As I consider purchasing a larger and more comfortable boat for long-distance voyages, I find it interesting to explore the different qualities of fiberglass and its seaworthiness. Fiberglass is not just fiberglass; it can consist of various components, and be constructed in different ways, and both price and quality are parameters I need to consider.
My background for writing this article is not as a professional. I am an architect and an experienced sailor, but very curious and do my best when researching. If you have anything to add, please feel free to write to me at [email protected] or leave a comment at the bottom of the page.
We all want the boat to have the greatest possible strength in terms of both compressive and tensile strength, to be lightweight, and to be rigid. The boat should also last for many years. Therefore, it is important what it is made of and how it is constructed.
What is fiberglass?
What we call fiberglass is essentially fiber-reinforced plastic. It can consist of various types of plastic, and reinforcement can be done with various types of (free) fibers and different types of mats.
The advantages of fiberglass include being inexpensive, lightweight, durable, having high tensile strength, and being highly moldable.
Different Types of Fibers for Fiberglass
The fibers in fiberglass do not necessarily have to be made of glass, but they often are. They can also be other materials, such as carbon, kevlar, or even paper or wood fibers, although the latter is rare.
Different Types of Mat for Fiberglass
There are many types of mat with quite different qualities, such as fiberglass cloth and mat, carbon fiber, kevlar, woven fiberglass cloth, biaxial, triaxial, quadrixal, unidirectional, and CSM / chopped mat.
The last one, CSM or chopped mat, is the most commonly used. It is inexpensive, and the fibers are laid in a random pattern. It is easy to work with, and the binder easily fills it.
However, woven mats are much stronger but more difficult to work with and more expensive. In the highest price range, there is carbon fiber and kevlar mat. Carbon fiber is almost exclusively used for masts and very ambitious racing boats due to its cost.
All types of mats add greater strength to the fiberglass than the free fibers, but some are stronger than others and weigh less, etc.
Fiberglass Work on Boats
One of the good things about having a fiberglass boat is that it is not so difficult to repair. For example, I have closed holes from old hull fittings with a simple kit from Plastic Padding, which also includes a mat. I did this following the boat builder’s instructions, so this piece of advice is passed on here.
Different Types of Plastics in Fiberglass
The binder (the liquid part) in fiberglass is typically either polyester or epoxy. Other types of adhesive can also be used, and it can be problematic if there are water-soluble components. So it is good to know what plastic the boat is molded from before purchasing it.
The Difference Between Epoxy and Polyester
In general, epoxy is stronger and more resistant than polyester, but polyester is cheaper. All older boats are made of polyester because epoxy is a newer product. However, polyester is still the most commonly used product due to its price.
Polyester is more prone to osmosis than epoxy and is more difficult to work with.
When repairing a fiberglass boat, it is important to know what it is made of. If you want to repair with polyester, the boat MUST be made of the same material because polyester does not adhere well to epoxy, even if it appears fine and cured. Therefore, it is always recommended to use epoxy on top of existing fiberglass.
Different Molding Methods for Fiberglass Boats
Hand-Laid Fiberglass
In hand-laid fiberglass work, the boat is molded directly in a mold through manual labor. You can read more detailed information on how this is done at Siencedirect.com.
The disadvantage of this method is that moisture from the air can potentially enter the fiberglass, so it should be done in a controlled environment with temperature control. If there is moisture in the construction, it is more likely to delaminate and develop osmosis, which is manifested as a vinegar-like odor.
Vacuum-Infused Fiberglass Molding
With this method, vacuum is used to fully infuse the plastic into the fiber material and mold the shape of the hull. Since it is completely airtight, the risk of moisture in the construction is minimal.
VACUUM INFUSION
Quote from Composites
Either a solid or flexible backing form is used, or a flexible film is applied.
Air is removed to create a vacuum in the form with the dry glass. Often, a glass fiber called flow mat is used. It has a core that allows easy transport and impregnation of vacuum polyester (matrix material) in liquid form into the fiber reinforcement.
