When people talk about 'plastic boats' they are generally referring to boats constructed from polyethylene. Plastic may seem like a strange boat-building material, but of course what we call fibreglass is, in fact, a form of plastic. So why should it surprise so many boaters that another plastic, albeit one with different properties, also turns out to be an excellent boat-building material?
But what are the advantages and disadvantages of 'plastic boats' or polyethelene, as opposed to the alternatives like fibreglass (often referred to as FRP or GRP) and other composite construction like carbon fibre, wood, aluminium or even steel? Read on to fin out a bit more.
The advantages of plastic boats
In a nutshell, here are the major advantages and disadvantages of polyethylene as opposed to fibreglass or aluminium:
- ADVANTAGE: Polyethylene is extremely impact-resistant, and we’ll go as far as to say that poly boats are virtually indestructible in the normal course of recreational boating. Smash into a rock jetty, much less a piling, and a poly boat will just bounce right off. Whack the hullsides with a sledgehammer (Triumph will invite you to at the boat shows) and there’s zero effect. One of our editors owned a 10ft polyethelene boat which fell out the back of a pick-up truck while doing 50 MPH, and after bouncing down the road and off onto the shoulder, other than a few scuff marks it remained undamaged.
- DISADVANTAGE: Polyethylene isn’t as structurally stiff as fibreglass or aluminium, so poly boats are limited in size. There are few over 20ft and many of the relatively large models require structural hull supports built from different materials.
- ADVANTAGE: Poly boats are moulded, so like fibreglass boats, they can have hulls with complex shapes and compound curves; decks can have moulded-in compartments; and large accessories like seat bases or consoles can also be moulded. Aluminium boats aren’t moulded, so they tend to have much simpler hullforms and accessories must be secured in place with fasteners.
- DISADVANTAGE: Moulding tolerances are not as exact as they are with fibreglass, so items like hatches may not fit as perfectly as they would on a fibreglass boat. Many aluminium boats also have more exact tolerances, even though the parts are fabricated as opposed to moulded.
- ADVANTAGE: Waxing and polishing are maintenance chores of the past, when you own a plastic boat. A scrub brush and soapy water is all you’ll ever need to get the boat looking as ship-shape as possible.
- DISADVANTAGE: Poly boats don’t look quite as nice as fibreglass boats, because they don‘t have a glossy gel coat. Some modern painted aluminium finishes also out-shine plastic.
- ADVANTAGE: Polyethylene boats are often considered more environmentally-friendly than fibreglass, since they can be recycled.
Polyethylene boat construction
So, just how is a plastic boat built in the first place? The specifics vary from one builder to the next, but the process is generally similar. The boat begins as plastic beads or powders, which are loaded into a closed mould. The mould is then heated to melt the plastic, and is rotated to evenly distribute the material. After the mould cools, it’s opened and the hull and/or deck can be popped out.
In the case of very small, simple boats like dinghies or kayaks, the molding process may account for virtually all of the construction process. But with larger or more complex models, after the major parts of the boat have been moulded a good amount of additional work may be necessary and construction is more or less like that of a fibreglass boat. Structural components are added as necessary, hulls and decks may need to be joined, and voids may be filled with foam.
Construction quality for these later stages can vary quite a bit from manufacturer to manufacturer, so before buying a plastic boat you need to do some homework and make sure it’s up to the job you plan on tasking it with. We’ve seen, for example, one small two-part poly boat (remember that 10-footer that bounced down the road?) where the hull and deck were merely stapled together, then covered with a rubrail. Sure, the staples were heavy-duty, but they weren’t exactly stainless-steel—after four years of saltwater use they corroded and the hull and deck began to separate.
Polyethylene boat construction also leads to some very odd properties. Stickers don’t stick to their slick surfaces, for example, which can make putting on registration decals and numbers a challenge. (Tip: Stencils and a black Sharpie permanent marker actually work quite well). Adding accessories like cup holders or fishing rod holders can also be a challenge since screws rip through polyethylene more easily than fibreglass or wood, and adding backing plates is often necessary. And in some cases bottom painting requires special treatment, such as “flashing” (heating but not melting) the bottom with a torch prior to application.
Plastic sailing boats and rowing boats
The feel when rowing or sailing a plastic boat is very different to fibreglass as the boat isn't as stiff and gives slightly. With sailing craft the construction method is generally used for beginner dinghies and plastic boats are very popular with sailing schools. Their use has expanded rapidly over recent years. You will find a host of kayaks and canoes available in polyethelene, and a wide range of sailing dinghies, including youth classes.
Is a plastic boat the best choice for your needs?
You’ll have to take all of the things we’ve discussed here into consideration before making up your mind, but if you’re looking for a dinghy, kayak, or very small fishing boat (under 12ft), especially if you are after a relatively low maintenance and robust craft, the answer is pretty obvious.
As far as larger sizes and more complex styles of boats go, your range of poly choices will shrink as the fibreglass and aluminium options quickly expand. Still, if you’re looking for something between 12ft and 20ft there are strong arguments to be made for buying a polyethylene boat.