Chainplate U bolt replacement

[differentroads]

Hi
The U bolts on Offbeat, my Offshore 34, are showing danger signs - they look a little rusty, there are places on the horizontal plate that trap water and, lo and behold, soaked balsa core now that I've removed them. They'll have to go. Thing is, they are 12mm diameter and I can't find any 12mm u bolts to fit the holes in the thick stainless plate they bed into (which I really, really don't fancy drilling for new fittings.) But I've found some M10 U bolts that are the right dimensions
http://www.baselinemarine.com/shopexd.asp?id=5635

I don't know what working load to expect on my rigging despite searching forums and my copy of Calder. My heart says stick with M12 because that's what is coming off and they looked reassuringly massive, but my head says that a fairly modestly rigged 11m cruiser doesn't need 12mm chainplates. Should I follow my heart and keep searching (or have some fabricated) or my head?

 

[ANDY_W]

It is possible that M10 might be sufficient. However, if there were to be a subsequent failure, I suspect that
your insurer would reluctant to meet any claim on the grounds that the original specification was not followed.

Apart from that, you might be happier when in fresh conditions knowing that your rigging was as the designer intended!

Andy

 

[Poignard]

I wouldn't hesitate to have some fabricated. I would assume the designer knows more about these things than I do and if he specified 12mm, that's what's needed.

 

[Scarboroughsloop]

I wouldn't hesitate to have some fabricated. I would assume the designer knows more about these things than I do and if he specified 12mm, that's what's needed.

Agreed. When I bought my boat I had the 4 u-bolt style chainplates replaced. It wasn't as cheap as off the shelf but the peace of mind is worth the additional cost in my view.

 

[vyv_cox]

A2A4 http://www.a2a4.com/acatalog/A2A4_U_BOLT_3800.html and http://www.a2a4.com/acatalog/A2A4_U_BOLT_WITH_TWO_COUNTER_PLATES_3803.html list 12 mm U-bolts in 316. The first link seems to show the width as slightly less than the 10 mm bolts you have highlighted, the second one doesn't say. Might be worth asking.

 

[differentroads]

thanks everyone - sound advice. Offbeat was home completed (so might have been not to the design spec) and impressed me with the way her fittings seemed oversized, especially compared to the new Jenneau that I'd been sailing on. So I'd better stick with like-for-like; its too late for regrets on something so vital out there in weather that's testing everything to its breaking point

I hadn't come across the A2A4 site in my hours of trying to find a U bolt to fit. The M10 one is perfect but the table says that the distance between the legsof the M12 is 60mm and mine measure 48mm. But I notice that the table says the 'U' diameter for the M10 model is 12mm, and that's where I measured mine. So maybe they are M10 after all - M10 legs and bolts, that is.

I'll double check that and buy M10s or have M12s fabricated if not. Thanks again
Mark

 

[West Coast]

Westerly used to fit these on all sizes of boats, including 36' plus. They originally fitted the normal U Bolt type, but I understand there were some failures where the soft radius of the U Bolt became distorted over time. They were changed over to a V type fitting, very similar to the U type.

This article explains it better than me! http://www.bmse.co.uk/articles/decking-u-bolts/

 

[alahol2]

But I notice that the table says the 'U' diameter for the M10 model is 12mm, and that's where I measured mine. So maybe they are M10 after all - M10 legs and bolts, that is.

I'll double check that and buy M10s or have M12s fabricated if not. Thanks again
Mark

I'd be very wary of using those U bolts. The drawing shows the 12mm rod for the 'U' turned down to an M10 thread with a very 'square' shoulder. That sounds like a perfect stress raiser and you wouldn't be able to see what was happening.

 

[differentroads]

I'd be very wary of using those U bolts. The drawing shows the 12mm rod for the 'U' turned down to an M10 thread with a very 'square' shoulder. That sounds like a perfect stress raiser and you wouldn't be able to see what was happening.

Cheers. Managed to find some 12mm rod U bolts that had M12 nuts, nice big bases and the right leg distance at my local chandlery. Real life 1, t'internet nil! Who knew? Didn't manage to get them fitted today - rained off. But otherwise a happy bunny. Thanks for good advice, people