Gelcoat cracks near toerail

[Rick]

This topic is close to the recent posts regarding how to repair deck crazing - I've got lots of that in my '72 Aquarius! - but another issue is the more severe cracks I've got between the toerail and the deck - hull joint. They are more severe in the chain plate areas. Here are some pics





I'm wondering what the best plan of attack would be here. I was thinking of glassing over the area from the deck-hull joint over the toe rail to cover the cracks and provide additional strengthening to the joint. However, Tim said it isn't advisable to fiberglass the joint in a smaller boat (the boat is only 21'), but that 5200 is a better solution there.

Is it better to grind the cracks down and fair with some thickened epoxy? Grinding these tight areas will be a challenge, as will fairing them afterwards. I could try to fashion some sort of wooden toerail/rubrail combination to hide the repairs. Let me know what you think. It's finally getting warm enough outside to dive back into these repairs! Thanks

[Tim]

The cracks shown in your photos are clearly an indication of a basic structural weakness--as you said, the worst is in way of the chainplates, so it would seem that loads incurred by the rig have caused undue flexing and movement in that area, causing the cracks. This is extremely common in small, inexpensive boats, which are rarely highly engineered for the potential loading--nor are the boats particularly overbuilt--and are also intended for non-indefinite life spans.

When there are indications of structural movement like this, the first step is to correct the root cause. It seems to me as if the rig loads are essentially "squeezing" the hull together in that area because of a lack of internal stiffening and athwartships strengthening. What is your current chainplate arrangement?

Basically, you need a means of tying the hull and deck together in this area to resist the "squeeze" caused by the tensile loading of the windward rigging as the boat sails.

Once you address the root cause, then you can deal with the cosmetic issue of the surface cracks. Unless you have indications that your entire hull-deck joint is poorly engineered, I maintain there's no need to consider glassing over the joint. But to help hide the cracks, you may be well served to include fiberglass encapsulation in your repertoire.

[Rick]

Tim asked

When there are indications of structural movement like this, the first step is to correct the root cause. It seems to me as if the rig loads are essentially "squeezing" the hull together in that area because of a lack of internal stiffening and athwartships strengthening. What is your current chainplate arrangement?

The chainplate setup is very weak. Here are two pics of the chainplates before I removed them





There is no substantial bulkhead in the cabin. The aft section of the vberth spans the cabin at a low level and the galley provides some support on the port side of the centerboard trunk.

[Tim]

That's about as I suspected.

To strengthen the arrangement and therefore correct the flexing problem that created the cracks you have, I suggest a reasonably-sized knee glassed to the hull and deck in that area. You can either reconfigure your chainplates to secure them to the new knees, or keep them as is; either way, the knee will substantially stiffen the hull, and the hull-deck joint and eliminate the flexing.

[Rick]

Please excuse my ignorance - this is my first sailboat and sailboat renovation - but is the knee you are referring to a triangular piece of plywood glassed into the angle where the top of the cabin meets the hull?

How thick should the plywood be and what length should the sides be for a "reasonably sized" knee?

Do you think i should also glass the deck/hull joint, or stick with the 5200?

Finally, would you recommend securing the chainplates to the new knees or leaving them attached to the hull - maybe with a backing plate?

thanks again for sharing your knowledge.

Rick

[Tim]

... is the knee you are referring to a triangular piece of plywood glassed into the angle where the top of the cabin meets the hull?

Yes, or some generally similar shape. You can create a curve or S-type shape too (on the edge away from the hull) if you like the look. Something generally trapezoidal is what you normally see. Since they're exposed, it would be nice for them to be generally aesthetically pleasing.

How thick should the plywood be and what length should the sides be for a "reasonably sized" knee?

9mm (3/8") would be more than adequate for your boat. Sizewise, I'd suggest that it extend about 6" athwartships beneath the deck and perhaps 9" down the hull. When glassed in, this would be very strong. When creating the shape of the knee, allow enough bearing surface along the hull and deck so that you can extend tabbing 3" or so onto the knee. In such a small boat with minimal loads, you don't have to go crazy with the tabbing the way one might on a larger boat, particularly if the knees were also to be the main support for the chainplates.

One layer of 15 or 17oz. biax tape, 6" width, would be sufficient for stiffening knees. In your specific boat,I'd add a wider layer of something like 10 oz. cloth over the top if you decided to support your chainplates off the new knees. These laminate schedules are not intended to be thought of as general-purpose quantities for all installations, but for this specific case.

You can fully encapsulate the plywood with one layer of material if you want, but in your case there's no real benefit to doing so.

