Are the predicted lifespan and build quality of boats considered during design?

Many sailors can only afford boats from the 1960s and 1980s, and I doubt that they were built with the intention of lasting for another 50 to 70 years. Throwing money around in buckets, or at least more than normal, will undoubtedly keep things moving, but eventually, it has to become prohibitive.

 

Boats are always about tradeoffs. Trading longevity for weight is one..

 

Wooden boats were not built to last 50 to 70 years either. In general, boats get neglected as they get old because the value decreases. At some point the value is less than the cost of maintenance or repair, so it is cheaper to buy another used boat.

 

longevity predictions are not publicized, but certainly must be a part of any design process.
Production boats need only hold up for their warranty period, while custom designs can be built with varying degrees of longevity in mind.
You cannot generalize the question to encompass all boats, Do you have a specific boat in mind?
Your best defense as a buyer is knowledge, and lacking that, you must rely on qualified surveyors.

 

Yes they are, but it's seldom a first row problem for pleasure boats. The value of a boat it's not in the hull and deck but in the systems, and those have a pretty clear lifespan. There is also the issue of the original customer, most of them are not willing to pay for a lifetime they are not going to use, so the builders fit what is adequate, not the absolute best available.
Then there are a lot of areas where the materials are considered obsolete for esthetic reasons instead of functional ones. Best examples are upholstery patterns and baby blue formica countertops.

If a restauration is financially responsible has more to do with the individual condition the vessel is in, then with the original build quality.

 

Yes it is and it is called Factor of Safety. It is the ratio of Ultimate stress to the Working stress. Working stress is a value chosen that when a load is applied, the structure will not yield/fail. To define a working stress, it must be a value that is below the yield point of the material of which generally is about 60% of the ultimate strength. Below means it is not the yield strength you are designing to but its limit you assign. The yield point is usually arrived at by testing and publishing the result.

There are other factors that determines yield strength such as temperature, corrosion, purity of material, and accuracy of data, but let us not delve into that.

So how does this relate to lifespan? If you keep stressing the material to its limit or near limit by several thousand cycles, it will fail due to fatigue. So for longevity, the working stress should be much, much less than the yield strength. A safety factor of 1 means it will definitely fail, 2 means you are below the 60% limit of most material, 3 means you are only using 1/3 of the ultimate strength of the material and way below the yield strength.

 

Older fiberglass boats were so overbuilt that fatigue failure of the hull is a non-concern. Of course there are the usual service components that need to be regularly taken care of like thru hulls, rigging, etc, but at that point is a question of what the used market can bear and not what the used item can bear.