Moving the chain plates

[alahol2]

Someone has already mentioned it but I think it's worth repeating. In the last couple of years I have been removing and refitting all the through deck fittings. I have found two U bolts that have corroded through inside the deck via crevice corrosion. If your chainplates are constantly in a wet environment inside the deck I would at least remove them and check closely whilst deciding on corrective action.

 

[al.carpenter]

I would not attempt to move the chainplates on the hull without the advice of the designer or at least the yard that build your boat. The moments of the application of forces will be different and your hull/deck junction will be sollicited in directions that might need reinforcing. You might cure one probleme but create another or may be more...(compression, depression, opening, shutting, you might create a "hard point" on your nearest bulkhead, knee, partner or even stanchion base...) Not a job for the week-end boatbuilder without a sound pro supervision. Mind you I have seen so many abherrations!!! 6 inches on deck, from your spreader tip... not quite the same pull. Have a look at :

The Elements of Boat Strength: For Builders, Designers, and Owners by Dave Gerr

you will probably find the answer to your question in it, (It's my bible but I am not at home right now so cannot send you the paragraph on rigs. All the formulas are in and directly applicable to your own calculations).

I know nothing about petrol boats but personnaly I would dismantle, clean or replace then re-bed the originals. All the calculations were done for them why do you want to modify? Safe sailing. Al

 

[john_morris_uk]

I
Interesting..................makes you wonder how much actual proper engineering design is involved in boat design. AND how much tolerance is built in to allow for poor construction. Not a lot I fear when one looks at the number of failures of rig, keel etc we read about!!

Not sure that stacks up. The number of rig failures is minute compared to the number of boats that sail around for years and years. There is often a very good reason for rig failure - and I suggest that faulty design on the average cruising yacht is fairly low down the list...

That is what I have been thinking.
The chain plates have been replaced and I was thinking if I removed them and had a flange welded on the bottom and then refitted them with a smaller plate slotted over the top of the chain plate then bolted the lot together with a good dollop of sikaflex that should stop all the problems?
Assuming I can get the chain plate back in with the flange welded on?

I inherited leaky chain plates and rebedded them and found I still had problems with one because I'd made a classic mistake when I used the sikaflex. I'd fully tightened the fitting and squeezed all the mastic out!

I have now cured it by using the better method of cleaning up the fitting and refitting it with some small spacers (Match sticks?) just holding the fitting up off the deck. Allow the sikaflex to cure and then tighten the fitting down on the gasket of sika flex you have cast under the fitting. No more leaks - even when the thing flexes.

I agree with others who say that you need to double check that the flexing isn't excessive and caused by some underlying fault. If the fitting itself is flexing then a s/s fabricator will make a beefed up version for you for a few pounds. Otherwise follow the suggestions about structures below being beefed up.

Out of interest, our rigging goes from shroud to deck fitting through bolted to s/s plates which are bolted onto LARGE bulkheads etc which were glassed into the hull at build. (Note that its much easier to get a strong joint with Polyester Resin at build time before the chemical reaction has completely gone off.)

Moving the chain plates might solve the problem, but you might introduce problems of sheeting angles etc etc that will affect the sailing performance of the boat.