What is a Fibreglass Moulding ?

The only items produced by Kingston Mouldings today are GRP model boat hulls, which in almost all cases, are supplied with scale drawings to build the rest of the model, and every single one is produced in-house. Although GRP (Glass Reinforced Plastic) is the correct technical description for these materials, in this case it is exactly the same thing as fibreglass, a term that most people are probably familiar with. It’s important to point out that these hulls are a very different proposition from the moulded plastic items that are to be found today in many model kits. Although some more expensive kits do contain GRP or fibreglass hulls that are in most cases much the same as the ones available from Kingston Mouldings, many more contain hulls that are heat formed from sheet plastic. Some of these heat formed, usually vacuum-moulded hulls are very good, but many others are not.

People often ask if GRP is the same as styrene or ABS plastics, which are two of the materials commonly used for heat-formed hulls, and the answer is an emphatic No. In the vacuum forming process, a sheet of plastic is heated and sucked over a male or into a female mould. After cooling, the stuff becomes hard again, and it then retains the mould’s shape. Very quick, very simple, a relatively economical manufacturing process in fact, but these heat softening thermoplastics do have a number of significant drawbacks. One is that they will continue to soften each and every time they are heated subsequently, as many who have allowed a styrene or ABS based model to cook near a radiator or in the back of a car on a hot day, can confirm.

Another problem is that the vacuum forming process has trouble coping with sharp inside or outside corner radii, and unlike GRP, it can’t reproduce fine detail from the mould. Perhaps the most important single disadvantage of vacuum moulding though, is that the plastic sheet must inevitably be stretched by the forming process, something that can make the hull very thin indeed in some areas, particularly in deep hull sides and over sharp edges. This often results in a moulding that is thick and strong in places where it doesn’t really need to be, but relatively thin and weak in other areas where strength and rigidity are essential. To partly overcome the problem, many kits using vacuum-formed hulls have to incorporate quite elaborate built-up wooden strengthening structures in their design. In a good fibreglass moulding on the other hand, the thickness will be controlled very accurately without any thin and weak areas, as extra glass reinforcement can easily be added to any critical or highly-stressed areas during the normal moulding process. How neatly and accurately this is done, is entirely dependent on the skill of the moulder concerned however.

Almost all vacuum moulded hulls are made from some variety of unreinforced plastics, often styrene for cheaper examples, and possibly ABS or a related material for the better ones. Both of these materials can be difficult to cut or drill accurately, and they are not particularly easy to rub down to remove minor defects or prepare the surface for painting. Thin mouldings will also tear relatively easily, whereas the glass reinforcement in a GRP hull makes it much more resistant to damage of this kind. The smooth outer surface of a fibreglass hull is easy to drill, fill, cut or rub down, and as the material is more rigid than styrene or ABS hulls, paint bonds to GRP better, and as a result, it is less likely to flake off in normal use.

You’ll gather from all this that I’m not the greatest fan of styrene and ABS hulls, and in general that’s true. However, it’s only fair to point out that there are some heat moulded hulls around that are of a high standard, those produced by German kit manufacturers like Robbe are good, to give just one example, but at the other end of the scale, some quite dreadful flimsy lop-sided and shapeless vacuum-formed hulls are foisted on the model buying public. Like so many things in life, this is a case of ‘caveat emptor’, for those not versed in Latin, let the buyer beware. Whatever you are thinking of buying, whether styrene, ABS or GRP, have a good look at it first, or at least something else made by the same manufacturer before you part with any money, as I’d have to admit that there are some rather poor quality fibreglass hulls around as well.

GRP is the product of a non-reversible chemical reaction. Essentially, every moulding is produced by laying glass fibres in the form of mat or woven cloth into a female mould, which in our case would be model-boat shaped. The glass is thoroughly impregnated with a mixture of liquid polyester resin and hardener, and this takes quite a lot of skill, so depending on the complexity of the moulding, it can be quite a lengthy process. After it has all been allowed to harden or cure, usually for about 24 hours, the moulding can then be separated from the mould, a perfect replica of the original former that the mould itself was taken from.

This is much simplified of course, rather like ‘War and Peace’ in a couple of paragraphs, but I’m not trying to blind you with science. A good GRP hull is a durable item that should last for years, and little short of the most extreme heat, soaking in organic solvents, or jumping up and down on the thing is likely to damage it significantly. So GRP is more durable, and in practical terms generally rather stronger than vac-formed plastics in almost all respects, but you won’t be surprised to learn that it does have significant drawbacks of its own. Nothing in life is perfect after all, and the most important disadvantage of GRP mouldings is a slow labour intensive manufacturing process with lots of scope for introducing minor defects. This makes the quality of the final article almost entirely dependent on the skill of the worker involved, and it also means that GRP mouldings can never be as cheap as mass produced items.

That’s not to say that fibreglass hulls are expensive though, as in most cases it would be very difficult to construct a decent hull from wood to most of the designs seen here for significantly less than our prices, in fact it could easily cost considerably more, and that’s just from working out the cost of all the basic materials . Making a good model boat hull from wood is time consuming and highly skilled work, and once you’d built the hull of course, you would also have the additional problems of sealing the wood surface to accept a decent quality paint job, as well as ensuring that the result was perfectly watertight.

These are all problems that you can forget about when you build your model on a Kingston Mouldings fibreglass hull. Your pride and joy should have a long and trouble free life, and you’ll never have to worry about leaks or cracks in the hull letting in water and spoiling the paint finish, something that often happens with wood hulls, as joints open up as the material that model was made from ages.…

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