Canvas Covered Plywood Hull

[northboundtrain]

Hello,

I'm considering building a simple dory, about 20' LOA. I'd like to use plywood over sawn frames and I'd really rather not work with epoxy. I know epoxy is the best--some say the "only"--glue to use, and I may in fact decide to do epoxy-glued lapstrake instead, but for the sake of this discussion I'd like to consider an epoxy-free alternative.

So I'm wondering about sheathing the plywood (3/8" or 1/2" marine fir) with canvas bedded in paint in the same manner as canvas-covered canoes. The bottom will have a slight rocker so the canvas will want to stay tight to the hull once it's stretched and secured, as it will on the sides of course. I would most likely use PL Premium to glue the plywood to the frames.

Has this been done? Is it a decent way to build a boat or would it be problematic?

Thanks for any input

[Peerie Maa]

May be extremely difficult to get the canvas to drape properly as it comes off the bottom and up the sides. You should just ensure that you fit the ply to the chine logs properly using waterproof glue and then paint it, the canvas is not needed on a ply boat. The only reason to glass a plywood dory is for abrasion resistance under the paint.

[northboundtrain]

Thanks Nick.

I was actually thinking of doing the canvas in three separate panels--two sides and one bottom--which would ensure a perfectly flat, wrinkle-free fit. I could canvas the transom as well, but I may want to do a bright-finished cedar transom instead. I would lap the side panels down around the chines and then trim out the seams with oak strips which would double as rub rails on the bottom.

My rationale for the canvas is two-fold: First, if I don't want to use epoxy, then the canvas covering bedded in paint would provide an additional waterproofing layer. Second, I think it will look better. The canvas-covered decks I've seen look pretty nice, whereas bare painted plywood hulls that I've seen telegraph the imperfections through the paint (footballs, seams, etc.). Obviously I'm not terribly caught up on aesthetics, but I would like it to look as nice as possible.

[WX]

How about getting a piece of ply and trying out your idea on that to see if it will work? If you were to just go with a ply hull you could use a high build primer to fill any imperfections.

[skaraborgcraft]

NO NO NO!!! eventually your canvas may not be bonded to the ply in places,and so moisture will be in there and the start of rot. My folkboat decks are canvassed,but it only took one small area to let go to cause big problems further down the line. No need for the canvas,just paint it,no worries. Cheers

[Cuyahoga Chuck]

Thanks Nick.

I was actually thinking of doing the canvas in three separate panels--two sides and one bottom--which would ensure a perfectly flat, wrinkle-free fit. I could canvas the transom as well, but I may want to do a bright-finished cedar transom instead. I would lap the side panels down around the chines and then trim out the seams with oak strips which would double as rub rails on the bottom.

My rationale for the canvas is two-fold: First, if I don't want to use epoxy, then the canvas covering bedded in paint would provide an additional waterproofing layer. Second, I think it will look better. The canvas-covered decks I've seen look pretty nice, whereas bare painted plywood hulls that I've seen telegraph the imperfections through the paint (footballs, seams, etc.). Obviously I'm not terribly caught up on aesthetics, but I would like it to look as nice as possible.

You can't just slap canvas or any other fabric on and paint it. No matter how you attach it too the wood because it's on the exterior of the hull the weave must be filled with something so that the finish will be smooth. In the old days it was white lead which is poisonous to the microbes that eat cotton and wood. Now the canoe guys have something less toxic but they have to go thru the same procedure of rubbing it into the cloth to fill and establish a flat surface for the paint.
What little I know of the old canvas covered dinghies, the canvas was attached with some kind of aromatic solvent glue that was popular at the time and, because of the large volume required, will really give you a buzz if you breath it. Today we'd do it with epoxy because there are no solvent discharges.

[dredbob]

This kind of thing has been done, and also has been discussed on this forum sometime in the past. It's definitely not for a boat which will stay in the water. But for the boat that spends its time mostly on land with occasional use, those who have used the technique seem to be satistied with it. It is certainly a "quick and dirty" technique. If I recall, the folks who did it considered it a step up from plain painted plywood, not a step down from epoxy. Some used cotton canvas, others used various synthetics, from curtain scrim cloth to heavier stuff. They claimed that it helped keep the paint on and the ply from checking like plain painted plywood is apt to do.

Do some searches on the forum and the internet; you should be able to find some examples. I can remember seeing a picture of a paisley canoe someone made for his daughter.

Bob

[Bert Langley]

I am just curious. We see a lot of "I do not want to use epoxy" threads. Northboundtrain, can you tell us just what your objection is to using epoxy?

