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Old 27-05-2014, 13:10   #1
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Sagging Boom

Took our new boat out for the first couple times this weekend and ran into a problem with the boom height. It looks like the main is up all the way and the luff is tight but the aft end of the boom is really low, nowhere near level. This is on a Kirby 23 which is basically the same as a Sonar. It appears that this is the original main, but I can't imagine that this is the way it is supposed to be. I feel like I'm missing something. The second day out, I was able to attach the outhaul to a grommet slightly above the clew and this helped raise the mast some but it leaves a fold of unused sail at the bottom and may not be the best for the sail shape.

One thought I had is that this mast sweeps back at the top. This is my first experience with a fractional sloop but from what I understand, and other pictures I've been able to find, it seems like this is by design. However, it seems that the mast bending back could lower the aft end of the boom?

Any insight would be greatly appreciated!
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Old 27-05-2014, 13:48   #2
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Re: Sagging Boom

Raking the mast aft or bending it by tensioning the backstay (on a "fractional" rig, such as the Kirby 23) will cause the boom to sag.

So, the first checks are, at the dock, with the sail down:
- Is the backstay almost slack?
- Is the mast straight?
- Is the mast vertical?

In windy conditions, it's useful to (slightly) bend the mast because it helps reducing the sail camber, shedding some power.

Alain
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Old 27-05-2014, 15:21   #3
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Re: Sagging Boom

Ok, maybe I have the back stay over-tensioned. So, at the dock the back stay should be almost loose?
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Old 27-05-2014, 16:11   #4
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Re: Sagging Boom

your sail is stretched, you can have it resewn or get a new one
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Old 27-05-2014, 16:24   #5
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Re: Sagging Boom

Quote:
Originally Posted by Hard A Lee View Post
So, at the dock the back stay should be almost loose?
Yes. On this type of rig, the backstay isn't necessary to keep the mast upright. This is done by the aft-leading shrouds and spreaders.

In light winds, going to windward, the mast should be straight (not necessarily vertical) to get the full draft on the mainsail. When the wind is stronger and the boat could be overpowered, you tension the backstay. This bends the mast and flattens the mainsail. It's as effective as reefing.

On dinghies (without a backstay), this is obtained by a *very* powerful vang, which pulls the boom forward against the gooseneck and again bends the mast.

Alain
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Old 27-05-2014, 16:48   #6
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Re: Sagging Boom

How much weather helm do you have? maybe you need to take some of the rake out...
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Old 28-05-2014, 09:19   #7
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Re: Sagging Boom

Thanks for all the replies! You've all given me some things to check out. Weather helm wasn't bad when we had some good wind the other day. However, I think I had the jib sheets running through the wrong sheaves so who knows...the rigging on this boat is a bit different than a normal cruising boat that's for sure!

I had wondered about having the main re-sewn so that could still be an option and ill try to get the rake out of the mast. I'm wondering if its a little bent because it seemed to rake back a bit even before the stays were attached. I hope that's not the case.
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Old 28-05-2014, 09:25   #8
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Re: Sagging Boom

my comments about the sail were assuming you mast is not excessively raked or bent back...make sure forestay is correct tension as well as others before cutting the main

also since its an original main its more than likely a bit stretched so that still holds true...

cheers
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