Fibreglass and sandwich boats

Fibreglass and epoxy resin boats - How they are made

Information by Stefano Salvo Shipyard

S.S. 131, km 100 - 09070 Siamaggiore (Oristano)

Phone 0783 34114 - Mobile 346 5762510

E-Mail: info@cnsalvo.it - VAT number 01105600959

Short guidelines on materials and building's techniques of fibreglass and epoxy resin boats.

Fibreglass boats

If you want to understand before buying a boat what you are actually buying and if the price is fair, you firstly need to know the materials it is composed of and how it is produced. Nowadays many shipyards' brochures use too many times the term "composite material", as if it was referred to a technology that can't be used by those who have hand-crafted yards and who work fibreglass in traditional ways.

Anyone who mixes resin - the polyester, vinylester or the epoxy one, and glass fibre - mat, tissue or any other kind of yarn - creates a composite material, that is the fibreglass!!

So, if you mix of two or more materials, you get a very particular material whose characteristics are not the simple mix of its components. The composite material uses resins as matrix or binding for the reinforcement got by glass fibres (or carbon or aramidic fibres). So you discover that ferrocement boats are also made of composite material (matrix = cement and reinforcement = steel)!

In this way if you read in a brochure that those boats are made of composite materials, it's sufficient only to add here and there some carbon, aramidic or Kevlar (patented mark that better persuades you) and you'll think to have bought not a simple, traditional boat but one of those produced by technology's experts. But is it true?

Boats built using the total fibreglass solution

The hulls of fibreglass boats can be built with the traditional system, through total manual stratification got through different reinforcement layers (glass fibre materials, roving, mat, etc) bound with fibreglass, usually polyester or vinylester, in different layers and by including the different hull's reinforcements (stringers or cross-beams) in order to reach the desired thickness and sturdiness.

This kind of manufacturing, performed by expert staff in a workmanlike fashion, by using good materials and the necessary shrewdnesses, and by operating in the external layers of the isophthalic resin, guarantees some good results and boats don't have any problem for years or also for decades.

Anyway, this statement is not valid for boats' hulls that are faulty because of staff's mistakes or of unsuitable climatic conditions, or also of low-quality materials. Each of these staff's mistakes, or low-quality materials will also cause some very serious problems in the course of time, like osmosis, ungluings or localized and spread delaminations.

The total glassfibre boats' manufacturing - also if correctly performed - has an high weight if compared with other kinds of manufacturing we're going to analyze.

The sandwich boats

Sandwich is a system used to lighten some fibreglass boats'structures; practically, a light and compression resistant material - called core - is placed between two thin fibreglass layers - called "skins"- in order to space out skins, to improve the sandwich bending resistance and to reduce the quantity of resin and reinforcement fibres within the boat.

There are different kinds of core materials, the lightest are the honeycomb ones, with very little surface and big empty spaces; there are also different plastic foams, for instance with closed or open cells, and different thermoplastic extruded materials.

If you use foams or extruded plastic materials, usually down market, except for some particular manufacturings at high pressure in checked environments, you have to know that these materials have a very low mechanical resistance. For this reason, the fibreglass skins' gluing must be done carefully, usually through structural adhesives and respecting specific temperature and damp standards; if you don't use these solutions, skins will suffer from ungluing, because they absorb almost all the shocks of hulls.

The honeycomb materials also comprise the aluminum and the aramidic ones that are very light and that lighten the total structure. These are very technological materials, that need very complex manufacturings and specific standards checks, but if the manufacturing is well performed, they allow to produce boats with excellent lightness characteristics.

Unfortunately, a faulty manufacturing of these materials, causes serious problems to the hull, with very expensive and difficult repair services. We also need to say that core materials are light and technological but in case of localized and concentrated crashes they don't make a stand and easily get a hole in them. Furthermore these materials don't practically allow the assembly of any fitting without risking the spinning or the breaking of fibreglass skins, and for this reason these areas reinforced through the ply.

Sandwich fibreglass boats with epoxy matrix and top lamellar core.

Another material that can be used as core in boats building is the mahogany lamellar or top lamellar, that is a multilayer approved for sea use that definitely has a higher weight than very light materials or foams and a higher price. Anyway, it has several advantages.

First of all it is a structural and very resistant material; if the weight is equal, it is three times more resistant than steel and it is made of many thin wood layers glued with very strong glues that are able to resist the boiling for over one hour; it is a composite material. It is able to resist loads and bumps of boats' structures; in case of skins ungluing (but it's nearly impossible), it is cut and compression loads resistant.

The system is very light if compared with the total fibreglass solution, so if the resistance is equal, the weight of lamellar sandwich boats with epoxy matrix fibreglass is lower(20-30%) than boats built following the total fibreglass solution.

Obviously, since any material isn't perfect, it has one only disadvantage: it can be glued and protected only through epoxy resin, because the use of polyester or vinylester resins would lead soon to the ungluing of the fibreglass, because of the water permeability of these resins, and to the lamellar's impregnation.

On the contrary, by using the epoxy resin, alone or strengthened with glass fibre, you get a perfect gluing, thanks to the compatibility of the materials and the great adherence strength to the matrix. Obviously you must respect the necessary temperature and damp standards that are useful for a good manufacturing; there's no need for particularly complex equipment or manufacturings.

At the same time, epoxy can perfectly integrate with multilayer, so by completely laminating the hulls you can get some monolithic boats with an exceptional cohesion matrix-reinforcement-core. The water permeability and the shrinkage of the epoxy resin is practically null and it also allows the boats produced with this technology to have the same maintenance as those made of traditional fibreglass.

Now you are probably asking yourself why all the shipyards don't follow this technology to build boats: the answer is very easy. First of all the lamellar and the top lamellar are very expensive materials, hardly bending and, above all, it is impossible to do it automatically through machineries. The labour plays an important role, and there is no economic benefit for a limited production.

It's not possible to put the wood in a die and make it stick to it, but it needs to be pushed gradually and slowly on a framework, and once glued, go on with laying and gluing the fibreglass reinforcements; this procedure is time-consuming.

So, a lamellar sandwich boat with epoxy fibreglass behaves in a predictable way, no ungluings or delaminations in case of strong bump. Obviously if the bump goes beyond the breaking limit any structure will breake, but this building technology allows easy restoration of the structural continuity through re-gluing.

We don't mean that the building method of sandwich-epoxy-top lamellar-glass is absolutely the best one, but the purpose of this guide is to let those who want to buy fibreglass boats know the building techniques and the materials of these boats.

In this way, they can consider not only the aesthetic side of a boat, that is really subjective, but also the importance of a correct information, considering that buyers have to spend a large amount of money; so, asking the yard or the seller what you are buying is an inviolable right.