[Fitz]

Cuyahoga is right. Canvas on canoes is just stretched - doesn't have to be stretched all that much either. Some folks do it by hand. It is not glued on, just tacked at the gunwales and the stems. That makes it relatively easy to replace. Undo the fasteners and it falls right off. The weave of the canvas is filled with canoe canvas filler, which is a mixture of paint, linseed oil, turpentine and plenty of silica and mildecide. Lead can be used as a fungicide. There are many "secret" formulas for fillers. You can also buy mildecide treated canvas. The filler is rubbed into the weave and allowed to cure for about six weeks. To give you some idea of the durability, I went at a cured canoe today with a ROS and 60 grit and hardly even scratched it.

Penn Yan and maybe a few other companies used aircraft dope to fill the canvas and that may explain the buzz.

[Outlaw]

on my kayak I used tomsom water seal then painted 4 coats of exterior housepaint. been on for almost 12 yrs. nice an smooth and no leaks. next yr I will recover with nylon.
why don't ya use MDO on the boat and primer an use good exterior house paint. nice and smooth, no problems.

Outlaw

[northboundtrain]

why don't ya use MDO on the boat and primer an use good exterior house paint. nice and smooth, no problems.

Can someone tell me what MDO is?

[northboundtrain]

I am just curious. We see a lot of "I do not want to use epoxy" threads. Northboundtrain, can you tell us just what your objection is to using epoxy?

I'm not completely opposed to it, and as I said up front I may go for glued lapstrake, but I have worked with epoxy in the past and just found it messy and unpleasant. I know it will do what no other glue can, but I want to enjoy building this boat as much as possible. I'd like to minimize the amount of time I have to wear gloves, respirator, and other protective gear. If there's really no other decent way to build a boat out of plywood, then I'll use epoxy, but right now I'm just looking for alternatives that could produce a nice looking and well-crafted boat.

[johngsandusky]

MDO-Medium Density Overlay, plywood with stuff bonded to it at the factory.

[pipefitter]

MDO is what they use for billboards and road signs exposed to the weather for years at a time. It has a phenolic paper fabric well bonded to the wood. It holds paint and adhesives quite well. There is ways to carry the paper around the chines from the sides so that the seam is hidden on the bottom with some creative forethought to the cut layout and to save with bodywork that it would take to protect the end grains and give the hull a seamless look.

As far as using construction adhesives, these can be as or more messy than using epoxy and more care needs to be taken with the fastening schedule. Only time I have really seen construction adhesive used semi-successfully, is when it was instantly, quickly and permanently followed behind with glue coated staples or nails from pneumatic guns, hidden from view and not as a stand alone system but to hold hands with the many fasteners, so to speak.

By the time you work around avoiding dry bonds with the stuff, the mess with getting it on your skin, it's more trouble than it's worth, IMO.

I loaded thickened epoxy into gun style caulking tubes for fillets etc and it went down neatly and at a pretty amazing pace.

[northboundtrain]

Well, thanks for the replies and advice. Using canvas still has some appeal to me if it could be done well. I've heard it's durability touted, and I think it could look good as well. But I would need to know exactly what to bed it in if paint alone is inadequate, and I'm not going to use really heavy-solvent toxic chemicals; that defeats the purpose of foregoing the epoxy.

I suppose I could do an epoxy coating on the outside, perhaps with a layer of fiberglass as well. I'd rather not have to do that to the inside though. I'd prefer to simply oil the inside thoroughly (many coats) as that will be by far the easiest to maintain.

If I end up just painting the plywood on the exterior can anyone tell me what would be a good painting regiment? Also, what can I use to either fill or caulk the seams?

Thanks

[skaraborgcraft]

Why are you going to have seams on a plywood boat? This "checking" seems to be an issue with fir ply,that we just dont use much in Europe,so we dont have this problem. Paiting does not have to be anything special. I have used a metallic pink primer(international) as a base coat, undercoat then top gloss. 3 layer system on a 30+ year old plywood sloop that has never been glassed anywhere. You could put a light glass mat on the exterior to prevent checking and to reduce painting in the long term. I just built a 15ft ply skiff,and glassed the bottom only, everything else had 3 coats,inside and outside of epoxy resin. Im no fan of epoxy either,hate working in rubber gloves,cant stand sanding the crap,but admit that in this case,the result was worth it,long term too. Now i have more time to spend maintaing my traditional clinker boats....win ..win. Cheers

[northboundtrain]

Why are you going to have seams on a plywood boat?

I just mean the seams where the plywood sheets break. There will be two per side and one on the bottom.

