Keeping up Appearances - Part Two

A lot more years ago than I care to admit, I owned a steel boat, (God forgive me - and it was a yacht too!). I bought it in Sydney and bummed around the north Queensland coast in it for a couple of years (ah, youth).

It sure taught me a lot about boat maintenance and being on a financial shoestring meant that I had to do all the work myself.

Of all that work, none was worse than that which involved the underwater sections. The problem the boat suffered from was a thing called 'paint rejection', and the agony of hauling the ship out of the water only to see that this hideous affliction had struck once again, causing vast areas of the underwater surfaces to be totally bare of paint in spite of all the best attempts to overcome the problem at the last slipping, was at times almost too much.

I would gaze in absolute envy at the boats around me, invariably constructed of fibreglass, as their owners merely seemed to give the hull a quick wash down and re-antifoul before it could go back in the water. Maintenance free, yes, that's how fibreglass seemed to be in those days to all us peasants in steel, timber or concrete boats, and I for one vowed that my next boat would definitely be built in glass.

A lot of years have passed under the keel since those days. I've owned a variety of boats in both timber and plastic, and if the years confirm wisdom, then the wisdom I have learned is that nothing is maintenance free, particularly boats. I no longer worry about paint rejection, but a fibreglass hull does bring its own peculiar set of problems, and it is these I'm going to discuss in this article.

BLISTERING TERROR
Probably the most serious of the problems to affect the underwater portion of a fibreglass hull would be blistering, more commonly referred to as osmosis. Nothing is more calculated to strike terror in the heart of the boat owner, nothing will reduce the value of the boat more and nothing, it appears to me, is less understood.

At this point I should like to state that I am not an expert in fibreglass, nor do I pretend to be. However, I have owned four fibreglass boats, I have been involved in a major osmosis repair of the boat I currently own and I've seen many fibreglass boats being built from the resin drum stage to the actual launch.

Over the years I have observed a lot of hulls stricken with the 'pox', as it is commonly referred to, and spoken to many experts on the problem, so for what it is worth I offer my own observations.

WHERE IT STARTS
Last month we looked at the initial stage in the manufacture of a fibreglass boat. A mould in the shape of the hull is manufactured and the inside of this mould is polished to a mirror finish before the gelcoat is applied to the surface. This is not the only way in which a fibreglass boat can be made, but it is by far the most common.

The resins used to build up the hull thickness are complex and generally only fully understood by the chemists who made them; however, polyester resins used by the boatbuilding industry are of the cold curing type, which means they will cure to a hard solid without the application of heat.

Curing is achieved by the addition of a catalyst. For those who remember chemistry from school, a catalyst is a substance which promotes a chemical reaction but does not take part in the chemical reaction itself.

This curing is important and ideally 100% of the resin should be set rigid by the chemical reaction.

Unfortunately, microscopic pockets of uncured resins like tiny air bubbles can exist in the material, and it is these which will cause problems, as we shall see.

By itself the resin has little strength, being very brittle, but if a fibre matrix is incorporated then a material approaching the strength of steel is the result. The type of fibre most commonly used is glass, although carbon and Kevlar are sometimes used.

Just as the addition of a steel matrix into concrete results in an enormous increase in strength, so the addition of the glass fibres produces the same result.

A continuous glass filament can be produced, typically around ten microns thick, and this filament or fibre can be processed to suit particular applications demanded by industry. It can be woven to produce a very fine, cloth-like fabric similar to cheesecloth; it can be chopped into short strands, coated with an adhesive and rolled out to form a coarse mat; bundles of fibres can be twisted together to form a product that looks like yarn (called rovings); or it can be woven into heavy fabrics that resemble a woven reed floor mat. All of these varieties have their own unique properties that, when incorporated into the construction of a fibreglass hull, produce a product that is sufficiently strong for the task required.

After the application of the gelcoat into the mould, generally by spraying, the first layer of glass and resin is placed over the top of this and is usually referred to as the 'tie' layer. This tie layer normally consists of woven rovings of glass fibre as the weaving process has produced a mat of high strength in both the 'north-south' and 'east-west' directions, or bi-directional cloth.

Because the weavings of this cloth can often be seen through the gelcoat when the hull is removed from the mould, a tissue of extremely fine weave is sometimes placed between the rovings and the gelcoat to help prevent this.

After the rovings are placed in position, they are saturated with resin and this is rolled out by hand to remove any air that may have been trapped. This work is demanding to say the least; the vapours given off by the resin require the wearing of full protective clothing and respirators and a large hull requires a lot of labour skilled in the task if a quality product is to be produced (sadly, this is not always the case).

UNDER THE GUN
After the tie layer of woven rovings, further hull thickness is built up with glass fibres and resin. In a modern powerboat manufacturing facility this is usually achieved using a depositor, more commonly called a chopper gun.

This complex tool, not unlike a spray gun, has the resin and catalyst delivered to its spray nozzle under pressure and, if the gun has been adjusted properly, will deliver the correct proportions of resin and catalyst in a heavy spray.

At the same time as the trigger is pulled on the gun, the operator can feed into the resin spray strands of glass fibres, produced by feeding continuous rovings into a rotating knife and then into the resin spray.

The skill of the gun operator is paramount. Incorrect mix settings can produce under-cured or over-catalysed resin, lack of attention can result in a hull which is too thick in places and too thin in others.

