Grand Laker Gunnels

[chrisg]

I am wondering if anyone has ever done a mortise and tenon joint instead of scarfing ash for their gunnels, Canoe is almost 21 feet long and I could not find any boards of that lenght for a resonable price, I bought a couple of 8 footers and I am looking at 3 possibilities for joining them:

1 - Scarfing.

2 - Laminating thin strips and stagering the joints.

3 - 2 inch mortise and tenon (anyone have a trick for cutting these on an 8 footer, I have a tenoning jig for my table saw but I would need to haul everything outside for clearance)

I would think the laminating or tenon would create the strongest gunnel, scarfing would be quicker but a weeker joint. Just looking for some opinions and pros and cons of each method.

[Tom in MN]

Scarfing by far is the best choice. Mortise and tenon is the worst choice. If you do the scarf joint properly (8:1 or 10:1) scarf, pre wet the wood with unthickened epoxy and then adhere with thickened epoxy the joint will be stronger than the wood around it. If you don't believe me, try it. Make a couple of scarfs the right way (it will be good practice), then try and break them. I'll bet the wood breaks in other areas before the scarf joint gives. The lamination will not be as strong as the scarf, as in the lamination, your weakest point is at any seam, because now you have lost that fraction of the total thickness. So, if you have three layers, at any joint the gunnel is only as strong as two layers. One scarf stronger than the wood around it is much better. there really is no sacrifice in strength in a scarf, the downside is the extra labor it takes over a full length piece. but, 21' boards are not cheap or abundant, so one must do the next best thing, a scarf. All the methods will work, and even full length gunnels can break as well.

Take it from one who has tried all the methods, the scarf is the best way to go. Rough cut them on a band saw, then use a sanding disc with a jig on the table saw to true them up to the right angle. Or, build a quick sliding jig and just cut them on the table saw.

[chrisg]

Thanks, that's what I wanted to hear, I would much prefer to do a scarf joint, and had pretty much settled on it, but wanted to explore other options after reading some of the builders experiences with failed joints. The bend is not too dramatic on my canoe so I should not have any problems. I am also thinking that the laminated ones would be quite a bit heavier due to the extra epoxy needed. I will give it a go this weekend.

When you mix your epoxy, do you use micofibers or just plain sawdust, I am using the West system, I have read a few threads that mention using sawdust and am curious if it would be suitable.

[Glen Smith]

As a thickening agent you should use the microfibers, sawdust or rather sanding dust is added in small quantities to obtain the desired colour.

[pyrofly73]

I don't buy that explanation on how the lamination is weaker. In a scarf you have a joint(seam) that is max about 12" long and as you point out when tested it will break else where. Then you point out that a lamination's weak link is the seam
"The lamination will not be as strong as the scarf, as in the lamination, your weakest point is at any seam, because now you have lost that fraction of the total thickness." it seems contradictory to me.

I have not built my first canoe(yet), but have plenty of experience under my belt building and fixing other water craft. every time you want something made out of wood to be dimensionally stable, rigid, and super strong the lamination wins. Your glue joint instead of being 12" suddenly becomes 20'. and as for the thickness. you could theoretically build up your laminate till you had 6" gunnels if that is what you wanted.

you could also use smaller pieces of wood, by staggering the joints with no ill effects. lets not even bring installation into the equation. what do you think is easier to bend into shape a 1/8" layer of maple or ash or a 3/4" board.

think about it.

Xavier

[chrisg]

I had not considered actually building the lamination on the boat itself, I was thinking of doing it on the bench and then mounting the same as a regular full lenght gunnel, would definitely be easier bending thin strips, I planed my ash planks this weekend but held off on ripping them, now I am really not sure what route to take, I will think about it for a while.

