Alu Gunwales Closer Look Details

[døv]

Plenty info on wood gunwales, hoping to get closer to details of alu gunwales construction. About to do retrofit on swede form race hull with black wenonah alu gunwales, 1"OD, 0.038" wall thickness thwarts and alu 3/16" poprivets to replace wood and x85+ SS screws for (~1-3lb) weight savings and overall more stiffness.

• I have noticed many commerical made canoes outfitted with alu gunwales with no deckplate. Simply not neccesary?
• Along every instance has "deck" endcaps, does it has function in overall construction?
  • Gunwale end to be capped would be sufficient?
• Several ways to mate thwarts to hull (examples I have examined)
  1. Thwart ends bent to 90deg and 2x rivets thru gunwale
  2. Thwart ends bent to 90deg and 2x rivets thru hull ONLY, 2-4" below sheerline
  3. Thwart ends left flat 1x rivet to Alu L bracket that is 2x riveted thru gunwale
  4. Thwart ends left flat 1x rivet to Alu L bracket that is 2x riveted thru hull ONLY, 2-4" below sheerline.

Observation:

• Only saw few instances of #3/4 is effort to bypass concerns of thwarts unfolding and only for "main" thwart right behind paddler station
  • Guess would make sense since its area where it gets most abuse weight loading wise during shoulder carried portages?
• Not sure about below the sheerline, more lower/wetted surface hull stifness perhaps?

I am curious on your observation, thoughts and experience.

 

[Glenn MacGrady]

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I don't have a canoe with aluminum gunwales and have never worked with them, but I'm of the opinion that decks don't really serve any useful function unless they are absolutely required for some construction purpose. Otherwise, they just add weight in a place I especially don't want extra (swing) weight, the ends. Most people, however, probably like decks for reasons related to aesthetics and tradition.

 

[Gamma1214]

Welcome. Like Glenn, I have no experience w/ aluminum gunwales but I agree with his assessment of decks. Yes, I suppose they could provide a little extra stiffness at the bow & stern but I'd think they're primarily for aesthetics. Use them or discard them as you wish.

I know a few that have used aluminum on here (either on builds or retrofits) but, you are correct, there's not a ton of info available here. Please post your experiences to help build the archives for future searchers.

 

[Alan Gage]

I think end caps are a good idea for aluminum gunwales because those cut ends are pretty sharp. They (gunwales) also provide no protection at all for the tip of the canoe because they do not extend in front of it like wood gunwales do.

Alan

 

[Jim Dodd]

I picked up end caps, when I purchased a set of Bell gunnels, from an outfitter in Ely Mn. a few years ago.
I had some aluminum tubbing, that I used for thwarts and grab handles.
There was no prebending of the gunnels, so the thwarts have some tension on them.

here are a few picks.
This is a composite I built.

Jim

 

[Alan Gage]

For thwart attachment I think I'd go with whatever would work best with with that gunwale profile and what you find most aesthetically pleasing.

The gunwales that Jim showed above, from Bell (now Northstar) have an inwale that are wide and flat, which makes it easy to rivet the thwarts directly to it.

Other inwales do not have a profile that makes this easy so it might be better to rivet through the hull.

Since this is a racing canoe it probably won't see a lot of abuse or load on the thwarts so it probably doesn't matter much.

Alan

 

[døv]

Thank y'all for welcomes!

Good to hear on general assesment on utility of deckplates, I'll try not worry about it!

Plan on designing a cap out of 3d printed ASA just enough to cover ends of gunwales, instead of rubber "deck endcap". . Out of concerns of safety and decent look. Printed ASA footbrace and seat mount proven to be durable.

Sweet build!! Is your bell gunwales 2 piece system? Hides the mushroomed poprivet ends like Northstar? Nearly no information out on internet. Good to know about tension part & lack of prebending, did you use 3/16" pop rivets? I managed to find Wenonah black alu gunwales from local dealer, hence going with it and forgo shipping. Inwale ledge on bell gunwale system is sweet!

Ironically abuse is part of inspiration why I'm replacing cherry wood for alu. I added fourth wooden thwart and after few training & portage sessions, whole thing get loose again. Running with boat on shoulder usually does it. Locites, nylocks, fresh new holes only will prolong the cause of issue.

 

[MrPoling]

I've noticed deck caps in wooden canoes add a lot of strength to the end of the canoe. They prevent the end of the gunnels from flexing together and apart.

Following gunwales replacement, my fiberglass Mad River Explorer seemed floppy at the ends. I didn't have deck caps, so I bound the ends of the gunwales together with a 1.5" piece of aluminum stock riveted to each one. It is as far up the ends as it would fit.


The results is the end handle and gunwales form a very tight trapezoid, nearly a triangle. It doesn't flex much, and the canoe feels stiff when paddled.

The picture shows a problem with aluminum gunwales - galvanic corrosion. I used stainless bolts to attach the small aluminum brace and the carry handles. I paddle in the ocean, and you can see the corrosion in the picture.

I sanded everything down, repainted it, and replaced all the stainless fasteners with aluminum rivets, and added end caps.

Edit: However, after further reflection I've concluded connecting the gunwales together creates the potential for galvanic corrosion regardless of similar metals. I'm going to remove the brace and replace it with something non-conductive. I'll probably use two layers of ABS in its place, and then reinstall the cap on top.

 

[Rippy]

Some kind of a cap on the ends is a good thing for me as I tend to bang the stern end from time to time while portaging (downhill) and loading. Saves me wear and tear on things that would be harder to repair.