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Tafa 03-13-2012 11:28 AM

Chainplate reinforcement
 
Hello Sailnet :)

I have a little problem as shown below.

http://img849.imageshack.us/img849/6558/imgp2460g.jpg

I bought the boat recently and cannot find information on how did that happen. So I am assuming the cause was poorly adjusted rig tension. (Other chainplates look perfectly fine).

I am planning to open and reinforce the area and put the chainplate back.

I need some advise on;

- What kind of material should I use for reinforcement (specific advise with brand name would be superb)
- There is no sign of leak. Should I really worry about drying the area thoroughly. If yes how can I make it dry(accept opening and letting it dray. We have some rainy days ahead). Acetone, hot air, etc. are safe to use on fiberglass deck?
- What caulking material you would use? Butyl Tape, Sikaflex 295, Sikaflex 291 or other?


Many thanks in advance for your help.

Tafa

overbored 03-13-2012 12:04 PM

Re: Chainplate reinforcement
 
Make and size of boat might help other owners of the same give you some advice as the way they are installed can be very different between boat builders

MedSailor 03-13-2012 12:41 PM

Re: Chainplate reinforcement
 
Chainplate failure is a more common cause of rig-loss than you might imagine. For some reason owners often think they'll last forever, when really they're subject to crevice corrosion even more than the rigging is. (The rigging is out in the fresh air). Everybody replaces the rigging on some kind of schedule but often the plates are not replaced.

If you're going to all the labor to un-bed and remove and re-bed the plates, I'd recommend replacing them while you're at it. A stainless shop ought to be able to make up a set cheaply. Of course if all you do is light-air day sailing, that might be overkill, but judging by the picture, the plates get loaded at least sometimes.

MedSailor

Tafa 03-13-2012 12:45 PM

Re: Chainplate reinforcement
 
My bad..... You're right

She's a Nash 26

Tafa 03-13-2012 12:50 PM

Re: Chainplate reinforcement
 
Quote:

Originally Posted by MedSailor (Post 845001)
Everybody replaces the rigging on some kind of schedule but often the plates are not replaced.

If you're going to all the labor to un-bed and remove and re-bed the plates, I'd recommend replacing them while you're at it.
MedSailor

Great point MedSailor... What do you think would cause the problem rust of metal exhaustion. If the main concern is rust, its easily inspect-able. Is there such concern as metal exhaustion on ss.

Thanks,

Tafa

MedSailor 03-13-2012 01:06 PM

Re: Chainplate reinforcement
 
Quote:

Originally Posted by Tafa (Post 845006)
Great point MedSailor... What do you think would cause the problem rust of metal exhaustion. If the main concern is rust, its easily inspect-able. Is there such concern as metal exhaustion on ss.

Thanks,

Tafa

Yes, the "metal exhaustion" you refer to is called "work hardening". When the stainless steel family of metals is flexed under load (anything other than a perfectly in-line load) it becomes more hard and brittle over time. It's a little counter-intuitive but it can actually become "stronger" with work-hardening but more brittle. Suffice to say the characteristics of the steel of your chainplates were selected for a reason at construction and hardening of them over time is bad. You don't want brittle metal with a shock load of a crash-jybe.

Reading on work-hardening here: Article: Mechanism and measurement of work hardening of austenitic stainless steels during plastic deformation

The type of corrosion that stainless suffers from is called "Crevice Corrosion" and it happens in an anaerobic environment. It's unavoidable with bedded stainless hardware. Silicone bronze (marine bronze) doesn't suffer from this problem but is more expensive and isn't "shiny" like stainless. Most of the time the corrosion appears as brown staining but unfortunately it's not always visible. Micro cracks on the surface can lead to destruction of the core of the chainplate with the only visible evidence being the (hard to find) micro-crack.

Reading on crevice corrosion here:http://soar.wichita.edu/dspace/bitst...pdf?sequence=1

Image of crevice corrosion on a chainplate:
http://www.gyatso.net/images/cp02.JPG

jrd22 03-13-2012 01:15 PM

Re: Chainplate reinforcement
 
If that is the interior of the boat the way it looks (external chainplates?) then I would recommend a large SS backing plate and longer bolts.

Faster 03-13-2012 01:30 PM

Re: Chainplate reinforcement
 
Is this the bottom of a lower shroud 'chain plate' connection? It doesn't look right for a cap shroud chain plate, they are usually attached to something more robust like a bulkhead or a knee..

Also is the crack in a liner molding or the deck structure itself??

GeorgeB 03-13-2012 01:45 PM

Re: Chainplate reinforcement
 
Tafa, can you take a couple more pictures of your rigging? (From the topsides for example.) Am I’m looking at a lower shroud and that your cap shrouds are chainplated into a bulkhead, frame or hull? My guess is the crack you are seeing is from a molded-in headliner and that the problem is there is a gap between it and the deck proper and that tightening that one nut is the culprit and not a question of over tensioned wire. When you remove the topside “chainplate”, clean the bolt holes really good. Tape over the hole bottoms and pour in the epoxy to fill the gap and re-drill. You probably have wood core here and check to see if it is wet and rotted. That too will cause your problem. Mainesail has an excellent website that shows how to do these kinds of repairs. You will probably want to add a proper backing plate. You can fabricate one out of 1/8 inch stainless (polished) plate. However, this is expensive and requires cobalt drill bits and saw blades. Downscale, you can use 3/16 inch G-10 (Garolite). This is easier to work with but lacks the finished look of polished stainless. Are you missing lock washers on the those bolts or it the picture quality? You will want lock washers. If you use SS backing plates, all you will need are the locking washers and nuts (plus an acorn nut to finish it off). If using Garolite, then add a flat washer.

bwindrope 03-13-2012 06:31 PM

Re: Chainplate reinforcement
 
Thought I would add my experience of recently replacing my chainplates for precisely the reasons enumerated here. Here is my blog post: Stories of Aeolus- Our Gulf 32 Pilothouse: New Chainplates!''

Mine were original to the boat in 1988 and so 20+ years old, and like many boats, passed through the deck in a unseeable way. Sure am happy with my new, thicker, well sealed with butyl rubber new plates! It had been on my list, and now is fully off.


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