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Old 08-12-2013, 07:30 AM   #18
brian eiland
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City: St Augustine, FL
Vessel Name: RunningTide
Vessel Model: 37 Louisiane catamaran
Join Date: Jul 2013
Posts: 903
Why Steel?

Why steel for the hull,...why not fiberglass like most other production boats these days? One of the key words here is 'production boat'. Sure making up the plugs, then the molds for a production run of boats makes sense. But what if you don't really know how many copies you may build,...what if its a limited run geared for a specific market?? Then you are trapped with an up-front, expensive bit of tooling that you can not amortize over a goodly number of vessels.

But if we still consider a fiberglass hull, we certainly know by now we don't really want, nor need, sandwich core construction in the hull structure below the water line,...for that matter we might well leave it out of the hull structure altogether. That leaves us with solid fiberglass construction utilizing some decent resins, some decent fiberglass, and some good gel coats. Great Harbor Trawlers brags that their hull bottoms are solidly built with “laminates of more than 1-inch thick”.

When I start thinking about the labor hours to lay-up the laminates of that thick solid glass bottom, and their cost of quality resins in today's new oil price market, I just have to come back to the reality that just as tough a hull can be fabricated from a single, much thinner thickness of sheet plate steel at a fraction of that cost. And the steel's ductility makes it all the more appealing.

Why steel? It's an inexpensive material, easily fabricated, and very durable. It's a material that inspires confidence in a boat's survivability from mishaps and collisions by both experienced boat owners and newly minted ones.

Can we build the steel hull shape we might want, and can we build it at a reasonable price? I certainly believe so. I believe we could build an almost identical hull to that existing one in steel. I also believe it could be made even easier by modifying the hull slightly to a single chine, or maybe even a double chine if so desired.

I would propose that this steel hull could be built in a 'frameless fashion'.
This type of hull is built inside a frame rather than over frames. It is a very fast building method and I completed a 34ft hull & deck, completely welded and shot blasted and prime painted in 3 weeks flat
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As noted the computer cut steel panels are welded-up together while supported by this external jig-frame. Then the internal framing members (stringers, frames, bulkheads) can be added as deemed necessary. I've attached another photo example of a bulkhead with stringers. I think the Pilgrim design could get along fine with 5 of these major bulkhead types tying the hull sides together, and supporting the thick sandwich-cored deck I wish to place on top of their upper edges.

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Note that the welded-up hull, with the bulkheads all installed, could remain in the jig-frame fixture while the engine and other equips are being installed (no deck is installed yet). The deck piece, and then major cabin superstructure, could actually be assembled on another part of the shop floor and then brought over and placed onto the assembled hull.

There are several other advantages to this steel hull idea. You will note that I mention 'computer cut panels' of steel. This not only shortens the time of construction of the steel hull, it also makes it a potential kit-boat candidate.

It has yet another potential benefit. Unlike a fiberglass hull where I am married to a single bottom design, I can change this hull's bottom design readily if something new looks feasible.
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