I wrote this for a different venue but it may address some of your questions. Westsails are a classic case of a very heavily laid up hull, but one that was laid up using techniques that are now known to shorten the life of the fiberglass and are also boats that have minimal intgernal framing. Since these boat vary widely in fit out its hard to say specifically how your boat will last especically since I have been on Westsails that did not flex at all, and another that seemed to wrack in heavy going. (Here is the article that I wrote on the lifespan of a fiberglass boat)
"I would not think that a well- constructed fiberglass has a life span per se. Neither concrete nor fiberglass inherently breaks down or loses strength simply on their own without other factors coming into play. They require other causes. In the case of fiberglass loss of strength can result from one or more of the following,
-The surface resins will UV degrade.
-Prolonged saturation with water will affect the byproducts formed in the hardening process turning some into acids. These acids can break down the bond between the glass reinforcing and the resin.
-Fiberglass is prone to fatigue in areas repetitively loaded and unloaded at the point where it is repetitively deflected. High load concentration areas such as at bulkheads, hull/deck joints and keel joints are particularly prone.
-Salts suspended in water will move through some of the larger capillaries within the matrix. Salts have larger molecules than water. At some point these salts cannot move further and are deposited as the water keeps moving toward an area with lower moisture content. Once dried these salt turn into a crystalline form and exert great pressure on the adjacent matrix.
-Poor construction techniques with poorly handled cloth, poorly mixed or over accelerated resins, and poor resin to fiber ratios were very typical in early fiberglass boats. These weaker areas can be actually subjected to higher stresses that result from much heavier boats. It’s not all that unusual to see small spider cracking and/or small fractures in early glass boats.
-Of course beyond the simple fiberglass degradation there is core deterioration, and the deterioration of such things as the plywood bulkheads and flats that form a part of the boat’s structure.
Earlier boats had heavier hulls for a lot of reasons beyond the myth that designers did not know how strong fiberglass was. Designers knew exactly how strong the fiberglass of that era actually was. The U.S. government had spent a fortune developing fiberglass information during WWII and by the early 1950’s designers had easy access to the design characteristics of fiberglass. (Alberg, for example, was working for the US Government designing F.G. composite items when he designed the Triton and Alberg 35) The reason that the hulls on the early boats were as thick as they were had more to do with the early approach to the design of fiberglass boats and the limitations of the materials and handling methods used in early fiberglass boats. Early designers and builders had hoped to use fiberglass as a monocoque structure using an absolute minimal amount (if any) framing which they felt occupied otherwise usable interior space.
On its own, fiberglass laminate does not develop much stiffness (by which I mean resistance to flexure) and it is very dense. If you try to create the kind of stiffness in fiberglass that designers had experienced in wooden boats, it takes a whole lot of thickness which in turn means a whole lot of weight. Early fiberglass boat designers tried to simply use the skin of the boat for stiffness with wide spread supports from bulkheads and bunk flats. This lead to incredibly heavy boats and boats that were still comparably flexible compared to earlier wooden boats or more modern designs. (In early designs that were built in both wood and fiberglass, the wooden boats typically weighed the same as the fiberglass boats but were stiffer, stronger, and had higher ballast ratios)
The large amount of flexure in these old boats was a real problem over the life of the boat. Fiberglass hates to be flexed. Fiberglass is a highly fatigue prone material and over time it looses strength through flexing cycles. A flexible boat may have plenty of reserve strength when new but over time through flexure fiberglass loses this reserve. There are really several things that determine the overall strength of the hull itself. In simple terms it is the strength of the unsupported hull panel itself (by 'panel' I mean the area of the hull or deck between supporting structures), the size of the unsupported panel, the connections to supporting structures and the strength of the supporting structures. These early boats had huge panel sizes compared to those seen as appropriate today and the connections were often lightly done.
