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Why Fiberglass A Boat?

On May 28, 2015, in Designer Articles, WebLetters, by Gayle Brantuk

The following article is excerpted from our book, “How to Fiberglass a Boat”.


It may seem self-evident why one should want to cover a boat with fiberglass. But the surprising thing is that many people do not realize the REAL reasons. Some just assume that it’s the thing to do because they’ve seen it done before. Others have misconceptions as to what the product can do. For example, many novices consider the fiberglass sheathing to be a “wonder” material that will cure all future ills.

Unfortunately, much of the misconception surrounding fiberglass sheathings is the result of promotional efforts and false information passed on from those with vested interests, i.e., the people who want to make a buck selling the materials. The primary reasons for covering or sheathing a boat hull with fiberglass, however, are quite basic, and are as follows: 1. Reduce hull maintenance 2. Improve appearance 3. Keep water out of the boat 4. Protect the hull from impact and abrasion. These are the REAL reasons, and any ONE of the above may be reason enough to go through the work and expense of doing the job if you think your boat is worth it. Of course, there can be secondary reasons, the importance of which will vary considerably depending on the type of boat, the waters in which it will be used, and the service to which it is put.

For example, you can add new life to an old boat by covering the hull with fiberglass (assuming it is of suitable construction, as will be discussed in Chapter 8). This can often add some strength and watertightness to the seams and joints, as well as reduce moisture absorption which adds unnecessary weight to a boat. Or you can use fiberglass materials for repairing or restoring old or damaged parts within the boat, thereby extending its useful life. Or you might cover a new boat with fiberglass materials just to protect it from marine parasites such as shipworms or teredos, or rot. In all cases, the smooth fiberglass surface reduces resistance and drag underway, adding to fuel economy.

One of the biggest misconceptions that the novice has is that a fiberglass covering will add considerable strength to a hull. However, while partly true, generally this is a fallacy. The fiberglass covering, which usually utilizes cloth and resin, should be considered as a non-structural protective or cosmetic covering only. For this reason, the boat owner should not be misled into thinking that he can take a structurally weak or unsound hull, slap some cloth and resin on it, and make it sound, or reduce planking thickness and make up for it with a fiberglass covering. Such an approach is usually doomed to failure.

Few realize it, but fiberglass on a weight basis does not have nearly as much stiffness as does wood for example, and is in fact quite flexible. Thus there is no practical way a thin layer of fiberglass can “stiffen up” a hull that may be flexing, especially if the flexing is caused by an unsound structure. There are some approaches to restoring older boats with fiberglass, however, as described in Chapter 14, but these consist of more than a lightweight, thin sheathing, and are much more involved than a simple sheathing application.

Probably one of the most repeated claims about fiberglass (whether for sheathing uses or as applied to the factory-built fiberglass boat) is that “you’ll NEVER have to paint your boat again, EVER!” This statement is ONLY true if you don’t care what your boat looks like!

It IS true that the resin coating used with the material, as well as the resin gel coat (outer coating) used on factory-built fiberglass boats are finished surfaces in themselves that offer some degree of protection. However, even though the gel coats on factory-built fiberglass boats contain a “molded in” color, and resin can be pigmented in covering work applied over other types of boats, such surfaces still need the protection of a paint system or other specialized coating. If not protected, they will sooner or later fade, lose their color intensity, become “blotchy” with atmospheric exposure, or perhaps “chalky”, and generally become unattractive from the normal scrapes and bumps all boats are subjected to.

In fact, one of the bigger problems that has developed with surfaces of many factory-built fiberglass boats (at least below the waterline) is a phenomenon known as gel coat osmosis, an unsightly blistering and pockmarked appearance that can lead to extensive and expensive repairs. In short, just about all boats will require surface protection and periodic recoating with paint or other coating systems to enhance or restore their original appearance, depending on the extent of exposure and use.

