Hey Tim,
Your method also works really well with a transit and tripod. Set up directly behind the boat, sight the keel and get it plumb, and then sight up to the mast. You can use the crosshairs to get it "dead-on".
--Jim Farmer

Sorry.
Latter should read ladder.

-Tim

David,

I think it is much more important to get the mast and the keel on the same vertical plane. This is fairly easy to do. All you need is a step latter and a piece of string.
First drive you boat to a flat part of the parking lot (the boat does not have to perfectly level). The latter should be placed approx. 100 feet behind the boat and it must be placed directly behind the boat (as close to the extenuation of centerline of the boat as possible).
Next tie a string from the top rung of the latter to a low rung. Align the string with the trailing edge of the keel then sight up the string to the top of the mast (adjust the string horizontally on the latter rungs). Ultimately the top of the mast and the sail grove should be in line with the trailing edge of the keel. This should all be done with no blocks in at the partners.
To get a proper sight put one knee down and try and stabilize your body as much as possible than just use one eye to glance up to the top of the mast and back down to the keel. Having a friend with you to confirm what you are seeing is not a bad idea.

When you are confident that the mast and the trailing edge of the keel are on the same vertical plane then check to make sure that you are at the max J dimension. Now you are ready to put the mast partner blocks in. I would recommend spartite.

-Tim Healy

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I have an older J-24, 1979 vintage, and I'm trying to update it for racing according to the latest measurements. To do this I have found that the mast has to be all the way back in the partners. Now I want to be certain that the mast is centered over the keel. What do you recommend as the best way to determing this?

Good question.

The shear is the deck, and the stemline is the front edge of the bow. THe stem fitting is the stainless piece of hardware that the forestay and genoa attach to. That fitting has a flat part that rests on the deck and a flat part bolted to the front face of the bow. The point where those two pieces intersect is where you should measure from.

Good luck
Will

I'm doing some modifications to my boat, which had never been raced prior to my ownership, and I'm trying to get it up to specs. I know this is an ignorant question, but how do find the intersection of the stemline and the sheerline. Is it the tip of the bow, a point further out, or somewhere else? How far does the back of the mast end up from the edge of the opening in the deck? TIA
Mike

Thanks! I got an email from Geoff Evelyn last night stating the same thing (wrong band). I feel a little dumb, but happy that I'm not going insane (debatable). Thanks for setting me straight. Good sailing.

WRONG BAND - The correct band is only a few inches above the deck. The two measurements are only 1/2 inch different.

Kevin

WRONG BAND - The correct band is only a few inches above the deck. The two measurements are only 1/2 inch different.

Kevin

Think about the trigonometry for a moment. Assume we have nearly a right triangle formed by the mast (no rig tension), the deck, and a line from the stem/sheerline point to the bottom of the mast band. The old "J" dimension was 2910mm, or about 9.5 feet. This is side A of the right triangle (along the deck). Let's say the bottom of the black band is about 2.5 feet above deck level. The mast is side B of the right triangle. If A squared + B squared = C squared, then C (the line from the stem/sheerline point to the bottom of the band) should be about 3" longer than A, not 2925mm - 2910mm, or about 1/2"!!! Some of my figures are not quite correct, I know, but somehow I'm off by several orders of magnitude. I'm pretty sure my mast band is correct and the headstay is max length. If you look at the trig above, it implies that the mast must actually lean forward with no rig tension applied! Can this be right?

Two things to check quickly are whether the lower band is correctly marked and whether your forestay is maximum length. My change from blocks and "old J" to spartite and "new J" ended up with the mast in about the same position. I think you are right to suspect something is amiss. Good luck!

I was getting set up to do my Spartite installation yesterday. I was doing some measurements and found something very strange. I pulled out my old wooden mast blocks, which were set up so the mast was at max "J" according to the old class rules (2910mm from forward face of mast at deck level to the stem at the sheerline). I then re-measured the "J" using the new rule (2925mm from the forward face of mast at bottom of the band to the stem at the sheerline) and found that I'd have to move my mast forward about 3" to achieve the new measurement! Is one of my numbers wrong? I can't believe there would be that much of a difference between the old and new measurement. Help!

Not if it is done properly.

Does the spartite make it difficult to pull the mast if you need to after you have used it?

Are you talking about at the base or at the deck? At the deck, wooden blocks were traditionally used but there is a relatively new product out called Spartite that works much better. Layline carries the kit. At the base, the mast step should be bolted to the bearing beam.

What works best for positioning the mast in place
and holding it there?