Hammer
30' Sport Fisherman Boat building project
design and build of a center console offshore sportfishing boat
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Hammer
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The Materials I guess you would call this a "sandwich" construction but then I guess all fiberglass boats are sandwich? Anyway this particular sandwich is .750 inch, 5.5# Core Cell foam skinned each side with three layers of 1808 biaxial non-woven fiberglass. For those not familiar with structural foam, it is not like insulation foam which is made from things like urethane and Styrofoam. ATC Chemical ,the company that makes this foam, calls it a linear foam but I don't know what it is. My guess it is some sort of modified PVC. Airex (softer and more elastic) and Divinycell/Klegecel (harder more rigid) are some of the other types of foam available. The CoreCell seams to be in the middle, claiming more compressive strength than the Airex and more ability to elongate than Klegecell. The transom is cored with 1.5", 13# Klegecell. I tried to make sense of the physical properties of the various cores and each type of foam seemed to have strong points but I had the idea that the ultimate strength of the foam had to be tempered with toughness so I chose the Corecell. I went with a glass/resin/core system that has been successfully used by custom boat builders in the Northern Gulf Coast area. Mainly, I have relied on the advise of my materials supplier Hugh Dykes, the technical sales rep. of Seemann Fiberglass , who is very familiar with this type of construction. Unless you are an experienced builder and have used a particular building technique, I can't stress enough how important it to deal with qualified technical people who can provide assistance with the The resin is General Purpose Ortho Polyester. This is low tech resin but it laminates well. I am using ATC's Poly-Fair/Poly-Fill fairing and primer system and Duratec Vinyl Ester primer on the bottom. The hull bottom as well as the top sides are sprayed gelcoat blended with Duratec Hi- Gloss Additive. This additive reduces the viscosity of the thick gelcoat resin and allows you to further reduce the mixture with a common reducer such as fast lacquer thinner or MEK. The result is reduced finishing and buffing time. Why I chose a cored construction My 1968 SeaBird is a balsa cored hull and it has been bust'n waves for 30+ years and particularly rough use by me in the four years I owned it. It is still in great shape. Its hull is light and stiff so I had good feelings about cored hulls. Secondly, using a core gives you a mold to build the boat on. More on that later.
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