More about polyethylene 

History

In 1951 two researchers from the Phillips Petroleum company accidentely discovered polypropylene while searching for ways to produce new fuels. They realized that the residue of one of their experiments had interesting specifications. They replaced the propylene with ethylene and polyethylene was created. One of the first consumer goods produced in polyethylene was the hula hoop.

Development

The last few years there has been a big development in the polyethylene world. The manufacturer of Windrider uses superlinear polyethylene for its products. The result is improvements in impact, stiffness, hardness and heat distortion temperature. Together with a special pigment system the material will not suffer from the radiation of the sun.

Advantages over other materials

The polyethylene used today by the manufacturer of the Windrider has many advantages over the use of wood or polyester:

Polyethylene is completely recyclable
Wooden ships are painted or varnished to keep the wood dry. This makes that the wood cannot be used when the boat has lived its life.
The use of polyester is one of the biggest problems in our environment. A polyester hull can never be recycled and the material will not dissolve in nature. You can only burn it, the result is many toxic gasses.
Polyethylene however has no negative effect on the environment when burned. You can also melt the material and re-use it in other products. 

Polyethylene is maintenance free
Polyester boats are created from two parts which are laminated together. After a few years of use, these parts can delaminate, the two parts will not bind anymore. Water will come between the layers and the boat will become heavier and heavier. To prevent this, you will need to repaint the boat every few years and make many repairs to parts where the delamination process has started.
Wood is a material that expands when it comes in contact with water. That is why wood always needs to be prevented by varnish and paint. You will need to sand and paint the wood many times during the lifetime of a wooden boat.
The polyethylene Windrider hulls are one piece, so no delamination is possible. The color is in the material so it will hold its color forever. You will never need to paint a polyethylene boat. 

Polyethylene is very strong
When a polyester boat comes into a collision with something else on the water, the boat will probably break or small cracks will appear. These crack are very serious because the (glass)fibers that give the polyester it strength are then broken. You will need to repair that part of the hull which is a dirty and difficult task.
Wood has the same problem as polyester. It also breaks very easily.
Polyethylene however can only crack in extreme circumstances. When you run your boat into an obstacle it will be probably not even be damaged. Because the polyethylene is a material that reminds its shape, it will take its original shape if a big dent gets into the boat.

About rotational molding

Rotational molding is a highly versatile manufacturing option that allows for unlimited design possibilities with the added benefit of low production costs.

Process Overview
The rotational molding process starts with a good quality mold that is placed in a molding machine that has a loading, heating, and cooling area.

Several molds may be placed in the machine at the same time. Pre-measured plastic resin is loaded into each mold, and then the molds are moved into the oven where they are slowly rotated on both the vertical and horizontal axis. The melting resin sticks to the hot mold and coats every surface evenly. The mold continues to rotate during the cooling cycle so the parts retain an even wall thickness.

Once the parts are cooled, they are released from the mold. The rotational speed, heating and cooling times are all controlled throughout the process.

Design Advantages
Rotational molding offers design advantages over other molding processes. With proper design, parts that are assembled from several pieces can be molded as one part, eliminating expensive fabrication costs.

The process also has a number of inherent design strengths, such as consistent wall thickness and strong outside corners that are virtually stress free. If additional strength is required, reinforcing ribs can be designed into the part.

Rotational molding delivers the product the designer envisions. Designers can select the best material for their application. Additives to help make the part weather resistant, flame retardant, or static free can be specified.

Inserts, threads, handles, minor undercuts, flat surfaces that eliminate draft angles or fine surface detail can all be part of the design. Designers also have the option of multi-wall molding that can be either hollow or foam filled.

Cost Advantages
When cost is a factor, rotational molding has the advantage over other types of processes as well. In comparison to injection and blow molding, rotational molding can easily produce large and small parts in a cost effective manner. Tooling is less expensive because there's no internal core to manufacture. Since there is no internal core, minor changes can be easily made to an existing mold.

And because parts are formed with heat and rotation, rather than pressure, molds don't need to be engineered to withstand the high pressure of injection molding.

Production costs for product conversions are reduced because lightweight plastics replace heavier, often more costly materials. Which makes rotational molding as cost effective for one-of-a-kind prototypes as it is for large production runs.

Other Advantages
The color can never crack or chip off, because it’s molded-in, all the way through. Of course, this means no painting is required.

Generally lighter in weight than metal or fiberglass, rotomolded plastic products are easy to handle and less expensive to ship. They’re tough, long lasting, and maintenance-free.