Aluminium Boats vs Fibreglass Boats

If you’re in the market for a boat, you’re most likely looking at a either fibreglass boats or aluminium boats – but what are the advantages and disadvantages of each?

Fibreglass Boats

The invention of fibreglass, also known as GRP (Glass Reinforced Plastic), dates back to the 1940s. As the name suggests, fibreglass is made up of glass fibre strands usually laid in a mould, embedded with a resin matrix. Once set, GRP makes a lightweight, strong and robust material that is easily mouldable into virtually any shape.

But hang on – my shiny white boat doesn’t look like a mix of glass strands mixed in plastic! That’s because most boats are generally laid up with a “gelcoat”, a material used to provide a high quality finish on the visible surfaces. If you look below the gunnels you will often see the matting and resin in its raw state. Gelcoat is typically laid between 0.5mm to 0.8mm thick – this is what you’re removing to surface a new layer when the boat is polished.

Let’s cut to the chase – what are the advantages of fibreglass? Depending on the thickness of the layup and design, a fibreglass boat tends to have a softer and quieter ride than an equivalent alloy boat. You can mould fibreglass into any shape you can think of. An alloy hull is constrained to how you can bend and weld the metal. 

Another advantage of fibreglass is that it’s not prone to corrosion. Yes, you can have similar crippling affects such as water ingress, osmosis and delamination, but a fibreglass hull will never suffer from electrolysis.

What are the downsides to fibreglass?

On the flip-side, although gel coat has a high UV resistance, when constantly exposed it will begin to fade and become porous. This means you will need to keep up with maintenance such as polishing and waxing, otherwise dirt will stain the exterior of your boat and become hard to remove, along with the fading. As well as regular polishing, the centre core a fibreglass boat is one of its downfalls. This is typically made from either balsa or foam which improves strength. This means that if any water enters the centre core, it will tend to rot from the inside out.

While there are plenty of ways to avoid this, for example sealing anything screwed through the fibreglass, when buying a second hand boat it can be hard to know if the previous owner has done so. The most common areas to check on a fibreglass boat are the transom and stringers, which if soft, will need to be cut out and replaced. This is quite an extensive job.

Aluminium Boats

The first trace of aluminium boats date back to 1920s, although they didn’t really take off until the 1960s with brands like de Havilland and Quintrex. Physically very similar to steel, aluminium weights approximately a third of steel – making it an ultra-lightweight option. As well as being lighter than steel, alloy is highly corrosion resistant – but not to the extent of fibreglass. Techniques for moulding steel aren’t feasible in the boat building industry, which means aluminium boats must be cut and welded.

So what sort of advantages can you expect with alloy? Aluminium boats are usually lighter than fibreglass, and offer better fuel economy. They can also fit smaller horsepower engines on similar length boats. This also extends to the trailer you need for your boat. You can have a bigger boat with a single axle trailer because it’s lighter, and also have a less powerful tow car. Alloy is much harder to gouge. While it is quite common to find a fibreglass boat has gouges out of the gelcoat, this will be less evident on an alloy boat. Sure, if you hit hard enough you will likely dent the alloy.

What are the downsides to alloy?

Firstly, paint usually covers the top half of an alloy boat. This is because without it, it will have a raw and rugged look. Some people feel the look of an alloy boat is less appealing. However today, manufacturers do a great job of making them look as good, or if not better. Paint also means that if you pull up alongside a wharf and scratch it, you won’t be able to buff it out.

Secondly, they also tend to suffer from peeling over a period of time when exposed to salt water and not washed properly. With a fibreglass boat, you can buff a new layer back. The only option for a painted boat is to respray it or touch it up. Lastly, alloy boats can fall victim to electrolysis. This happens when electricity passes through and causes your alloy surfaces to decompose. This can only happen when the ions are free to move (for example, when submerged in water). This can happen when a sinker or fishing hook drops between the cracks of the deck and into the bilge, and is submerged in saltwater as it rolls up the back.

It won’t happen overnight, but over the course of a few years you’ll likely find electrolysis. You can avoid this by being careful with fishing gear. For moored boats, installing the correct anodes with adequate bonding systems will also help. Many of the manufacturers are now designing aluminium boats with sealed decks and plastic bilges to ensure no metal objects can make their way to the bottom.

What about Plate Aluminium Boats?

Any alloy that’s 4mm thick or more is known as Plate alloy (or Plate Aluminium). This type is popular in the boating and fishing world at the moment. By using a thicker alloy, it can be designed with fewer support ribs. It is usually a more robust grade of alloy. However, design of the ribs design and other hull characteristics are limited because it cannot be pressed. Because it is thicker and heavier, it will also present a softer ride closer to that of fibreglass. There are many popular Australian boat brands emerging. For example, the Bar Crusher, which provides a high quality finish with the thicker plate-alloy material used. 

What Material Makes a Better Boat – Aluminium or Fibreglass?

Truth be told, there really is no “better” material, although people will have their own personal preferences. Boats that permanently live on water are more commonly made from fibreglass. However, an adequately maintained aluminium boat can be just as good. Charter operators often choose aluminium because of the fuel savings with day to day use. We are seeing a rise in the popularity of aluminium trailer boats. This is thanks to the sale of bigger and better alloy offshore boats. You must take the maintenance and lifespan of both needs into consideration when purchasing. Other important factors include ride quality if there’s a lot of offshore work.

Now you know the difference about aluminium and fibreglass boats, learn about the four major drive types here.