Sunday, September 19, 2010

Transom Extension

The first time I sailed on the Honcho I noticed that the transom was immersed as we motored out of the harbor, dragging a small wave along with it…. Not good. Later, under sail, even with the boat heeled ten degrees, there it was, a little wave following the transom around everywhere we went. That little wave was telling me that Honcho’s transom sucks.  I mean it sucks a little wave along behind it, squandering energy that could and should be used to make the boat go. For a yacht designer this simply won’t do.

Beneteau 36s7 with Immersed Transom Trouble
Later, another problem became apparent. There is a very stylish recess in the transom that serves as a step and a place to bolt on the boarding ladder. It’s very French.  That is to say that it looks good but, mon amie, it does not work so well. There is a nice recess for the ladder, but no place to put stuff or stand if the ladder is not deployed. Having an inconvenient boarding ladder is, well, inconvenient.  But having a transom that sucks, that's just wrong. 

So I decided to build a small transom extension that will do three things. First it will stop the transom suckage (an industry term). Second it will provide a place to put stuff and stand on when boarding the boat from the dinghy or just checking the transom, which I do periodically. Third, it will increase the sailing waterline length by about a foot.  As all students of yacht design know, the theoretical hull speed of any boat is 1.34 times the square root of its waterline length. I’ll save you the math, on the Honcho that translates to an increase of approximately one tenth of a knot in theoretical hull speed. Putting it another way, Honcho with the extension will go roughly two miles further than Honcho without the extension in a 24 hour run. Let’s face it, that’s not much….But, I’ll be a lot more relaxed over the next 10,000 miles, or however many we sail, whenever I look over the transom and see a nice, clean, non sucking wake behind us. After all, cruising is supposed to be relaxing, right?

Here is a J/44 with Transom Trouble that was vastly improved by adding an extension. In this case we added a very substantial extension that included engine exhaust, cockpit drains and bilge discharge thruhulls. Honcho's modifications will not be nearly as extensive as these
Over the next week or so, I’ll explain how to build a transom extension.

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