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Attaching one-piece gunnels

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Sep 4, 2019
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Hi - after three weeks of mangling several pieces of perfectly good cedar and about half of a 5x18 board of ash, I finally have a serviceable set of one-piece ash gunnels ready to install on my canoe (wanted cedar for its lighter weight but finally bit the bullet on ash, which will cost me over a pound extra but is a lot better suited for the job I think). They are 13/16 wide by about 7/8 high. After sealing the groove with a coat of epoxy, I would like to screw them on with stainless screws from the inside and use a marine bedding compound to keep water out and firm everything up (even though they are only around 4.5 pounds I still haven't given up on something a lot lighter so want them to be removable). Have only heard of thickened epoxy as a way to install one-piece gunnels - does this screw-on approach raise any red flags?

Thanks
Tony
 
Jim will of course disagree with me but I never glue gunnels on. I always counter sink the screw head, always use stainless and be very careful not to go all the way through. I predrill through the inner gunnels and the hull and slightly into the outer gunnels. I also use a cordless drill for the screws and set the torque down a ways. Good luck on whatever you decide to do.

Personally I would skip the Marine compound, just make sure the gunnels are well oiled before you put them on and with wood you will need to be willing to do some annual maintenance.
 
I never glue my gunwales in as I know down the road they will have to come off for one reason or another. Like BWCA I countersink the screw holes and then starting at the middle with many, many, many claps work my way out to the ends installing the screws. I am a varnish guy, an age old debate about treating gunwales! ;-)

dougd
 
I have done many one piece gunnels on my boats, but I have always filled the slot with Cabosil thickened epoxy and been done with it, no screws whatsoever.
I have used the thickened epoxy to fill the inevitable variations in gap between the gunnel slot and the sheer line section.

If your sheer line is very uniform in thickness (mine do vary) then half the battle is already won.
An issue might remain, depending on how tight a fit you have between the gunnels and sheer. Any gap will be taken up by the screws you use drawing the inner part tight to the hull as the screws bite into the outer part of your gunnel. In order for that to occur, your gunnel will need to deflect, which it likely will, hopefully without cracking.

As long as you have as tight a fit as possible, you should be fine.
Another issue to consider with a one piece, slotted gunnel is that they have considerable strength in both planes that you need them to deflect to match your sheer line profile. Depending on your hull shape, those gunnels may fight you as you force them to conform.
I would be sure to clearance the inside hole and the hull as you drill for the screws...the screws should only grab the outer part of the gunnel, any other condition will waste the tensile pull of the screws, and potentially leave the gunnels loose on the hull.
 
One piece gunnels are a challenge !

I set my Inwhales about 1/8" high, and the outwhale is cut to cap the hull. It closely resembles a one piece, in that it covers the top edge of the hull ( Shearline)

The advantage to me capping the hull and epoxy is the extra strength, and sealing moisture out of the gunnels. The moisture is the real detroment to gunnels. If it can enter screw holes, or gaps. It will and drasticallt shorten the life of gunnels !
I've replaced gunnels on several hulls that were screwed on in place. I have yet to replace gunnels that were glued . Period.

Cutting the upside down " L" shape in the outwhale, is the rare time I use a Tablesaw for building my canoes ! I could do it with a router, but I have much better luck with the Tablesaw !

This first pic is the gunnels prefit, ready for epoxy + filler, and install. Note the screw holes in the inwhale. They will be covered, by epoxy and the outwhale. NO screws showing ! The way I like it !

IMG_0410_zpsjpxyhgj8.jpg

IMG_0410_zpsjpxyhgj8.jpg

IMG_0410_zpsjpxyhgj8.jpg
IMG_0410_zpsjpxyhgj8.jpg
 
I am with Stripperguy, saturate with unthickened epoxy, then use thickened .... I like to prepare the hull by applying painters tape just below where the uniwale sits, then when the thickened epoxy squeezes out, it is easy to use a finger to remove the excess and form a small fillet where the gunnel end meets the hull. This creates a very tight seal inside and out, looks very good as well.

The fact that it is glued also provides maximum strength along the gunnel ...

