View Full Version : glassing a carvel planked hull (again)

Charles Neuman
05-01-2005, 10:13 PM
I brought up this topic a few months ago. The issue is whether it's OK to glass a carvel-planked hull. In general, the answer seemed to be "no".

Off the top of my head, some of the comments on this topic or other related topics are: Paul Oman reminds us that wood expands with moisture while epoxy expands with heat. David Carnell has demonstrated that epoxy is not waterproof: the wood will not stay dry.

So, when the wood gets wet, it will expand, but since the seams are filled with epoxy, the wood fibers will crush. Perhaps the surface will show some problems.

I was exposed to this technique in the Jan/Feb '04 WB issue, which described William Garden's Tom Cat design. He built his boat CATSPAW carvel planked with epoxy/microballoons in the seams and biaxial cloth over the hull. At the time I didn't realize who William Garden was. Now I know that he's been in the business for decades. He must have beeen aware of these issues. Maybe we can try to get into William Garden's head and see why he wasn't worried about using this technique.

One question I still have remaining is: If the boat is trailer-sailed, it might see about 8 hours of water every week or so. How much water would the wood absorb with this exposure? Would it be enough to matter?

Another question: If this technique is really as bad as people suggest, what would be the long-term damage? Would the fiberglass crack? Would the paint show cracks or unevenness? Would the planks start to split?

Still curious,


[ 05-01-2005, 11:33 PM: Message edited by: Charles Neuman ]

05-01-2005, 10:38 PM
The difference is that TomCat is designed to be glued-carvel and fiberglassed while you were, as I recall, proposing to fiberglass a normally carvel-planked craft.

Normal carvel construction is designed to have the planks expand and contract (for whatever reasons they wish, moisture content being a major factor) while the caulking keeps them both structurally sound and also watertight. Fiberglassing would remove this movement, thus eventually damaging the structure.

Glued-carvel is a dangerous way to build unless you fiberglass, as it is not designed to move. The glued planks will split, since they can't move in compressing the caulking; the fiberglassing prevents this by controling moisture content (and I suspect in this case because it's really a monocoupe hull, the wood being used as a spacer between fiberglass shells.)

There are good things (and bad things) about almost any method of boat construction. Mixing and matching them to get successful boats with long lives calls for understanding how they do or don't work together.

[ 05-01-2005, 11:44 PM: Message edited by: htom ]

Cuyahoga Chuck
05-01-2005, 10:46 PM
Haven't read the article, Charles, but I'm familiar with most of the arguments.
Most of the "anti" sentiment stems from years of hearing about old hulks being covered with 'glass and resin to keep them afloat. It usually turned out to be a short term soluntion because only the outside was covered and delamination eventually occured.
It can work if both sides of the planking are encapsulated but that is difficult when there is interior structure in the way.
If the author has found some way to keep water from getting at both sides of the planking it should be possible.
But the basic engineering difficulty is wood's ability to expand across grain far exceeds epoxy/'glass matrix ability to expand with it. Putting resin between the boards doesn't, of itself, cancel out the possible expansion of the wood.
There has to be an angle to this guys technique.
I'm curious to see why he is successful when so many before him were not.

Bob Perkins
05-01-2005, 10:49 PM
I don't remember if I chimed in the last time... But a friend has a 5.5 meter he just got that needs full restoration. It was glassed over mahogany planks in the 80's.

It is amazing to see that all of the problems start at the glass line. The stem is rotted out, frames, planks.. It is very obvious the glass killed the bottom 1/2 of this boat. At least it peels of easily.

Don't do it.. Make a planked boat - or a glassed boat.

My .02$

Don Kurylko
05-02-2005, 12:14 AM
Don’t know what size of boat you have or it’s condition, but if you want to cover the hull with FG, then get the book “Covering Wooden Boats with Fiberglass” by Allan H. Vaitses, International Marine Publishing. It will either turn you right on to the idea, or right off!

Basically, he advocates creating a multi-layered laminate of glass (not cloth) about 1/8” to 1/4” thick over the hull, that is also stapled to the wooden sub-structure. It sounds bizarre, but the argument he puts forth is compelling if you are into that sort of thing. In essence, you would create a substantial fiberglass hull over the original wooden one that is strong enough to support even the most rotten of hulls. Best of all, there is no expensive Epoxy involved, just straight old polyester resin.

