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Old 11-30-2013
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Chainplate Re-locating

Hello to all!
Would like to get feedback on above topic. Nothing annoys me more than a chainplate fitting popping through the deck right smack dab in the middle of the topside walkway like on Gulf Star or CT. Irwin and others put them out on the outside of the hulls keeping the walkways clear of trip hazards and shrouds. My primary question is - can these/why can't these deck popping ones be relocated 18" outboard with proper backing, bracing and reinforcing installed ? I read on one forum where a guy actually moved them from the outboard position, inward, to a more inboard position, for greater stability he said. Is this true ? I find it hard to believe an extra18 " or lesser18" of steel cable either way is going make that much of a difference for a cruising, not racing, sailboat? And there would be much to gain in ease & quickness of access to the bow area from the cockpit when trying to walk while underway. Is there a huge physics property at work here that I am not understanding correctly?

Mahalo
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Old 11-30-2013
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Re: Chainplate Re-locating

tagged for further input

I have the same questions concerning moving a mere 6 inches. My CPs come up in the center +/- of a 12" deck. I'd like to move them outboard. I have a pair of bolts thru the hull into the aluminum "knees" inboard that the CPs fasten to now. I don't see why an attachment plate could not be bolted on the outside, extending up under the rub rail to 'catch' the existing CPs. The change in angle of the shrouds/stays would only be a few degrees, if that. Calculates out to .1.873 degrees from the spreaders down and .87 from the masthead. What could be bad about that!?
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Old 11-30-2013
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Re: Chainplate Re-locating

Moving the chainplates outboard will widen the sheeting angle and you will not be able to point as high. That may not be an issue for you, or it may.

Moving them inboard gives less support while at the same time adding compression to the mast - a real stupid idea without a naval architect's advice.
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Old 11-30-2013
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Re: Chainplate Re-locating

For access forward the better arrangement is to have the chainplates tight against the cabin side so you can walk around the rig altogether. This also allows you to bring headsails in closer to centerline and perhaps improve windward ability (to a degree.. the ultimate success of this depends on other factors). However the narrower shroud base creates more engineering difficulties with supporting the rig (tighter angles, higher loads?)

In some respects you may not actually prefer the shrouds outboard.. yes, it moves the chainplate out of mid deck, but I reckon now you can 'swing' yourself around the uppershroud on your way forward without a lot of difficulty. Move the chainplates to the hull sides and you now end up 'ducking' and somewhat more awkwardly swinging yourself inside the lower shrouds.. the spreader configuration and mast height will determine how much of an 'obstacle' the lower shroud might present. And, of course, this arrangement seriously compromises sheeting angle on an overlapping genoa.

btw "Topsides" is the area of the sides of the hull between deck edge and waterline.. where you walk is the 'deck'.
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Re: Chainplate Re-locating

Quote:
Originally Posted by S/V Ohana View Post
Is there a huge physics property at work here that I am not understanding correctly?

Mahalo
yes, if you have a tight wallet it will be a much more difficult project. any thing can be done if you through enough money at it. moving chain plates is a lot of money. Going sailing and walking around the chainplates not as much money
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Re: Chainplate Re-locating

The wider the base the lower the shroud loads, since the lever arm grow. The downside is that the sheeting angle for the headsail must also move outboard, reducing pointing ability, or requiring getting rid of a big jib and switching to non-overlapping small headsails.

Moving them either direction also supposes that their is a hard point that is suitable to attach them too. Mounting them to the sides of the boat, absent internal support, won't work. The unsupported sides are not likely strong enough to support the loads, and moving them inboard almost always means there is nothing to attach them too.

Either way you need the ok of a NA, absolutely all new rigging, spreaders, chainplates, ect. Moving inboard you may also need a new mast to handle the increased compression loads, and a new compression post if the mast is deck stepped. Worst case you could also need to rebuild the mast-keel tie if it isn't strong enough.



Frankly moving major structural elements like this needs a NA, and it is usually cheaper and easier to just replace the boat with one that doesn't have the problem.
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Re: Chainplate Re-locating

For what it's worth, I had a similar dilemna a few years ago.
I always felt like the chainplate attachment on my boat was poorly designed and weak (several others including a surveyor told me the same thing) so I decided to move them outside and they are now attached to the hull.
I am very happy with it.
Structurally, I feel a lot more confident about the strength of the rigging.
I love being able to walk to the bow with the shrouds out of my way.
I never have to worry about leaks where the chainplates enter the deck.
Yes, I lost a few degrees of sheeting angle on the headsail but it's a very small loss and surely the pros far outweighed the cons in my particular case.
It was quite simple to do in my case.
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Last edited by JSailer; 11-30-2013 at 11:25 PM.
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Old 12-06-2013
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Re: Chainplate Re-locating

Now that it's been mentioned.... swinging inboard of the shrouds *would* be more problematic than the little space I have to swing outboard! Time to re-think the whole thang Thanx
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