Boat Hull Materials: Pros and Cons of Each

What a boat is made of is one of the prime considerations when buying a boat. The main options are:

• Fibre Glass (GRP)
• Steel
• Timber
• Ferro Cement

Each of these materials has its advantages and disadvantages and also admirers and detractors.

Fibre Glass (GRP)

Fibre glass or GRP is the most popular. GRP boats have been around since the 1940s but didn’t start being used for boat building on a large scale until around the 1960s. GRP doesn’t corrode, is fairly low maintenance and is relatively light weight. Well built and maintained GRP boats seem to be standing the test of time well. However GRP does age and deteriorate, especially in high load areas where the rigging is attached to the hull.

Below the waterline, osmosis will almost certainly occur eventually as water is absorbed into minute air bubbles in the laminate and expands into blisters. The extent of osmosis in a GRP hull seems to be related to the quality of the layup of the fibreglass laminate. In most vessels this is largely cosmetic, with just a few isolated blisters that can be dealt with individually during the annual haul out for antifouling. More extensive blistering can be repaired in a full “bottom job”. Many boats are over 20 year old before requiring this treatment. A very small number of vessels have massive deep blistering and delamination of the hull and should be avoided. A few years ago osmosis was being treated as some kind of pariah and any boat showing the least sign of it was avoided. Certainly when GRP boat building became popular a lot of boats were built badly by inexperieced people getting in on the boat building boom. The chemical process was poorly understood and the cheapest rather than the best resins were used. GRP boat building materials and processes have improved enormously and very bad osmosis is now rare. In fact osmosis is just a maintanence problem like rust or rot.

GRP boats have smooth shiny (when new) outer coating called gel coat. This is a cosmetic layer, the surface of which deteriorates in the elements. Regular polishing prolongs its cosmetic appearance but it is prone to cosmetic hairline cracking in high stress areas.

Some GRP boats are built with foam or balsa cores. This produces a stiffer, lighter hull and is popular in catamarans. The main drawbacks to be aware of is the delamination of GRP skin from the core and ingress of water into the core where through hull fittings have not been sealed adequately or the hull has been damaged.

Epoxy resins are starting to be used and produce a lighter, stiffer hull with more resistance to osmosis, for a slighty higher cost.

Generally speaking GRP hulls are easy to repair and, due to its popularity, skilled repairers are common in Australia.

GRP boats are the most common, cost the most to buy and are the easiest to resell.

Steel

The next most common boat building material is mild steel. Very few recreational power boats are built of steel but many cruising yachts are.

Steel retains a popularity amongst cruising yachties due to the belief that if you run into something like a reef or other hard object it will only sustain minor damage. Also it is a very cheap and forgiving material. Many people have built their own steel boats. Steel yacht hulls are cheap and easy to repair and facilities and skills to do this are readily available all over the world.

The down side is that the quality of steel yachts is very variable. The steel must be protected for the harsh marine evnronment which means ongoing vigilance and maintenance to stop rust becoming a problem. Steel boats are relatively heavy, slowing them down a bit.

Timber

Very few boats are built in the traditional timber boat building manner any more. Superior structural integrity of other methods, cost and scarcity of appropriate timber, and cost of skilled labour all contribute to this.

There are still quite a few well found older timber boats around which can be bought relatively cheaply.

Timber boats require more maintenance more often that other constructions but, for the right person, you can own a classic looking boat in which you take pride.

Cold moulded timber or plywood

Generally 2 or 3 layers of timber or ply wood strips glued together with epoxy over a removable frame sheathed in a GRP skin on the outside.

A popular construction method in New Zealand. Well built examples are often relatively cheap due to unpopularity of this method in Australia. The hull is stiff and strong but care must taken with sealing of the hull to ensure rot cannot get into the ply or timber.

Ferro Cement

Special cement is plastered over a steel rod and mesh frame to produce the hull.

This one really polarises the boating community. You either hate it or you love it. Many ferro cement boats were badly built by backyard builders giving this method a bad name. However a well constructed ferro boat will last just as long as any other.

You can pick up an real bargain and be sailing around on a much bigger, better boat than you ever thought you could afford.

The downside is that ferro cement boats can be hard to resell and difficult to insure.