Wood and Glue for Sailing Canoe

I’m building a 15’ light sailing canoe/kayak with ‘some features’ similar to the Dierking Ulua. The build method will be 6 plywood planks fastened to stringers. The stringers will be fastened to the stem and stern and to a ring rib (no bulkheads) at the ¼ and ¾ positions on the hull length. The fore and aft quarters will be decked. The hull will not be glassed; but instead will be sealed and painted. I have checked out materials and have the following queries:

Stringers – I plan to rip the stringers, including keel and stems, from 16’ length of 2 x 6 either lodgepole pine or ‘clear’ cedar (Northern White cedar, Thuja occidentalis as opposed to western red which is Thuja plicata). One exception might be hemlock fir for the gunwale and laminated ply for the upturn on the stems. Are these good choices or are there better options?

Plywood – Marine plywood is limited in my local. I’ve narrowed the choice to 4mm, 3 ply South American mahogany (the core is not the best in my opinion). For ‘half the price’, I can buy non-marine (but exterior glue) ¼ Russian Baltic birch (5.2mm, 5 multi-ply) with guaranteed no voids. This is imported from Russia (not China) and made from northern trees. Since the canoe will be dry-sailed and stored when not in use, and if properly sealed and coated, can I get away with the birch plywood?

Glue – As an alternative to epoxy and glass, there are several much lower cost options such as: Gorilla glue, Sikaflex 291, Slick Seam, 3M 5200, or the latest version of PL Premium construction adhesive. I’m leaning toward the latter. Most of these are polyurethane glues. Are they all equally as good for intended purpose, or are certain ones better than others?

 

Your method of construction sounds similar to my own. I built a couple of successful canoes using marine ply (Okoume) with cedar stringers along the chines. I use laminated pine and cedar for gunnels which looks nice. I have used Baltic birch ply which I have found to be excellent, but heavier and stiffer than Okoume; I find it good for inner stems, knees and seats.

Where I can get a perfect joint, I use Titebond III which is strong and grabs quickly. I formerly used Gorilla Glue with success, it is strong and also expands to fill a gap but gets weaker as the gap gets wider; what foams out of the joint is soft and very easy to clean up. I have had success using Premium construction adhesive as well. All those adhesives need to be well clamped. If I can force paper into a dry-fitted joint I use epoxy, clamping is less important so long as the joint doesn’t move during setting, however it is harder to clean up.

I have used latex house paint (3 coats), porch paint (2 coats) and water-based urethane varnish (7 coats) with excellent results, however I never leave any exposed end grain. I never use glass and for normal use my boats last well, but they are not suited to hard use such as white-water, cruising or assaulting rocky beaches, and they are dried after each use. As an experiment I stored one outside uncovered during a harsh Ontario winter and it survived fine. It started out right side up but I found it half-filled with water and snow so I emptied it and turned it on its side against a fence. Then it got buried under several feet of snow and ice and stayed like that until the thaw; only ill-effect was a slight flattening of one gunnel. One caveat though, my boats are not for sailing which imposes far more strain than paddling.

I find it easiest to glue the stringers and inwales to the sheer planks using Titebond III then bend the sheers to shape and plane the stringer/ply edge to fit the next plank, for that joint I use epoxy. My stringers are between 3x and 4x the ply thickness. If you plan to bend the stringers around the mold then glue the planks to the stringers, the stringers will have to be thicker to resist the force of planing and clamping the planks. When I use ribs they are added after the hull is built so they are no help during construction.

Good luck!

 

AK - Thanks for your detailed input as well as your input on initial thread when I was planning the build-mode for this project. As you note, extra reinforcement is required in a sailing canoe. This will be provided by having solid ribs at the fore quarter, midship and rear quarter. The fore/aft ribs will be a continuous one-piece ring so that the sides and decking are fastened to a solid base at this junction. The fore will be a thicker rib (likely laminated) as this area is where iakas will be attached and later integrated with a thus-piece for the mast. That's great that you found success with cedar and pine for stringers and gunwale.

There is one question I have related to stringers. Since I am lofting the strakes, it stands to reason to attach the stringers to the ribs and stems so everything stays put during the lofting process. If a stringer is ripped from 2 x 6, it will be 1-1/2" wide. I was planning to have two adjacent planks overlap the same stringer (3/4 inch each to the center), even if this requires a bit of beveling on the stringer. I am thinking that this way, the outside seam would be easier to fill and would eliminate taping on the inside. I was considering fasteners/staples for the plank edges, but a good job of gluing should be adequate. I'm interested what you thunk of this idea?

