rusty chain plate Backing Plate-pre-cruise question - CD33

[brian w]

Pre-Cruise backing plate question - cd33

After reading so many posts on chainplate/backing plate issues, I examined the starboard hanging locker a few weeks ago to discover 5 inches of the chain plate backing plate that's visible was indeed rusted. A picture is below.



The picture shows the section of the backing plate below the front-most chain plate. The horizontal part that the chain plate bolts go through had some flaking, but seems largely in-tact. The vertical part of the angle iron, however, was loose enough to give up about a 3x1inch piece. Aft of that, where it bolts to the bulkhead, the vertical section is sound.

I treated and painted the rusted section. The flat backing plate still seems sound such that it can distribute load, and the first thought was to address it in the off season (I imagine it has been like this for several years). But now that I've seen it, would it be foolish to take the boat cruising?

And depending on the reply, has anyone replaced the backing plate(s) on a 33? I have come across several postings on Typhoons, 22's, etc. but so far haven't seen anything on a 33. Curious how significant an undertaking it is.

Thanks,

Brian

[Paul D.]

I have not done this job but I would be interested too in a 33 or 36 owner's experience doing so.

The backing plates on Femme still have the paint on them; a little flaking of it but no rust. They are a fairly complex system of weldments going down the side of the hull. I know some have moved them outboard and ran a plate down the top sides to replace.

[joemerchant]

I had helped a friend a few years back replace the plates on an Island Packet that were glassed in. Not familiar with how they are setup on the 33, but from the pictures and description, looks like a similar job.

No, I would not cruise until you address it. Once the cancer starts, there is no way to really stop it.


Get some quotes from yards to get an idea of what you are up against and decide how much if any of the work you want to do yourself.

[Russell]

What do you mean by "take the boat cruising?".

You know the issue needs to be addressed, but if you really feel there is enough "beef" in the metal there, it might be okay for another season? Perhaps, a photo cant show, only you can judge that.

But when you say "cruising" are you talking about bumping around LI Sound for the summer? A trip to Block and Cuttyhunk? Or further to Maine? Or are we talking Bermuda? Or are we talking Azores and Europe? Or even further?

If you are talking some local cruising, and you feel confident that there is plenty of steel under the rust, I would say cruise and have fun and deal with it in the winter. If you are talking going beyond your home grounds, then now is the time to fix it, before you go.

[TerryO]

It looks like you have lots of fastener length. What about temporarily placing a piece of stainless right over the corroded steel angle for the season. I say stainless since it is stronger than mild steel and you could get away with using thinner material. Maybe use a piece of angle or has some flat sheet bent for stiffness. At least it would spread out the load past the weakened areas and get you by until the off season.
Good luck.

[Russell]

It looks like you have lots of fastener length. What about temporarily placing a piece of stainless right over the corroded steel angle for the season. I say stainless since it is stronger than mild steel and you could get away with using thinner material. Maybe use a piece of angle or has some flat sheet bent for stiffness. At least it would spread out the load past the weakened areas and get you by until the off season.
Good luck.

I am no expert, but I thought mild steel was actually far stronger then stainless (other then when its a big pile of rust of course).

[TerryO]

Just a quick check shows stainless has about twice the yield strength and slightly higher ultimate tensile strength. Either one should work fine especially for the short duration. My thoughts were that the stainless was stiffer so you could get away with thinner material and still spread the load from the weakened portion of the chain plate.

[brian w]

Thanks for the replies.

Russell, you're correct as far as cruising - stretching the LI Sound, with Block probably the farthest destination. Bermuda boat travel is limited to the water taxi between Southampton and Hamilton.

It may be false confidence, but even the rusty section of backing plate seems as though it could take a lot of load. Also, the gelcoat on the boat is not immune to stress cracks, and yet none exist near the chain plate. Not that stress cracks would be the only indicator, just that it seems as though if there was flexing occurring from a compromised backing plate, this would be a great spot for it to occur

Speaking with the yard yesterday, the sentiment seemed shared that there was still solid reinforcement going on, and that even if that whole chain plate were to pull out, a de-masting would be unlikely. I had also thought of sistering in a reinforcement piece and discussed it with them yesterday. The question would be if you put in maybe 5 inches of metal in the rusty spot, or if you need it to be a few feet in length to "tie it in" with the bolts of the middle chain plate? The latter is obviously a lot more involved.

As far as replacing the whole piece, the diagram in the manual seems to imply it's glassed into the hull. Where it's glassed in does not seem obvious when looking at it, so figuring out where it's glassed, and how to "un-glass" it seems tricky.

-Brian

[Jim Walsh]

Every time I see the mild steel used as backing plates I cringe. My CD31 has an aluminum backing plate which spans all four chain plates (this is a cutter so I have an intermediary) on each side. I would have thought since they had gone to aluminum backing plates on the CD31's that they would have incorporated this improvement right on down the product line. I wonder if some other CD's have aluminum and not steel?

