Materials and Construction

GRP (glass reinforced plastic) commonly know as fibreglass is extensively used in boat building. Not all fibreglass is made equal! You should ask you builder what resin is used, the construction process,the type of fibers and the laminate thickness above and below the waterline . The SABS/ISO standards are voluntary guidelines for boats under 9m...

To understand your boat's construction you first need to understand a few terms.

Toughness - the ability to endure flexing, this is determined by the resin used and the resin content of the laminate. A laminate that is not tough would be described as brittle. When you hit a rock you want your boat laminate to be tough.

Stiffness- the ability to resist flexing, this is determined by the resin, fiber reinforcements and the thickness of the laminate . A laminate could be stiff and brittle or it could be stiff and tough. When you are constantly pounding into waves and chop you want your boat to be stiff- flexing leads to failure overtime.

Strength- the amount of load it could carry if used as a beam, this is determined by the stiffness and toughness of the laminate. If you take a wave over the bow or get rolled you want a strong boat to avoid catastrophe.

Construction Methods:

Gelcoating- this is either brushed/rolled on or it is sprayed on. Sprayed gelcoat has a more consistent thickness which leads to a much better finish long term.

Brushed/rolled gelcoat leaves thick areas that are prone to cracking.

The Chopper Gun-The worst construction method. It produces laminates with short fibers and high resin content. To compensate for the reduced strength the laminate is made thick and thus heavy. This does however produce a boat with a soft ride.

Hand Laminating- This varies substantially depending on the skill of the laminator, it is not a great job so skilled labour tends to avoid it. However a skilled laminator can build a quality laminate if the correct fibers are used.

Typically you end up with a laminate that is inconsistent and only has a 30% fiber content(70% resin). So the laminate is brittle compared to better processes.

Vacuum Infusion

This is by far the best method of building boats. Producing a consistent, tough and strong laminate with around a 60% fiber content (40%resin). The process takes a little longer and requires a high level of skill so is only used on high end boats and yachts.

RESINS:

Gelcoat

This is typically polyester based and is the UV resistant/waterproof coating that is used to "paint" boats. It is very brittle and needs to be between 0.5 and 0.75 mm thick to avoid cracking.

Polyester Resin

This is the standard resin used for boats. It is brittle and absorbs water overtime, particularly if it is subjected to constant flexing which causes micro-cracking. For this reason it needs to be covered with Gelcoat of a good paint suitable for submersion. It is also important that the laminate is stiff enough to avoid excessive flexing.

Vinyl Ester Resin

This is a more expensive resin, sometimes referred to as a modified epoxy resin. It is less brittle, tougher and stronger than Polyester. It is also waterproof and used as a skin coat against the gel coat in higher end boats. In some instances premium boats are offered in a full Vinyl Ester version

Epoxy Resin

This is a premium resin mainly used for ultralight race and high performance boats. It is a lot tougher, stiffer and stronger than the previous 2 resins. It is completely waterproof, but does not really work with gelcoat, so boats usually have a painted finish.

GLASS FIBERS

Chop Strand Mat (CSM) this is the basic glass used in most boats. The short fibers make it easy to work with and provide strength in all directions. Because it has short fiber lengths it is not very strong or stiff.

Biaxial Glass Fiber (Biax)

This consists of continuous strands of fibreglass bundles knitted together in 2 layers at 45degrees to each other. Much stiffer and stronger than CSM

Uni-Directional fiber(UD)

This consists of continuous strands of fiberglass bundled together, all running in the same direction. It is very stiff and strong, but only in the direction in which the fibers are running. So it is used to reinforce high stress areas.

Quadraxial Fiber (QUAD)

This is a layer of Biax knitted with 2 layers of UD running at 90 degrees to each other. It is very stiff and strong in all directions.

Ultimately you should get what you are paying for so it is worthwhile understanding what goes into your boat. A good gage here is to have a good look at older boats from a manufacturer. A well built boat will age significantly slower.