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Steel hulls are made of plates of Lloyd’s approved marine quality steel. The steel is pre-primed at the steel mill. Plates are precision laser cut, using computerized design instructions called cutting files. Cutting files minimize wasted steel, and ensure a good fit. Deck plating is typically from 5/32-in to 1/4-in (4-6 mm), and hull plating is from 1/4-in to 5/16-in (6-8 mm) in thickness.
Typically the hull is assembled ground up, by raising web frames and longitudinal stiffeners, and then attaching the hull plates, followed by deck plates and superstructure.<ref>The Complete Guide to Metal Boats, Bruce Roberts-Goodson, International Marine, McGraw-Hill Corporation, ISBN 0-07-136444-7</ref> A few builders are using transverse instead of longitudinal stringers.
Steel construction requires some heavy equipment; and experienced welders to get a fair finish to the hull. Joints are double welded below the waterline. Above, they can be single welded but it is better to weld them inside and out. After welding, joints are ground smooth and filled in where necessary. A team of three welders might take about 1000 hours to assemble a complete 60-ft hull.
A critical join is between the deckhouse and deck. Although the deckhouse could be simply welded to the deck, it is better to have structural pillars extending up from inside the hull. This can be accomplished by having strong mullions. Extreme waves have been known to tear off deckhouses.
Similarly, the bow, keel and bilge keels should be reinforced in case of an accidental grounding.
If you have a larger budget, you could have a steel hull and aluminium superstructure. This reduces weight above decks and keeps the centre of gravity lower. Galvanic corrosion between the dissimilar metals is avoided by using an explosion-bonded bimetallic strip to join the steel and aluminium. These strips were first developed for the US Navy.
The strips are composites of aluminium and steel, bonded together at the molecular level by an explosive force. The aluminium deckhouse is welded to the aluminium strip, while the steel hull is welded to the steel strip.
Steel will give you a homogenous leak-free hull. It is more difficult than fibreglass to get a fair finish. To prevent corrosion, it must be primed and painted. It must be protected from galvanic action. It is very strong and not damaged easily. It can withstand some pounding when grounded. It will dent before it allows penetration. Any welder anywhere in the world can put a patch on easily.
== References ==