DS Marine Surveys

991 Ridgemount Blvd. Oshawa Ontario L1K2K7 Ph: 905-449-2176
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Surveyor - C. David Sandford SAMS® / AMS®

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Fiberglass Boat Construction - The Basics

Fiberglass is a composite material consisting of a hardened liquid resin and glass fibers in various forms combined together in layers to form a matrix that is stronger than the sum if it's individual components. This type of construction when used in conjunction with both male and female molding techniques can produce objects and structures of almost any shape making it ideal for both hull and deck / superstructure construction.

Materials Used in Fiberglass Boat Construction

Resins

These are the glues (so to speak) used to maintain the position of the glass fiber mats and rovings that make up the fiberglass matrix. Resins are thermo set plastics that will not harden on their own but require a chemical catalyst to provide the necessary chemical reaction and resulting internal heat to harden the material. There are three basic formulations if resins currently in use today.

Gelcoats: A pigmented, thickened resin which is the first or exterior component in the laminate schedule. Is usually sprayed into a female mold and provides the colored, smooth surface of the component. It is also fortified with additives to provide moisture and UV resistance.

Polyester: The most commonly used resin in boat construction today. Is is cheap, easy to use and although not the strongest or most moisture resistant resin when used properly is more than adequate for production boat construction.

Vinylester: A combination of polyester and epoxy resin. It is stronger and more moisture resistant than polyester but has the disadvantage of being more expensive for the manufacturer. Until recently it has seen little use in boat construction but with the increase of blistering and delamination seen in older polyester hulls it's use is becoming more widespread at least in outer layers of hull laminations.

Epoxy: The "Cadillac" of all the resins in use today. Is is by far the strongest and most moisture resistant of all the resins. It also bonds tenaciously to most materials. On the down side it is very expensive, tricky to use and is very sensitive to UV radiation. It's use has also been limited but it is starting to show up on higher end production boats and is in widespread use by custom manufacturers. It is also a chief component in Wood / Epoxy construction methods.

Glass Fibers

The "Strongback" of the fiberglass matrix. If is produced in various forms but for our purposes here we will group them into two basis forms.

Glass Mat: Short strands of glass fiber (usually less than 2") combined in random orientation with a binder material and compressed into a spongy mat. Manufactured in various thicknesses (weights).

Woven Rovings and Fiberglass Cloth: Long strands of glass fiber combined in a woven pattern (like a weave in regular cloth). Manufactured in various thicknesses (weights).

Laminate Configurations:

Layers of the conventional laminate sequence usually consist of alternating layers of mat and rovings saturated with resin. This process is repeated until the desired thickness is achieved. Fiberglass hull construction techniques can be broken down into two main categories.

Single Skin Construction: The simplest and until recently the most popular construction method. It consists of an exterior gelcoat and alternating layers of mat and rovings saturated with resin until the desired thickness is achieved. It produces a strong, water resistant component which is relatively easy to repair. It is not very stiff and in the case of a boat hull usually needs to be reinforced with some type of interior structural grid or inner liner. It also provides no insulation qualities, is noisy and interior condensation can be an issue.

Cored Construction: It features all the components of the single skin technique but the laminate is split around a central core material. Core materials are usually various types of closed cell foam, end grain balsa wood, plywood and both red and white cedar. The later two favored mostly by custom builders. Cored construction is used almost exclusively in decks and superstructures with end grain balsa and plywood usually being the core materials of choice. Cored hulls are light, stiff (usually not requiring any internal stiffening structure) and have good sound deadening and insulation qualities. They are however more prone to delaminaton from moisture intrusion and can be more difficult to repair.