 

1-1/2" sq stringers should provide sufficient gluing area for 2 planks of 4 mm ply, nearly 5x the thickness, but at 3x is not really enough to hold 6 mm ply. You want the joint strong enough so the ply breaks first, otherwise the joint may "unzip" under stress. It's not the glue that breaks when such a joint fails, it's the outer veneer that splits across the grain. However, I don't use tape or glass cloth in my boats and the seams with the stringers (also called chine logs) are as strong as the ply.

You can hide the outside seam by bevelling the planks slightly if you wish, but the planks have to be fitted perfectly. Alternatively and much easier, put on one plank at a time and plane its edge down to the stringer before adding the next one overlapping - this exposes end grain however. How picky are you?

For a boat with gentle curves like a canoe the planks will bend easily. The main problem will be flexing of the stringers as you plane them, with only the stems and 3 frames/ribs to hold them on a 15' canoe they will be bridging gaps of about 4 ft. If you add temporary frames between the ribs that will reduce the gap to about 2 ft and the stringers will flex far less.

To plane the bevels, add an extension on your plane that can ride along the adjacent stringer. Be aware of the fact that the plank bending axis may not be normal to the direction of the stringer, that will affect the bevel angle. You can check this by dry fitting the plank and noting how it bends, then if necessary touch up the bevel with the plane extension across the bend. Make the length of the extension at least 1-1/2 times the greatest plank width to allow for this. It's much easier to do than to explain.

A good glue joint is stronger than any fastener, however fasteners resist shock better than glue. Also fasteners are handy to hold the joint together while the glue sets. If you decide to use screws, put in steel ones for gluing and change them to brass or (better) bronze after, as steel is stronger.

For my light duty boats I use staples and remove them when the glue has set. Staples are only needed on one side of the plank, the other side can be clamped of course.

Hope I'm not giving too much detail here: I tend to revert to lecture mode when giving advice!

 

AK - you're one of the best at the finer details! Several points to clear up. First, you're right about the number of station molds, as I failed to mention that I was planning 7 stations (3 permanent and 4 temporary). As a result of your positive feedback, I will be using the white cedar and pine for all structures, even laminated ones.

As to plywood, the Baltic birch is 5.2mm, 5 ply (thus much stronger), but at the same time lighter and more bendable than the 1/4 (6mm) marine fir; which definitely rules out the fir. I think I will visit the Windsor Plywood store again and weigh a sheet of the mahogany and the birch. There is a question among woodworkers of just how 'waterproof' the birch glue is, but I may be able to identify this through the supplier. This might be worth doing before I purchase; especially since I want a light boat. The amas will provide some extra stability.

I need to clear up one issue; maybe due to the way I wrote it. You noted stringer at '1 1/2 sq.' but I was thinking 1 1/2 wide by 5/8 thick. According to your formula, this should do with the 4mm planks - you think? I will be lofting and fitting each plank as I go and bevel stringer only if necessary, as you noted.

You wrote

Did you mean this as written? Will proper copper shank boat nails or rink nails be okay for fastening to the 3 permanent stations? I will use your idea of staples for plank to stringer until glue sets.

It's interesting to find someone who uses alternative glues, as many refer to epoxy as supreme and all else as junk. Somehow, this doesn't sink in for me, given I grew up in a land of wooden boats and marine paint!! I like your idea of gluing strake to stringer and use epoxy for the outside seam. If a narrow strip of glass was used on the outside seam only, would this add much weight and could the stringer be less studier in that case? I have seen others use a narrow aluminum strip along the keel line and for fore stem as protection in small sailboats. Is this a feasible option to glassing the bottom in a canoe?

Thanks for the great info, AK!
SR

 

Baltic birch has generally high sugar content and it's easily infected by all kind of microbies..
"glue" is generally a film used in most plywoods nowadays and it's waterproof..

 

Are you using both 4mm marine ply and 5.2 mm Baltic birch? a glue width of 3/4" for the Baltic birch may be marginal unless you are just using the birch for the extra thickness or stiffness; for 4 mm marine ply it should be fine. I use this formula as a guide but always make and break test pieces before building a boat:

Let R = (with grain strength)/cross grain strength)
Then minimum glue width = sqrt(R) x T (ply thickness)

Lots of times I have discovered that I can reduce dimensions or reinforcement; a lot of the “rules” are driven from practices that do not take full advantage of modern materials and adhesives, or have allowances for loss of strength in wood that is saturated which does not happen with a “dry-sailed” boat. However, I am a bit worried about reducing the depth of wood behind the joint to 5/8" especially for Birch; you should test that!