I should mention the intended use for the boat. It's "home port" is a freshwater lake in NH and it will probably be in the water for weeks at a time. I'd also like to take it to the coast and do some salt-water sailing. I suppose the most abusive environment it could potentially face would be spending several weeks in salt water. It will always be hauled out in the off season and thoroughly maintained.

Thanks

[skaraborgcraft]

Quite the opposite,sitting in a fresh water lake will kill it faster than it being in salt. You could just glass the chine then,or just round it off and give it a few coats of epoxy,no need to do the whole boat if you have decent ply.

[Frank R]

Use a low odor epoxy. I have never worn a respirator and the fumes are almost non-existent. Certainly nothing unpleasant.

Latex gloves are needed only to prevent contact dermititis from uncured epoxy.


Also, canvas may lessen but not prevent the telegraphing of flaws.

[Oldad]

Fiberglass and epoxy, why reinvent the wheel?
No appreciable odor from any I have ever used. And no particular danger other than mentioned above.
Common sense and rubber gloves and you're good to go.
The "seams" you mention should be covered with a layer of fiberglass tape set in epoxy and the whole hull covered with a layer of glass on the outside to prevent checking
You can download the west system book for free, answers lots of your questions and gives detailed instructions for building using epoxy. IMHO If boat builders had had epoxy 100 years ago we wouldn't be having this discussion. It would be the traditional way to build wooden boats.

Oldad hopes it wont rain this weekend for the WBS

[Fitz]

IMHO If boat builders had had epoxy 100 years ago we wouldn't be having this discussion.

I have several canvas covered canoes in my garage that are over 100 years old. Just replace the skin and they are like new. I very much doubt an epoxy/glass covered boat will last that long.

Who is re-inventing the wheel?

[Oldad]

A canvas canoe and a plywood boat are apples and oranges, why not go back to covering the hull with animal skins, maybe birchbark? Plywood and epoxy and glass are proven combinations was the point I was clumsily trying to make. A plywood boat covered in epoxy and glass will last just as well as your canoes given the same care and attention. Sadly both are often neglected.

Oldad had a Lincoln canoe from the 20s that he foolishly gave away when the son of the original owner wanted it and then left it to rot on his side porch. I used to have to drive by and see it sitting there, heartbreaking.

[chas]

" I suppose the most abusive environment it could potentially face would be spending several weeks in salt water."

The water you need to worry about comes from above. Seal the inside of your open boat; while I'm a great fan of construction adhesive, you need to keep it dry.

" Only time I have really seen construction adhesive used semi-successfully, is when it was instantly, quickly and permanently followed behind with glue coated staples or nails from pneumatic guns, hidden from view and not as a stand alone system but to hold hands with the many fasteners, so to speak."

This is not how construction adhesive works, especially with plywood that is somewhat self-fairing. You want to 'tack' your ply in place and allow the ply to nestle into the frames; the glue will settle in evenly with the pressure and set up with an even bond. After a green-dry, which could be weeks with some specially-formulated sub-floor adhesives, you may drive fastenings as back-up to alleviate your conscience. The glue is fairly permanent when the joins remain dry. / Jim

[northboundtrain]

Thanks again for the suggestions and opinions. I value the accumulated wisdom and experience here, and I very much respect the consensus that the various epoxy systems produce a superior boat. I've done a lot of research on this (I probably could have built a boat already with the amount of time I've spent) and I am considering a couple of different epoxy systems. But I'm also inclined, for a variety of reasons, to try something else. It may not be as long-lived or durable a boat as it could possibly be, and that may be okay with me too.

So as I said at the outset, for the sake of this discussion, let's assume epoxy is not an option. I'd like to know what I could do instead. Bare painted plywood is one option. Some of you have been skeptical about trying a canvas covering but others have sounded more encouraging. If I were give it a try--and this isn't a boat that I'm going to put a huge amount of time or money into so I don't mind if there's an element of experimentation--it sounds like I should use more than just paint to bed the canvas.

Fitz, you mentioned earlier using "a mixture of paint, linseed oil, turpentine and plenty of silica and mildecide." Have you done this and do you have a specific recipe?

Thanks

[Cuyahoga Chuck]

Fitz, you mentioned earlier using "a mixture of paint, linseed oil, turpentine and plenty of silica and mildecide." Have you done this and do you have a specific recipe?