[Russell]

Every time I see the mild steel used as backing plates I cringe. My CD31 has an aluminum backing plate which spans all four chain plates (this is a cutter so I have an intermediary) on each side. I would have thought since they had gone to aluminum backing plates on the CD31's that they would have incorporated this improvement right on down the product line. I wonder if some other CD's have aluminum and not steel?

My CD36 they are aluminium as well, but I think early 36s were not, I assume the changeover happened when CD redid the interior, 82 or so?

[Paul D.]

Our December, 1982 CD 33 has the steel weldments. She only has mild flaking of the paint on them however. I assume after a few months in salt water though I would start seeing some rust.

Thinking if this were my situation, I would just get in there best I could with some rust eating stuff and a wire brush to try to get down to steel and have a good look. It would be messy but then I think you could see a little more what you are dealing with. It is no wonder when most guys replace their chainplates on many different types of boats, they go for the stainless down the topsides. But on CD's, that wouldn't make use of the reinforced areas and the bulkhead tabbed to the hull from shear to keel - a nice detail.

[Steve Laume]

Raven's hull was laid up, late in 1983 and has Alum backing plates. I had no idea what I was getting at the time I purchased her but am grateful to have the Alum backing plates.

In looking at the pictures I would be more concerned with the weldments to the reinforcements to the hull and bulkhead than with the rust on the plate itself. If everything is still well connected it seems like there is plenty of steel left there to do a coastal cruise without any worry about losing the rig.

I need to pull the bolts on Raven one of these years and see what they look like. The backing plates are fine and I have newer standing rigging but the whole is only as strong as the weakest link and I am not certain about those bolts, Steve.

[John Stone]

The backing plates on the Far Reach are steel. Except for the chain plate forward, which I replaced with G10 and documented on my website, the rest remain intact and appear to be in good shape. Not everyone has been so lucky. However, I have often thought about how I would replace them--there are lots of options from replacing in SS, aluminum, G10, to external plates as others have done. Other than just completely rusting apart, I think the important part is the weld between the vertical plates glassed to the inside of the hull and the horizontal steel plate through which the chainplate pad eyes are bolted. You should be able to get in there to see the weld reasonably well.

For the short term if they looked "OK" . . . but I wanted a little extra piece of mind I would add an additional layer of G10 in 1/4" or 1/2" thick. I would secure the mast in place with halyards, slack the rig, and pull the chain plate bolts (not a bad idea anyway). I would make a template of the chainplates from underneath, cut the G10 to fit, drill holes down through the original holes, bed the fitting with butyl rubber, secure the bolts and sail on.

The steel backing plates are one of only a couple "shake your head and wonder what they were thinking" issues for the Cape Dory. On a good note, they can be dealt with.

[brian w]

Thanks for the replies. In the short term, we picked up some metal from HD - a flat piece of steel, and angled piece of steel, and an angled piece of aluminum. The angled aluminum naturally has less flex than the flat steel, and given the weight, etc. seems the better choice for about ten inches of additional backing plate. It would be good to tie it in further aft, perhaps to the stainless tang bolted to the bulkhead, but may be getting more complicated for the in-the-water repair. So current plan is to undo the two stainless bolts from the front-most chain plate, put the aluminum in, and rebolt.

The yard suggested nylon washers, sealant, etc. between the two pieces. The existing steel, having the treated rust, is not perfectly flat, so something between the two would be important. I had never heard of butyl rubber, but searching on it, would this not be the equivalent of rubber roofing patch? I have a roll of Grace roofing patch in the garage, which appears to be butyl rubber. I wouldn't have thought of it, but it does seem a very appropriate material to use as a gasket-of-sorts.

Thank you,

Brian

[joemerchant]

I would worry about a yard that recommends what I am hearing you say. Ask them if they can email those recommendations to you in writing. Preface it to say that I am not completely familiar with the original CD33 design, but have dug out a few rusted plates in my life with the last being the dreaded Island Packet.

Once any metal begins to rust, you will never stop the cancer unless you stick the offending piece of metal in a desert that sees less than an inch of rain per year, or remove all of it - thus why rust is equated with cancer.
Once chain plates rust to this level, the rust will find and exploit any original manufacturer defects. Meaning an internal void or stress will cancer itself into a crack, especially around bolt holes as veins become brittle. The aluminum and roofing sealer would not be my idea of a good solution either unless it is to jury long enough to get back to a home port to repair properly as I feel your solution is only good for a very short time. And even then, I would spend more time worrying about my rig than enjoying truly sailing the boat.

Best solution is to start cutting it all out and have new plates made. I have even seen this done on a budget where the owner found long heavy duty tangs and had them welded together with a plate and bolted/bedded the whole thing in. The fabrication is not a huge expense all things considered owning a 33' sailboat. But the costs are far less than losing the rig or the entire boat. Suffice it to say your insurance will deny the claim with your proposed solution if the rig fails.