Choosing The Right Polyurethane For Your Boat

Polyethylene is a type of plastic that is increasingly being used as a boat-building material. It is impact-resistant, maintenance-friendly, and environmentally friendly. Poly boats are also highly durable, with some describing them as virtually indestructible in the normal course of recreational boating. However, polyethylene has disadvantages, including limited size capabilities due to its lack of structural stiffness and a less glossy appearance compared to traditional boat-building materials. Despite this, polyethylene boats, such as those offered by Polycraft and Polyboats, are becoming a popular choice for boating enthusiasts.

Polyethylene boats: pros and cons

Polyethylene may seem like a strange material for building boats, but it is actually an excellent choice for boat construction. Polyethylene boats have several advantages over fiberglass or aluminium boats, but also some disadvantages.

Advantages

Polyethylene is an extremely impact-resistant material, and polyethylene boats are virtually indestructible in the normal course of recreational boating. They are also non-abrasive against gel-coated and painted surfaces. Poly boats are moulded, so they can have hulls with complex shapes and compound curves, and decks can have moulded-in compartments. Accessories like seat bases or consoles can also be moulded. Waxing and polishing are not necessary for polyethylene boats—a scrub brush and soapy water is all you need to keep the boat looking ship-shape. Polyethylene boats are also considered more environmentally friendly than fiberglass boats, as they can be recycled.

Disadvantages

Polyethylene is not as structurally stiff as fiberglass or aluminium, so polyethylene boats are limited in size—there are few over 20 feet in length, and larger models often require structural hull supports built from different materials. Moulding tolerances are not as exact as with fiberglass, so items like hatches may not fit as perfectly. Poly boats also don't have the glossy gel coat of fiberglass boats, so they don't look as nice.

Overall, polyethylene boats offer a number of advantages in terms of durability, maintenance, and environmental impact, but they may not be suitable for larger boats or for those who prioritize aesthetics.

Polyester or epoxy resin?

Polyester is an adequate adhesive but not as good as epoxy. As a general rule, the tensile strength of a polyester bond will be around 20% weaker than the same bond made with epoxy. That makes epoxy resin usually the best choice for fibreglass repair work.

There are a few exceptions. When the repair will be finished with gel coat, the laminating or filling needs to be done with polyester. While epoxy adheres tenaciously to cured polyester, the reverse is not true, so the bond between an epoxy repair and an overcoat of polyester gel coat will not be strong. Use polyester for repairs that will be gel-coated.

Cost is another consideration. Epoxy is three to five times more expensive than polyester. This is relatively insignificant for a small repair, but where the damaged area is large, using polyester resin significantly lowers the cost of the repair.

What about vinyl ester resin? Something of a cross between polyester and epoxy, vinyl ester is typically substituted for polyester when improved resistance to moisture permeation is the objective. Vinyl ester resin is often used when resurfacing a badly blistered hull, but for most other do-it-yourself repairs, you should probably choose the economy of polyester or the strength (and impermeability) of epoxy.

Polyester is much lower priced than epoxy and, as such, is the most common material used in boat building. Epoxy is reserved for ultra-exclusive custom yachts, where the cost is less of a concern. Polyester is also compatible with gel coat, which is how most production boats are finished. However, epoxy is much stronger than polyester, so resulting boats can be lighter. This is why epoxy is used in high-performance construction.

Polyester is also harder than epoxy, which can be considered a weakness because it is more brittle and will crack more easily. Polyester is also more permeable to water, so if you are making a boat that will live permanently in the water, you will want to use epoxy.

Polyethylene vs. fiberglass

Polyethylene and fiberglass are two types of materials used in boat construction. Both have their advantages and disadvantages, and the choice between the two depends on various factors, including the intended use, desired features, and preferences of the buyer. Here is a detailed comparison between the two:

Polyethylene Boats:

Polyethylene, a type of plastic, is an excellent material for building boats. It offers high impact resistance, making polyethylene boats virtually indestructible in recreational boating. Its durability is demonstrated in its ability to withstand collisions with rocks or pilings, leaving little to no damage. Polyethylene boats are also moulded, allowing for complex hull shapes, moulded-in compartments, and built-in accessories. They require minimal maintenance, as a simple scrub with soapy water is sufficient to clean them. Additionally, polyethylene boats are considered more environmentally friendly since they can be recycled.