Thanks

He has. He is an extremely fine wood-canvas canoe restorer.
If you want to get in the game you have to know the drill. With canoes the cloth can be stretched tightly over the hull without any laminating glue but the cloth has to have the weave filled because it needs to be smoothed and there needs to be a very good water barrier. There is bare wood behind the cloth and the filler compound and the paint are what keep the water out.
If you want to try the drill here's what to do. Take scrap canvas and make a mitten. Pile a wad of the mixture on the hull and start rubbing with the mitten. You have to physically force the mixture well down into the weave. You may have to go over the hull several times. You can't shortcut the process because if you miss a spot there will be a leak.

[potomac]

You have two different issues:
1. Adhesive- sure lots of people think epoxy is the best and lots of designs are based on its use, but it's not the only thing out there. Do a little research on 3M 5200, PL Premium, and Sikaflex 291, heck even Titebond 3. All have been used to build fine boats.

2. Covering- maybe canvass will work. To me it's just another way to hold water against the hull causing rot. Want smooth and simple, check out MDO. Again, fine boats have been built with it. It looks great and is cheaper than marine ply.

[jameshow]

Hi

I recently read in classic boat, of a folkboat deck canvas covered with titebond glue.
I covered a summer breeze skiff with exterior paint and dust sheet! that has held up very well.

Yours James

[Fitz]

What Chuck said about fillers. The canvas is attached to the hull with no glue etc., just fasteners. The canvas filler goes on the outside to fill the weave, make a durable surface, make a waterproof surface and to make a hard smooth paintable surface. It is brushed or rolled on and then rubbed into the weave. I make three passes. Then it has to cure for about six weeks before painting. You can buy canvas filler - Check out the WCHA site for vendors, or mix your own.

There are quite a number of recipes here:

http://www.wcha.org/canvas-fillers/

[northboundtrain]

Hi

I recently read in classic boat, of a folkboat deck canvas covered with titebond glue.
I covered a summer breeze skiff with exterior paint and dust sheet! that has held up very well.

Yours James

Seems to me that what you might do one a deck is very different from what you want under the water line. When you say dust sheet are you referring to thin cotton fabric like a bed sheet?

[northboundtrain]

I think I've decided the traditional cotton covering is no longer an option, primarily because I want to launch the boat sometime this fall if at all possible. So I guess I'm looking at bare painted wood or some kind of epoxy coating.

So despite my initial intention to keep this thread on the subject of an epoxy alternative, I have a couple of questions regarding an epoxy coating:

I've read widely ranging opinions on whether it's necessary or even desirable to coat both the outside and inside of the hull. The standard epoxy systems--strip, cold-molded, stitch and glue, etc--employ epoxy and or epoxy and glass coatings on both sides of the hull with the intention of encapsulating the wood core and keeping it bone dry. There seems to be a relatively small minority of naysayers who suggest that it's unrealistic to think that the wood can be effectively encapsulated and that moisture will eventually find a way in but not be able to breathe out, thus rotting the hull. In any case, I would much prefer to coat only the outside because I'd like to have a fair amount of traditional framing (I'm not trying to build an ultralight boat) which would get in the way of coating the inside and leave lots of uncoated areas where moisture could find it's way into the hull. Plus I'd like to oil the inside and not need to paint or varnish it which would be necessary over an epoxy coating.

So, opinions on coating the outside only?

[willin woodworks]

I just don't understand what it is you're trying to accomplish. A simple plywood dory is an easy build and you seem to want to needlessly complicate it. It's not a canoe and it doesnt sound like mixing these methods is feasable. You don't want to glass it; not a real problem. Use good ply or MDO, seal it, prime it and paint it. I primed my exterior ply dory with CPES, touch sanded it, recoated with CPES and then hot coated with Petit Easypoxy when CPES got tacky. Sanded the first two coats of paint and it looks great. A little checking here and there but I'll give it a quick coat of paint mid season.

[Oldad]

Let me again suggest that you get the free download of Geougeon (sp?) Bros West System boat building manual. Very comprehensive and worthwhile reading even if you do not use epoxy as extensively as they do. As Willin said, don't complicate it. He makes a good case for a simple plywood build, especially since you state that you are not so much concerned with longevity. Sealing the edges of the ply with something is a must IMHO. Personally I would choose epoxy for that task. No point in inviting failure.

[willin woodworks]

I should add that I soaked the plywood end grain and cut edges with CPES repeatedly; basically until no more was absorbed. The plywood must be sealed with something and I think the CPES gets decent penetration and I know it's a great primer for the Easypoxy.

[northboundtrain]

Ok, thanks guys.

I guess I'm hesitant to just paint the plywood because I think I know what that's going to look like and how it's going to weather over time. I'd rather have some coating on it, even if it's just epoxy without glass, though perhaps I'll glass the seams and chines. Anyway, I like the look of traditional ribs and so I'm going to build it that way. In fact I already have the wood and have begun the frame. I also like the look and feel of oiled wood and would really like to just oil the heck out of the interior.