To secure these knees, once they're cut to fit install them in a bed of thickened epoxy (using cabosil) and then create a broad, easy fillet between the plywood and the hull, and between the plywood and the deck. This will allow your fiberglass to more easily span the gap and also helps spread the loads over a wider area. You can either leave this arrangement till it cures, then wash/sand the fillets and laminate your tabbing over the cured material, or, if you feel up to it, you can glass either directly over the fresh, uncured fillet, or wait several hours and glass over a partially-cured, "green" fillet. It all depends on your comfort level with fiberglass and related work.

Your means of securing the knees to the hull during the curing process may also drive the ultimate way that you glass them in. Clamps or braces might get in the way of a good job, so you may bve forced to wait till the adhesive and fillets cure before glassing.

Sorry that there are so many variables here...but I don't know enough about your boat, or your inclinations to be absolute.

Do you think i should also glass the deck/hull joint, or stick with the 5200?

Do you have problems specific to the joint, or only related to the cracking caused by the lack of stiffness in way of the chainplates? Your actual hull-deck joint looks like a shoebox from the photos, in which the deck molding fits over the hull a bit (like a shoebox lid) and is then secured. Whether or not you undertake the large job of trying to successfully glass this joint depends on too much information about your boat and more that I don't have.

Finally, would you recommend securing the chainplates to the new knees or leaving them attached to the hull - maybe with a backing plate?

Other than the cracks in the joint caused by "squeezing" the hull together at deck level, are there any indications that the current chainplates are an issue at all? It'd be more straightforward to leave them as is, and simply stiffen the adjacent areas with the knees. If they seem secure as is, and aren't causing stress cracks in the hull or other signs of weakness or damage, I'd probably choose to leave them be.

It seems to me that the best approach is to thoroughly address the root causes of the problems that you have, but to not get bogged down in relocation or reconfiguration projects that aren't necessary as a part of the actual repairs of the root cause. Projects can grow uncontrollably enough on their own, and don't need human intervention in the form of unnecessary changes.

Somtimes, changes are required, or highly desirable. Other times, changes just mean more work that really has no overall benefit.

[Rick]

Thanks for the great info Tim. I'll keep the chainplate configuration and install the knees as you described.

Tim asked

Do you have problems specific to the joint, or only related to the cracking caused by the lack of stiffness in way of the chainplates? Your actual hull-deck joint looks like a shoebox from the photos, in which the deck molding fits over the hull a bit (like a shoebox lid) and is then secured. Whether or not you undertake the large job of trying to successfully glass this joint depends on too much information about your boat and more that I don't have.

I don't know if the joint has problems. It is a shoebox and I can see in some areas where the material in the joint seems black and dry. I haven't had her in the water, so I don't know if it leaks. I'm thinking that with her age and condition along with my plans to paint her deck and topsides, it would be best to do this work now. Also, I originally was thinking of glassing over the joint up to the toerail in order to try to deal with the cracking in the gelcoat that appears in the initial photos in this thread.

Would you recommend another plan to address these cracks?

Thanks again

Rick

[Tim]

While I think that glassing over the cracks is a good idea as a way of containing and stabilizing them, it doesn't necessarily mean that you need to fiberglass the hull-deck joint--in that area or any others. You can successfully stabilize the cracking by glassing just over the affected areas, as far down as the edge of the deck, but it doesn't strictly require glassing down onto the hull.

Maybe it's the best plan--I honestly can't say from here. What is the basic profile of the exterior of the joint? That is, how much does the deck extend beyond the hull? The shape of this profile will determine the feasibility and potential ease of glassing the entire joint, onto the hull and over the molded toerail.

Another option, based on the photos I have, would be to glass the inside of the joint, which appears to be a fairly smooth transition. You'd have to remove the screws or bolts that are there, grind away any paint or other coating, and then apply the glass from inside. It's a big job, but it looks like you have more or less full access to the joint.

If the original bond and seal has begun to fail, it's almost futile to attempt spot rebedding or resealing, since it would be hard or impossible to get the material truly into the joint where it's actually needed. Just applying sealant externally doesn't do the trick, at least not for very long.

The condition of the external sealant doesn't necessarily mean that the whole seal of the joint is bad. It may be bonded well up inside, but the exposed material has dried out. Then again, it may not be OK, either! Unfortunately, I can't really judge that.

Rebedding always requires the separation of the parts in question, then resecuring them with the new bedding material in place on the bonding surfaces. The potential inability, or impracticality, of separating parts may affect how one goes about the job.

You can test the watertight integrity of your hull-deck joint by spraying a hose from the outside up into the underside of the overhanging joint. Don't be shy with the spray and pressure. If you can get another person to watch from inside, you'll get a good indication of where, if anywhere, the joint leaks, and how badly. This would be good to know before you proceed with any plans for repair.

[Rick]

Tim, thanks for the advice - I never stopped to think that I could just check the joint out with a hose - DUH!! I'll do that this week and see if the joint leaks. If not, I'll move on to just dealing with the cracks.