Pardon the rant, but this is one of my pet peeves and a blatant demonstration of two things: One is the fact that it's very possible to build a nice looking stripper without really knowing what the hell you're doing and the other is that the internet contains a boatload of bad information which should be ignored.
When you build a stripper with 6 oz. glass on the outside and 4 oz. glass on the inside you have basically just guaranteed yourself that you've built a weak boat and drastically increased the chances that it's going to break. A stripper is a sandwich which combines three layers of material (two of glass, placed on either side of one layer of wood). None of these layers are strong or stiff enough to stand on their own and make a canoe, yet when combined properly, the result is a light boat with quite decent strength, durability and rigidity. It will never rival a plastic canoe in terms of taking a pounding, but with reasonable use and care it will be durable and repay the owner in other ways (hull stiffness and efficiency, lighter weight, better shape, better looks, etc.)
You may have noticed.....that unlike a wood/canvas canoe, there aren't any ribs inside your stripper. The wooden core is actually quite uni-directional - meaning that the grain of the wood is providing much more strength and rigidity lengthwise than it does cross-wise. Cross-wise it's strength is limited to the grain strength of the wood (the resistance of the strips to splitting with the grain) and to a lesser extent the strength of the glue bonds between the strips (which is usually, but not always, somewhat greater than the wood's grain strength). This means that if we bend the bare wooden hull until it breaks, the break is most likely going to be lengthwise and in the wood, rather than at the strip-to-strip glue joints.
The wooden part of the boat really isn't that much different in strength and stiffness from the planking on a wood/canvas boat, but rather than bending 40 or 50 wooden ribs in to add our cross-grain and transverse strength, we do it with thousands of cross-wise yarns of fiberglass, sandwiching the core. We also gain surface hardness, abrasion resistance and some lengthwise strength, but the cross-wise reinforcement is the biggest addition that the fiberglass is contributing to the project. By separating the fiberglass layers with a reasonably durable, thicker, non-compressible wooden core, we create the sandwich and in the process, we gain hull stiffness, abrasion resistance, moisture resistance to keep the core wood dry and a whole lotta' cross-grain strength and durability.
Once we're out on the water, there are a variety of forces that our sandwich must resist or stand up to in order for our boat to survive and work properly. Excessive flexing is one and over a period of time it will weaken the hull and could even break it. Running over rocks can obviously do some damage, both in terms of abrasion and impact as well as possibly causing extreme flexing. Unless you routinely put on spikes and jump up and down in your canoe, you'll find that most of these dangers come from the outside of the hull - and most of them are pushing inward from the outside. Thus, the inside lives a fairly quiet, worry-free life. Or does it really?
The tendency of builders to think that it does and use lighter glass inside as a result, in order to save weight, may seem perfectly logical. The rocks are outside the boat....right? We want some beef out there to keep those rocks from gouging the core and abrading the hull...right? This is true, but unfortunately, that's about all the help that the outside glass can provide - and basically it boils down to providing hardness and a suitable amount of skin thickness to shield the soft core. The forces acting on the outer fiberglass layers are putting them in compression. Fiberglass has low compressive strength. It's hardness means that it will be much harder to scratch or gouge than bare cedar would be, but it is not in a position where it can provide much real hull strength (the fibers are basically being pushed-on or pushed together).
The job of holding the boat together then falls to the inside layers of fiberglass. When the hull is flexed or when it suffers an impact from the outside, the inner glass layers are put in tension (essentially the fibers are being pulled on, rather than pushed together). Luckily, fiberglass has very good tensile strength. It can handle being put in tension much, much better than it can handle being put in compression and in this case, it is providing the vast majority of the strength that's needed to improve the cross-wise grain strength of the wooden core and hold the boat together. In terms of preventing serious structural damage from typical canoeing situations, the inside glass layers on a stripper are far more important than the outside glass layers. Reducing the weight of the cloth used on the inside of the hull makes the sandwich much weaker in the place and direction where you actually want and need the most strength. It may look like the inside glass leads a charmed life, but every time the hull flexes in waves or you slide over a rock the inside fiberglass is being tested and is what is keeping the hull from splitting wide open.
Hopefully after all this you're starting to see that using a lighter layup on the inside is usually not a smart move. You might save a few pounds, but you pay dearly for it in terms of hull and sandwich strength. If anything, it should probably be heavier fiberglass than that which you apply to the outside. In practice, matching the outside and inside layups tends to work pretty well and produces a pretty good boat. You should be able to hit a rock at speed, fully loaded, slide over it as long as it's not too sharp and leave nothing more than a scratch on the outside of the hull. Seventy-five percent of the new builders who decide (often by second-guessing the designer's specifications) to lighten-up their canoes by skimping on the inside layup are totally unaware of what they are doing structurally to their hulls and all too often their follow-up forum posts are "My boat broke or split on the inside - what do it do now?"
Now back to your regular programming.
