a question on canoe building

guys, i had a thought today that i wanted to ask you all about.
since there is a lot of sanding and fairing to do on the planks (stitches and glue plywood boats) and in my understanding, skin on frame doesn't have much if any sanding to do, ( i do not have any experience in that matter),would it be possible to build the frame and attach 3mm ply planks to the frame, without even connecting the seams, or with if necessary, and then to put the skin on that? saving the sanding and still make it look nice?

 

U will still have some sanding to do that way, if i understand what ur saying.

Skin on frame, yost style (yostwerks.com then go to wooden kayak builders manual) is a very fast, cheap and durable way of getting on the water with a light boat. However, if ur interested more in outriggers and sailing, it may not be ideal for that purpose. I recomend u keep it in ur head as an option though especially if u like paddling, and one day want to build a lightweight kayak. If i were paddling in cold waters that's what i would do, a rollable kayak or else and outrigger canoe. I had a capsize in a small monohull recently in cold water an even with the wetsuit suffered pretty bad cold shock.

 

Re: my one-sheet canoe:

How much does it weight? Slightly less than 7 kg without seat and paint/varnish, say 8 kg finished
What is it's displacement? I hope it will support me, (dieting, down to 90 kg, maybe 85 kg for the launch) but around 75 kg total displacement is ideal
Thickness of the sheet? 3 mm, okoume marine ply, 4 mm if a more robust boat is required.
Was it built and tested before? No . . . a new design - like most of my boats the design is a first-timer. I like to live dangerously
Is there a way to get the plans? I don't keep very good records and I'm not a qualified boat designer but if you wish I will try to dig it out of my computer.

What is The Bass-Ackwards Design method? Most boat designers decide the shape of the hull, then calculate the plank developments, which are what the planks look like when flat, then bend the planks around a form to build the boat. So the hull shape determines the plank shape. In the BAD method I modify the plank shape just enough to make it easy to mark and cut with straight edges, then build the boat. It suits some designs like narrow 5-plank boats and flat-bottomed sailing skiffs, but only a minority of designs can be treated this way.

What system do you use to build it? I'll summarise my blog, but the first page for the building of the canoe "Dora" provides useful images.
Cut off a strip from the ply sheet for the "extensions".
Cut sheers and bottom planks; set aside rest of ply sheet for later. The sheer planks must be identical mirror images.
Note: bottom plank is less than the length of the ply sheet but sheer planks are longer.
Splice extension pieces into sheer planks, using butt blocks (cut from scrap ply) or scarf joints.
Glue battens along both edges of bottom and top, bottom and end edges of sheer planks to increase the gluing area for later.
Cut a midships form to the inside hull shape from cheap or scrap sheet material.
Bend bottom and sheer planks over form to hold them in position at midships.
Pull in bow and stern of sheer planks and glue to stems (pieces of thicker ply that define the shape of the bow and stern).
Add pieces of wood called cheeks to the stems to increase gluing area for a later step.
Add bottom plank and glue to the tops of the stems.

There are long gaps between the sheer and bottom planks that have to be filled in by the bilge planks. These are curved planks, and are obtained from the leftover ply pieces when the bottom plank was cut out. The bilge planks require triangular shaped extensions at each end. The glue joint along the edges of the bottom and sheer planks is planed to form a bevel, so that the bilge planks will fit snugly. My boats are not left soaking in the water for days or weeks, they are stored indoors under cover or outdoors but upside down. Therefore I can use a merely adequate glue like Titebond III rather than a first-class boat building glue like epoxy for all the previous gluing steps. But for the bilge planks the glue must be epoxy. The step of gluing the bilge planks is the only tricky step and I usually spend an hour getting them into position and finding the best way to clamp and wrap them so they stay put while th epoxy sets; this is called the "dry run". It makes them easier to handle if some of the excess material is removed from the bilge planks but leave a little overhang in case something moves during gluing.

Once the bilge planks are in place you have a hull that requires finishing work, trimming off the bilge plank overhangs, adding the outer gunnels or outwales, Thwart, seat and breasthooks - which are very small decks that reinforce the connection between the sheer planks at the stems. And then, on to the sanding and painting, a job that I hate and have sometimes postponed for years.

Hope this clarifies the blog, but that is your best guide. regarding designs, the best way to exchange prototype designs is by using a common hull design application. I use FreeShip mostly, which is available as a free download - just Google it.