This fatigue issue is not a minor one. In a study performed by the marine insurance industry looking at the high cost of claims made on older boats relative to newer boats and actually doing destructive testing on actual portions of older hulls, it was found that many of these earlier boats have suffered a significant loss of ductility and impact resistance. This problem is especially prevalent in heavier uncored boats constructed even as late as the 1980's before internal structural framing systems became the norm. The study noted that boats built during the early years of boat building tended to use a lot more resin accelerators than are used today. Boat builders would bulk up the matrix with resin rich laminations (approaching 50/50 ratios rather than the idea 30/70), and typically used proportionately high ratios of non-directional fabrics (mat or chopped glass) in order to achieve a desired hull thickness. Resin rich laminates and non-directional materials have been shown to reduce impact resistance and to further increase the tendency towards fatigue. The absence of internal framing means that there is greater flexure in these older boats and that this flexure increases fatigue further. Apparently, there are an increasing number of marine insurance underwriters refusing to insure older boats because of these issues.
I have been looking at a lot of older fiberglass boats in the past few years. One thing that has struck me is the sheer amount of noticeable flexure cracking in areas of high stress, such as bulkheads, chainplate attachment points, hull to deck joints, cabin to deck lines, engine beds and rudder posts, and other high load hardware positions.
There are probably other forms of hull degradation that I have not mentioned but I think that the real end of the life of a boat is going to be economic. In other words the cost to maintain and repair an old boat will get to be far beyond what it is worth in the marketplace. I would guess this was the end of more wooden boats than rot. I can give you a bit of an example from land structures. When I was doing my thesis in college, I came across a government statistic, which if I remember it correctly suggested that in the years between 1948 and 1973 more houses had been built in America than in all of history before that time. In another study these houses were estimated to have a useful life span of 35 years or so. As an architect today I see a lot of thirty five year old houses that need new bathrooms, kitchens, heating systems, modern insulation, floor finishes, etc. But beyond the physical problems of these houses, tastes have changes so that today these houses in perfect shape still has proportionately small market value. With such a small market value it often does not make sense from a resale point of view to rebuild and these houses are therefore often sold for little more than land value. At some level, this drives me crazy, since we are tearing down perfectly solid structures that 35 years ago was perfectly adequate for the people who built it, but today does not meet the “modern” standards.
The same thing happens in boats. You may find a boat that has a perfectly sound hull. Perhaps it needs sails, standing and running rigging, a bit of galley updating, some minor electronics, a bit of rewiring, new plumbing, upholstery, a little deck core work, an engine rebuild, or for the big spender, replacement. Pretty soon you can buy a much newer boat with all relatively new gear for less than you’d have in the old girl. Its not hard for an old boat to suddenly be worth more as salvage than as a boat. A couple years ago a couple friends of mine were given a Rainbow in reasonable shape. She just needed sails and they wanted a newer auxiliary, but even buying everything used the boat was worth a lot less than the cost of the “new” parts. When they couldn’t afford the slip fees, the Rainbow was disposed of. She now graces a landfill and the cast iron keel was sold for scrap for more than they could sell the whole boat for.
Then there is the issue of maintainable vs. durable/low maintenance design concepts. Wooden boats for example represent the difference between a maintainable construction method versus a low maintenance/ durable method. A wooden boat can be rebuilt for a nearly infinite period of time until it becomes a sailing equivalent of ‘George Washington’s axe’ (as in “that’s George Washington’s axe. It’s had a few new handles and a few new heads but that is still George Washington’s axe”.) The main structure of a fiberglass hull is reasonably durable and low maintenance but once it has begun to lose strength, there is nothing that you can do.
The best deals on older used boats are the ones that someone has lovingly restored, upgraded, and maintained. Over the years they have poured lots of money and lavished lots of time into maintaining the boat in reasonably up to date condition. No matter how much they have spent the boat will never be worth anything near what they have in it because there is a real ceiling to how much an older boat will ever be worth and they will often have several times that ceiling invested.
And finally if you buy an old fiberglass boat, paint the bilges white. It does nothing for the boat, but if you ever have to sell the boat, then someone may look in your bilge and say “Lets buy her because any owner who would love a boat so much that he went through the trouble to paint the bilge white must have enjoyed this boat and taken great care of her no matter what her age.”
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay