Sunday, December 14, 2008

Planing in a 5O5

Nice example of planing.

Did you know that boats have a top speed determined by their length at the water line? Here's the formula: hull speed in knots = (square root of the hull length in feet at waterline) * 1.34.

When I learned of this limit a few months ago, I was surprised. Imagine if cars were like this. Imagine shopping for a fast car: No need to bother about its width or height or weight. Check its length and there's your max speed.

But unlike cars, boats make waves. The wavelength of these waves imprisons the boat, from bow to stern. Well... so long as the boat is in the water. A boat at the surface of the water, a boat that is planing, can break this hull speed rule.

The capsize at the end of the 5O5 video is all too familiar. Although the crew slides onto the centerboard quickly, the boat seems eager to turtle.

Like the 5O5, my V15 sits high on the water after a capsize. A few seconds of wind and wave action and it's upside down.

I agree that a capsize is "part of the fun" of sailing a little racing dinghy. But a turtled boat is no fun at all. When turtled in shallow waters, the tip of the mast can bang against the lake or ocean bottom. It can bury itself so hard that the boat won't move. Then you've no option but to call for a motorized rescue. Even so, the effort to pull the boat free may dismast the boat.

A float at the top of the mast can keep the boat from turtling for several minutes - long enough for the crew to get the boat upright. The downside: any weight at the top of the mast makes the boat less stable and may increase drag.

At this point, I'm not taking my boat anywhere without some sort of float on the mast. Four empty 2-liter soda bottles seem to do the trick, albeit without elegance. Three soda bottles --trust me on this-- do not suffice.

I'm shopping for a better answer. The Hobie Bob looks heavy. I'd like to see the Flying Dutchman float, which seems to integrate with the top of the mainsail.


  1. Thanks for stopping by my blog. I honestly cant remember how I found yours but I'd like to add one more shared interest which is sailing.