Don't ever feel stupid for asking a question. Feel stupid for thinking that it's more important to look smart than it is to learn.
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1) Is it true that most small fiberglass boats have wood support structures that will eventually rot?
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No - it is true that most small fibreglass boats have wooden componenets somewhere that COULD eventually rot.
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2) Are there builders who do not use wood? Is that what "all-fiberglass hull" means, or does that description exclude other things hidden away between deck and hull? (I know about the Cape Cod Bullseye...are there others that are wood-free?)
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'All-fibreglass' usually means that there is no core material in the hull. Fibreglass boats can be broken down into two categories - cored hulls and solid hulls. The first FRP (fibre-reinforced plastic) boats were built using lots of resin and lots of fibreglass. They were built a layer at a time. As one layer started to set, the next layer was applied on top of it, while the preceding layer was still slightly adhesive in order to allow for a chemical as well as a physicl bond between the two layers. The centreline, bottom and lower side areas of the boats were usually thicker than the middle of the sides and the fibreglass was thinnest (but still substantial) at the top along the sheer line (where the deck meets the hull).
Initially, these layers of glass were applied by hand and then resin was brushed on to the fibreglass and 'worked in' with brushes and specialised rollers to get the fibreglass thoroughly saturated, thereby ensuring it's strength and structural integrity. It takes a long time to do this properly, as air bubbles form very easily and frequently in the resin during the layup process. This is referred to as "hand lay-up" and it is still a practise in many boatyards.
As fibreglass boats became dominant in the marketplace, manufacturers began to experiment with various techniques to speed up the manufacturing process and build better quality hulls. They also began to look for ways to save money.
Hence, chopped strand mat which is basically a porridge of very short glass fibres suspended in resin, became popular for a while. It is shot from a spray gun and can be applied very quickly. It has very little structural integrity though and is seldom used today, and never ( I hope) for any part that will be subject to stress or wear.
In the early seventies, cored hulls made their first appearance on the mass market. They were introduced in an effort to save both weight and money. At the time, gas prices were quite high, hence the cost of resin had increased dramatically. It was determined that by using a lightweight core between two thin layers of fibreglass, boats could theoretically be built stronger for less money, as the core material was less costly than fibreglass resin.
They had the added benefit of being better insulated and in some cases, stiffer, than solid glass hulls. The most widely used core material was end-grain balsa wood.
Many boatyards had been using this method of construction for decks for a few years, in order to add stiffness while minimising weight. The coring material used for the decks varied widely, some yards preferring plywood, some using balsa, some even using Masonite.
As the years went by, it became apparent that where there were cores, there were potential problems. In a nutshell, the cores can get wet and rot inside the boat, with no visible external signs of deterioration.
Today, there are many manufacurers that make cored hulls, but a lot of them have moved from balsa and plywood to synthetic materials such as Airex or Core-Cell et. al.
The synthetics don't rot, but they can still get wet, and the flexing of the inner and outer skins of the boat as it sails can make the cells of the foam operate like little diaphragm pumps, forcing the wetness throughout the structure.
If any and all holes through the cored sections are properly sealed, it is not likely that wetness will become a major issue with either a cored hull or deck. The big problem though, is that when one buys a used boat, one has no idea of what kind of maintenance or repair has been performed on it, or whether it was done properly, so the wet core is a definite possibility.
A survey can frequently identify problems areas with a deck and can sometimes identify problems with hulls, but it is still a somewhat inexact science.
Solid glass hulls do not suffer from these problems, however they can still suffer from osmotic dissolution, delamination and UV deterioration. Fibreglass is water-resistant, it is not waterproof, so eventually hulls absorb water. An awful lot of the resins used in boatbuilding can actually dissolve in water, so this introduces a whole host of other problems BUT it (usually) takes so long for the resin to dissolve that it is more a point of scientific curiosity than a real cause for concern.
Oswmotic blistering and 'the pox' are pretty commonplace with hulls that have net been barrier-coated, but the problem is usually cosmetic rather than structural. In all cases though, you need to investigate to determine that the osmosis is limited to the surface layer.
The exception to this would be some of the resin rformulations developed during the "energy crisis" at the time of the Carter Presidency. There were several made that were particularly vulnerable to osmotic deterioration.
Today, most new boats receive a 'barrier coat' of specialised epoxy resin, either at the time of manufacture, or shartly afterwards, and many older boats have been similarly protected by conscientious owners.
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3) Of course there must be different grades of wood used by those that use it. What should I be looking for/asking about?
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The primary concern here is that all plywood, if there is any on the boat, be actual marine-grade plywood. This differs from standard plywood in that it is void-free ( there are no holes or irregularities that could become holes in any of the plies used to make the sheet), and it is manufactured using waterproof glues. The only glue that I am aware of that is truly waterproof is resorcinol glue. The best grades of marine plywood use this. It has a distinctive dark purple colour.
Other than that, make sure that wood is properly sealed everywhere. Exposed wood will wick water very quickly, then expand. This expansion can crack fibreglass effortlessly. If the wet wood is frozen, the expeansion of the water inside the cellulose, destroys the structure of the wood creating a rotten mush that will turn black and eventually smell.
Wood in salt water willl usually last far longer than wood in fresh water, as the chemicals in the brine serve to 'pickle' the wood and preserve it.
In many boats, areas of high stress are cored with plywood rather than balsa, as it has greater compressive strength and can stand up to tightening of bolts and such things better. It deteriorates more quickly than balsa when wet however, so if holes have not been sealed well. these are often problem areas for all boats.
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4) How quickly does wood rot set in? Is this something I need to be worried about for instance with a 2-year-old boat that has sat in the marina parking lot for its entire life? If I get a boat in good condition and make sure it's dry in the winter, will rot still be a problem?
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Wet rot needs the correct combination of wood, water, temperature, and most importantly, bacteria to really get going. It is an organic process. It can happen at any time and progress fairly quickly or not at all.
That said, if you continue to take care of a boat that has been taken care of so far - it's not a big concern. If you keep your wood sealed properly, it may never set in. The wood will eventually need to be replacd due to structural fatigue, but it won't rot.
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Please advise me! (And sorry again if this is a stupid question. I have a lot to learn....)
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If you like the boat and it is in good condition - buy it ! Get out there and don't be afraid to make mistakes, because sometimes the best way to learn what you should do is by doing what you shouldn't.
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Rot: the basics (small boats)