Allan also discusses the merits of light glass cloth over carvel planked hulls in the book. His advice: DON’T!!!

Have you considered 2 or 3 layers of 1/8” wooden veneers Epoxy glued over the old hull? If the basic hull is sound, but tired, this may be a good alternative. It has been done successfully before - most notably by Tim and Pauline Carr over their 100 year old 30’ gaff cutter “Curlew.” It was written up in WB several years back and is definitely worth checking out.

05-02-2005, 06:53 AM
One question I still have remaining is: If the boat is trailer-sailed, it might see about 8 hours of water every week or so. How much water would the wood absorb with this exposure? Would it be enough to matter?
Its a very small, trailered boat. My two cents is go ahead and glue and glass it. I would.

05-02-2005, 07:05 AM
Having read Vaitses book, I found this mostly a way of keeping older wooden work boats working.
You must staple the cloth to the hull with very large staples every 6 inches or so and cover with significant thickness of woven roving cloth building up to thicknesses such as 3/8 to 1/2 inch to get the strength you need, Thick layers will prevent glass from peeling away and splitting. Of course the wood will continue to rot but the wood is no longer a large structural component of the boat. The boat will ride up higher in the water, displacement actually increases.
I have used another product extensively in my own repair work called Permaflex made by Sanitred.
The stuff is like liquid 5200 and is tough. you could even staple regular FG cloth to a hull gluing this on to the hull with the permaflex.
And you would need only a couple of thin layers. It is waterproof. Part of what preserves the inside of a wood boat in salt water is the constant weepage of salt poisoning the rot, so you would have to consider this if leaving a boat exposed to rain water or fresh water. On my own boat, I found as the hull was new, frames were more likely to get fresh water exposure and rot sets in early but as the hull deteriorates and weepage of salt water begins, the rot slows down, but then the fastenings start wasting away and the whole structure steadily weakens and worsens over time until it is really not safe.

Go ahead and laugh but in my own case, I removed the planks, renewed the frames, coated the floors, frames and inside of the planks with permaflex, reatached all the planking, sealed the plank edges with polyurethane window and door sealant from HD and now am coating the outside with sanitred using a small roller.

Just about everyone who has seen what I am doing,
is very interested in the stuff and thinks I have done a good job.

05-02-2005, 10:17 AM
Wasn't therte a different thread recently involving using different oils to saturate wood and thus preserve it? Tung oil, walnut oil, linseed oil, etc.? Is this another alternative for boats that don't sit in the water most of the time?

Charles Neuman
05-02-2005, 10:30 AM
A lot of useful responses.

My personal interest is in new boat construction. The goal is to have a small trailerable carvel planked boat. I am also interested in more appropriate techniques, such as glued lapstrake, but I don't like hearing "you can't have..." when it comes to a style of boat. Maybe I am influenced by my 2-year-old son.

I suppose there could be a way to "carvel plank" using plywood. But how would you back out the planks? That would be a mess of plywood splinters I imagine. Alternatively, I don't know if a plywood plank could be cupped properly. But if you're using epoxy and have enough clamps and screws, I suppose anything's possible.


Ian McColgin
05-02-2005, 10:57 AM
I am not looking at the article, but I'd thought that Cat's Paw was more like strip plank than carvel.

There are three major ways to handle plank to plank sealing. In carvel construction with planks wide enough to need backing out at the turn of the bilge, caulking is really integral to the structure and you must use something firm enough that when the wood swells there is good skin compression right around the boat.

"Tight seam" construction where it's wood to wood contact usually involves narrower planks, often riveted. Like carvel, this method utilizes wood's swelling to achieve the final skin structure.

Neither carvel nor tight seam are really happy drysailing as both structures need to take up a bit for the hull skin to become structural. If you work these boats without swelling them, the planking and frames work against the fasteners and everything falls apart.

Various ways to make a rigid structure wet or dry all come down to the wood being cut and fashioned such that such swelling as happens is minimized. The easiest way is strip planking. Epoxy can find a happy home in the seams and glassing is perfectly easy if you want.

The major variation that uses dimensional wood is "Ashcroft planking - a dual diagonal method of at least two layers, sometimes a third longitudinal layer outside - originally developed for use without glue but readily adapated to cold molding.

After Vaitsais (sp approx) pioneering work, it was found that some carvel hulls can have the seams reefed and routered and then soft wood set in epoxy splined and the whole hull sealed with epoxy. In this method, glassing over does not add to the structure and is not recommended as it just allows rot.

