Shroud attachment location at the chainplates - SailNet Community

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  #1  
Old 06-23-2012
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Shroud attachment location at the chainplates

Here is a picture please forgive the roughness I am not an artist. Unlike the picture the mast is not straight but has a bend in it to the bow and more or less centered at the spreader. In other words the mast forms an arc and the curve of the arc is centered more or less at the spreader and points to the bow. The leech of the main sail has some flutter which seems to be, being caused by the bow in the mast ie not straight. As mentioned in my first post if we switch the upper and lower shroud chainplate attachment points then we can staighten the mast with the lower shrouds.

c_witch

PS this boat had a jury rigged bowsprit when we bought it and also has a second jib? which we figured had to do with the PO having tried to set it up as a cutter rig.
The furler we have is a Barton and relies upon a s/s wire rope sewn into the leech of the sail. This is why we cannot reef with it.
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Old 06-23-2012
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Re: Shroud attachment location at the chainplates

lossen the forestay, tighten the back stay, look straight up the mast, adjust untill the mast is vertical in all ways. rake it back a tad for preformance. No mast should bend forward under no load
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Old 06-23-2012
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Re: Shroud attachment location at the chainplates

Another picture/drawing to try and explain what is going on here.

I should also point out at this point that the second forestay is as loose as can be made with out having it swinging freely about. The aft stay has also be loosened and does have a bit of a sag in the wire from the masthead to the split stays leading to the transom. We have a transom mounted rudder.

c_witch
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Last edited by c_witch; 06-23-2012 at 08:20 PM. Reason: addtional info
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Old 06-24-2012
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Re: Shroud attachment location at the chainplates

Wow. A question: are you lower shrouds attached to the hull even with the mast, slightly forward of the mast or slightly aft of the mast?

I think you need to loosen all stays and start over, as it were. Take a halyard and use it to get an equal distance from side to side to insure your mast is straight up and down, not leaning towards one side or another. Tighten up your forestay and backstay when your mast is straight up on the forward and back plane of the boat. Once you have your mast oriented where you want it and tightened down you then work on the lower shroud. Check for mast bend by attaching a halyard to the base of the mast and seeing if the mast is as straight as the line. Then, lastly, tension the lower forestay.

I must say that on my cutter rigged boat, there is a stay that attaches close to my lower forestay and goes aft of the mast, a bit aft of my shrouds. The job of this stay is to provide a counter force to the forward pull of the lower forestay so what is happening to your boat doesn't happen to mine. I think that is what is missing in your boat's configuration. You should have a rigger look at it to advise where and how to attach such a stay. You don't have to do a wire stay but use rope and, with a block and tackle system, you can have a running backstay to control some mast bend as needed.

Tod
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Old 06-24-2012
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Re: Shroud attachment location at the chainplates

Hiee Tod,

I know the halyard trick. When she was on the cradle I had her level and used a plumb bob to set the mast true and have a 2 percent rake. When we put her in the water I re-gauged the rigging to check and ended up adding some tension to the aft stay, but didn't notice the bend in the mast.

If you look at my posts you will see some drawings showing where the shrouds are attached relative to the mast foot. Also again the 2nd forestay is basically loose and Not causing the bend in the mast. The aft stay has also been loosened almost to slack and the bend is still there. We did find that by pulling back on the lower shrouds that the bend will come out RE: my question about swapping the location where they attach to the chainplate.

c_witch
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Old 06-25-2012
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Re: Shroud attachment location at the chainplates

I had looked at your pictures but it wasn't clear to me regarding the placement - attachment points of your shrouds vs your mast. Your uppers should be even with your mast. It seems to me that most boats have 2 sets of lowers, 1 set attaches to the chainplates forward of the mast and another aft. You only have 1 set of lowers. That should attach aft. Hopefully that adds enough pressure to counteract the forward pressure of a properly tensioned inner forestay. If not, you should consider addition of running backstay.
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Old 06-25-2012
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Re: Shroud attachment location at the chainplates

I would agree with the suggestions to swap the current connection points for the upper and lowers so the lower is aft and the upper is in line with mast. That would give you the ability to counteract the pull of the second forestay.
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Old 06-25-2012
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Re: Shroud attachment location at the chainplates

Thanx Jim and Gladl,

The spreaders were angled backwards and only location to attach was the aft chainplate. It appears as though at one point they where attached to be 90 degree's to the main sail sail track. We will be dropping the mast today and moving them back to what appears to be the original locations and then we can attach them to the chain plate opposite the mast and they should be opposite the mast on each side with the lowers attached aft of the mast which should counter act the pull of the 2nd forestay. I've seen on a number of sites that the angle between the wire and speader tip should be the same for the upper side and lower side of the upper shrouds. In working out some calculations it appears as though we will have to angle them upwards about 8.5 to 9 degree's to accomplish this.

c_witch
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Old 06-25-2012
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Re: Shroud attachment location at the chainplates

Actually that bow you have looks pretty normal. It's called pre-bend, and is critical for good upwind sailing. Without knowing what boat you have I couldn't guess at how much you need, but my Olson 30 needs about 4", while a J-35 carries almost 17" of pre-bend.
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