So is it feasible to epoxy coat just the outside of the hull and use linseed oil on the inside? Obviously I can't use linseed oil over epoxy; that would be useless. I'd need to do several coats of varnish or paint which is much more tedious, especially given all the framing.

I will indeed read through the Geougeon manual and perhaps I will find all the answers there, but in the meantime if anyone has an opinion they wouldn't mind sharing I'd certainly appreciate the help.

Thank you once again.

[Oldad]

I know nothing about oiling the interior (boat soup?) of a wooden boat, but i might point out that plywood is not, in a sense, wood as in cedar or oak. There is the thin surface veneer and then a waterproof glue that would probably inhibit saturation any deeper into the "wood". Maybe read this thread, especially the last entry
http://forum.woodenboat.com/showthre...p-for-Interior keeping in mind that the boats described were wooden boats. Varnish sounds like a better alternative or even a light gray paint.

Oldad heading for the WBS tomorrow, yea

[Bob Cleek]

I'm afraid this thread is a good example of the way this forum seems to be going to hell in a handbasket. The blind leading the blind with directions given by the nearsighted. This forum used to be a good place to discuss traditional boat building crafts and skills. Now, it seems increasingly, it is full of people who know nothing about building wooden boats tossing out their "better mousetraps" and others pontificating about how to solve the problems their thinking "they know better" cause for them. Why is it so hard to accept that wooden boat building is a pretty mature technology and the way it has evolved for the last couple of centuries reflects the wisdom and experience of generations of craftsmen who forgot more than we will ever learn? This sort of discussion is certainly a good example how folks who want to get into wooden boats are done a grave disservice by the manufacturers who have created no end of problems trying to fit round pegs in square holes in pursuit of the almighty dollar. Your instincts are correct, but your solutions betray that you've "drank the Kool Aid" dished out by plywood and adhesives manufacturers.

I'm not completely opposed to (epoxy), and as I said up front I may go for glued lapstrake, but I have worked with epoxy in the past and just found it messy and unpleasant. I know it will do what no other glue can, but I want to enjoy building this boat as much as possible. I'd like to minimize the amount of time I have to wear gloves, respirator, and other protective gear. If there's really no other decent way to build a boat out of plywood, then I'll use epoxy, but right now I'm just looking for alternatives that could produce a nice looking and well-crafted boat.

Northbound, if you are "just looking for alternatives that could produce a nice looking and well-crafted boat," then go out and buy John Gardner's books ("The Dory Book" is a good start.) and build your dory exaclty the same way dories have been built for going on three hundred years: out of naturally grown wood. Just like "processed food," "processed wood" has its drawbacks. "Go organic." "Go Green." If you need some "modern" perspective, or "go traditional," it doesn't matter. You'll end up in the same place anyway.

You are entirely correct. While modern adhesives have their appropriate applications, they are certainly "messy and unpleasant." Neither is plywood much fun to work with. Take a piece of plywood and try planing the edges. Take a piece of natural plank and try planing that. Although many have built plywood hulls, it is not nearly as suitable a hull material as "unprocessed" wood planking. It is difficult, if not impossible to repair. It looks just like what it is, plywood, unless you slather it with epoxy and glass or any other fabric, in which case it then also looks exactly like what that makes it, a fibreglass boat. Don't get me wrong. Fibreglass sheathing has its place, but fibreglassed boats aren't anywhere near as enjoyable to build as a traditionally constructed wooden boat and often much more difficult to build, as anyone can see from the number of posts here about the problems people encounter trying to do so.

There are few small boats as easy to build traditionally out of real wood as dories are. Gardner's books contain all the information necessary to do so. It ain't rocket science.

Oh, and did I mention that building a dory traditionally with natural materials is far, far less costly than all that processed sheet product and resins and hardeners? It remains a mystery why people who want to build a boat will drop $150 to $400 for a single sheet of "marine" plywood and $150 for a gallon of epoxy resin because "boatbuilding lumber is too expensive." Sheesh!

Okay, rant over. Now the rest of the crew can go on telling you how great plywood is, and how to overcome all the problems inherent in its application as a boat building material. Let me save the forum some bandwidth. Check out this article telling you how "plywood is the perfect boat building material." http://www.boulterplywood.com/sailmag.boatworks.html Of course, it's written and posted by Boulter Plywood. They make the stuff. They should be good for an unbiased opinion, no?

