Some call it GRP, others refer to it as GFK in German, but more commonly, we are talking about a material known as “fiberglass.” This material has brought massive innovation to various technological sectors and has led to the construction of excellent fiberglass boats, whether through manual lamination or vacuum infusion.
Since the choice of material is always an important concern for anyone opting to buy a boat, I thought it would be useful to discuss fiberglass hulls here, covering construction methods and common issues that unfortunately need to be monitored, especially for older boats.
What is Fiberglass?
Often, names can be misleading; other times, they reveal the true nature of things. In the case of fiberglass, it’s the latter: we are referring to plastic reinforced with glass fibers. Some of the common acronyms used for this material include PRFV (Plastica Rinforzata con Fibre di Vetro), as well as the English GRP (Glass-Reinforced Plastic), GFRP (Glass Fiber-Reinforced Polymer), or simply “fiberglass.”
The construction of fiberglass boats began in the 1960s. Over the years, this material, which already had excellent basic properties, has consistently improved; today, it is much lighter, stronger, more resilient, and durable.
Interestingly, early fiberglass hulls were often overcoated, even when it was unnecessary. In terms of strength, overcoated fiberglass boats gained a lot, but they became heavy and sluggish when it came to putting up the sails.
Construction Methods
Chopped Strand Mat
Early boats almost always used Chopped Strand Mat (CSM), a fiberglass fabric made from short cut fibers that are bonded together.
The process involved:
- Preparing the gelcoat, a thin and smooth outer layer.
- Spraying the gelcoat inside a waxed female mold.
- This created the first layer of Chopped Strand Mat, which was placed inside the mold and “wet” with resin and rollers.
- Once the layer hardened, enough layers were added to achieve the desired thickness (known as the “lay-up” phase).
Vacuum Infusion Technology
As an alternative to manual lamination techniques, there is vacuum infusion, which is often discussed but poorly understood technically.
In vacuum infusion, a pre-calculated amount of resin is injected in a controlled and even thickness. This process technically ensures a more uniform result and generally reduces the presence of air intrusions in the fiberglass hull, enhancing its strength.
Moreover, another aspect not to be overlooked is that the toxic fumes from solvents created during the polymerization process remain inside the bag and can be disposed of safely.
This method produces a nearly impermeable product that is highly durable when combined with high-tech fiber materials. It is mainly used in racing boats due to the lightness of the structure, although it comes at a higher cost.
The Osmosis Problem
A coating, such as polyester or epoxy resin, can also be applied over bare gelcoat for added protection against water ingress through osmosis.
In some cases, the boat builder will propose an epoxy resin coating from the outset as extra protection against osmosis.
In any case, buyers often encounter the issue of osmosis, although fortunately, this typically affects fiberglass hulls built before the year 2000.
Often, osmosis may not be as severe as it appears, and many affected boats can last for decades after undergoing corrective treatment. This treatment usually involves stripping or sanding down the gelcoat and the top layer of fiberglass that has absorbed water.
At this point, the hull should be washed with fresh water and then thoroughly dried. Sometimes, large vacuum pads are applied to the hull to ensure that no water remains on the structure.
However, it is crucial to take action to treat a hull affected by osmosis, using vacuum bags to extract moisture and addressing the situation with a tailored intervention once the problem exceeds a certain level of seriousness.
The risk of underestimating osmosis is that your fiberglass boat may start to delaminate!
After the treatment, the warranty typically covers five years. It is advisable to choose a good maintenance professional before proceeding with the treatment, or if you don’t have one, ask your trusted marine surveyor for recommendations.