Fiberglass is a material that is made by laminating glass fibers together, using a resin. This can be done in various different ways with a variety of materials. Traditionally the resin has been polyester, a low-cost durable resin that has been used for 50 years. The disadvantage is that polyester is prone to osmosis if not sealed properly and the quantity needed makes the hull heavier than necessary compared to some of the more modern resins.
Other options are Epoxy or Vinylester. Epoxy is strong, durable and absolutely damp-tight. It is also impact resistant and can be used in smaller amounts than other resins, resulting in a slightly lighter boat that is not prone to osmosis. The downside of Epoxy is that it is significantly more expensive and would add thousands to the price of a 42-foot boat.
The third option is Vinylester, which has a lot of the same benefits as epoxy but without the cost. It is durable, strong, not prone to osmosis and the quantity required to make a good laminate is less than polyester. Vinylester is our preference, as the balance of cost versus gain is most favorable.
By using sandwich foam core laminate for both the deck and the hull structure above the waterline, the Offshore 42 not only benefits from the lightweight material but also from the sound and thermal insulation being part of the main hull structure. To prevent water ingress into the foam core, the mounting areas for deck hardware will be made of solid fiberglass.
The stiffness of the hull is generated by laminating 3 transversal bulkheads as part of the integral hull structure and by running stringers along the full length of the boat. With this construction, you can put a lot of tension on the rig without deforming the hull. In addition, the 3 integral bulkheads also provide an extra measure of safety by being water tight once the appropriate doors and cable penetrations are installed.
When it comes to keel structure, almost every production boat is built with the mandatory safety factor of 6 for transverse bending. Transverse bending is a situation that occurs when a boat is knocked down by a wave. By adding just a couple more structural floors over the solid fiberglass keel sole, close to the keel bolts, we managed to build in a safety factor that is 3 times greater than the market standard without making the boat heavy or impractical. The cost increase of this slightly more complicated structure is minimal.
The hull construction of the Offshore 42 will not break any technological ground, but with meticulous engineering, a strong and light structure is achieved.