Chain Plate

[Thistle]

For various reasons I'm looking to replace one of the chain plates on my Jaguar 23.



At the top end it is bolted through the deck/cabin top moulding with both ends of the fastenings accessible. But what about the other end, circled on the photo above? The six fasteners go through the internal moulding. I can't get any access, even for an endoscopic camera, between this moulding and the hull so I can't see if there are nuts on the end of machine screws or if there is a block of wood for heavy wood screws to bite into or ... . Undoing wood screws would be a doddle; undoing machine screws with no access to the nuts would be a disaster.

Any suggestions for sensible approaches to the problem would be very welcome.

Thanks in advance.

 

[jlavery]

Try gently undoing one, and see what happens?

Hopefully someone with more knowledge of the Jaguar's construction can be more helpful.

 

[Thistle]

Try gently undoing one, and see what happens?

Hopefully someone with more knowledge of the Jaguar's construction can be more helpful.

Yes, I wondered about that. No problem if it's a wood screw but I'd be concerned about ending up with (another!) loose nut on the boat.

 

[jlavery]

Yes, I wondered about that. No problem if it's a wood screw but I'd be concerned about ending up with (another!) loose nut on the boat.

I agree!

 

[PetiteFleur]

They may be just screwed into the grp or maybe there is wood behind it. As suggested, try to unscrew it... If they screwed into grp they may be impossible to remove - when I bought my current boat I noticed the stern ladder, fixed with M10 screws to the transom did not have any nuts internally so was going to fit longer bolts with washers and nuts - but the screws were impossible to remove so decided to leave them as the transom was about 12mm thick.

 

[B27]

I'd be loath to muck with that.

If the top of it needs replacing, maybe a short new chainplate could be bolted to the old one?

 

[Thistle]

I'd be loath to muck with that.

If the top of it needs replacing, maybe a short new chainplate could be bolted to the old one?

Interesting idea. Thanks.

 

[Tranona]

Pretty sure that plate can only have been installed after the internal moulding was bonded in and the deck attached. So the chances of there being nuts are small. could be machine screws into a tapped plate bonded into the moulding but that would require precision unless drilled and tapped afterwards. My money is on self tappers possibly into a ply block but more likely just into GRP. Take one out.

 

[vyv_cox]

Difficult to believe that a builder would attach a chainplate with screws. I would expect a tapped plate bonded into the moulding, which is how Sadlers are built. It is possible to detect these plates using an ultrasonic device for finding pipes and wires behind plaster in houses. May be difficult with the chainplates in-situ but would work if the plate was a lot bigger than the chainplate. Otherwise unscrewing one part way will reveal the thread type

 

[B27]

Get a strong magnet, that might tell you there's a steel plate behind.
I've seen similar on GRP dinghies and dealt with it by re-tapping.
But nothing this critical.

Few things that boatbuilders might do when stuff is out of sight would surprise me.
A drilled and tapped bit of mild steel is quite likely.
IF you're lucky, it might be galvanised.
Neither would self tappers or woodscrews be unexpected, the heads kind of hint that...?

If messing with this goes wrong, it could write off your sailing season, if not your boat.

What's plan 'b' if the fasteners can't be replaced in such a way as you'll trust them?
Maybe the new strap could extend further down to get more fasteners in?
I don't know, there is a limit to what can be inferred from one picture.

 

[Thistle]

What's plan 'b' if the fasteners can't be replaced in such a way as you'll trust them?
Maybe the new strap could extend further down to get more fasteners in?
I don't know, there is a limit to what can be inferred from one picture.

The plan, so far, is to try to find out what I'm dealing with THEN plans "a", "b", ... , for how to deal with it!

 

[Sea Change]

I would pick a suitably out of the way spot to drill a hole and poke a borehole cam in, so that you can see what's going on.

 

[Thistle]

The bottom end of the offending chainplate was hidden behind the galley woodwork so Saturday's job was to remove the galley. This revealed a cutout in the 6mm thick moulding that a previous owner had made for running the gas pipe. I could just get my hand through this to feel what was behind the screw-heads: penny washers and nuts. Nothing extra moulded in; no shakeproof washers; no nyloc nuts; just single, common or garden nuts. I guess the chainplate must have been attached to the internal moulding before the three mouldings were put together.

Still, all this has the up-side that I now know what I'm dealing with. I know I can remove - and refit - the chainplate. I've got someone I trust coming to look at the fibreglass repair and together we'll look at re-designing the chainplate so that it's straighter, fits better where it comes in contact with the fibreglass, spreads the load a bit better ... and has a decent backing for the fasteners.