Rotomolded Polyethylene Boats: What It Means, How It Works, and Why You Want One

When it comes to boat construction, all sorts of materials can take part in the assembly. Bigger vessels need heavy-duty structures to last, but even materials like polyethylene can make an excellent case in the water. Rotomolded polyethylene boats are a top-notch example of that, using a unique manufacturing approach to create durable and lightweight materials.

If you're not familiar with the term, rotomolding can sound somewhat intimidating, but we're here to give you the details on the process and the boats that come with them.

What Is Rotomolding?

Rotomolding is a portmanteau of rotational and molding, which describes the process of how we can make these materials. Generally, this approach allows us to produce large plastic parts in a way that's cost-effective and creates a durable material, rather than combining different pieces with seams that have a risk for breaking apart.

The origins of this technique lie back in the nineteenth century, and it actually has very little to do with boats. Rotomolding got its start in the British military, to make even thickness in the walls of artillery shells. Over time, it's made its way into the more mundane aspects of life, such as candy, lawn decorations, and—you guessed it—boats.

So how exactly does this process work that makes it an effective construction technique?

How Rotomolding Works

Since the origin of the term has "rotational" and "molding" as the roots, you'd be right to guess that we're going to rotate something to make our polyethylene shell. And that process happens to start with a mold.

While many different products use rotomolding, we'll be focusing on boats to help you get a clearer picture: specifically, polyethylene kayaks, which are one of the most common personal watercraft options made through this process.

Starting with a mold in the shape of a kayak, we'd then pour polyethylene pellets inside. These pellets are tiny, and there are thousands of them to provide enough material to make the complete shape we want. From there, we close up the mold and attach it to a rotating device, which will lead to the central part of the process.

While rotating, we apply heat to the outside of the mold. This step will allow the pellets inside to heat up and spread evenly around the edges of the frame, forming the shape of the kayak. Think of the way you slow cook a rotisserie chicken, and you've already got an image of what rotomolding does.

After the polyethylene has had time to melt thoroughly, we turn the heat off, still rotating the mold until everything's had time to cool and settle into place. From there, we can remove the frame, and, with some finishing to smooth out rough edges and a few extra parts, we have one polyethylene kayak ready to go!

Rotomolding and Boats

Overall, rotomolded polyethylene is popular in smaller boats, generally because it makes a stable material that can take a beating, and the whole rotomolding process is excellent for mass producing, thanks to the use of molds. Generally, you'll find rotomolded polyethylene in smaller vessels like kayaks and sailboats.

It is possible to make larger boats from rotomolded polyethylene, but there's a specific size where having the whole vessel in one mold becomes inefficient. It is possible to build ships by combining multiple pieces of polyethylene, but it's also easy to not secure the sections together well, which takes away some of the durability factors. Because of this, you generally won't see polyethylene boats longer than twenty feet.

Even if the whole ship doesn't consist of rotomolded polyethylene, numerous manufacturers, like G3 Boats, use this material to make parts of their vessels.

Benefits of Having a Rotomolded Boat

Alright, so now we know how rotomolded boats get made. What are the plusses to these vessels, then?

Durability

While it's heated and rehardened plastic, rotomolded polyethylene is pretty sturdy. Remember how we mentioned that rotomolding got its start as a way to make even artillery shells? By rotating the plastic and letting it harden along the way, gravity does its work and essentially makes the entire mold as level as possible—and that provides structural stability.

That's why polyethylene boats can sturdily take a beating from rapid waters and rocks, and it's stronger in comparison to other common boat materials, like fiberglass. Rotomolded polyethylene is capable of taking scrapes and hard impacts.

However, that durability works best when the boat is all one piece, rather than more attached. The individual parts will hold up well, but weak connecting elements won't last as long.

Price

Rotomolding is widespread as a manufacturing technique because it's cost-effective, which means that it's also inexpensive on the consumer side of things. If you compare two boats of similar specs, but one uses rotomolded polyethylene, and the other doesn't, then you can guess which one will cost less. Unless you're picking out a somewhat larger vessel, you likely won't have much need for a boat payment calculator.

Because they tend to be inexpensive, polyethylene vessels make for excellent starter boats, and you’re likely to find them with used motors as well.

Recyclable

Polyethylene is a type of plastic, which means that most vessels made from this material tend to be recyclable, creating a sustainable way to dispose of your boat once it's reached the end of its life.

Though you'll want to thoroughly wash the boat first and confirm recycling policies, in most cases you can break the polyethylene down into parts and recycle them as is. Additionally, it's possible to make rotomolded boats from polyethylene, which further helps reduce environmental impact from the creation and disposal of materials.

Cheap Repairs

Not only are polyethylene boats cheap to make, but they're also inexpensive to repair if necessary. Part of the low maintenance costs is because of how durable the builds are in the first place since they can take a beating and you won't have too much damage in the first place. But if something does need fixing, it won't be overly expensive to get the job done.

Most rotomolded vessels are also smaller, so you won’t have to worry much about looking for larger replacement types, like used outboard motors.

Other Considerations for Rotomolded Polyethylene Boats

While these vessels have numerous benefits, they aren't appropriate for all situations. For kayaks and the like that are regularly going to go through strenuous conditions (think white water rafting with lots of bumps and impacts along the way), more specialized and durable materials will be better in the long run.

However, for anyone that wants an inexpensive vessel that can survive harsh conditions on occasion, rotomolded polyethylene exceeds in both of those categories can make an excellent pick, especially if you care about sustainability.