The deterioration of fiberglass laminates because of the formation of osmotic blisters became something of an epidemic in the late 1970s and 80s. In fact, during that time as many as one sailboat in four was falling prey to the polyester mite. Companies such as Valiant, Beneteau and Jeanneau suffered significant financial loses because their boats too often were blistering and in some cases delaminating. A war was waged by boat builders and several undertook to do some basic research to solve the problem.

Everett Pearson, who runs Tillotson-Pearson in Rhode Island and is one of the most experienced fiberglass fabricators in the world, analyzed the building process from start to finish and experimented extensively with resins, cloths and building techniques. In the late 1980s he was able to offer a lifetime guarantee against blisters for all boats coming out of his factory. Moreover, working with companies such as Gougeon Brothers and the American Bureau of Shipping, Pearson pioneered the use of epoxy resins for bottom coats. He and many of his competitors in the field now offer guarantees and are building hulls to specifications developed by the ABS.

The result is that modern cruising boats should be far less prone to blistering than those built prior to 1985. Yet, the problem of living with a somewhat porous thermoplastic submerged in water for long periods is not entirely over. Even modern boats, when sanded repeatedly, scraped on the bottom or otherwise damaged by use and age, are liable to show signs of blistering and can, over time, suffer minor damage to gelcoats and laminates.

The ongoing process of protecting the bottom of cruising boats from blisters arises every time a boat is hauled for painting. So it makes sense when fitting out a vessel to attack the problem head on and make sure you have a complete bottom system that will not only beat the barnacles with the appropriate antifouling paints, but will also protect the fiberglass hull from the ravages of long term immersion.

Basic Precautions to Prevent Blisters

The best time to apply the first level of protection on a boat's bottom is as soon as it comes out of the mold where it has been laid up. Once the mold-release has been washed from the hull a barrier coat can be applied by the builder that will keep moisture from migrating through the gelcoat and begin the process of osmotic blistering. Some manufacturers offer this treatment as a standard part of their product while others treat an epoxy barrier coat as an owner's option. Such a barrier coat should be a high-impact epoxy such a West System epoxy, which will stand a lot of wear and tear and will stand up to moderate sanding in the years to come.

Yet buyers of new boats do not have the potential problems faced by those who are buying a used boat. While a boat that has been in the water for 10 or more years may never develop blisters, there is no way to predict which will and which will not.

On older boats, the best system to ensure that the gelcoat and first layers of laminate remain in tact is to lay up a bottom system that seals the gelcoat and is durable enough to last many years. It is important to remember that gelcoats are formulated from polyester resins — orthophalic, primarily — that are slightly porous. In other words, a gelcoat will vary gradually permit water molecules to migrate into the polyester structure, by osmosis, and those water molecules will in time begin to react chemically with the resin. The result is a small pocket of liquid that expands and forms the blister. If left to continue the blister can gradually migrate into the laminate and cause minor structural problems.

It is extremely rare to find a boat of 10 years or more that will suddenly begin to have serious structural damage. On the whole, if a boat is going to blister badly it will do so in the first few years in the water. Later, as the hull remains immersed, tiny blisters may form behind the gelcoat, but these are normally cosmetic and can be fixed with spot grinding and patching.

To protect an older hull from small blisters, it is necessary to grind the bottom down to the gelcoat, to remove all growth, and give the gelcoat a good sanding. Because a hull will hold moisture, it is important to let the hull stand out of the water in a dry place for a month or so before treating it. If possible, the boat should sit out on a warm surface, pavement or gravel, to permit it to cook somewhat in the warmth of the sun and to retain heat through the night.

Once the bottom has been sanded, faired if necessary with an epoxy putty, and cleaned, the barrier coat should be applied. Avoid applying a barrier coat when the air is too cool or in the early morning when dew and ambient moisture can still be on the hull. It is best to allow the hull to warm in the sun and to be thoroughly dry before starting. According to the excellent manual prepared by Gougeon, five coats should be applied to give adequate protection to the hull. Epoxy cures quickly when spread in a thin film so it is possible to build up fresh coats on top of previous ones. Yet, to get the best adhesion, the new coat should be laid on soon after the earlier coat has begun to cure. If the earlier coat is allowed to fully harden, then the bottom will have to be sanded lightly to permit the next coat to adhere.

Applying an epoxy barrier coat is a tricky job, best done by two people working together. While one rolls the coat on with a fine nap roller a second should come along behind and lay the epoxy out with a foam brush. This will flatten the coat and more importantly will remove any bubble left on the surface by the roller. Bubbles, even small one, leave a void in the coat which can in time become a pathway for water molecules.

Once the five coats have been applied, the epoxy should be left to cure for at least a day. The bottom will have to be sanded again — with 150 or 180 grit paper — before the antifouling paint can be applied. Such a barrier coat will last many years. Yet each time you haul the boat for cleaning or painting, it is important to check the whole bottom for scratches, nicks from groundings and other abrasions. If the bottom paint has been scraped away in any places, check to ensure that the epoxy coat is still in tact beneath it. If not, then a touch up will be necessary.

Renewing a Blistered Hull

Blisters are not a serious problem on most boats. Even a hull that has dozens of small blisters can be treated successfully and kept from deteriorating with occasional patching. Only when the hull becomes seriously pocked with masses of blisters and there are signs of delamination should you consider removing the gelcoat and first layer of laminate.

To repair small blisters, you have to grind the blisters down until you hit dry fiberglass. As the blisters are attacked with the grinder the soft gelcoat will pop and fluid will bleed out. Using a soft feathering disk and 40 grit paper you can make quick work of them. The area around the blister should be faired and all the soft laminate removed. The hull, once ground down, should then be left to dry for as long as possible to allow any moisture in the gelcoat to evaporate.

Once dry, the voids can be filled with epoxy putty. To get the best adhesion, the Gougeons recommend wetting each void with pure epoxy before applying the putty. When the surface is fair and all the indents have been filled, each should be given a five-layer barrier coat. When it is time to apply antifouling, each repair will have to be sanded so the paint will adhere.

On boats that have many blisters, it may become necessary to remove the gelcoat entirely and renew the whole bottom. This is a huge task and should only be undertaken if you know you have delamination. One way to test the bottom is with a moisture meter, that will give a reading of the moisture content in the laminate. Yet, such meters are not exact. If the boat still has bottom paint on it, or if it has been standing is cool weather over a damp surface, the meter can give an in accurately high reading. If you suspect you may need to renew the whole bottom, first remove all bottom paint and let the hull dry out in a warm place for at least a week before testing it with a moisture meter. Then, if the meter indicates a high moisture level, you will know that the problem you suspected is real. For the cost and trouble of removing the bottom paint, you may save yourself the much greater cost of removing all the gelcoat.

Until recently the only way to remove gelcoat and the first layer of laminate was to sandblast. This was dirty and inexact work. Toxins were released into the environment and the bottom was left with an uneven surface. The development of bottom peelers, which are basically electric planes operated either by hand or on an articulated arm, enable boat yards to cut away an exact amount of resin and glass. While still a messy job, the bottom can be peeled quickly and the remaining surface will be smooth and even.

Once peeled, the bottom has to be left to dry for a month. Some yards will built a tent around the bottom and run dehumidifiers close to the hull. This is not particularly effective because it is almost impossible to make the tent air tight, so the dehumidifiers end up trying to dehumidify the great outdoors. It is best to leave the hull in a dry shed with a concrete floor. Over time, the moisture in the hull will evaporate and the new bottom can be applied.

The easiest way to lay on a new sub level of glass and epoxy is with a chopper gun. Because the layer will not normally be structural, the chopped strand and resin will provide a solid build up without the impossible task of laying up glass mat upside down. With a new layer of glass in place and faired, the bottom can then be sealed with an epoxy barrier coat.

The cost of such a job will be significant. For a standard 40-footer, you can expect pay a professional boat yard $20,000 or more. Unless you are an expert with resins and glass, it seem impractical to tackle the job on your own.

Beating Barnacles With Antifouling Paints

While relatively few boat owners will have to face the problem of blisters, every one of us must find the best way to keep the bottom clean. There is little debate about the effects of growth on the bottom. Aboard Clover, a dirty bottom will slice a full knot of speed during a passage. We strive to prepare the bottom a thoroughly as possible whenever we have it out of the water because we tend to leave the boat in tropical water for 18 months or more at a time. That means finding the most potent paint and then putting enough of it on to last a while.

It used to be relatively easy to choose a paint to last for that period. The tributyl-tin paints available throughout the 1980s were so effective you hardly had to repaint from year to year. Paints such as Micron 33 became famous for multi year lives in the tropics. One friend of ours hauled his boat after three years in the Caribbean and found only a light slime which was washed off with a garden hose.