Hannu's blog http://koti.kapsi.fi/hvartial/ has some neat ideas, his boats are a little easier to build, I think, but mine look nicer IMHO - his designs tend to be a little iconic.

 

Gentlemen; Why are so many people so much opposed to fairing and sanding? What the hell, it is not as if sanding was some kind of cruel punishment. A good sharp plane is a pleasure to use and those beautiful chips can give you a rush. Sanding a smooth curve or flat surface is a boat builders artwork and It aint that hard to do. The rewards are visible and I,ll be damned if you are justified to compromise design, just to avoid a basic component of decent craftsmanship. For a kayak or canoe, we are talking only a few hours of labor to nicely finish a boat that might very well last for years.

 

I enjoy planing wood sometimes: feeling the blade bite in and start cutting, watching the shavings curl, smelling the fresh wood.... I've never really been able to get into sanding, though. It's just a necessary evil to me.

Except on my rifle stocks. I sand and steel wool and rub those for hours between coats of shellac, tung oil or a mix of linseed oil, beeswax and turpentine, until they feel smooth and soft as a baby's bottom--rather than cold, slick and hard, like a glossy polyurethane varnish. A nice piece of walnut or arctic birch can feel almost cushiony under your fingers with an oil finish, and look like it's semitransparent and you're staring right into the center of it.





This one isn't quite as gorgeous. But considering it spent several years lost and half-buried outside before it was found again and I bought it, and keeping in mind the wood was sun-bleached, fuzzy and cracked, I'm not complaining about the end results. Especially since it shoots better than most new ones...



Sorry; I plead guilty to charges of thread highjacking....

 

Sanding is hard, dusty and unpleasant work. So is gardening IMHO. Some people like that stuff. Fine by me. I’ve just finished a job that needed hours of it, but if I can avoid it I do.

Now you’re talking. Planing is a joy, a beautiful action, the weight and fit of the tool in your hands, the satisfaction of pulling 16 feet of curled wood from a plank in one pass, or an almost transparent film, the amazing precision. It’s dust-free and I just plain love the sound. Even sharpening the blades is not a chore when they are good steel. A good plane is the most perfect tool ever created. Don’t forget it’s little brother the spokeshave either. I wish I had a drawknife . . .

I’m rather astonished by that statement. Efficient use of time and environmentally sound materials does not compromise design and requires more, not less craftsmanship for a satisfactory and enduring result. Sanding to get a smooth surface is fine, but sanding to get the shape right is often a fix for an error.

Speaking solely for myself, I use wood whenever I can and minimize the use of epoxy. I very rarely use filler or fasteners and avoid glass in all its forms. I build my boats in such a way that fair shapes result from the natural bending of the wood. The long, smooth lines of a chine log are a consequence of accurate cutting with a good quality finish blade and good planning, and it’s at least the visual equal of any strip of plastic under the Sun no matter how painstakingly faired and sanded.

While on the subject of efficiency, I take some pride in getting the maximum results for each hour of work. I arrange the order of planking to permit the use of a router to trim plank edges, with the previous plank used as a guide, and to maximize the width of the glued joint. There is very little sanding to be done, and the resulting boats are very light, and strong for their weight. Their strength derives from careful planning, whatever little craftsmanship I possess and the properties of the wood, rather than the investment of hours of manual tedium and being encased by high-tech materials.

 

What I meant was that you build a frame. Maybe a bit lighter than the actual skin on frame, you glue plywood planks to the frame after fitting them to each other roughly but no epoxy putty between the seams and then instead of putting glass and epoxy on the outside (and a lot of sanding in between each layer of epoxy) and then paint (and again sanding and another coat of paint and sanding again), just to put over the plywood a ballistic nylon or pvc, maybe with a bit of glue between the plywood planks and the inner side of the pvc. You save the epoxy, glass and paint, you save all the sanding and you get much more robust boat then just skin on frame. Since I did not see something like that anywhere, there must be something in that system that has a big down side to it that I do not see. I was wondering what is that downside.

ancient kayaker, i appreciate your thorough answer. in this BAD system i like the fact that i could use as little epoxy as possible. I could not understand how you connect and seal to be water tight, the longitudinal seams between the planks? also, did you mean that only between the bottom plank and the bilge planks you use epoxy (do you use putty and glass tape in this case?) in the seams because it has the most exposure to water than the other seams (bilge planks to sheer planks) ? is it enough to plan the longitudinal edges of the bilge planks and the longitudinal edges of the sheer planks to fit and put glue on the planed edges for the planks to stay glued? (something I could never manage to do on a 4 or 6 mm plywood with a planer. maybe with a router) Or you use some kind of other longitudinal narrow pieces of wood along the seams, (shaped in the proper angle to fit the seam angle) to increase gluing surface? (“Add pieces of wood called cheeks to the stems to increase gluing area for a later step”.) Is that it, or I misunderstood this phrase?

