Specing out a new vessel

Discussion in 'Fiberglass and Composite Boat Building' started by Guest, Sep 20, 2004.

  1. Guest

    Guest Guest

    All, Im now in the phase of specing my soon (hah hah) to be built vessel. Some questions I have about what to use..

    1) Attaching deck to hull.. Im planning to have this bolted and glassed over. What kind of bolts to use here? It should be stainless im assuming? Like 316L or ?? I read some time builders bolt, use 3M 5200, and also glass over? Is this true, if so how much and what type of glass are used, generally speaking for a really solid and heavy duty vessel.

    2) Engine room vents.. What is a good choice for the material covering engine room vents? Is a good choice 316L stainless?

    3) How are deck cleats and railings fastened on? Bolted yes, then sealed with something?? Also they need to be reinforced underneath somehow, but the question is with glass? If so, how many layers, what type and there needs to be some material for stiffness, like wood yes?

    I guess this is it for now. But I have tons more questions..

  2. Eric Sponberg
    Joined: Dec 2001
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    Location: On board Corroboree

    Eric Sponberg Senior Member

    You really should consult a naval architect for answers to your questions. These first three are fairly simple, so here goes.

    1. Presumably you are contemplating fiberglass construction. Usually, hulls and decks are bolted and glued, and yes, usually using 3M-5200 caulking. Some people also use Plexus, which is much stronger, but also more expensive. 5200 works fine and is an industry standard. Some builders also glass over the joint on the inside, but this is not universal. Bolts do not have to be 316L stainless. In fact, I don't know if anyone makes 316L fasteners. 316 or 304 stainless is fine for deck bolts. 316L is recommended for welded stainless steel assemblies at or near the waterline, or for bilge piping welded fittings inside the boat. The L designation means it is a low carbon alloy that has a better resistance to corrosion in the vicinity of welds. That is, there will be little or no carbide precipitation at the weld area, which can later pit and corrode.

    2. Engine room vents can be just about anything, and again 304 or 316 stainless should be fine. The vents should be high enough above the waterline so that you do not need the L designation. Sometimes fiberglass vents are made out of fiberglass or other plastics.

    3. Deck cleats and ALL hardware should be sealed with 3M-5200, through bolted, and backed up with back-up plates. These back-up plates can be plywood (soaked with epoxy resin), stainless steel, aluminum, fiberglass, or even other plastics. They are meant to spread the fastener loads across a larger area. If the deck is cored, the core has to be routed out in way of each fastener hole and filled or sealed with epoxy. When well planned, all the hardware is specified as to type and location before the deck is built. Then in areas where the core is in way of hardware, a much harder denser core can be inserted so that water does not get into the rest of the surrounding core.

    If you want to consult further, you can contact me privately to anwer more of your questions.

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