Of the following types of fiberglass reinforced plastic (FRP), which is not recommended for marine applications?

Polyester resin is typically not recommended for marine applications primarily due to its susceptibility to water absorption, which can lead to issues such as osmosis and hydrolysis. This material has lower chemical resistance compared to other types of fiberglass reinforced plastics like epoxy and vinyl ester resin. In marine environments, the exposure to saltwater, UV radiation, and variable temperatures can compromise the integrity of polyester resin over time, resulting in structural weaknesses, delamination, and a reduced lifespan of the vessel.

In contrast, epoxy resins offer excellent adhesion, water resistance, and overall durability, making them ideal for marine use. Vinyl ester resins also provide superior resistance to water absorption and are better suited for the harsh conditions found in marine environments. The term "better quality FRP" generally refers to advanced formulations or improved products which enhance mechanical properties and longevity, therefore making them suitable for marine applications.