Jeff H. You were speaking on the construction materials and it appears you said this about the Vanguard?
"Shorter fiber lengths and more brittle resins meant a very flexible and at the same time fatigue prone material."
Short fibers? In woven roving? How do you figure? Short compared to what? I would consider short fibers to be more like the chopper gun products that have been manufactured the last 30 some-odd years to be the champion of short fiber lengths. And what's this about vacuum-bagging? There were companies working without vacuum systems into the 1990's, only relenting to closed systems, not for the end product quality, but for the demands of the EPA, so I'm not seeing how that's relevant either, be it on Vanguards or any other fiberglassed anything made (in an open setting) up til the EPA mandated it be a closed system.
You are still asking these same questions after all these years?
To addresss your "Short fibers? In woven roving? How do you figure? Short compared to what?" :
I have explained much of this to you before and referenced my comments with a roughly 10 to 12 year old marine insurance industry study that looked at the strength of older fiberglass boats. The study was produced because the insurance industry was finding that older boats seemed to be having greater impact damage claims than would seem to be expected from the impacts that they were actually encountering. The study tested actual hull and deck panels cut from older boats and discussed the reasons that were believed to have caused the unpredicted decrease in strength in these materials. That study was available online when you and I first discussed this, but regretably, I am no longer able to find this report available online since if available I would have liked to have provided a link.
In any event, to address your short fiber question, the glass fiber in the fiberglass fabrics (mat, woven roving and woven cloth) that was used in the early days of GRP boats was produced using a process that called a staple fiber process. This produced individual fiber lengths that were comparatively short in length (typically less than 2 feet) which were then bundled into the yards used in roving and cloth. This process not only produced fibers which were comparatively short in length, but which were also less uniform in diameter and more prone to breakage if the woven fabics were not properly handled at the boat builder.
Generally, boat builders of the 1960's were not aware that fiberglass fabrics needed special handling. When I visited Pearson during the 1960's fabrics were precut, then labeled and folded, and stored in neat piles on racks ready for lay up. This folding of the fabric caused some breakage of the individual fibers, and concentrating fiber ends, along the fold line further shortening the fiber length along the fold lines.
At some point in the late 1960's and into the 1970's, the method of producing fiberglass fibers used in boat building changed to a continuous fiber method, which as the name suggests produces longer, nearly continous fibers that were also more uniform in cross section. Also by the 1970's and early 1980's manufacturers also had routinely adopted better fabric handling techniques, storing cut fabrics flat or on rolls.
Fibers produced using the continuous fiber method, and where the fiberglass fabrics are handled properly, are less prone to fatigue and are less brittle over the life of the laminate.
Fiberglass construction during the 1960's was a more casual affair. In the 1960s metering of the resin mix was not done with the high level of precision that is routine today. Resin admixtures were very popular during the 1960's to allow a longer working time, while accelerating the ultimate cure to allow the parts to be removed from the molds sooner. The imprecise mix ratios and the accellerators in use back then, made for a comparatively brittle and factigue prone cured resin as well.
In the 1960's, resin to cloth ratios would vary widely within individual laminations with the layup. Looking at plug cut from a 1960's era boat, you would see variations in the layup with lenses of resin that varied in thickness from layer to layer. And ideal resin to cloth layup results in a material with better flexural strength and resistance to fatique and rupture. This combination of shorter fiber length, less ductle resin formulations, and the lenses of resin rich laminate that was typical during the 1960's boat industry, resulted in a comparatively brittle and fatigue prone laminate.
So while slightly thicker than hulls which followed, hulls like the 1960's era Vanguard, lacking in internal framing and with laminate which the marine industry study showed to be comparatively brittle and prone to fracture, are not the excessively strong hulls which many people assume them to be.
To answer your other question "And what's this about vacuum-bagging?" I know of no boat building company that adopted vaccuum bagging as a way to address air polution problems. There were cheaper ways to do that. In the 1980's, some manufacturers began using vaccuum bagging as a way of better controlling the resin content within the laminate. The problem with hand laid up construction is that it is hard to completely wet out the cloth to a uniform resin to fabric ratio. What happens with vaccuum bagging is that the laminate is fully wet out and then air and resin is sucked out through ports in a membrane. The process compresses the laminate and removes excess resin before the resin sets. It guarenttees a more complete wetout, while reducing the resin left in the laminate to a closer to ideal level. Its an expensive process in that it requires more labor, equipment and there is more resin used, the excess of which is vaccuumed out before cure. But vaccuum bagging produces a much stronger and durable panel.
Where vaccuum bagging is especially effective is in sealing coring in balsa or foam cored decks to the skins where the vaccuum does a more effective job in clamping the core to the laminate and drawing resins further up into the core materials.
I hope this clears this up for you,