenth in feet) or
Max Hull Speed mph = 1.54 times (square root of water line length in feet ).
So for your Hobie ( 12ft 1 ) if we assume a water line leghth of 11.5 feet.
Max Hull Speed mph = 1.54 times ( square root 11.5 ) = 5.22 mph.
Spookily close to the figure you are recording.
I have experimented in my old scrambler using a gps to record speed and could exceeed its max hull speed, but only for a few seconds. The effort required was massive. IMHO anyone who can keep a kayak on plane for much time at all is really a terminator disguised as an angler.
Since I found out about this effect I stopped wasting effort trying to fight the natural limit of my yak and now just happily cruise at a speed sufficiently below the max for minimal effort. I also try stay well away from anywhere where wind and tide might create a current near my max speed.
- Regards Lurch