Thread: repair of carvel planking on old boats by cold molded sheathing

Skinning a carvel is one way to address some issues, though, like other options, raises new ones. Generally, it costs more to repair/restore the structure (planks, frames, floors, stringers, etc.), then place a set of veneers over it, compaired with simply making appropriate carvel repairs. On the other hand, a veneer or stripped skin does seal up the hull, making it much more trailer friendly and less prone to some of the issues associated with carvel. Weight is another major concern with a sheathing ('glass, veneers, strips, etc.), which can be considerable and on small boats a real performance killer. Larger craft have less a problem with this. Additionally, some of the thickness of the original carvel planking can be removed to make up for this added sheathing weight. I did this on my 37' Atkins double ender, by milling the 1.5" (38 mm) planking down to just under an inch and applying two diagonal layers of 1/4" plywood. In the end, you have to offset and justify the costs and effort of this treatment, compared to traditional repairs to the hull.

Thanks for the thoughts PAR, what do you see as the big difference between skinning with veneers and a covering of fibreglass, V's just covering with Fibreglass. Not trying to stir up any purists out there, which I probably count myself amongst. Just to understand the differences.

I see that the veneers with fibreglass skinning would still allow some movement between the skin and the carvel planks.

Would fibreglass straight over the carvel planks be more likley not to adapt well to any movement in those same carvel planks?

Were you happy with the weight of the rebuild you completed after trimming down half an inch from the planking thickness. I can see how adding a few hundred kilo's of weight in skin and glue would be a death sentence for some smaller boats. I guess this would apply particularly to motor boats, I guess Yachts with lead ballast, it may not be so much of an issue.

Cheers

From a technical stand point there's no difference between a veneer/'glass sheath and a straight 'glass sheath. Both are affixed and don't allow movement or at least shouldn't. Veneers are typically stapled to the planking, a straight fabric sheath relies on the goo bond. This said, a straight fabric sheathing tends to be much heavier, because you need a lot of fabric weight to gain the same strength and stiffness of a few layers of veneer. Additionally, asking a fabric skin to stay stuck to an old carvel hull can prove problematic at best. Some that have done this actually go to the bother of stapling the cloth to the hull, during wetout, to help this issue. Simply put, it's important to "scale" the sheathing for the task it must perform. Too thin and it'll sheer from the planking, too thick and you're carrying around a bunch of goo and weight you don't need.

After I redid the planking schedule on my boat, she came in a full ton lighter then when she was first hauled. This is how much moisture she lost during the process. Since the bilge is dusty, not a single leak and she's more solid feeling, now that the planks aren't "working" any more (I glued these to the frames, during reassembly). The neat thing is she still has her planking seam runs visible, but they don't change in dimension, as they're just faux seams now. Paint stays stuck too, because the planking is much more stable, especially at the boot stripe, where it would wet/dry cycle constantly (a natural thing). I'm a big fan of monocoque structures and this is a classic example. The hull shell is a homogenous unit, no longer an assembly of parts with a high probability of movement. It's this movement that causes leaks, breaks frames, stringers, etc., so if you can lock it down, without introducing stress concentrations, you've engineered a good product.

Again, it's not an inexpensive way of "saving" a hull. Quite the contrary, but this boat is John Atkins last commissioned design and was one of his favorite boats, having spent many a night aboard, with her owner. This means she needed to be saved and had the pedigree to warrant the extra effort and cost. Lots of old classics are saved this way, but you have to justify the costs and effort. In the end, it's usually much cheaper, just to fix the carvel conventionally and deal with what carvels as what they are. Lastly a fabric skin is most often used to hold together a carvel for a few more years, before it's dragged off to the land fill. A lot of reasons for this, but the main one is simply because, most don't put enough fabric and goo on to physically hold the planks tight, so plank movement shears the skin loose, water gets between it and the planking and rot takes her toll in short order. Conviently enough, the hull is surrounded by a big, hard plastic bag, which makes containing the rotting mess easier, when the time comes to drag her to the land fill. I've seen a lot of boats die this way.

From a technical stand point there's no difference between a veneer/'glass sheath and a straight 'glass sheath. Both are affixed and don't allow movement or at least shouldn't. Veneers are typically stapled to the planking, a straight fabric sheath relies on the goo bond. This said, a straight fabric sheathing tends to be much heavier, because you need a lot of fabric weight to gain the same strength and stiffness of a few layers of veneer. Additionally, asking a fabric skin to stay stuck to an old carvel hull can prove problematic at best. Some that have done this actually go to the bother of stapling the cloth to the hull, during wetout, to help this issue. Simply put, it's important to "scale" the sheathing for the task it must perform. Too thin and it'll sheer from the planking, too thick and you're carrying around a bunch of goo and weight you don't need.

