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Forums28
Topics4,053
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May 14th, 2026
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Joined: Feb 2010
Posts: 17
Member
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Member
Joined: Feb 2010
Posts: 17 |
I have a huge amount of mast bend when my backstay is slackened of completely with no pull on it whatsoever. could anybody tell me the right procedure to lessen this bend. I am told that there should be about 4inches of bend if you took a line from the deck to masthead at the widest part.
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Joined: Apr 2004
Posts: 457
Senior Member
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Senior Member
Joined: Apr 2004
Posts: 457 |
Check your mast butt position-it should be 1" behind the step in the cabin sole in the head. Any further aft and prebend will be substantially increased. Also, remember (I'm sure you know this) that the shrouds also induce mast bend due to the swept spreader configuration. Detune the rig slack all around, check mast butt position, then retune according to a good tuning guide.
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Joined: Jul 2004
Posts: 148
Senior Member
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Senior Member
Joined: Jul 2004
Posts: 148 |
With the rig slack, how much is "huge?"
We used to bend Lightning masts to straighten them out. If the unloaded spar is bent, I would call the manufacturer.
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Joined: Apr 2007
Posts: 493
Governor at Large
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Governor at Large
Joined: Apr 2007
Posts: 493 |
If you have blocks behind the mast at the partners, that will induce more prebend.
Tighteneing the uppers adds prebend.
Tighteneing the lowers reduces prebend.
Dennis Bartley
Planxty, s/n 23994
hull 205
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Joined: Feb 2010
Posts: 17
Member
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Member
Joined: Feb 2010
Posts: 17 |
I would guess that I have at least seven inches of bend with backstay off. Thanks for the advice, will wwork on it this weekend
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Joined: Feb 2010
Posts: 17
Member
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Member
Joined: Feb 2010
Posts: 17 |
Checked out the rig set up this weekend and yes it looks wrong, the mast is blocked forward in the partners and the butt is two and a half inches behind the vertical step in the cabin sole in the head. I looked at the butt of the mast and couldn't figure out how to move it forward. My hull number is 126 and year is 1979 I think.
I am most grateful for your comments and help. I am in a bit of a vacuum here in Grand Cayman as I'm only one of two J30's on the island.
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Joined: Apr 2007
Posts: 493
Governor at Large
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Governor at Large
Joined: Apr 2007
Posts: 493 |
The only way to do it on my boat (hull #205) is with the mast off. There are 4 screws on the top of the mast step.
Dennis Bartley
Planxty, s/n 23994
hull 205
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Joined: Mar 2003
Posts: 156
J/30 Class Measurer
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J/30 Class Measurer
Joined: Mar 2003
Posts: 156 |
Lift the mast up a couple of feet and you will see 4 screws holding the mast step in place. Loosen the screw and move the mast step forward. Remember that the front edge of the mast must be 1 inch aft of the front edge of the mast step. Larry Christy J30 Class Measurer alchristy@comcast.net
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Joined: Apr 2004
Posts: 457
Senior Member
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Senior Member
Joined: Apr 2004
Posts: 457 |
I would recommend pulling the rig to move the step. Mine was corroded in place and it took many tries to get it to move forward, and I think the likelihood of success with the mast butt swinging around your head is limited.
Your prebend must be pretty dramatic with the combo of partners forward, step aft. Make sure when you correct the problem to extend your headstay to the class maximum (35'-10 1/2"). You will be amazed at the difference in point and power with proper rig positioning.
Grand Cayman...just heard a forecast for snow tonight. Do you need help tuning that rig?
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