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SJ23 Hull Speed - How fast can she go?

A - Hey Ron.... 4ish knots through the water for a San Juan 23 in an estimated 10 knots of apparent wind is probably about right.  Are you having fun?  I began a comment a week or so ago, talking about theoretical hull speed and being supposedly 1.34 x the square root of the waterline length, but even this author nodded off.  Long boats go faster than short boats due to physics of the wave a boat makes; one at the bow and another at the stern, and the boat is usually stuck somewhere between them.  Enough said, except that a clean bottom and not dragging your transom in the water make a huge difference.

The SJ23 is capable, under the right circumstances, of exceeding their theoretical hull speed.  It can happen going downwind, and with the help of a wave, the boat will surf down the face of the wave.  Back when our speedometer worked, I noticed 9.5 knots broad reaching, maybe wing and wing, in the San Juan Islands.  The waves were short-period and steep-faced, and if you kept the boat sailing downhill on the wave face, the boat would break through the bow wave, accelerate nicely, and the helm would be neutral, for a nice feeling for the driver.  Under these conditions, the driver needs to think of steering the boat just like a circus seal balancing a beach ball on its nose.  Often that requires letting the boat heel slightly to weather to ensure the helm remains neutral. 

But enough of that stuff.  My old sweetheart/sail maker/sail designer/14 helmsperson/shellback and more, taught me a few things:

1. Fast racing keelboats usually top out at about 3 knots speed made directly to windward while racing.
2. Cruisers are exempt from having to sail upwind while cruising; if it is not a fetch to your destination, you are allowed to motor.
3. SJ23s can go 55 knots dead upwind, down I5 with no spray on the deck.  This is quite useful on a limited time budget.

So sail on a clean bottom, sail lots of downwind or fetches, and enjoy the ride!  Cheers, and sorry for the yawns!

SIDE NOTE: About wind pressure.  When we sailed SJ24's in the Dallas area during a hot summer, we had good talent on the boat.  There was plenty of breeze, up to the higher teens.  We were choosing sail combinations similar to those we used in the cooler Northwest; smaller jibs and reefed mainsail.  We were slow.  It dawned on us that the hot air was less dense than we were used to, and therefore offered less force on the rig.  We pulled up the pants on the sail plan and our speed came back.  Lesson to learn is to adjust the sail size relative to the wind pressure. 

Cheers. Gleno.
 

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