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Old 06-05-2012, 01:22   #1
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Relocating Shrouds

I am considering relocating my shroud attachment point from inboard to outboard chain plates. Are there any special points I should consider before doing this ? My boat currently has 1 lower and 1 upper shroud and I would like to have 2 lower for more support. Any constructive help is much welcome.
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Old 06-05-2012, 03:48   #2
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Re: Relocating Shrouds

A lot will depend on the type of boat, type of rig, how far you plan to move them etc. Without some more detail, advice will be fairly general.

FWIW, I moved from inboard to outboard chainplates for the lower shrouds but it reality it was only moving the attachment points about 2 inches outboard so the issues were minor.
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Old 06-05-2012, 07:55   #3
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Re: Relocating Shrouds

You cannot relocate to any place. You may have to build in knees / supports / beef up the laminate / etc. prior to placing the shroud there. Make sure the angles / forces are OK and the mast is well supported. Make sure the tanks / fittings on the mast (too) are aligned with the forces (this may require building new mast fittings or relocating the old ones).

Why?

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Old 06-05-2012, 18:24   #4
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Re: Relocating Shrouds

The current location of the shroud attachment is just inside the toe rail. I would like to move just the lower shroud outboard and then be able to add 1 additional lower to help support the mast. The total amount of relocation is only 4-6 inches. The overall goal is
to make it stronger for an anticipated cruise. Maybe just step up 1 size in wire would be
just as good ?
Thanks
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Old 06-05-2012, 19:33   #5
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Re: Relocating Shrouds

First question . Why do you think that will make it stronger than the original designer had planned? More wires do not always mean more strength.

Second. Do you intend to fasten to the same point on the mast (as the other lowers) and what affect do you expect as far as pre-bend is concerned. Will it negate the Vang and prevent forward bend for instance? Or as another example, will the changes induce or reduce mast pumping?

Suggestion. Talk to a qualified rigger and shipwright as well as getting suggestions from the internet.
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Old 06-05-2012, 19:45   #6
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Re: Relocating Shrouds

Going to outboard chainplates will decrease the angle that the shrouds make with the mast. That will lower the compression load on the mast for the same sidways resistance. Less compression load for the same results is always better unless you are trying to increase the sheer of the deck line. Lower shroud angles are always better if they don't mess up your sheeting angles too much. But, Hey, who cares about getting that extra degree or two of pointing ability when your pounding into 5' plus headseas for more than a few minutes. Most of us cruisers will be heading off 10 degrees or more to make life a lot more enjoyable when the going gets rough.

Double lowers also should be better as they will triangulate the support for the mast below the stays and better fix the mast in position. You may lose some control of the shape of the main because it will be harder to bend the mast to flatten the sail. Then again, that's probably a good thing on a cruising boat as you don't want some bent noodle of a mast when things get dicey out on the big pond. Double lowers are always better in my way of thinking.
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Old 06-05-2012, 19:55   #7
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Quote:
Originally Posted by PEACETIME
The current location of the shroud attachment is just inside the toe rail. I would like to move just the lower shroud outboard and then be able to add 1 additional lower to help support the mast. The total amount of relocation is only 4-6 inches. The overall goal is
to make it stronger for an anticipated cruise. Maybe just step up 1 size in wire would be
just as good ?
Thanks
Just curious. What is the boat? Might help in giving advice.

One can assume the boat should be left as designed, however the current mast support could be "adequate" if not a compromise on production costs when considering the manufacturers intended use as a weekender or daysailer.

We had a lower shroud failure at the deck attach point. The fitting failed not the wire. It was a no brainer to replace all the fittings on the boat with one size larger. We did not consider changing the wire shrouds themselves or going larger.

Lots to consider when adding rigging. Primarily the question is will the intended change result in the desired outcome. It seems your desired outcome is twofold. Move the shroud attachments off the side deck and make moving around the boat easier and also to improve the stability of the mast for some presumed heavier weather passaging.

There are wicked smart guys here but I don't think measured advice can really stick unless the boat type is known.
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Old 06-05-2012, 20:22   #8
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Re: Relocating Shrouds

When you say 'just inside the toerail' then have a good look below deck - is the plate attached to the hull or to a knee? If to the hull, then moving it outboard seems pretty simple. Still, depending on how long the shroud is, moving the lower end 5 inches may add to the strength (wider shroud base/angle) but you must control how this changes the alignment of the fittings on the mast - you do not want any fittings to be exposed to bending, etc..

Adding another line to support the mast may make it stronger but you want the line to be balanced - the shrouds being laid out either exactly opposite (when in pair) or else in a 2x2 or 2+1 set-up. You only make things stronger/more stable if everything is balanced, otherwise resulting forces may bend the mast out of tune and compression can do the rest of the job. All this said, in a well designed rig, adding additional shrouds/stays is not necessary. For if the rig is not designed for the job then probably/maybe the hull isn't either?

If the wire and the fittings are sized for the job then going one size up with the wire will only add weight and remove some give, none of which may actually add to the overall strength and resilience of the rig.

There are some good books on rigging so before you modify anything you may just step into the local marine bookstore and get some. I always found the freebie at Selden pretty informative too (although probably too basic for the job at hand). Look it up anyway, maybe it will help you decide on the best solution.

http://www.seldenmast.se/download.cf...=595-540-E.pdf

BTW I found many local riggers willing to come along and give me free advice on my boat. Look around, if there is one somewhere close to your boat they may just cast a quick look and tell you whether you are right or wrong in your plans.

Cheers,
b.
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