The resin used to build your boat holds everything together. Polyester resins are popular, but polyester is a generic term covering a vast array of brands and types, differentiated in both name and performance by the type of acid used to make each one. Those acids are orthophthalic, isophthalic and terephthalic. Orthophthalic acid is used to produce general-purpose marine resins. Isophthalic acid is used to produce a more chemical-resistant and slightly stronger grade. Terephthalic acid is not common in boats.
You’ll also hear “DCPD modified resin” bandied about. Without getting overly complicated, DCPD (dicyclopentadiene) is a big molecule. Within a polyester resin chain is the ester linkage — like a repeating linkage in a long chain. This linkage is a chemical bond that can be attacked by water over the long term. Eventually water can break this bond, starting a long-term degradation process that can lead to blistering or even your bottom cracking open. DCPD shields against water, rendering the ester linkage more stable in a wet environment. It also reduces the cost of the resin. Its downfall is its brittleness. It can reduce the crack resistance of your boat.
Also in this category are the vinylester resins. They are more expensive but do not have the ester linkage. Instead, they have an ether linkage, a more moisture-stable connector in the molecule. These resins have great chemical and moisture resistance. They are also much tougher and more flexible than the others. This means that design stress levels can be higher in the composites. This equates to a lighter, more durable boat that can take a beating and keep on ticking without cracking or breaking. Vinylesters are what gave us a revolution back in the early ’80s, when builders could begin to produce hulls that would not blister. Blistering, as you recall, is an indirect result of the ester linkages breaking in the presence of water. Therefore, vinylester resins are the resin of choice for the seeker of a trouble-free experience. You should make sure that your boat is produced with them if the boatbuilder works with polyester resins.
Epoxies are in a similar realm to vinylesters when it comes to performance in a marine composite, though you won’t find many production boats using it. It’s more fickle to use and more sensitive to heat, and some workers are allergic to it. However, if a custom boat is what you seek, it’s a fine alternative. And improvements in chemistry have helped overcome its manufacturing problems.
Generally, the higher-tech and lighter the construction, the more likely you are to find an epoxy choice in resin systems. Vinylester resin is the more likely to be used in a modern marine composite associated with a quality production-boat builder.
The most important consideration concerning all of the materials discussed is the quality of competence of the builders. This has been the biggest ball and chain ever dragged by the industry. Builders who do not have a quality manual probably don’t have a program, and if they don’t have a program (and I mean a good one), you will not have a trouble-free experience. Take it from someone who has done many a quality audit: It does not matter how good the materials are that you are buying. If you do not use them correctly and make sure that is the case every day, you cannot build a trouble-free boat. I do mean trouble-free for years. These days, the industry leaders are doing pretty well here. Many others still are not. The structural “guts” aspects of today’s boats are fairly good and well understood. All the other systems on a boat will need to be dealt with next. When that happens, your boat will be a lot like your car. It will be predictable, reliable and somewhat trouble-free.