Chain plate problems?

[CaptainForce]

Originally Posted by SailorNate

have you considered Titanium? 6al-4v would be an excellent choice for this application, with your old plates as templates it would not be that expensive to fabricate. (I was quoted .....Nate

SailorNate, 'sounds like an excellent idea. I googled titanium fabricators and found many to choose from. What fabricator with experience with marine applications gave your quote? Thanks,
Aythya crew

[pander1203]

I requested a price for shroud chain plates from Pacific Seacraft. Their response is below.

A full set of shroud chain plates with back-up plates would be $605.00 plus crating and shipping. Most who have ordered these, have opted for new hand polished carriage bolts as well. They are $15.00 each for the carriage bolts, washers and nuts.

Pete

[niftynickers]

Pete etal,
I also did some checking-found 316 ss straps 1/4"x2"x36" at MSC supply for $91.19.Figure two chainplates per strap.Need to be cut ,drilled ,bent and polished.cPanel® bolts and washers at McMaster Carr-www.mcmaster.com again need to be polished.More work =much less money
Chuck S/V NiftyNickers

[niftynickers]

MSC website should read--www.1.mscdirect.com

[Petethenomad]

I've looked at quite a lot of 80's Crealocks since I replaced all mine on my 1984 PSC34 and I have found cracks on almost all that showed rust. I was in a rush when mine showed cracks and I had PSC ship me a complete set with backing plates and nuts and bolts - cost about $1000US. The bow looked OK and was not included. It was pretty simple to expose the nuts on the inside and replace them.

Regards,

Pete

[knothead]

Originally Posted by RichH

Rust blooms on any stainless cyclically loaded part should be a strong warning for two phases of degradation going on: 1. fatigue cracks and 2. crevice corrosion.

Rich, your entire post is excellent, but this first sentence is really great. Very concise. May I quote you?

There is no question that where you have rust, you have corrosion. Just like where you have smoke, you have fire.
I have consistently noticed over the years that where I find evident "bleeding" from thru-deck chainplates that there is usually a crack. Either in a bolt or the plate itself.
Where there is a concentrated rust spot on a piece of 1 x 19 wire, there is usually a broken strand.

I also really agree that bonding the chainplate to the hull is a smart thing to do. I know that there are many who shudder, but I always use 5200 to bed chainplates.

Lastly, I would strongly recommend that square holes be avoided at any cost. Choosing carriage bolts because of how pretty they are is really silly when you consider how much of a propensity there is for cracking to occur at the corners of square holes.

[RichH]

[quote=knothead;536407
Lastly, I would strongly recommend that square holes be avoided at any cost. Choosing carriage bolts because of how pretty they are is really silly when you consider how much of a propensity there is for cracking to occur at the corners of square holes.[/QUOTE]

Absolutely NO square holes i n any cyclically loaded structure .... a square hole forms in material engineering and stress analysis/design what known as a 'stress-riser'. A stress-riser will severely reduced the ability to carry stress and WILL be the site of where fatigue cracking starts to propagate. With cyclically loaded components like chainplates you want NO sharp edges, all 'smooth', the LEAST amount of holes ... and those 'holes' having 'rounded' chamfers, etc. With a square hole stress riser and without actually dynamically testing one to failer, I'd probably reduce the fatigue endurance limit (30000psi) for 304/316 Stainless down to 20Ksi or even lower .... thats how BAD 'square holes' are.
Square holes (window shapes) were the cause of the early British Comet Jet passenger aircraft to catastrophically fail and break apart in flight .... NO square holes if you want a cyclically loaded part to 'last'.

[whigmaleerie]

Ive done the chainplates on my ohlson 38, just to let you know that you can polish stainless steel very easily with a special soap and a buffing pad on a brill, its very satisfing and its amasing what other things on the boat that can be made to sparkle give it a go, heads of bolts also come up great.

[pander1203]

Here's an update on my situation. I had a rigging inspection done last week. The chain plates were inspected to the extent of checking for cracking at the stress points, by polishing and observation with a magnifying glass. There was no dis-assembly. Not one of the plates showed any cracking whatsoever, so I'm not planning to take any action.

Pete

[niftynickers]

Pete,
Lucky you,looks like you dodged the bullet.Mine on the other hand are bleeding rust pretty badly and I'm replacing them.Just dont feel comfortable off-shore with them.The boat is on the hard and that's one of my winter projects.We will be driving down to the Keys this winter and maybe we can meet up for a dinner.
Dianne and Chuck Burke S/V NiftyNickers C37 #139