And about the debate regarding sanding, I do not have good craftsman skills. I love building but I am terrible in the little details. My work is relatively well functional but always looks less then average. I learn to accept it and I am looking for systems to fit my skills and working ways. I think it is about not getting the pleasure out of investing many hours in the work of beautifying the things I am working on so I am looking for short cuts on the expense of the fine end result. I know that there are people that their favorite part is beautifying their work. I respect that a lot because that is something I am not able to do and their work looks amazing. Maybe it is this Zen thing about learning to enjoy something that to me seems boring and monotonous.

thanks you all for your interesting comments

 

and i forgot another thing regarding working with epoxy. i could work here with epoxy without heating the workshop especially for it to cure, maybe 4-5 summer month a year and in these month i try to sail as much as i can (beside the job i should do), so winter is great time to build a boat.

 

+1 on using the router as much as possible. Especially on a hard chined boat, a rounding bit is magical in how much time it saves and what a perfect curve you get!

Yoram, I think you are referring to a very well established boat building system that came out before epoxy, which is called plank on frame. I have never built one that way because it is essentially the same as using a chine log, except you have the extra work of building a frame. It works better for larger hull forms though. But for a canoe, making identical panels and directly connecting them to one another is the simplest, fastest way to go.

Yoram, you are thinking too much . Break out that wood pile and post some pics!!!

 

Yoram: I use epoxy for the joints between the bilge planks and the bottom plank, and between the bilge planks and the sheer planks; 4 joints, o rather seams, in all. Epoxy is highly resistant to the exposure to water that these seams get, and being gap-filling, does not demand the perfectly fitted joint that most other glues require. It is more difficult to get a perfect fit on a rolling bevel that is being cut on a poorly-supported plank edge, than it is between a straight chine log and a flat ply plank, so a gap-filling adhesive is necessary. I do not use glass, either cloth, tape or mat.

If the angles between the bilge panks and sheer/bottom planks are constant for the entire length it is theoretically possible to pre-plane or route the bevels. In practice, even when I attempted that it didn’t work out; it requires considerable pre-planning and precision and I find planing the rolling bevels is fairly simple; I use a power plane so there is very little force to distort the planks, and fit it with a large ply foot plate that extends across the entire width of the gap between the bottom and sheer planks, where the bilge plank will go.

For these 4 seams I use an epoxy formulation that is self-thickening and is applied from a tube using a caulking gun; there are several on the market from manufacturers such as System Three. It is rather expensive but since I use so little the convenience and assured results are worth it IMHO. I don't know if it is available in Denmark and shippers may be reluctant to transport epoxy.

The angle planed on the bottom plank is about 150 deg so it’s width is double the combined thickness of the plank and its pre-attached chine log. The bevel angle on the sheer planks is not as sharp, but the chine log is thicker so the joint width is about the same for both seams.

When using epoxy on the bilge planks the hull is inverted and no longer has any gaps, if both planks are done at the same time. The temperature can be raised to speed up epoxy etting by a simple light bulb, if the location is sheltered from the wind.

Peter is right: just do it; you’re running out of excuses!

 

Guys, thanks for the encouragement.
I have just finished building a canoe and I am getting all this info because I am dieing to start building a new boat but I have to wait for a few things to happen here. I am living in a special school here and conditions right now are not favorable for building but it should change in a week or two. I am “brewing” now on all the options for the new boat to build, hence all the questions. I want to build them all!!

About the system of boat building, I still think I am not making myself clear. I am asking if it is possible instead of coating a canoe with epoxy and glass and paint, or just with epoxy and paint, which needs a lot of sanding, to coat it with pvc like the skin on frame guys do but on the planks. The main point in the question refers to the outer layer. The canoe gets a water tight coat that doesn’t need any fine finish job of sanding and painting. What is the downside to that?

 

Interesting idea. Not sure how well it would hold up though, and not sure how you would fix rips/gashes/scratches. You could coat it in a skin of polyester or nylon fabric I suppose, then paint it in polyurethane, that's how most sof guys (including myself) skin their boats...