After I redid the planking schedule on my boat, she came in a full ton lighter then when she was first hauled. This is how much moisture she lost during the process. Since the bilge is dusty, not a single leak and she's more solid feeling, now that the planks aren't "working" any more (I glued these to the frames, during reassembly). The neat thing is she still has her planking seam runs visible, but they don't change in dimension, as they're just faux seams now. Paint stays stuck too, because the planking is much more stable, especially at the boot stripe, where it would wet/dry cycle constantly (a natural thing). I'm a big fan of monocoque structures and this is a classic example. The hull shell is a homogenous unit, no longer an assembly of parts with a high probability of movement. It's this movement that causes leaks, breaks frames, stringers, etc., so if you can lock it down, without introducing stress concentrations, you've engineered a good product.

Again, it's not an inexpensive way of "saving" a hull. Quite the contrary, but this boat is John Atkins last commissioned design and was one of his favorite boats, having spent many a night aboard, with her owner. This means she needed to be saved and had the pedigree to warrant the extra effort and cost. Lots of old classics are saved this way, but you have to justify the costs and effort. In the end, it's usually much cheaper, just to fix the carvel conventionally and deal with carvels as what they are. Lastly a fabric skin is most often used to hold together a carvel for a few more years, before it's dragged off to the land fill. A lot of reasons for this, but the main one is simply because, most don't put enough fabric and goo on to physically hold the planks tight, so plank movement shears the skin loose, water gets between it and the planking and rot takes her toll in short order. Conveniently enough, the hull is surrounded by a big, hard plastic bag, which makes containing the rotting mess easier, when the time comes to drag her to the land fill. I've seen a lot of boats die this way.

Thanks for the technical explanation, I'd never quite got why they did a whole article in the US wooden boat mag around sheathing using glass and the difference just wasn't clear at the time.

Absolutely agree about the Pedigree of the boat needs to warrant the coast involved.

So if you happened to see a boat not quite up to the same pedigree to warrant a full cold molded style sheathing I guess you would look back to filling in any really big gaps with softwood splines and replacing other planks where rot demands etc. Otherwise just re-caulking where needed.

You must be pretty happy about both having dry bilges and a lighter boat due to the lack of water uptake in the planking. Have you got any photos of the process and the finished boat?

Having just been through this entire process, see the posts "sheathing with veneers" without doubt to do this effectively is a lot of work, for me I enjoyed the whole process, the weight gain on my boat was 200kg, but she will float higher as the cubic capacity of the boat has increased, you must be sure in your own mind tho' the boat is worth it and you have staying power.

Originally Posted by carmen

Having just been through this entire process, see the posts "sheathing with veneers" without doubt to do this effectively is a lot of work, for me I enjoyed the whole process, the weight gain on my boat was 200kg, but she will float higher as the cubic capacity of the boat has increased, you must be sure in your own mind tho' the boat is worth it and you have staying power.

Thanks Carmen,

I enjoyed browsing through your thread and certainly admire your dedication at sticking with such a big project over so many years. I'd imagine it wasn't always the easiest thing to leave a nice warm house and go outside to do some epoxy work or the like...

If doing a traditional repair on a carvel and you have crushed or "soft" seams, the wood should be replaced, not spined. These spines are a different repair method and not generally used piece meal, but wholesale, typically on the bottom, topsides or whole hull, but not here and there. In other words, if you spine a plank seam, the whole seam needs to have the spine, not just a section of it.

To fix a truly bad seam, you replace the wood that's bad. This might mean a whole new plank or simply a scabbed in section, to replace a soft area or crushed seam, etc. There are a few things that happen to the wood inside a seam. One and pretty common on a boat that's be caulked a lot or possibly incorrectly (too hard), is the wood in the seam gets crushed and work hardened, from the caulk being pounded in too tight or just after repeated caulkings. The wood fibers get bashed down, from the caulk and when these dry, huge gaps open up. Plank movement also tends to scrape away seam wood, as they slide back and forth against each other. Careful application of steam can sometimes restore these portions of seam, but it's a tedious job and you'll need a steamer that can focus a lot of steam in a steady, fine stream. I have a grout cleaning tool (I stole from the other half) that does a great job of this, but again, it's tedious slowly working down the seam with this tool, just hoping it'll do the trick. The other route is to replace the wood, be this a new plank section for the affected area, or splitting the plank and installing a "dutchman" type of scab, to place good wood, back in the seam. The other things that happen are contamination, because water has been flowing through it for a while, which causes rot, mold, fungus, etc. to form, contaminating the seam. Usually, it can be "reefed" clean and recaulked, if the wood is solid. Lastly, as planking get to a certain age, it stops being planking. I know that sounds weird, but planking just like an oil filter in your car has a life span, which when it's done, is well, spent and needs to be replaced. Wood can only take so much of a beating, before it just says "no more" and simply spits out every attempt at recaulking you try. A good caulker will recognize seams like this, as they're pounding in the caulk, though the novice might not. Most of the time these things will become apparent, as you tear into the project and an economic choice is made at some point. Do I tear it out, fix, restore and reinstall or do I tear it out, knowing it'll be replaced with new. As a rule, a new replacement is faster and cheaper, if you're paying for labor. This is because you're not paying to restore stuff, which is time consuming. If you're "eating" the labor, you can afford to spend the time to restore and repair things, possibly saving some planking that other wise might just get ripped off and replaced.