Because the curing process produces heat as the chemical reaction takes place, care must be taken not to deposit too much material too quickly, as severe shrinkage can result in local areas of the mould. This is known as 'pre-release' and shows up as major gelcoat blemishing when the hull is removed.

During the time the gun operator is weaving back and forth in the hull building up thickness, other workers are busy wetting out, which involves rolling the deposited glass and resin with rollers to ensure the complete removal of all air and to make sure that sufficient resin has been laid up with the glass, because resin starvation will cause major problems later in the boat's life.

Finally the job is completed to specifications, the hull is allowed a few days to cure before being released from the mould and then it is placed into the production line for the next stage of assembly.

THE NIGHTMARE BEGINS
Let us now fast forward. The boat has been in the water for a few years and has just been hauled out for its annual maintenance. The hull bottom has been jet blasted with high pressure water to clean it and is now being inspected by the owner...

It is here that his nightmare begins when he notices small blisters the size of his little fingernail around the bow area. They are not all that easy to spot; possibly they were there last year and were not noticed, but if the area is lightly rubbed with abrasive paper, the high spots become more readily apparent.

The owner consults with experts and his worst fears are confirmed, the boat has the pox. What caused it? We'll leave that one till later. What is the result of it? That is a lot easier to explain.

Most composite mixes are porous to a greater or lesser degree and fibreglass is no exception. From the day the boat was launched, water molecules have been slowly drifting into the hull structure.

The water molecule is not very complex, being simply two atoms of hydrogen to one of oxygen, and it can easily penetrate into the hull although in only microscopic amounts. Fibreglass, timber and concrete hulls are all permeable; what varies is the amount of water each medium takes up.

If this was all that happened then there would be no problems, but bound up in the composite mix of the fibreglass hull are those minute pockets of uncured resin we spoke of earlier. The water molecules will drift into these pockets and dilute them down to the same level of salinity as the water surrounding the hull.

This process is termed osmosis and occurs naturally many times in nature, even in the tissue of the human body. It explains why osmosis in boats is much more severe in freshwater than in seawater as the salinity difference is much greater between freshwater and the resin it is between than saltwater and the resin.

Unfortunately, the much larger and more complex resin molecule cannot get out of the pocket and the water will continue to drift in until saline balance has been achieved. The pressure build up in the pocket can be huge - enough to force the surface of the hull to form a bulge to accommodate it, and the result is the blister.

It is important to stress at this point that blistering is not a disease. All the potential blisters a boat can get are there from the day it is launched. The closer to the gelcoat those pockets of resin are, then the earlier they will be noticed. Deep voids can take years to develop.

ORIGINAL SIN
Getting back to the first question as to what caused the problem in the first place, ie, those pockets of uncured resin. Well, that has caused much thoughtful scratching of backsides amongst experts for many years and a variety of opinions have been put forth.

Some manufacturers seem more prone to it than others, and even regions can attract a poor reputation. High humidity during lay-up is often blamed, but I have seen boats manufactured when water could have been rung from the air, and yet not seem unduly affected.

Personally I think the problem is caused by a wide range of factors, a lot of them human such as poorly adjusted equipment, resins that are past their use-by date, sloppy work practices and so on.

Laying up a fibreglass hull is a physically demanding and extremely dirty job, largely accomplished with lowly paid workers, so perhaps it's not too surprising that errors occur. I suspect that if all boats were made under laboratory conditions, osmosis would be a much rarer occurrence.

Time is very much a factor. Small pockets just below the surface can appear after just 12 months in the water. These blisters tend to be small and really only raise the surface of the gelcoat.

Larger blisters may take years to develop and generally indicate the pocket is deep in the hull thickness. When they are opened up an evil-smelling dark liquid seeps from them. The size the blisters attain can be alarming; I have seen them as big as dinner plates, although this is not common and I think other factors may also be at work, such as an extremely dry lay-up resulting in delamination in the actual fibreglass itself.

BLISTER-BUSTING
The repair of osmosis really depends on how badly the boat is affected. Small gelcoat blisters are probably best left alone, but they are unsightly and do lower the price of a boat if it is up for sale.

The best method is to carefully grind the blisters out using an angle grinder - care must be exercised so as not to inflict more damage on the hull than the blistering was causing - and then filling with a good quality filler, preferably epoxy.

Large blisters resulting from deeper pockets of uncured resins in the laminate itself will have to be repaired, and this is generally best left to the experts.

Different yards have different methods. In the case of my boat, it was lifted from the water for three months to allow the hull to completely dry out. A peeler, which is a power tool not unlike a power planer, was used to plane off all the gelcoat from the underwater sections and expose the laminate underneath.

All the blisters were opened with a grinder and the hull washed with freshwater every night for a month in an effort to leach out the resins.

When the hull was deemed to have dried thoroughly, a complete new bottom was laid up using a depositor gun and 200lt of vinylester resin. When this had cured, two coats of high-build epoxy were applied and faired to the hull before anti-fouling and final return to the water.

As you can imagine, it was a time consuming and expensive exercise, but I don't think there is any real alternative. If the osmosis goes deep, then simply grinding and filling will not result in a repair with any strength.

I contend that most, if not all, fibreglass boats will get blistering over the years. My boat was over 25 years old when the repairs were effected.

I have never heard of a boat sinking from the pox, nor do I think it jeopardises the general integrity of the hull, but things ignored seldom get any better so a constant repair and maintenance program is the best answer.

Well, assuming that we have done the work on the hull, and everything is in good order, next month we'll attack the running gear and make sure that is up to scratch.