In general it is cheaper and better to repair a wooden boat the way she was constructed but there have been examples of tired wooden hulls getting an extra few decades with the application of lots of glass and goo. It's expensive and adds huge weight. In the end such glassing is probably less cost effective than junking the boat and starting anew, but sometimes it makes some limited sense.

Comparing the Cat's Paw to the original Beetle Cat, we can see that the Beetle Cat would suffer from weight and rot if glassed. If dry sailed, a Beetle Cat would also wrack her fastenings out, disintigrating from within fairly quickly.

05-05-2005, 09:25 PM
Charles, your first sentence in this thread pretty much says it all. Vaitses' method really amounts to building a new fiberglass hull over a wooden one, not just covering wood with one or two layers of 'glass to keep it from leaking. The latter was in vogue for a short while, until the failures started to multiply.

09-24-2009, 06:10 PM
Some of the "newer" models of Chris-Craft I believe had fiber glassed hulls below waterline, didn't they? The 1930's row boat I'm intending to finally getting around to refinishing had an original canvas covering. I have a real concern of the fiberglass and canvas having two different sets of physical properties i.e expanding/contracting compared to the wood. Still need to do more research and this link is helping. Thanks!

09-24-2009, 07:01 PM
This is a post I made over on Thursdays with Carl and the WB editors ,"An Article on Sheathing " .

"I was discussing just this last week with a boatbuilder , now retired at 70 .He has spent his career building coldmolded craft in a wide variety of styles .

We were talking about the possibilities of cold mold sheathing new or recent carvel construct ,not as a last ditch repair of a dying hull ....the reason my sound a little strange .....but I have a friend with a steel boat who used to cruise for 6 months then haul the boat out onto a boat transport and have it hauled home to his shed and workshop for the unbearable ,sailingwise :(,Australian summer .It was an excellent arrangement , no mooring fees , no worrying in tropical storms ,ease of annual maintainence (like me he lives 30 mile from any available moorings ).

The idea of a process that would render a carvel boat capable of withstanding such treament is of interest .Our current thinking is a very strong (x3 layers of 1/4" cca pine + dynel (polypropylene ) sheathing ,all epoxy glued ).The inside of the hull well sealed with red lead and gloss enamel ."

What thinks the panel ?

peter radclyffe
09-25-2009, 04:06 PM
why not it cuts down on maintenance
more time to sail http://www.woodenboat.com/forum/images/icons/icon7.gif

09-25-2009, 10:54 PM
It's hard to get a comment on some of these things isn't it .It's a real question but not one that concerns most I suppose .

peter radclyffe
09-25-2009, 11:21 PM
yes i guess if someone wants to do it, i think pen duick is glassed

09-25-2009, 11:24 PM
Just for the record, it is done here all the time. If it didn't work, someone would have caught on by now.:)

09-25-2009, 11:38 PM
Just for the record, it is done here all the time. If it didn't work, someone would have caught on by now.:)

:D or been caught by the local marine constabulary! No, seriously SB, what techniques have you seen?

peter radclyffe
09-25-2009, 11:48 PM
Just for the record, it is done here all the time. If it didn't work, someone would have caught on by now.:)
which authority approves it

09-26-2009, 12:16 AM
I'm more interested in a Curlew style cold molded skin ,hopefully to make a carvel hull dry storable in a hot climate , rather than the US cold weather dry storage .

What do you think Peter ? Imagine storing a boat dry through a Spanish summer ? Could it be done ?

peter radclyffe
09-26-2009, 12:27 AM
i think cold moulding is a better way to go than glass, & yes it will stabilise it in a severe summer, many years ago cascover sheathing was an approved method, & ive learnt here that dynel is similar, but i cant know for sure

09-26-2009, 12:34 AM
I'm giving it a lot of thought and bouncing it around with an old boatbuilder of my aquanintance who has specialised in cold molded work for many years .

I think it could be a very useful technique .Being able to dry store a boat here would be a godsend , moorings are getting hard to find and expensive .Some can also be unpleasantly exposed in strong winds ....not the kind of thing that helps you sleep 50 miles away .

09-26-2009, 12:51 AM
which authority approves it
The authority of the people who put their lives at risk in'em.

peter radclyffe
09-26-2009, 01:35 AM
structurally its fine, i'm asking about the longevity