Surface Cracks Over Chainplate

[russh347]

I'm refitting a mid-1960's sailboat with a GRP hull. There are surface cracks in the paint & gelcoat around each of the chainplates. I've attached a picture. I hope you can see the cracks, they are a lot easier to see using edge detection.

I am hoping this repair is as easy as peeling the paint & gelcoat down and reinforcing the area with a layer of glass.

I'd sure like to hear from others that have tackled this type of repair.

Thanks in advance,
Russ

[ShipShape]

I can't make out what the pictures are, but having cracks around each chain plate makes me think that the chain plates are, or have been, loose, or there is some other significant issue. It is important to find the cause of the cracks!

Pull out the chain plates, check the integrity of their bulkheads or whatever they are bolted through - be sure to check the tabbing too. If you think the bolts are more than 15 or 20 years old, or if they are bent, rusty or compromised in any way, get new bolts. Drill a few 1/8" holes in the underside of the deck around the chain plates to see if the core is wet - dry core is sawdust, wet core will stick in the flutes of the drill bit. Also check the hull-to-deck joint in the area. And now is a good time to check the chain plates for crevice corrosion, use a Visible Dye-Penetrant Detection Kit, I get mine from www.mcmaster.com, part #s 1383T4, 1383T5, and 1383T7.

[russh347]

Thanks for your reply ShipShape. I guess I won't assume that there isn't some deadly fault behind those cracks.

Regarding the images: The first is an ordinary picture of the outside of the hull in the vicinity of one of the chainplates. It is possible, but difficult to make out the cracks. The second is the same picture after running it through an edge detection filter. In this image, I can easily see the stress cracks in addition to what appear to be cracks from an impact just aft of the chainplate (to the right).

I have yet to figure out how to pull the chainplates. I don't see any bolts or fasteners for them. I fear they may be molded into the GRP. But I will make a concerted effort to examine them both above and below the deck. The interior is a mess with several layers of flaking paint which makes it hard to find anything.

Assuming I find the bolts, they could be as old as 47. I could be wrong, there's a lot of this boat's history that I don't know.

[zeehag]

if there are crackis in the gelcvoat over the chainp-lates, there is corrosion of the chainplates. might investigate. look inside the hull and closets for the internal chainplates. what kind of boat is this?? also look for the source of the leaks that are making the chainplates swell and crack the fiberglass.

[russh347]

The boat is a 1963 Hurley Silhouette Mk3.

There are no visible chainplate bolts and there is nothing of the chainplate visible on the outside of the hull. Inside, the chainplates are totally enclosed in GRP below the deck (pic attached). Assuming moisture seeped in from the top and caused corrosion, I can think of no way to extract the chainplates other than grinding off the GRP enclosure. Once that is done, I don't think the presence or absence of corrosion will make much difference. It seems like I would need to fabricate a new chainplate solution.

Any suggestions?

Note: the bolts visible in this picture are for the lifeline stanchion.

Thanks,
Russ

[roverhi]

Encaspsulted chain plates are almost guaranteed to have crevice corrosion. There is no way to keep water completely out. A little electrolyte in the absence of oxygen and you have the perfect environment for cracked chain plates.

There are two reasons gel coat cracks. The first is the gel coat was applied too thick and, since it's relatively inflexible compared to the FRP laminate, it cracks. Had that happen to my last boat. Had to grind the deck down to bare glass and repaint. The other is the laminate is flexing under load and the result is the same as above. If the cracks are only in the area of the chain plates and the gel coat isn't much more than 1/32", the area around the chain plates needs to be reinforced with additional laminates and/glassed in stiffeners.

As far as replacing the chain plates. grind them out and bolt new ones into the bullkhead or knees if they, the knees, are still in solid shape. If bulkhead/knees need to be reinforced/replaced it's the time to do it.

[SailFastTri]

Russ -
Those chain plates are highly "suspect". Stainless does rust if cut off from the air, and those were enclosed by fiberglass for ??? years.

Start by grinding away the fiberglass on the inside of the chain plates with an angle grinder . Then you may be able to see how they are fastened and get a better idea what's going on. You should also search the archives or post a question at the owners association web site for your boat. There are probably others who have done been there done that with your model boat.

