Thursday, November 6, 2008

Mast Step rule update

The Shields class has a rule dictating how much rake the mast can have, and it's based on the relationship between the mast step and the mast partners. I recently asked the measurer for some clarifications on this rule. This was partially to see if I could move our mast step to get more rake, and also to prepare for measuring boats when we host the National Championship here in Chicago next year.

The clarifications I asked for regarded whether we were supposed to use the actual partner location, or the legal max aft possible position, and also if the bury measurement (from the mast step to the top of the deck) included partner boxes, such as the ones that we (and most of our fleet) have.

The answers were kind of surprising to me, but are actually the most literal interpretation of the class rules.

The partner measurement isn't based on the actual location of the partners, it's based on the max legal aft measurement of the partners, which is 135.75" from the bow chock on the Shields. Our partner box is exactly at this spot, so it's not an issue for us, but it does mean that boats with the partners further forward are able to get less rake.

The other surprise was that the bury measurment is from the top surface of the deck, even if the box extends above this by an inch or two. This means that boats with partner boxes have the measured bury lower than the effective bury, again meaning a bit less available rake. I wasn't sure on this in spring, so just to be safe the aft edge of our partner box is raked aft at about the 2 degrees of desired rake. Phew!

I recomputed our numbers based on this, to see if we could move the mast step or not, and definitely not!

Our partners are max aft at 135.75"
Our bury is 34.5 (not 35.5" as I said back in June, since we measure to the deck surface)
Our Y (from aft coaming to parner max aft) is 134.75
Our Max legal X (coaming to mast step) is 140.260
Our actual X is 140.250

While I like to think of myself as a "every last inch" type when setting up a boat, I'm not sure I want to chase down the last .01"! It only translates to a difference of less than a 1/16" of an inch at the masthead, and the possibility of the boat changing shape a bit in the water and making me illegal is definitely not worth it. As my old friend Kevin always says "thats worth 1 bad tack"

We've got our awards dinner coming up in 2 weeks, and that morning a bunch of us are going to meet up and measure the boats in the yard. I really miss sailing Shields, so this is about as close as I can get until spring.

No comments: