Solid and Sandwich Core Fiberglass Boat Hull and Deck Construction

One of the topics that I’m sure we will be doubt be visiting ad re-visiting in the future are issues surrounding fiberglass (FRP) construction and repair as it pertains to hulls, decks, rudders etc. In that vein I think that its prudent to discuss some of the basics and get some of the terminology straight so that we are all on the same page so to speak. I know that some of this will be old hat for some but for others I hope that it proves interesting and informative.

I have even done numerous seminar presentations on all of the above topics so in the next few posts I’m going to present some of that information here.

Relatively speaking fiberglass re-enforced plastic (FRP) as a method of boat construction is a fairly new technique, dating back to the 1950’s and really not becoming the dominant method of production boat construction until the late 1960’s and into the1970’s. I’m sure that these dates could be debated but in my re-search they are close.

Next let’s look at some the main components of FRP laminates and some of the common terms used:

Resin: The plastic or “glue” so to speak that is used to saturate the glass cloth or mat utilized in the hull or deck construction. The three most common types in use today are Isolathic Polyester, Vinylester and Epoxy. They all must be catalyzed by the addition of a hardener chemical.

Before we discuss resins further I want to define one important term:

Hygroscopic:  Readily taking up and retaining moisture. Taking it further, the ability of a substance to attract and hold water molecules from the surrounding environment.

This is what resin can do in varying degrees with the condition sometimes manifesting itself as gel coat blisters and softening of core materials. .

1-Isolthalic Polyester: The mainstay of fiberglass boat building. It’s been around since the beginning and when utilized correctly it can produce a quality product and is still in use today It is however the most hygroscopic of all the commonly used resins, has a weaker molecular chain and is the least expensive.

2-Vinylester: This resin is seeing more use recently in boat construction particularly in the outer hull laminate layers. It is stronger, has reduced hygroscopic properties and shows superior bonding and molecular strength.

3-Epoxy: The highest quality of the resins discussed here. It is used on almost all Carbon Fiber and Kevlar laminates, shows the best (almost no) hygroscopic properties, the highest strength in its chemical molecular chain and in bonding. Its high cost has limited its use in production boatbuilding but it is beginning to show up on higher end boats and in composite spar construction. Epoxy resins are often used both with glass re-enforcement and on their own to strengthen and waterproof wooden hulls and structures. Its superior bonding strength and reduced hygroscopic prosperities make it well suited for these purposes as well.

Next we’ll discuss the different types of spun glass re-enforcing materials.