But tin-based paints were so effective they not only killed organisms on boat bottoms but also killed everything in the water around the boat. In 1988 the Environmental Protection Agency followed the leads of countries in Europe and around the world by banning tin-based paints for fiberglass boats. Today, only aluminum and steel vessels may use the high-powered paints, while the rest of the boating community has had to find alternatives with copper as the toxic element.

The choice today is between copper based paints with different characteristics and varying degrees of the toxin. Paints range from 20 to 75 percent copper. The quantity of copper in the paint is a direct measure of its toxic strength. Those at the higher end pack more punch than those at the lower end. And, accordingly, those with higher copper content will cost more.

There are two basic types of bottom paints: abaltives and conventional paints. Ablatives are soft paints that are designed to work as water moves by the hull; the painted surface slowly sluffs off the paint as it looses its toxicity. Boats that are on the move or moored in areas where there are strong currents do well with ablative-based paints.

Conventional paints leech toxin to the surface of the coating in a slow process as the paint becomes increasingly porous. These tend to be harder paints that will provide a smoother surface. But, they also have a finite time over which the copper toxin will provide protection. The hard conventional paints are favored by racers and those not needing the longer service of the ablatives.

Four different bases are used to formulate copper bottom paints: copolymer, epoxy, polymer and rosin. Rosin is the oldest base and has been in use for many years. Paints with a rosin base are hard coatings that can be scrubbed and wet sanded for racing. Yet, rosin based paints, even those with high copper content, are not designed to last a year or more.

Copolymers and polymers have been formulated to give the longest possible service. They are soft or semi-soft paints and use the ablative approach to toxicity. Awlgrip's Gold Label is a well known polymer brand that has proved to be long lasting and effective.

Epoxy paints can be either hard or semi-hard coatings. Paints in this category, such as those from Pettit, are known for their long life and their ability to carry the most copper. While the heaviest of these, Trinidad, is one of the most expensive paints on the market, it is also one of the best. Among the offshore fleet in the tropics, Pettit's products are widely used and favored by many.

Since the demise of tin paints, sailors have been searching for a replacement that will do the job as well. One solution that has been found to work is adding the antibiotic tetracycline to standard copper paint. The drug is a broad based and powerful antibiotic that doubles as a powerful biocide. Several companies market tetracycline additives for bottom paints and these are reported to give the paint added punch.

Among the brands favored by cruisers you will find International's CSC copolymer, ablative paint and Pettit's Trinidad epoxy paint. We have used Trinidad for two years in the Pacific and find it durable and very effective.

One of the keys to dealing with softer ablative paints to the leave them alone. It is tempting to scrub a bottom before making a passage, and this can be helpful with hard paints. But, soft paints are designed to work best when the boat is moving quickly through the water and nothing will clean the slim better than a day or two of hull speed sailing. At the end of a passage you may have picked up a few goose barnacles, but if the ablative bottom paint is still in reasonable condition the boat's bottom will be clean. But, if you attack the bottom with a scrub brush you will accelerate the ablative process dramatically and shorten the paint's effective lifespan.

Applying Bottom Paints

Not all bottom paints are compatible. When you have selected a paint that will be right for your area and for the type of sailing you will be doing, you need to determine if it will adhere to the surface you will be painting over. Not all paints can be applied over others of a different type.

As a rule soft paints can be applied over hard paints that have been well sanded, but not the other way around. An ablative will begin to crumble under the veneer of hard paints which will flake off in time. Vinyls an be used over other vinyls, but should not be used over soft paints. Rosins can be painted over all of the other type of bases, yet if you are covering a thick cover of soft paint, it must be sanded until the surface is hard. Epoxies and polymers should be applied over hard surfaces, so soft paints need to be sanded thoroughly before they are covered. However, most paints will not do well used over coatings containing graphite or Teflon. These slick racing paints are rarely used by cruising folk, but if you have purchased a used boat you may have it on the bottom. Lastly, when in doubt, contact the manufacturer of the new paint or sand the old surface thoroughly and begin again.

On older boats it is common to find layer upon layer of paint, which in time can begin to become brittle and flake off. When the time comes to remove the build-up of old paint, the easiest way is to use a sandblaster. While this sounds complicated, most boat yards have blasters or units can be rented from rental agencies. Using a sandblaster is not difficult. However, care must be taken to avoid blasting into the gelcoat and damaging the surface. If you have taken the trouble to sandblast the bottom, it makes sense to fair it with epoxy putty and then coat it with a barrier coat.

