How would I test the strength of old planks and ribs?

I'm almost done stripping fiberglass from the exterior and varnish from the interior of my 1913 Old Town Charles River CS. With the stripping and sanding, I've lost some of the 108 year old wood. I'll need to replace a few planks and ribs, but most of them look pretty good. I'm stressing about whether the lost wood from stripping and sanding will weaken the boat significantly. I don't need to take the canoe down the Allagash, but I also don't want it to be too fragile to use. Any suggestions for a way to test the strength of the wood that seems otherwise healthy?

 

Tim, you are not the first person to face this question. A few pictures of the hull would make it easier to respond with certainty.
If your boat is anything like the ones I have done, you have nothing to worry about. The old wood is surprisingly durable. Replace what you think is bad (split, warped) and re-clinch all of the tacks. Don't skimp on this task. If the hull was glassed then you can be pretty sure that the tacks got yorked around whenever the boat was dropped.
WRT sanding, go easy on that. You don't want to damage the tacks. If you do sand, only hand sand. Stay away from the boat with the belt sander! I tend to use a small plane or a knife to fare the planking when it needs it and prefer to do that rather than do a lot of sanding.
You will want to put something on the outside of the hull to fill the wood. I use a blend of turpentine, mineral spirits and linseed oil. I heat it and then apply it to the hull with a brush. Most folks use heated linseed oil or something similar. There are folks that apply varnish. Search this forum for related discussion.
Your canoe should be perfectly fine for the Allagash after you put a fresh canvas on it. Any damage you might do can be repaired. That's the beauty of these old hulls...they can live 100 plus years and look great doing it.

 

So apparently I've been using the wrong side for the last 60 years. Dang. Who knew?

 

I would follow Benson's warning not to try this at home. Today, we would be at a disadvantage to the people in these photos. I did some research and found that people were smaller in previous times than we are today. By quite a bit as it turns out. I confirmed this fact through scientific research of the evidence in this post. I measured the tallest person in Benson's post at just a skoshe over 1 and 1/16 inches tall, while Dan's paddler is a whopping 2 and 3/4 inches tall. When you adjust for size differences and clothing, even the "giant" in Dan's post weighs in at a trifling 12 ounces or so. To test this theory, I put a 12 ounce bottle of "liquid spirits" on my oldest and most fragile canoe - both keel up and keel down as in the photos - it held the weight just fine. I tested the bottle with diminishing levels of spirits as I typed this. Then I reenacted Benson's post and put seven 12 oz. bottles of "Liquid Spirits" on the canoe. For accuracy I started as close to Benson's picture as I could get - 4 with caps on and 3 with caps off - but in the end, all the caps were off the bottles.

 

Along with John's calculations, I figured out that if the canoe with seven men standing on it is holding 3420 pounds, each fellow must weigh in at around 488 pounds!!! Al

 

The Haskell canoe also appears to be filled with sand. My skepticism had me looking very carefully at the photo but there doesn’t appear to be any obvious manipulation (which has been used to deceive long before Photoshop came along).

Tim - Hopefully removing the ‘glass didn’t peel off too much wood, and you shouldn’t sand too aggressively. But of course most restorations require some sanding and countless wooden canoes have been restored to become completely functional again. On the exterior I do as little as possible beyond re-clenching tacks and fairing the hull as needed (judiciously taking down raised areas). On the interior I don’t recall ever using sandpaper more aggressive than 120 grit, and often start on ribs with 150. Planking between ribs is usually sanded only with 220. The point is simply to avoid taking away too much wood, especially on the thin planking, and to keep tacks from being sanded through.

On the exterior oiling or varnishing will help rejuvenate the wood but won’t add where wood has been taken away. Sometimes fillers have been applied to the exterior apparently in attempts to fill divots at tack heads or to fill in where wood is missing or thinned. This is a recipe for disaster because, for one thing, anything that later comes loose under the canvas will cause problems.

In short, just take care and don’t be too aggressive. If pulling fiberglass takes chunks of wood with it, just replace those areas of planking. There’s no readily available means to test the strength of the hull especially since it will vary from place to place. In any case, these hulls were built to combine lightness and resilience. A careful restoration shouldn’t compromise those qualities.