[potomac]

"Indeed, many conservative dory builders still despise plywood and refuse to have anything to do with it as planking. This is unfortunate, for plywood, properly used, is excellent for dories. In addition, it is one of the best values available today in boat materials. Plywood is obtainable everywhere, and it is easy to use."- John Gardner, The Dory Book- the one recommended above

It is not necessary for something to be bad so that something else can be good.

[Oldad]

Northbound, thinking about your idea of canvas as a covering material for your hull i am reminded of the many variations Penn Yan went through over the years, first building boats much the same way canoes were built with steamed ribs and red cedar sheathing covered with filled canvas to two layers of sheathing with a layer of "plastic" material sandwiched between to bead and cove sheathing applied under tension. They used red cedar, oak and mahogany and probably other varieties as well.They gave the innovative designs names like composite, monowood, stripplank, striptite, dynamold and plastron. They finally began to build lapstrake boats using marine ply for planking and then went on to all fiberglass boats. Now, they might have stayed with wood and filled canvas and been fine but they were innovators and explored the options and had successes and failures as well and finally closed their doors as so many others have over the years.
You are part of that noble tradition who dares to think outside the box. Build your boat anyway you want but be sure to share the pictures.

[Bob Cleek]

"Indeed, many conservative dory builders still despise plywood and refuse to have anything to do with it as planking. This is unfortunate, for plywood, properly used, is excellent for dories. In addition, it is one of the best values available today in boat materials. Plywood is obtainable everywhere, and it is easy to use."- John Gardner, The Dory Book- the one recommended above

It is not necessary for something to be bad so that something else can be good.

Score one for Potomac! I suppose Gardner succumbed to the need to sell books. He certainly ought to know better. Plywood is indeed suitable for a limited number of dory designs when "properly used," particularly slab sided single plank models and it is "obtainable everywhere." That is, however, as far as it goes and begs the question, "Why would anyone who gave it any thought want to?" At the end of the day, it's still a plywood boat. I disagree with Gardner's opinion that it is "easy to use" or any innuendo that natural wood is not also "obtainable everywhere."

When comparing the various ways of doing anything, it is never all black or all white. There are always shades of grey. However, there's no way to make such comparisons without making qualitative judgments. There is a right way to do things and a wrong way to do things. Among those two categories there are "easier" and "harder" and "classier" and "classless" ways of doing something "right" or "wrong." Polyester stretch pants will cover a dame's butt as well as any natural fibre fabric, but the gals who wear polyester don't get asked out on Saturday nights as much, do they? In my opinion, and the opinion of many others, as indicated by Gardner's comment, using plywood as a planking material may arguably fall into the "right way" classification, but it sure as hell doesn't fall into the "easy way" when compared to traditional dory construction with natural timber stock.

The guy who started this thread certainly had given it a lot of thought and ran into a series of dead ends. He recognizes all the drawback of plywood and resin construction and wants to avoid them. He wants to enjoy building a fine boat. The answer to his questions is plain as day. He should build traditionally of traditional materials. Now, if he had said, "I love the smell of epoxy in the morning." and "I just love trying to bend a material that was engineered to stay perfectly flat in the first place." I'd have left him to pursue that dream. He did not. I just answered his question.

Consider your tag line: "A man builds the best of himself into a boat- builds many of the memories of his ancestors." -Steinbeck Do you really think plywood is the best of yourself? Do you really think plywood can ever do justice to the memories of your ancestors? I certainly don't. A plywood boat slathered in epoxy is the polyester stretch pants of boatbuilding.

That's my story and I'm stickin' to it.

[Cuyahoga Chuck]

This thread is turning into a rant against the most modern and popular method of boatbuilding. It should be remembered that not everyone has the knowledge,time, money and liesure to build with sawn frames and lumber planks. Life can change fast and it often leaves rotten half-finished hulls where the builder had to move on to other things. Boatbuilding is most enjoyable when the task can be completed in something close to the envisioned time span, money outlay and least disruption to every day life.
If a builder sees his efforts as a display of artistry and tradition and is willing to follow that trail whever it goes fine and dandy. But if he wants to get on the water ASAP that's OK too. The most important thing is to make a realistic estimate of what is wanted most and make choices that will get you there.

[beernd]

OK just one dumb question, if you don't glue the canvas to your hull won't it rip easy if you hit something nasty?

[Bob Cleek]

OK just one dumb question, if you don't glue the canvas to your hull won't it rip easy if you hit something nasty?