Most boat owners roll on bottom paint with a household roller and use a throw-away brush around the waterline and to get into the hard spots around the propeller and rudder. Using a roller is not difficult, however you must take care to apply the paint evenly and smoothly. If the paint has not been applied in a somewhat uniform thickness, it will begin to fail unevenly and barnacles and slime will form in patches here and there along the bottom. When rolling, keep the roller loaded with paint and keep stirring the paint in the can and in the roller tray to ensure that the heavier copper is well distributed through the mixture.

More and more boatyards are spraying on bottom paint. While it is possible to achieve a very smooth finish with a spray gun the coating can contain quite a lot of air and maybe much thinner and more porous than it looks. If you are intent on spraying, it is best to use an airless spray gun. Such a gun will give the best and most even concentration of paint, while also providing a smooth surface.

Brush painting may be the best way to get a thick and even coating of bottom pain onto the hull. Those who spray or roll often find at the end of the season that the areas tipped with a brush are in the best condition. If you have the time and energy, then laying on the paint with a good 4-inch brush may be the way to go. But, be careful to avoid putting on too much paint in one coating. A very thick coat will tent to become brittle and will not adhere to the old paint of the bottom as well as a moderately thick layer of paint.

How many coats should you apply? If you will be using the boat for a summer season and then hauling it again, two coats of a good quality paint will see you through well. Should you be planning to sail to the tropics over a winter and will leave the boat in the water for a year or more, then three coats over the whole bottom and a fourth coat along the leading edge of the keel and along the waterline will give a sufficient coverage. Those traveling a long way will find that paint on the leading edges wears away much faster than elsewhere, hence you may chose to add even a fifth coat on these areas before setting out.

Among offshore cruisers is it common to lay on a different color as the base coat so it is possible to tell quickly how far the whole surface has deteriorated. If you normally paint with blue paint, lay on a base of red. When the red shows through you'll know it's getting time to haul out and redo the whole job.

How long will copper bottom paints really last? In the tropics and among boats that are sailed actively, we found that 12 months was about average. Aboard Clover we sail with Pettit's Trinidad, which has a copper content of 75 percent. We apply three coats and then add a fourth along the leading edge and at the waterline. After 10 months the bottom begins to slime while sitting in harbor and then cleans itself as we are underway. At the end of a full 14 months in tropical waters we find the coating no longer resists grasses but is still mostly effective against barnacles. This is the point at which we repaint.

Others have not had as much success. In the fleet crossing the Pacific from Panama to Fiji in 1991, many were complaining of fouled bottoms by the time they got to French Polynesia. Once the fleet had migrated west to Fiji, a fair number found it necessary to haul out for a recoating. No doubt the problem was compounded for those who sailed to American Samoa where the harbor is badly polluted with fish tailings and sewage. Moreover, those who remained at anchor in Suva, Fiji, also polluted, found that growth on their bottoms was increasing at an alarming rate.

A Total Bottom System

There are few things more satisfying than getting the best performance from a boat, whether that is quick daily runs from port to port or fast passages across the ocean. And, equally satisfying is finding the bottom of the boat clean and unblistered when it is hauled out at the end of a season. The best way to achieve these ends is to make sure the bottom has a total bottom system before it goes into the water.

The best time to tackle a bottom system is as soon as the boat is purchased. If it is new, applying the full system will prevent water damage and will ensure that barnacles don't slow you down. With used boats, as soon as it comes out of the water is the time to tackle the job, to make sure that no further deterioration takes place and to rid the bottom of all unfamiliar and possibly incompatible coatings.

As we discussed above, the first layer of a total system is the epoxy barrier coat. All blisters and gouges should be ground out and filled and then the whole surface should be coated with five coats. We use West System epoxy because we have always found it easy to use and reliable. System Three is another choice also widely used by professionals.

Once the bottom has been coated with epoxy, it should be sanded fair and coated with two or more coatings of bottom paint. At the end of each sailing season this should be sanded virtually off to prevent a build up and to permit you to inspect the barrier coat for damage. If you will be racing or are a demon for speed, you may want to wet sand the final coat with 400 grit paper — hard coatings only — to get the slickest possible surface.

Treat the bottom with care and you will not only get the best performance from the boat but will ensure that the integrity of the hull is preserved.