What IS true about the fiberglass sheathed boat as opposed to the boat without a sheathing is that in most cases the boat will probably go two, three, or more seasons without needing paint. This is quite an improvement over old uncovered wood boats which require a fresh coat of paint each season. Paint coatings last considerably longer when applied over a substrate that’s made more stable by the fiberglass sheathing. Of course, for boats that remain in the water all season, a special anti-fouling bottom paint is still required in most areas on ANY boat regardless of what it is made from.

This plywood planked Thunderbolt was built by an amateur who had never built a boat before. The entire hull was covered with a single layer of fiberglass cloth and clear resin. The natural finished foredeck of ribbon grained mahogany was covered with lightweight deck cloth without staining the wood beforehand. The entire boat was finished with a sprayed two-part epoxy paint system for a rich, deep finish, using a clear finish on the foredeck. The resulting hull will be maintenance free for many seasons.

In short, whether the boat is made from all fiberglass or is covered with fiberglass materials, it WILL require maintenance, but probably NOT at the rate of boats made from other materials, or those NOT otherwise protected by fiberglass sheathing. Furthermore, it will be cheaper to maintain overall, and such maintenance will be easier when it is required. This is especially the case when one of the suitable epoxy resins is used in the fiberglass sheathing application.

As can be seen by the photograph of the boat above, a covering of fiberglass cloth and resin can do wonders for a boat’s appearance. Of course, this applies only when the job is done correctly according to the methods specified in this text, and assuming that exposed surfaces are painted or coated with a suitable product or system applied per the manufacturer’s instructions. To achieve success, FOLLOWING THE INSTRUCTIONS PROVIDED WITH THE PRODUCTS YOU WILL USE THROUGHOUT THE FIBERGLASS APPLICATION CANNOT BE OVEREMPHASIZED!

Generally speaking, the manufacturers of resins and paints or coating systems spend a considerable amount of time, effort, and money in testing and research to develop products which will give good results when used properly. By not following instructions, you’ll probably wind up with a boat that may actually look WORSE than it did before it was covered with fiberglass.

The combination of fiberglass and resin forms a seamless envelope around the hull which effectively keeps water from passing through seams or joints and into the boat, assuming such joints are structurally sound. This same capability can be put to good use on decks and cabin tops to keep water out of the accommodation spaces on larger cruisers, and in the case of wood boats, this can halt significantly the promotion of rot in the process.

Now that you know some of the REAL reasons for covering a boat with fiberglass, you can better decide if your boat should be covered and why you’ll be doing it. You’ll have to weigh the benefits of the covering, both with regard to the value of your boat as well as the cost and effort required to do the job. Because of the several combinations and options available in both the resins and sheathing materials that can be used, you’ll need to know more about these before you can make an informed choice, and that’s what will be covered in the following chapters.

Your Thoughts?

3 Responses to Why Fiberglass A Boat?

  1. Lorne says:

    I don’t agree. I built a strip/fiberglass kayak almost 30 years ago and have only put one coat of varnish in this time (that was just to cover scratches, the finish was fine).

    I still remember being surprised how much strength the glass added, and have made enough mistakes over the years to conclude that 1/8″ cedar strip with glass on both sides is shockingly strong.

    What I’m looking for now is carefully measured strength comparisons, but all I am finding is random opinions 🙁

  2. Angel Ayala says:

    Good article, fiberglass a wooden boat is expensive, add weight, got to painted and is not a ease task for everybody, need some special tools and equipment plus you need experience with dose quimical components. But when you finish the job…you have a better , more durable, better looking, stronger, more safety and is a new boat for a couple more years to go.

  3. Chris says:

    Good article, nice to see some truth about fiberglass coatings!
    One thing often overlooked and possibly covered in a subsequent article, is the added weight glassing a wooden boat adds!
    Can take a lightweight hull and add dozens to hundreds of pounds of extra weight, something often overlooked in the building process.

    Thanks for the articles!


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