do old ribs eventually get 'tired'?

[swededoc]

Hi,

I recently purchased a 1946 18' Old Town Guide canoe that was part of a fleet up on the Au Sable river in Grayling, MI. Now I'm wondering if she's just 'tired out'. The hull is fairly sound and has a very good shape--at least by my eye. It needs a full restoration: remove fiberglass, replace 6-8 ribs, replace 2 or more planks, gunwales, thwarts, decks, keel, bilge rails, re-do the seats, install canvas. Even when I add all this up it still doesn't seem to me like too much work or like it's just not worth it. I looked the hull over carefully from several angles before I bought it and determined that it a very smooth, pleasing and uniform shape. The gunwale line doesn't flow real smooth, but that's because they pieced it together in a previous repair. I think a good set of new ash or even mahogany gunwales should take care of that. But my question and concern is this: while the hull has a good shape, is it possible that the ribs might just be 'tired out'? She seems to flex very easily, even with the fiberglas covering. When I set it upright on sawhorses with just the weight of the canoe (maybe 80 lbs) it flexes right over the 2 x 4s--not a lot, but noticably. The interior of the hull was also painted at some point so I won't see everything until its stripped. I don't have any other wood-canvas canoe to compare it to so I'm not sure whether this amount of flex is normal. Do the white cedar ribs and red cedar planking retain their flex indefinitely, or do they reach a point where they've seen so much work that they've gone 'over the hill'? You guys that do this for a living or just know these canoes a lot better that I do have a lot of invaluable input. Thanks, ahead of time.

Jonathan
Ypsi Township, MI

 

[Todd Bradshaw]

Fiberglass on the outside of a canoe hull doesn't really contribute any noticeable stiffness to the structure. When you set the boat on sawhorses, the glass layer is being put in compression. It's stiffness and tensile strength come in when it is put in tension, not compression. All it will do is flex and the hull stiffness is going to be provided by the wooden ribs, just as it is on a canvas-covered canoe.

As to the wood, I'll tell you the same thing we learned in the ski industry about wooden skis back in the old days. We were told that every time you flex a piece of wood, some of the fibers get stretched or broken, and they don't grow back. The more often it gets flexed, the fewer remaining fibers are left to generate stiffness. It would follow that a wooden rib which has been flexed a lot over the years may be noticeably less stiff than it originally was. Whether or not this is a big enough problem to actually weaken or endanger the hull's structure is hard to say.

 

[Greg Nolan]

I write as the WCHA 2013 Assembly has ended. Many attendees have left, and the rest of us will be gone by tomorrow morning.

Scores of canoes older than your 1946 Old Town were here – canoes which were paddled here and are regularly paddled in home waters by their owners – with no apparent problems from a lack of strength – even when the use is not just paddling, but involves the stresses of sailing, or of car-topping. We don’t sail, but our two canoes –1922 and 1931 -- will have travelled more than 1500 miles this year alone by the time they return to Maine tomorrow, on all kinds of roads, though mostly on interstates at high speed. Most of the canoes at Assembly were car-topped or trailered a good distance to get here.




Wood and wood/canvas canoes are flexible – they are not designed to be as stiff as aluminum or composite canoes. Especially when on saw horses, the flex will be evident. Keep in mind that when in use, the canoe is supported by water evenly over every square inch of that part of the hull that is underwater, rather than on the two narrow contact lines provided by your saw horse rails.

Reinstalling a keel, as you are considering, will add a bit of fore/aft stiffness – noticeable, but not critical. The keel shape and dimensions suggested by Dave Wermuth are typical, and similar to the keels on our two canoes. Most canoes these days seem to be without keels, but if I were you, I would reinstall one, at least temporarily, if for no other reason than to fill the existing holes in the hull.

From what you have described, I think you have nothing to worry about.

 

[MGC]

A good set of inside and outside rails properly connected by solid seats, thwarts and decks will make that disappear. Might as well get on with the process and strip off the glass to see what you need to deal with. Once you get the boat restored I doubt there will be a problem.

 

[swededoc]

Another related question comes to mind: what are the pros and cons of half-ribs? The only two arguments against them that I can think of are additional weight and cost/time of installing them. Any guesses on how much weight they add? Also, all the half-ribs that I've seen (only in pictures) end at the flat, bottom of the hull. I'm wondering about the idea of extending half-ribs up the sides of the hull perhaps 1/3 of the way up each side. Since this is the 18' Guide model is has a broader hull than some others and since this is a restoration I can use the shape of the hull to hold steamed half-ribs in place just as with replacing full ribs. As for floor racks I'm guessing they just hold gear up above any bilge water but don't really provide hull strength. Is that right, and what about adding the standard half-ribs and my idea of longer half-ribs, say, 2/3 ribs?

Thanks again gentlemen for all the good input,

Jonathan
Ypsi Township, MI

 

[Jerry Fruetel]

I'm partial to half ribs. They strengthen the hull bottom, just where you need it, and they make paddling on your knees much more comfortable. Also, they add surprisingly little weight, less than a pound. I would extend the half-ribs into the turn of the bilge area, but see no advantage to extending them beyond that.

I don't know if floor racks strengthen the hull much or not, but they should reduce hull stress by spreading the weight of cargo loads across a broader floor area.

Good luck on your restoration.

 

[Gil Cramer]

2/3 ribs will tend to straighten when wet and deform the hull. Morris canoes have ribs extending into the bilge and deforming the planking. Half ribs should be very short in order to keep the hull shape!!!!!!!!!!!!

 

[Jerry Fruetel]

Gil, on Atkinsons and Chemauns I haven't experienced deformed planking from half ribs in the bilge area, but maybe I've just been lucky. I do think it's critical to thoroughly steam or boil the half ribs and pre-bend the ends to fit the bilge area before installing them.

 

[Gil Cramer]

The half ribs are probably tapered dramatically in thickness at the ends, and the canoes have likely had little exposure to soaking water. neither extend 2/3 of the of length of the full ribs.

 

[Jerry Fruetel]

Yes, the half rib ends are thinned to 3/16". And, they extend only part way into the bilge--- the ends are bent up no more than about 30 degrees from horizontal.

 

[Jerry Fruetel]

I should correct something I said in my initial reply to this thread, above. Cedar half ribs will add 3-4 pounds weight to a canoe, not "less than a pound".