Originally Posted by danjarch
A better way to learn about long term effect on materials is to look at airplanes. A airplanes fuselage almost never comes into contact with any other hard objects. However, after repeated long term flexing, it will start to crack, then rips apart. If you took a fiberglass boat, and continuously sailed it with out ever bumping into anything, it would start to crack and then rip apart.
What you're talking about is fatigue. Fatigue occurs when materials are repeatedly loaded and unloaded with stress above their endurance limits.
For fiberglass, the endurance limit is about 25% of its strength -- if the cyclic working stresses stay under this level, it doesn't fatigue.
Older boats were way overbuilt by today's standards. I have drawings here for a 46 foot ketch from the early 60s. Its topsides over the front half of the boat are a full 3/4" thick, tapering to 1/2" at the transom. Below the waterline it gets thicker yet. It also has structural stringers and bulkheads. Using the American Bureau of Shipping rule for composite boat scantlings, this hull is close to twice as thick as the rule today calls for. The strength of panels in bending goes up with the square of the thickness, so the stress in the fiberglass of this hull would be about a quarter of the stress seen in the ABS spec hull. Hulls like this will never fatigue.
Comparing fatigue in aircraft and boats is apples and oranges. Aircraft need to be as light as possible to fly. The factor of safety is typically 1.1, that is, the strength of each part of a plane is only 10% greater than the maximum load they expect that part to see. The stresses are much closer to the material's strength, and fatigue sets in quite quickly (thousands of cycles instead of millions or billions).
Boats, on the other hand, are designed to considerably higher factors of safety. Planing powerboats need to be light to plane, and they do lots of pounding on waves, so they do get into the stress levels that fatigue fiberglass. Racing sailboats are designed to be as light as possible so they put their hulls under high stress loads and they fatigue too (what people mean when they say a hull has become "soft"). Cruising boats, however, especially old heavily built ones, are much less likely to fail from fatigue.
So, getting back to the original poster's question, I say there's a lot of life left in that Alberg.