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Old 01-09-2012, 14:53   #1
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Raised Boom Affecting Mainsail Shape?

First of all I wanted to say thanks to everyone on the forums for being so helpful! I'm a complete beginner, and have learned so much from these threads. Hopefully someday I'll know enough to be able to contribute, rather than just pick people's brains.

I've had a 1994 Mac 26S for a month and a half now, and have taken it out 5 or 6 times. I've noticed that there is something very wrong with the shape of my mainsail - it is way way too slack. At first I thought it might be because I wasn't raising the sail high enough - maybe there was some sort of obstruction in the track that the sail slugs run in that was preventing me from raising the mast all the way. However, I checked for this the next time I set up the boat, and it wasn't the case. I also suspect that the age of my mainsail (original) is a factor in how slack it is (stretched out over time). Still, the sail seems to be way too slack for age to be the only factor. I realized the other day from looking at the mast that the previous owner had raised the boom in order to accommodate the bimini (picture attached). I have noticed from forum searches that others have raised their mast to accommodate a bimini. When you do so, do you also have to trim your sail size? I would think that that would be very undesirable, because it reduces the amount of wind you can catch... Am I missing something? Is there something else I can do to fix this problem? If I really have found the problem, I am considering moving the boom back down to it's original location, and cutting down the size of the bimini (a solution to the boom/bimini interference problem that I have seen others use).

I am going sailing on Monday, and will take and post pictures of my mainsail.

Thanks for any help/guidance!
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Old 01-09-2012, 15:31   #2
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Re: Raised boom affecting mainsail shape?

G'Day mate,

Without pix of the sail shape it is hard to say for sure, but if the PO raised the boom by the amount shown in your pic and didn't modify the sail, it would definitely affect the shape. You need to be able to get the luff fairly taught at the least, and especially if the sail is old, actually stretching it a bit will help move the draft forward. (One of the results of age is the sail stretching and the draft migrating aft. This reduces forward drive and increases heeling forces... both bad things for performance.)

Cheers,

Jim
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Old 01-09-2012, 15:38   #3
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Re: Raised boom affecting mainsail shape?

Does the first reef show a lot of wear?
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Old 01-09-2012, 16:31   #4
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Re: Raised boom affecting mainsail shape?

Is there a downhaul missing? Typicaly in a small boat you raise the main all the way with the halyard and you tension the luff with the boom downhaul. See if there is anything in your boats lockers that looks like a small block and tackle, and if it will attach to the bottom of the gooseneck. Does the top of the bimini show lots of wear from the boom dragging across it? You may not (if you are lucky) have a problem at all.___Good Luck______Grant.
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Old 04-09-2012, 12:28   #5
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Re: Raised boom affecting mainsail shape?

When you take those pictures of the main, use as wide angle a lens as you have, shoot from beneath the sail at the middle. Shoot the picture while going upwind, preferably in 8-10 knots of wind.

The OEM sails on MacGregors are lightly built. I'm not knocking the manufacturer. Most builders don't spend much on sails.

If you get a new mainsail built, you can have the sail built with a shorter leech so the boom doesn't interfere with the bimini.
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Old 04-09-2012, 13:23   #6
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Re: Raised boom affecting mainsail shape?

Forgot to mention another reason this conversion likely won't work. Furling mainsails require the clew to be a certain amount higher than the tack. The exact amount varies by furling system manufacturer. It will typically be expressed in either degrees or inches of rise per foot. In most cases the clew height relative to the tack will be greater than it would be for a conventional mainsail.
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