Brian
 
If screwing I don't see the advantage of using a single piece gunwale. Would be much easier to use separate inners and outers in that case.

Alan
 
Thanks for this guys.

Jim, right now I can only aspire to the level of precision and, well, beauty of the boats you produce. I am working on it but still have quite a ways to go. I find it interesting that the capped approach you use will get virtually identical results as a one-piece design, but looks like it can be done with much beefier gunnels than what I find manageable to install in a single piece. I will definitely remember this for my upcoming "spring" build. And I really like those "arrowhead" decks that wrap around the inwale ends. Do you glue the remaining outer gunnel ends as well, or use screws at that point to go through to the edges of the decks?

I am committed to the two remaining one-piece gunnels I have left for this build (I basically chewed through almost all my ash, including having one gunnel split on me under some light persuasion from a rubber mallet at the point of install, and one ruined when I stupidly forgot to lock the table saw fence for my last cut of the slot). On top of 3 or 4 failed or unsatisfactory attempts to make one-piece gunnels from cedar, I don't have any stock (or patience) left to try another.

Because of that, the point that Stripperguy made about the deflection of the gunnel side pieces, possibly to the point of cracking, when screwing them on has put the fear of God in me. I did not think of that but it is for sure a risk. I cut the slots wide enough to fit over the sheer lines without too much drama, and in dry fitting them I can get everything lined up and flush with the sheer line with duct tape alone (very gradual rise from centre to bow/stern in this boat). But this means there are definitely some side to side gaps at various points, such that they can wobble just a little them side to side once dryfitted. A quick measurement shows the gaps to be a little over 1/16 at the widest points, which the ash probably can handle in deflection, but even if it does its an additional source of constant tension once installed that might make them more vulnerable to splitting when they inevitable get whacked by something. So I am scrapping the screws and going back to gluing them on with thickened epoxy.

So on this, what exactly is Cabosil? I have seen it referenced a bunch of times in this forum but don't know anything about it. I was planning to just use wood flour to thicken the epoxy - I am using West System, and I know they have a bunch of fillet and bonding thickeners that if advisable I can get if I need something more or less equivalent to Cabosil. Also, how thick should the epoxy be - ketchup, mayo, or peanut butter?

Thanks again for all this input and help from everyone. Very much appreciated.
 
My outwhales are glued. The inwhales are glued and screwed. I've been using #6 stainless screws. They weigh next to nothing, but make it a breeze when I'm installing the inwhales, dripping with epoxy !

Cabosil is essentially a thickening agent, that you add to mixed epoxy. It works great and is weightless. I like to thicken epoxy to Peanut butter consistency.

Great advise from others also.

Good Luck with the one piece installation !

If you saw my first canoe, and compared it to the last one I built, you would likely be surprised at the improvements I've made over the years. I was a Slow learner ! School of Hard Knocks !
I'm positive your next build will be better !

Jim
 
You don't have to use cabosil, the idea is that unthickened epoxy (that is just catalyzed epoxy with nothing added) is good for soaking into wood etc, but if you add it to a joint, it will also just run out ... leaving gaps. By soaking/coating the wood with unthickened epoxy, gets a good base, using a thickener (think peanut butter) makes it so that you can put the epoxy in with out it running out.

To thicken, add your thickener, cabosil (fumed silica) will give an opaque finish, in your case wood flour will work just fine. Wet out surfaces with the unthickened epoxy, then thicken the remainder to the consistency of peanut nutter, slather and apply your gunnel ... this is where I like to have the painters tape already applied, it gives a line for wet out and when the gunnel is in place, it makes excess removal easier. Just use a finger/cloth/papertowel etc, to remove excess.

Brian
 
Put your thickened epoxy in a zip lock bag, seal it, and clip off a corner.
when you squeeze the bag it will lay a nice little bead inside your gunnel slot.
I’ve tried to use brushes and small strips as a spatula and it’s very slow and messy.
The ziplock trick (thanks Alan) is effortless and makes the whole application too easy. And it’s quick which really counts when you’re fighting the cure clock.
 
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