But you don't really have to coat a canoe in epoxy at all. Even just a couple coats of latex paint should be fine especially if it is stored indoors.

I am still not sure exactly what you want to build though, since it seems you already have a ply canoe but all your questions seem to concern a ply canoe

 

I am not sure myself yet about what I want to build. it started with idea of building a canoe with students here in the school but this has been delayed now to an unknown time so I still have the urge in my fingers to build a simple boat on my own. I might build another canoe. It is the right weather for epoxy but some how I am more incline to sof in order to learn a new system. I am brewing with all the information and since I have very little basic knowledge, when I read something about the subject, still there are many “holes” even after understanding the concept so all kind of questions constantly come up.

I found out 2 hours ago that we have here in the school wood strips that I could use. tools and glue are just there in the workshop to be used so I have material to build a frame for sof canoe though i like the one sheet canoe too. I red the Jost web site. He uses pvc to cover the frame. in some other places I saw sof with ballistic nylon and special material they apply on it to seal it and I also got this book from about 60 years ago that has all kind of boat plans including sof canoe and they use canvas and apply some other stuff on it that I do not remember now what it was.
Another problem I have is that I see on the net all the building materials but they are in English not in Danish (which I do not speak. I am from Israel, working here for some time in a kind of international school) but still I could at least try to find out once I have the Danish proper name. for example, Jost is using pvc which could come in so many different forms. We have pvc here that comes in big rolls and we use it to cover the floor and furniture when we paint the place. I have no idea if it is the same material that Jost is using in his boats. So I need to ask many nagging questions.

For example you wrote “You could coat it in a skin of polyester or nylon fabric I suppose, then paint it in polyurethane, that's how most sof guys (including myself) skin their boats... “
Sounds simple but polyester, polyurethane, are the chemical name of so many different product and nylon fabric has also so many different products. When you build something, you want the right product for your specific purpose and I have no one to ask in Denmark.
I try to ask around. There is a boat builder in the marina and there are 2 really big boat shops in the aria and they are willing to help but they never heard about sof system.

So I try to gather info any way I can with all those nagging questions. I really appreciate the time all of you guys put into answering my questions. I am learning thanks to you.

 

Adding a nylon or other skin over ply to avoid using epoxy is wasteful. A skin-on-frame boat makes more sense. Nylon is easier to work with than PVC IMHO. You will notl ikely find professionals building SOF boats as the buying public do not perceive them as durable.

Ply on frame is a heavy construction best suited to thicker ply with a heavy frame that can be nailed, and predates the development of epoxy and marine ply. The frame must be stronger than for glued construction to hold shape while the ply is added.

A marine ply hull glued with epoxy along the seams - regardless of what glue is used elsewhere - is a monococque construction where the strength is in the skin, like a modern airplane or car. There's some serious science and engineering behind these developments.

It is no big deal to make a fair, waterproof boat using either the stitch and glue or my preferred chine log method. Very little epoxy is needed. An alternative is to add an external chine log and drive small screws through this into the internal chine log. It is heavier but eliminates the need for epoxy, a good sealant will do within the joint.

As far as the finish is concerned, I use a coat of sanding sealer to lay the grain, since that tends to rise when using water-based paints. It is very easy to sand and get a smooth surface. Then 2 coats of latex primer, each one sanded, and 1 - or better 2 - top coats of outdoor latex paint. A semi-gloss looks better than full gloss in latex. Such a finish will lst for years on a small boat that is hauled out of the water after each trip, as most kayaks and canoes are. It would last for about 25 years on a house.

If you want to go ape-sweat to get the the furniture-quality finishes that some boats boast, a high-quality marine paint or varnish with up to 12 coats - each one sanded and the last 3 or 4 wet-sanded - would be required. Personally I think that kind of finish is more appropriate on a piano . . .

 

I guess that we would all love to have a hard finish without the sanding.

If you buit a frame work from plywood, and oiled it well, and applied some sort of skin to it, that might do away with sanding FG/Epoxy, which is the unpleasant job.

But then you have a softer skin, with all the downsides to that.

There is a club that actually enjoys sanding fibreglass and epoxy - but the president is dying from some lung disease and the other member has pulled a muscle in his back, so they arent much help these days.

But seriously - if you wear the right gear, keep a vaccum handy, and dont overdo it, the sanding part for a plywood craft is not a huge job, especially with the judicious use of peelply on the fibreglass

see http://www.boatdesign.net/forums/materials/peel-ply-14461-2.html#post467447