However, one disadvantage of polyethylene boats is their lack of structural stiffness compared to fiberglass or aluminium. This limits their size, as larger models often require additional structural hull supports. Polyethylene boats may also not be as aesthetically pleasing as their glossy fiberglass counterparts, and they may have less precise moulding tolerances, affecting the fit of certain components.

Fiberglass Boats:

Fiberglass, also known as fibre-reinforced plastic, is another popular material for boat construction. It offers superior structural stiffness and strength compared to polyethylene, allowing for larger boats without the need for additional hull supports. Fiberglass boats are known for their sleek appearance, featuring a glossy gel coat finish that enhances their visual appeal. They also have more precise moulding tolerances, ensuring a perfect fit for items like hatches.

However, one downside of fiberglass boats is the higher maintenance they require. Unlike polyethylene boats, they necessitate waxing and polishing for upkeep. Additionally, the construction process for fiberglass boats is more time-consuming, with builders producing fewer hulls per week compared to polyethylene boat manufacturers. This results in a higher cost-per-boat for fiberglass vessels.

In summary, polyethylene boats excel in durability, ease of maintenance, and environmental friendliness, while fiberglass boats offer superior structural rigidity, aesthetic appeal, and precision in moulding. The choice between the two depends on the specific needs and preferences of the buyer, with each material presenting its own set of advantages and drawbacks.

Polyethylene vs. aluminium

Polyethylene is a type of plastic that is increasingly being used as a boat-building material. When compared to aluminium, polyethylene boats have a number of advantages and disadvantages.

One of the key advantages of polyethylene is its impact resistance. Poly boats are extremely durable and can withstand collisions with rocks or pilings, as well as impacts from objects like sledgehammers, without sustaining damage. This makes them a good choice for recreational boating. Additionally, polyethylene boats are moulded, allowing for complex hull shapes and built-in compartments for accessories. They also require less maintenance than aluminium boats, as they don't need to be waxed or polished and can be cleaned with just a scrub brush and soapy water. Polyethylene boats are also non-abrasive against gel-coated and painted surfaces, making them a good choice for tenders. Furthermore, polyethylene is a recyclable material, making it more environmentally friendly than aluminium.

However, there are also some disadvantages to polyethylene boats. One of the main drawbacks is that polyethylene is not as structurally stiff as aluminium, which limits the size of poly boats. They are typically limited to under 20 feet in length and may require structural hull supports made from different materials. Poly boats also tend to have simpler hull forms and accessories must be secured with fasteners. Polyethylene boats may also not look as aesthetically pleasing as aluminium boats, as they lack the glossy gel coat finish of fibreglass boats and often have dull coloration. Additionally, items like hatches may not fit as perfectly as they would on an aluminium or fibreglass boat due to less exact moulding tolerances.

In terms of specific boat models, the Polycraft 4.10 Challenger is a compact fishing boat that can seat four adults and has ample storage space. The Polycraft 480 Brumby is another option, known for its ability to handle rough water with a deep V hull that can seat six adults while keeping them dry. For those seeking a stylish option, the Polycraft 5.30 Warrior is available in Centre Console, Frontrunner, and Cuddy Cabin models, offering versatility for various boating applications.

Polyethylene boat maintenance

Polyethylene boats are made from plastic, which may seem like a strange boat-building material, but it is extremely impact-resistant and virtually indestructible in recreational boating. They are also non-abrasive, so they won't scratch gel-coated or painted surfaces.

Poly boats are also low-maintenance. You don't need to worry about rust, corrosion, osmosis, or chemical washes. To clean the boat, all you need is a scrub brush and soapy water. There is no need for waxing or polishing.

However, there are some challenges to polyethylene boats. For example, stickers don't stick to their slick surfaces, which can make putting on registration decals and numbers a challenge. You can use stencils and a black Sharpie marker as a workaround.

Additionally, screws rip through polyethylene more easily than through fiberglass or wood, so adding accessories like cup holders or fishing rod holders may require adding backing plates.

In some cases, bottom painting requires special treatment, such as "flashing" (heating without melting) the bottom with a torch prior to application.

Frequently asked questions