New Boat

My new boat arrived in the back of a cargo van! It actually got here a few days ago, but this is the first chance I have had to post about it.

Here she is. Well almost. This is a red kayak, mine is yellow. That picture is small and crappy and IMPOSSIBLE to read, so click it. Doing so will open up a larger photo that highlights all the features of this thing.

I got EVERYTHING one can possibly get with this kayak. It came standard with the way cool Mirage Drive system, and I added the sail kit, daggerboard, and kayak cart. There is no cool link for the daggerboard, but it is just a keel. It has the shape of an airfoil, and sticks straight down into the water about 3 or 3.5 feet. Kind of like an upside down shark fin. It adds stability under sail power. When the boat is not under wind power, it will still add stability - but is not really needed.

The Adventure model is 16 feet long at the waterline. It is the fastest boat in the Hobie Kayak line. Kayaks, sailboats, tug boats, barges, and even aircraft carriers are ALL alike in one respect, they are all displacement hulls. This means they do not "plane" like a powerboat can. With displacement hulls, longer = more speed.

This has to do with the bow wave, and the quarter wave. When a boat moves through the water, it creates a bow wave. Water has to be pushed out of the way for a boat to move forward. This bow wave then creates a second wave, called the quarter wave - or stern wave. Maximum displacement speed is reached when the crest of the bow wave is just ahead of the bow, and the crest of the quarter wave meets the stern. To go any faster in a displacement hull IS possible, but it requires a whole lot of energy. More energy than ANY person can provide. You need a motor to get beyond hull speed.

And the greater the distance from the bow wave to the quarter wave the faster the wave can travel. So longer hulls are faster than shorter hulls - always and forever. UNLESS you are talking about adding an engine AND if the boat has a "planing" hull. Even the largest aircraft carrier in the US Navy can not go faster than the hull speed - as aircraft carriers are displacement hulls. It takes to much energy to get over the bow wave that is is not economical - or even impossible.

There is a formula to calculate maximum hull speed for a boat. And here is that formula!
Maximum hull speed = 1.34 * (square root of LWL)
Where LWL = length of the hull at the waterlie AND the results are in knots.

In the case of my new boat, this is easy. The hull is 16 feet. The square root of that is 4. And 4 times 1.34 = 5.36 knots.

1 knot (nautical mile) = 1.15 car miles. So the maximum speed I will be able to hold is 6.164 miles per hour.

Ain't physics phun?

And why is 1 nautical mile equal to 1.15 car miles? It has to do with the Earth. A nautical mile is defined as EXACTLY one minute of longitude at the equator. There are 60 minutes in one degree, and 360 degrees in a circle. Therefore, one can see that the Earth is EXACTLY 21,600 nautical miles at the equator. "Car" miles are based on the "fact" that at some time the foot of a king was measured, and then this king decided that there would be 5,280 of his "feet" in a mile. Since statue miles are based on nothing more than crap, they are shorter than nautical miles.

So what did we learn here? Who the hell knows. I might just know far more than I ever need to about things like hull speed.