Yes and no. Canvas glued to a solid backing is susceptible to being punctured, if not torn, when impacted by a sharp object. However, if it is sufficiently impregnated with some sort of resin, paint or epoxy, for example, it really becomes part of the structure. The real purpose of a fabric in that instance is not to provide watertightness per se, but to provide a matrix to hold the resin, the two being stronger than the sum of the parts. (This is, of course, the basic engineering principle of fibreglass hulls.) Any breach in the watertight integrity of the sheathing will permit water to intrude into the wooden substructure and promote decay. The rate of that decay will depend upon the sealing methods of the wood substructure and the wood species' propensity to rot and delaminate.

On the other hand, Canvas as a primary hull skin, such as has been used traditionally in the British, Irish and Scottish curraghs and the like, a form of skin on frame construction, works rather effectively to resist puncture damage because these boats are relatively lightweight and their canvas skin has great flexibility which spreads impact efficiently, up to a point. To a certain extent, it might be said that such boats sort of "bounce" on impact more that the heavier inflexible hull planking forms do. Even when such a skin is punctured, a "stitch and pitch" repair is quickly and easily accomplished "in the field" and lifie goes on.

[Fitz]

OK just one dumb question, if you don't glue the canvas to your hull won't it rip easy if you hit something nasty?

See the discussions above regarding canvas "filler". One fills the weave of the canvas with the traditional stuff that cures rock hard, or even uses thickened epoxy for filler if they like.

[mackaye]

Disclaimer ... Dare I chime in... I'm a rank amateur. As a result, I won't give any advice but merely relate my own experience. One - I've had good luck with PL Premium used in conjuction with fasteners although it has a short open time so I have to plan well and move fast. Two, - I hesitate to say it... I've used polyester fiberglass!!! I've used it on fir ply and have had good results. I've applied a coat of resin thinned with acetone followed by a thin layer of mat followed by woven cloth. Adhesion problems? I haven't had any on fir ply. Perhaps on other types of ply, adhesion might be more of a problem. Why not epoxy? The stuff is very toxic. I've met more than one guy that's had severe reactions to it. One guy ended up in the emergency room. I'm scared of it. Now polyester is no ride in the park and it smells tons. But I believe it's not nearly as toxic and not too bad if applied in a very well ventilated area. I've had a blast building a few glass over ply boats. Perhaps I have no idea what I'm talking about, so be warned, but perhaps this will provide you with another option to investigate.

[Fitz]

Not to beat a dead horse here, but Northboundtrain originally asked about using a canvas skin. Many a canoe, boat, dinghy, runabout were built with canvas skins. It is a proven technique. If your woodwork is not watertight, put canvas (or birchbark) on to waterproof. I only chime in, because there is a great misconception that you just paint the canvas. That is simply not true. YOU NEED a FILLER, unless you are building a skin on frame which you can get away with just layers of paint.

The biggest problem northboundtrain may run into is finding canvas wide enough for his dory, although art supply houses are a good source of canvas. Then there is the extra weight of a "filled skin" on his plywood boat. The filled canvas on an 18 foot canoe weighs about 25 pounds. I'm guessing the weight of all that epoxy is not much different. So why not experiment with a canvas skin? Worst thing that can happen is he ends up stripping the skin and epoxying the hell of out it later. With normal use, most canoes are serviceable for 15 to 20 years of hard use before a new canvas is warranted.

With respect to finishing a canvas skin, most people are amazed when it is revealed to them that the skin is filled canvas and not fiberglass.

[northboundtrain]

If there were a filler that would cure more quickly, I think I'd give the canvas a try. But I do want to launch the boat this season (I'm getting a later start than I'd hoped), and waiting 6-8 weeks after I build the hull and before I can even paint it will put me deep into the fall.

Not that I'm going to try it for filler, but I've found several threads here on the forum about using roofing tar and portland cement as a seam compound for traditional carvel planking. Makes me think there's got to be something simple that would cure more quickly and work well enough. I don't particularly want a boat that looks like fiberglass, so no need for a completely smooth glossy finish.

But I think Mr. Cleek's post earlier in the thread is well worth heeding. I'm a beginner boat builder and there's no need for me to be trying to reinvent the wheel. I should find an established and proven system that is appropriate to my situation and use it.

Cuyahoga Chuck also makes a very good point that the method should suit the builder's budget--both time and money. Staying perfectly true to tradition would indeed be very gratifying, but I don't think that's the best choice for me this time around. I've read many times and in many places that boats are always a compromise among many opposing criteria. I'm certainly finding that to be the case here.

Thanks again for taking the time to give me your suggestions.