[David James]

Chris G, I completely agree with Tom in Mn. The scarf joint is best for this job. Get yourself set up with a sanding disc on your table saw and get going. Be sure to presoak the two surfaces with unthickend epoxy first, don't clamp too tight and you'll have a nearly invisible joint. When you're done you will wonder why you fussed about it.

just my opinion...
Dave

[Tom in MN]

Pyrofly,

Lets say you laminate three pieces 1/4" thick to make a 3/4" thick gunnel. If you use a butt joint and stagger your seams, for most of the gunnel you have 3/4" thick wood that is probably a bit stronger than a piece of solid 3/4" thick lumber. However, every place you have a butt seam, you really only have 1/2" of wood giving you strength, because the butt joint provides no rigidity. If you do a 10:1 scarf with 3/4" stock,, you have equal strength along the entire gunnel. If you laminate, you have a few points where you have only 1/2" of strength. Now, if you scarfed the strips and then did a laminat, you might come closer to the strenght of a regular scarf. This is not to say that the 1/2" at the seam would still no be strong enough to serve it's purpose. When you laminate anything, and use a butt joint, your strength, at the joint, is reduced by the strength of one layer of laminate. That is why if you every read about plywood joining using a backer plate, the plate is always recommend to be a lot thicker than the plywood you are joining. Laminating gunnels can work, especially if the bend is really tough but a scarf will always be stronger if done properly than an equally sized laminate.

[Glen Smith]

If gunwales are laminated right on the boat and epoxied to it at the same time, you would be faced with the hassle of cleaning up the lower edge, I would steer clear of that route.

[chrisg]

Thanks all for you coments, Glen I agree it would be a mess to clean up, I do however plan on gluing them onto the boat, so I will have some cleanup to do. I will go with a scarf and offset the joints on the inner and outer gunnels.

[AlanWS]

I agree that scarfed gunwales are strong. There is one situation where a lamination makes sense: when you are trying to save as much weight as possible. Then only the outer layer needs to be ash or other hardwood, and inner layers can be lighter. But I would scarf join the ash outer laminate layer.

[pyrofly73]

Concerning the mess....

a couple of strips of 3" 3M blue tape would allow you to laminate the assembly using the hull as the form. After removing the tape you could then glue the entire assembly as a unit once the epoxy has cured (it could also be finished off the boat for the most part)

concerning Strength...
I understand the logic behind the 1 layer being but jointed hence the presumed weak part... I think that this might be a little 2 dimensional in your thinking. Imagine your solid piece of wood being stressed... eventually the wood would tend to split along it's natural grain. The strength of a built up laminate comes from the fact that the natural grain of the wood is broken up. even though as you point out dimensionally you would have a weak point (debatable). In realty the thinner structure is stronger. Also the laminate can be built up using any girth I suggested 1/8" for ease of assembly. this would also make the weak spot theory null.

Why do you see martial artists breaking strips of solid wood and not 3/4" cdx?

From the research I've done getting ready for my first canoe build I found John Michne's Ideas awesome. Take a look at this link.

http://michneboat.com/Gunwales.htm

I think by starting the first strip with the blocks then moving to the protected hull you could finish the assembly very easily and much much stronger than a solid piece.

Xavier

[chrisg]

I had read John's article, and really like the look of those inwhales, I may try something similar. Canoe is just under 21' long, 45" wide. For the outwhales I was thinking of ripping my planks to 1 and 3/8 and then scarf them and plane down to 1 and 1/4, they will be 3/4" thick, planks are 8 feet long, so I will have two scarf joints in each gunnel. That may be a bit of overkill, but since this will be motorized, I want it quite solid, hull strips are 3/8". For the inwhales, I was thinking of a bit lighter, maybe 1" X 3/4" What dimension do you use on your canoes? Does this sound like way too much for the style of canoe, I have read 3/4 X 3/4, but that seems a bit small on a freighter canoe.

[pyrofly73]

Are you building the grand laker with a transom for the engine? I was considering that design for my boat. But i really want a canoe that is pointy on both ends. :smile still a coin toss as I can really use the capacity of the grand laker.

have you weighed it? using 3/8" for stripping I assume this is going on a trailer?
Did you build like gilpatrick without the stems?

1-1/4" outwales would probably look alright on a boat as large as yours especially if you put some sort of taper into them. You could always shoot an email to Gil info@gilgilpatrick.com and see if he has any opinions to size...

Xavier

[chrisg]

Yes, it is square stern, will be trailored and powered with a 9.9, built a la Gilpatrick, capacity was my concern too, hunting and hauling back my catch, but also like to have a few luxuries with me when camping with 3 dogs to haul and long distances to cover. I have a 17foot canoe and 14 foot Kayak for the leisurely paddles, this is more of a work horse.

Have not weighed it yet, I am curious to see how much the finished product will weigh.

I have e-mailed Gil a few times, he is always quick to reply.