There are places where the glue joint does not normally get heavily stressed, such as the gunnels, especially if you use “wrap-around” laminated gunnels as I do. not sure if that applies to a decked canoe.

The advantage of screws for clamping the glue joint is, no vibration. Staples are OK too. The steel screws resist wear and breakage during insertion and removal. The brass or bronze ones look nicer and resist corrosion; you can also use stainless steel, but personally I like to give a little nod to tradition once in a while. I haven’t used copper boat nails but that’s traditional and it’s worked in the past!

Actually epoxy is supreme! But the rest is not necessarily junk. Titebond III is far stronger than any wood you are likely to use on a boat. Where epoxy scores is when the wood gets soaked with water; epoxy holds better than anything else then. But if your boat stays dry behind its coats of paint ... Epoxy also has better hold on end grain than anything else I know, up to 70% of the strength of Okoume, but I don’t rely on it.

Glass tape on the outside does not add much weight but that does not allow the stringer to be downsized. The glass works best in tension; its OK when used on both sides as is usual in S&G construction but stringers don’t allow you to do that.

I use brass strip to protect the stems and run it partway along the keel. Looks great, hides end grain and limits damage if you hit a log or a deck.

Don’t forget to post photos! When we’re not building ourselvs we can live vicariously on the efforts of others!

 

AK wrote:

I am going to go with the 4mm marine ply. I did some further checking. The Baltic Birch supplier informed that while the inner cores were solid ***** and void free (thus good exterior grade), the WBP phenolic glue was not of the same quality as that used in marine grade plywood. And also, thanks to Terry for the 'sugar/bug' tip about birch! By the way, I finally located a reasonable price supplier for clear grain western red cedar, so I'm checking that out too.

Ak wrote:

I will be doing that. There is a nice thread here by Geoff C. http://www.woodenboat.com/forum/showthread.php?t=89466/htm who is nearly finished a sail canoe where gunnels and decking are integrated at the fore and aft ends. I will also be using extra ribbing where the akas cross the deck.

I really appreciate the info on the brass and bronze screws and will definitely look at Titebond III. Elsewhere on this forum, I happened on a reference to one-part plastic resin glue at LV. It's in powder form that you add water to and was toted as having decent gap filling properties, sands well and is inexpensive compared to epoxy. I'm not what this is? By the way, which epoxy do you use and where would one buy a brass strip such as you used for the stem of your canoe?

I'm planning to start in first week of March and hopefully ready to launch when the ice and snow has melted!

 

Nice boat by Geoff and great pictures too. I noticed he used glass inside and out with no stringers, minimal fairing and few bulkheads and frames. The glass reinforces the seams and at least doubles the strength of the ply so effectively it becomes a glass-fiber boat with a wood core. I noticed that his plank joints, which are probably scarfed, are at the same longitudinal location - It is considered good practice to stagger them, but with 2-sided glass he can get away with that sort of thing. He put the inwales in after building the hull; I find it easier to put them on the sheer planks before hull assembly provided the hull shape is not extreme (easy sheer bends).

Titebond III is fairly easy to get, most hardware/lumber stores carry it. It grabs quite fast so you have to clamp it within 10 minutes or so, but slightly moistening the wood before applying the glue will give you about 20 minutes working time and does not weaken the joint according the the manufacturer. I remember using a one-part plastic resin glue many years ago, it was great, but don’t know if it is the same thing. at LV. Check on its waterproofing qualitites.

The epoxy I use is from System Three, 1:1 mix which I find easier than 5:1 and other ratios. S3 also have their epoxies packaged in very neat self-mixing cartridges that fit into a caulking gun. Very convenient and easy to use but a bit pricey. Any boatbuilding supplier will carry the brass strip which usually comes in a couple of widths (I use 3/8) and can be obtained pre-drilled. Accurate drilling can be difficult if you don’t have a drill press. You can google for boatbuilder supplies in you area alternatively Noahs will ship anything http://www.noahsboatbuilding.com/noahmain/index.asp

As a last thought, you will have noticed the clamps. You will never have enough, especially when attaching stringers and inwales to planks. A good tip from elsewhere in the forum is to slit a 3 or 4 ft length of 1.5" to 2" plastic drain pipe then cut it into 1" lengths. These make great clamps for thin wood not requiring heavy pressure, and they don’t seem to mark the wood either.