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PaulK 06-11-2018 09:49 PM

Seeking Advice From Stripperguy or Others on a Canoe Build

I built a 23' stripper modeled after my Wenonah Sundowner 18. Followed Gilpatrick's book mainly. It turned out nice. My hope was to race it this year in the 90 miler, but that will have to wait another year. As summer is here, I need to add ribs to it after paddling it for the first time last week. The bottom is stiff as hell to the touch, but I'll be damned under its own weight in water the bottom at midships flexes like jelly. Layup schedule is football-shaped 6oz glass inside and out, and then another full 6 oz over it inside and out. My strips are 5/16". So I cancelled my efforts to join the 90 miler this year and later this year I'll put half ribs in it, maybe 6, similar to Wenonah Crossrib style construction.

Anyway, I would love to hear from anyone who has glassed cedar ribs into a stripper. And maybe we can meet sometime this summer to work out the details and any good tips in person! I'm in Gloversville.

stripperguy 06-12-2018 01:55 PM

It's seems surprising that you would get oil canning with such a lay up.
How wide/flat is the bottom? For a given lay up, the weakest geometric config is flat. As the shallow arch, or vee increases, the hull will flex less for a given load.

If your hull shape is not inordinately flat, I would think the lamination is suspect.

But on to your rib question.
I wouldn't necessarily recommend glassing in cedar ribs. Unless you particularly like the look.
Cedar ribs would need to laminated to shape, or steam bent, to match each section where you plan to install them. If steamed, you would need to allow adequate time for the ribs to dry out before epoxying and glasing in place.
In either case, you would need to profile the ribs so that the glass can conform to the hull/rib interface. A shallow chamfer should be good enough. Or, in lieu of a chamfer on the rib edges, you could add a fillet to the hull/rib interface with some Cabosil thickened epoxy.
You should also use Cabosil thickened epoxy to install the ribs in the hull.

A preferred material for stiffening the hull bottom would be some H80 Divinycell foam. That foam is a closed cell PVC and is intended for structural applications,in other words, it's made for just this sort of work.
The foam could be cut into ribs, or a larger piece could cover a substantial part of your football. Epoxy that in place with some thickened epoxy, bevel/chamfer the edges, and add a layer or so of glass.
If you search back through my thread on the carbon copy Kite, you'll see that I had a very flexible football with my double layers of 6 oz glass and carbon.
After adding a 1/8" thick section of foam with a layer of carbon on top, I could stand in my bare hull (no gunnels) while it was on saw horses!! Very stiff indeed!!

PaulK 06-12-2018 09:25 PM

Thanks for responding. Every bit helps. The hull has a 39-1/2 beam. I built it to conform either to the C4 unlimited class or the Voyageur class (6 paddlers) in the 90 miler. I laid a 2' long straight edge in the bottom of the boat at center and there is 1/2" of depth or arch what have you. I did the same thing in my wenonah sundowner 18 with 36" beam and there is 1-1/4" gap. You can see more of the shallow arch in the Sundowner of course. When I built the forms I copied the Sundowner but I wanted stability in the stripper so I took out some of the shallow arch.
I love the stability of the stripper. I haven't been in it with six adult paddlers yet, only my family of three, and the boat is wonderfully stable, nimble (1-1/2" rocker) and fast. With three of us in it, has tons more freeboard.
Anyway, the cost of the H80 is disturbing when I have perfectly good cedar around and resin to do the job. I couldn't find less than a 4x8 sheet in 3/4" thickness for $250. 3/4" is the thickness (height) of the structural ribs in another cross-ribs Wenonah I have at the moment.
Glassing in a football floor of thinner H80 would be pretty cool though.
At the moment, I would laminate some cedar and cut them to the shape of the bottom and chamfer the ends for transitioning the load. I learned a very interesting thing from Todd Bradshaw on the Wooden Boat forum, he says it's the distance between the layers of resined cloth that gives strength, so make the ribs tall and narrow is much better than low and wide.
I appreciate your insight as to using thickened epoxy. will do. I wish I had seen this coming, I would not have varnished the inside of the hull and put in the bench seats and foot braces. Gotta take it all out and sand away.

stripperguy 06-14-2018 04:37 PM

The relationship between thickness and deflections is to the 3rd power...
So, all else the same (lamination schedule, geometric shape, material modulus), if you double the thickness, you will increase the strength (and reduce the deflections) by a factor of eight. 3/4" high ribs would add massive strength!!

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