[Todd Bradshaw]

Having worked with both, I would rate polyester resin as far more toxic than epoxy. Sensitivity to epoxy resin is basically a contact problem. Work clean, wear gloves and avoid getting green resin or the dust from sanding green resin on you and you shouldn't have any problems. Those polyester resin fumes are not just unpleasant smelling. They're quite toxic (think "sniffing glue" - it's the same stuff and will do the same lovely things to your body). Skin contact can also cause problems as the MEKP hardener is really nasty stuff. When you combine that with the flamability aspect, limited ability to seal wood due to the solvent it contains and the fact that there are no polyester resins formulated to seal or bond well to wood and it's just not a very good choice. Back in the early 1970s it was pretty much all we had, but it can't hold a candle next to epoxy for wooden boats and is less safe from a number of angles.

[Cuyahoga Chuck]

If there were a filler Not that I'm going to try it for filler, but I've found several threads here on the forum about using roofing tar and portland cement as a seam compound for traditional carvel planking. Makes me think there's got to be something simple that would cure more quickly and work well enough. I don't particularly want a boat that looks like fiberglass, so no need for a completely smooth glossy finish.
.

The need for a smooth exterior has more to do with "wetted surface" than looks. On boats that are paddled or rowed the "motor" is human muscle. A rough exterior surface will make the boat harder to drive thru the water. It also seems to make sense on powerboats because nobody intentionally puts out a boat with a rough half-finished exterior.
I would also suggest you stay away from discussions about carvel planking and tar and portland caulking. They just confuse the issue. You should be only interested in things that can advance your project. Drawing implications from what someone has done on a fifty-foot sailboat aren't going to help you in the least.
The standard methods of hull construction were thought out by people smarter and much more experienced than you or me. And the most successful techniques have been around for a very long time. Do yourself a favor and benefit from what has gone before. You'll see the sense of it once you are on the water.

[northboundtrain]

I would also suggest you stay away from discussions about carvel planking and tar and portland caulking. They just confuse the issue. You should be only interested in things that can advance your project. Drawing implications from what someone has done on a fifty-foot sailboat aren't going to help you in the least.

I was only making an observation that there are the traditional materials and methods for sealing a boat (many of which are no longer feasible due to the unavailability of the materials themselves, such as lead-based compounds), then there are the modern marine products which are usually very expensive, and then the homebrew concoctions made from readily available stuff found in any hardware or building supply store which have been invented or discovered by the very pragmatic and cost-conscious people who earn a living with their boats.

It just makes me think that if lobster boats were covered in canvas, someone would have figured out how to bed the canvas with off-the-shelf materials without needing to wait two months to get back in the water. But that was merely a tangential comment.

In my case, I don't work with boats, but I am looking for maximum enjoyment both in the shop and on the water relative to the cost and time invested. I started this thread to ask whether it is an established practice to cover a plywood hull with canvas because, from my extremely limited knowledge of boats, that seemed a very logical cost-effective thing to do. I had read in a traditional boat-building book (sold on this website) that small canvas-covered craft could be bedded with paint and/or thickened paint. I guess "thickened" is a slight oversimplification, and so from all that I have learned since starting this thread, canvasing no longer seems a viable option.

I'm still looking for the most practical--and an established--way to get this boat in the water by end of summer/early fall, which at this point seems will involve some degree of epoxy work, something I'm willing to do if necessary.

Thanks for all the help

[Bob Cleek]

Northbound, I'd reiterate that the traditional methods of dory construction are indeed tried and true and easy to do. You don't need super select quarter sawn stock for a lap seamed dory. In fact, what you want for laps that swell tight is slash cut stock. About the only problem you may encounter building traditionally is finding planking stock sufficiently wide, particularly for the bottom. Not to worry. It is very easy to simply join planks edge to edge with epoxy adhesive to yield wider stock. Don't make yourself crazy looking for the "perfect boatbuilding wood." Any of the rot resistant cedars, cypresses or pines will work fine. One is always better than the rest, but make do with what's available within reasonable limits. If the lumber yard will let you pick (promise to restack when you're done and do so) you should find suitable stock in most any lumber yard. Look for the clearest stuff you can find, meaning no knots. If there are a few small pin knots, no problem. If you have to live with a large knot, you can cut it out with a hole saw and epoxy a plug in its place. Get yourself decent sharp planes, which you will be using a lot. You'll appreciate having a bull nosed rabet plane, a #5 smother and a 12 degree block plane. (They don't have to be megabuck collector's items like Lie Nielsens. A used Stanley or Record, properly tuned and set, works just as well.) Those planes, plus a saw and a hammer and away you go. Follow Gardner's tradiitional building instructions. You'll end up with a fine dory and have a great time building her.