help needed

[sd11856g]

Hi
Iam in the process of building a 28' single engine performance boat. I am wondering what the best and lightest core material is for such a boat. What are your opinions full core or just core it in certian spots? Also I would like to get some input on suggested lamination schedules/materials. I would like to use epoxy resin and maybe a combination of biaxiale S glass, kevlar, and carbon fiber. Iam thinking carbon fiber stringers and top deck, for weight savings (top deck)and strength(stringers). Should I place a 10"-12" carbon fiber pad under the stringers to spreadout the load of such? I want to build the lightest and strongest hull possible. HP will be 500-750 stern drive speed 100-110mph
thank you for your help

[Eric Sponberg]

At that speed, the loads on the hull are enormous, and you should hire someone to engineer the laminate for you. A lot depends on the arrangement of the internal structure of the boat. Typically, the hull skin accounts for about two thirds of a hull's weight, and the internal structure (frames, bulkheads, stringers) account for about one third. So the rule of thumb is, to reduce weight, add more internal support structure.

Core strength and stiffness, which carry the shear loads in a laminate, are directly proportional to density: The denser the core, the stronger and stiffer it is. Using lightweight core in such a craft is a mistake, and it accounts for only a small portion of the overall laminate weight anyway. Also, with a denser core, you can use a thinner core, typcially. So everything depends on proper engineering of the laminate to select the right core and the right laminate for the loads.

Another good maxim to go by, from one who has vast experience in very fast boats (Val Jenkins, formerly of Cigarette Boats) is "build it strong, then add power." There is no point in building the boat if it is going to break.

Eric