Chainplate Backing Plate

[Viking23]

1977 Catalina 25 Standard Rig. Preparing for annual haul out/ bottom painting/maintenance. Have noticed the wood slightly dimpled on a couple of 4 bolts where the attach bolts go through the teak covered bulkhead and terminate on the other side of the bulkhead through the chainplate. This may be stress over a long period of time. Looks older and weathered to me. Plan on stepping the mast and adjusting the rigging during maintenance anyway. My sailing is very light and cruising type. Called Catalina Direct for tech support. They suggested, if bolt pattern was the same, buy two chainplates and have them modified (cut down) to put on the other side and reinforce the attach points (like a plate under a winch etc). Aside from the cost ($149 each) my bolt pattern is four in-line bolts on each side. Part from Catalina is a staggered pattern so will have to have made at a machine shop if I do this. The tech at CD said if I have it made it of SS it will need to also be electro-coated to preclude rusting. I would appreciate any similar experiences, concerns, or advice prior to doing this to strengthen this. Thank you.

 

[jssailem]

I have a cal not a catalina. When I removed chainplates I tested the wood backers. there was some minor indentation of the fender washers on the wood. No rot was evident. Looked like the tightening of the nuts had crushed some wood cells. Check it for density by poking it with an awl. Wood should be firm and not permit penetration. If not firm replace wood.

Have not heard of electroplating stainless. With my plates I polished the stainless to mirror finish then I had the shop "passivate" the material. Basically submerge the material in an acid bath. Passivation is needed to maximize the natural corrosion resistance of the stainless steel.

You want the plates to be exposed to air. When you go to install, check out MaineSail's info on use of butyltape to seal the thru holes for the plates. Very pleased with the easy and cleanness of my install. No leaks.

While not wrong (adding a plate over the wood). It seems like extra expense.

 

[Solarfry]

YOu can get rectangular pieces of aluminum in different thicknesses that you can cut to desired size and use as backing plates. 1/4" aluminum is pretty strong. Much better than wood. You can also use starboard not as tough as AL but denser than wood and harder to crush.

 

[Ralph Johnstone]

The tech at CD said if I have it made it of SS it will need to also be electro-coated to preclude rusting.

Not too clear if the SS is for an interior backing plate or is the external chain plate. If it is an external chain plate, the process will be electro-polishing to provide a polished surface. If they are for internal backing plates, plain SS is all you need. However, for backing plates, I would go with aluminum or starboard as Solarfy has mentioned.

 

[Ron20324]

Look at West or somewhere for "SS tangs, or Link Tangs, or Chainplates" .

 

[Viking23]

Thank you, Ron, for your suggestions.
Were you referring to West Marine in your reply?

 

[Viking23]

Thank you, Ralph,
Appreciate the suggestion about using aluminum backing plates or starboard.
I am not sure I have heard of starboard. Is it a synthetic teak product?
The bulkhead wall is teak veneer covered. Would the starboard be a better match
for the teak veneer and would it be as strong in
your opinion as 1/4" aluminum?

 

[Viking23]

Thank you Solarfy,
I appreciate the suggestions.
I think I will go with the 1/4 " aluminum for an interior backing plate.
Might consider starboard if it would match up better with the teak veneer on the bulkhead
and is strong enough to not experience the slight dimpling that is evident on the teak wall.
Respectfully,

 

[Ralph Johnstone]

I am not sure I have heard of starboard.

Starboard is high density polyethylene .................

http://www.kingplastic.com/products/king-starboard/

It's indestructible as far as marine applications go. It does exhibit some creep but as long as you're using fender washers, the deformation is almost non-existent with thick pieces.

Sounds like this is going to be exposed on your finished teak-veneered bulkhead so you might want to consider 1/4' anodized aluminum flat bar of an appropriate width. The aluminum is easy to work and would look sharp when in place. Might even consider polished SS acorn nuts for a real show.

You should be able to find any number of metal suppliers in the Seattle area.

If you're using SS bolts through this, consider using a dab of silicone sealant on the underside of the SS washers just on the off chance you may get some moisture and the risk of galvanic corrosion which may cause staining on the aluminum.

 

[Viking23]

Thank you Ralph,
I appreciate the thoughtful suggestions and the detailed finishing considerations of the acorn nuts and the silicone sealant.

 

[Solarfry]

I would not use silicone sealant with aluminum. In my experience, long term, it tends to eat the aluminum. Try any of the Polysulfide or other sealants. Most exterior grade home sealants work pretty good on cabin tops. Some have 30 year warranties. Even though I often wonder what the heck the warranty covers.

 

[Viking23]

Thank you Solarfy,
For alternative suggestion to siicone.

 

[Stu Jackson]

1977 Catalina 25 Standard Rig.

Good ideas here from many. Do you know these guys yet? http://catalina-capri-25s.org/

 

[Barnacle Bill]

I would use stainless as it is the same as what is used already and there will be no galvanic issues. The weathering suggests that moisture has gotten into the bulkhead and it is important that it is solid enough to support your mast. If it is soft and easily determined that it is not strong, then you have a bigger problem. If, as Catalina suggests, the bolts have not elongated (suggesting there is strength), then you can reinforce the existing chain plates with SS plates opposite the side where the chainplates mate up to the bulkhead. You can even use longer chain plate like straps where the top bolt of the shroud chain plate matches the top bolt of the backing plate and the backing plate is longer so that it extends below the reach of the shroud chain plate, which puts attachment the the lower and stronger area of the bulkhead. Obviously the new backing strap has to have the holes match those of the shroud chain plate.

 

[Viking23]

Thank you Stu,
For your suggestions and observations. They are appreciated.