Spray-Molded Fiberglass
Fiberglass is spray-molded by blowing the mixed fiberglass into a mold. The fibers are therefore added in the form of free fibers, and the construction is not as strong as if it were constructed with a mat. However, I think only small boats like kayaks and dinghies can be spray-molded.
What Is a Sandwich Construction?
A sandwich construction is a structure made up of several materials, which together have greater strength than the individual materials alone. Sandwich constructions in boats consist of several layers of fiberglass and a core of materials like balsa wood or some type of foam. When you say that a hull is built in a sandwich construction, it’s a bit like saying, “I have a cake.” We don’t know what kind of cake it is and what ingredients it’s made of.
Foam for Sandwich Construction
The foam in sandwich constructions can consist of materials such as divinycell (PET), PVC, or polyurethane (PU or PUV).
Advantages and Disadvantages of Divinycell
PET plastic (Polyethylene Terephthalate) is often simply called Divinycell. It is easy to work with, very strong, and has good properties against fire, smoke, and toxic fumes. It can withstand high temperatures and can be recycled. It cannot break down naturally, which is an advantage while it’s in the boat’s construction but, of course, a long-term disadvantage.
Divinycell is an expensive material.
Advantages and Disadvantages of Balsa Wood in Boats
Balsa wood is a fast-growing tree that can absorb up to five times its weight in water. Therefore, it needs to be dried for a long time to be used as a building material. Dry balsa wood is so fragile that it can be broken by hand and easily catches fire. When used in a sandwich construction, the wood absorbs moisture easily. The major drawback of using balsa wood in boats is that organic materials decay in the moist environment. If holes are cut, for example, for hull fittings, or if there are cavities due to poor construction (where condensation can occur), you risk mold and rot. We know that wooden boats need maintenance, but with balsa wood encapsulated in the construction, we do not have this option.
Balsa wood adds strength and rigidity to the construction and is found in catamarans because it is lightweight and inexpensive. If the wood rots, it is a significant safety problem.
Checking Balsa Wood in Sandwich Constructions
To check the balsa wood in a construction, it may be necessary to cut a hole in the hull and measure with a moisture meter.
You can also tap on the fiberglass with a small hammer. The sound should be solid. A soft thud indicates moisture.
Other methods to determine if the balsa wood may have started to rot are to notice if the material is soft—for example if the deck springs or if the plugs in a teak deck work their way up.
So, what should we buy?
That’s the big question, and it’s not so straightforward to answer. If you have a budget of several million, it’s easier to be choosy.
Buying the most strongly constructed boat is like a vaccine. Nice safety, but maybe not necessary at all. Even if you’re vaccinated, you can still get other diseases, so safety lies mostly, or just as much, in experience, skills, and knowledge.
I’ve met many sailors who aren’t so fond of newer boats. There isn’t as much thickness in them as there is in the older ones. This is probably because the new boats have been optimized for materials, but if you have that feeling, you should follow it. I probably belong to that type, while Henrik prefers the modern ones.
There are plenty of boats sailing around the world with balsa wood and chopped mat, and they are still being produced, and in most cases, they work flawlessly.
A point I often come back to is that cheaper boats are more likely to get out on the water than the expensive ones. Their owners have the time for them and may even enjoy getting them ready for sailing.
You can also save up for so long that you never go sailing.
FAQ about fiberglass boats
Depending on the quality of the fiberglass, you can expect a boat to last for more than 60 years. With proper care, many will be virtually indestructible.
It is actually not uncommon to apply fiberglass to a wooden boat. In most cases, it is done to achieve a watertight exterior on a boat that is otherwise difficult to seal.
Fiberglass is also often applied to cabin roofs and decks.
If you are considering buying a fiberglass-coated wooden boat, be careful. Sometimes fiberglass is applied over rotten wood, and it is not a durable solution.
NOTE: A fiberglass-coated wooden boat has almost no value when selling.