From what little you showed the boat looks like it might be in pretty rough condition. So you also need to think about what your budget and goals are for a refit. Are you trying to make it good as new or strong enough to go offshore, or do you just want to keep it going a few more years for weekend coastal or lake sailing? Boats grow old in a "death by a thousand cuts". Often it's not one major thing -- it's all the little things that add up to be major. You can put in a lot of work (time and $) to restore and have a boat that's not worth it on the resale market, or maybe you don't care about that. Give that some thought before you go too far down the road.

[ShipShape]

Whoa, thanks for explaining the images - that is very cool! Oh ... wait, no it isn't.

Yes, the one on the right is an impact, although it could have happened at the same time as the chain plate damage, it is probably unrelated to the chain plate cracks.

The chain plate cracks are very interesting, it looks like tension/compression damage. Picture the shroud going to the right, the chain plate would rotate somewhat about its center the top would follow the shroud and crush the fiberglass at the top right, and at the same time the bottom would move to the left and crush it on the bottom left. Then when the shroud moves to the left, the other pair of cracks would happen.

Several things could do this, but given the smack to the right my guess is that this boat was caught in a hurricane and the mast or rigging was tangled up with another boat and getting snapped fore and aft somehow, or who knows. Maybe a bunch of nasty jibes with slack rigging could do it, and the impact is dock rash.

Regardless, you may have more to repair than gel coat, same for the impact. Maybe someone will come along and tell you how to find out if the structure of the fiberglass and resin has been compromised. This boat was built before the strength of fiberglass was known, her hull is likely an inch thick and may be just fine. My guess is that these cracks were from individual incidents, not some "deadly fault" as you put it. And since the damage is back-and-forth I would say it is not from a rigging misalignment from someone re-rigging the boat incorrectly along the way.

It sounds like the chain plates have been built into the boat, get a hammer and chisel and chop them out. If they are bronze they will be ok, if they are stainless you Will need new ones, don't waste your time and money checking for crevice corrosion. Same goes for the bolts, although you may want to replace the bolts even if they are bronze because they have been subjected to a good bit of shear stress. When you replace the chain plates think about attaching them to the outside of the hull.

[ShipShape]

Oh, I see you posted a pic of a chainplate while I was looking at the hull cracks. That will be easy to chop out. Could you please do one of them carefully and post a pic of what it looks like in there?

[russh347]

I'm not planning on taking her offshore. She's only a 17' boat. If she were in pristine condition and so was I, maybe.

My plan is to get her in shape to sail for a couple of years on the Snake & Columbia Rivers (the only sailable water nearby). I haven't given a great deal of thought to a refit budget, I suppose I should. I know I'm in for some bottom paint, a bit of fiberglass work, and some rigging.

I see getting her back in the water as a step along the way. Sailing her will refresh our skills (which are rusty). And, while we sail her, I'll be looking for the next boat.

[Wotname]

Originally Posted by russh347

I'm not planning on taking her offshore. She's only a 17' boat. If she were in pristine condition and so was I, maybe.

My plan is to get her in shape to sail for a couple of years on the Snake & Columbia Rivers (the only sailable water nearby). I haven't given a great deal of thought to a refit budget, I suppose I should. I know I'm in for some bottom paint, a bit of fiberglass work, and some rigging.

I see getting her back in the water as a step along the way. Sailing her will refresh our skills (which are rusty). And, while we sail her, I'll be looking for the next boat.

Given your sailing aspirations (on this boat) and your locale, you might not have to worry too much. Just do a cosmetic repair and enjoy the boat; don't over-stress the rig, reef early or just pick your days weather wise.

The very worst that can happen is that you will lose the rig and mast but there is probably enough residual strength left in the chain plate for this not to happen. The boat won't sink and you radio for a tow, drift to the shore or swim home.

If you are planning trips further afield then a full repair is required. You can be sure the existing chain plate structure is significantly weaker now than is was when new. It would be fair sized job (and expensive) to cut them all out, have new ones fabricated and glassed back in. And you would need to replace all the rest of the sanding rigging at the same time.

So just sail the boat easy and enjoy or face up to a big job