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BUILDING STEEL BOATS
By Terry Marks
Terry is employed at
Bethlehem Steel. Construction of large boats is his personal
business and truly an art form.
Steel boats can be built in a
wide range of sizes and types from small pleasure craft to large
commercial ships that are 1000 feet or longer. At the present
time, 98 out of the 100 largest personal yachts in the world
have hulls constructed of welded steel.
For the purpose of this short
article, I will discuss the boat that I am currently building,
the Seaton 53-ft. long, range motor yacht. The boat actually
has an overall length of 56 feet and a waterline length of over
51 feet. The beam, or width, of the vessel is 17 feet 9
inches. The weight or displacement of the boat is 100,000 lbs.
The building process normally
starts with a set of blueprints drawn by a naval architect. On
this particular boat, the transverse frames are plasma cut from
5/16 Cor-ten® steel. The
transverse frames are set up on an I-beam strongback at the
proper frame spacing. The elevation is then shot and the frames
are tack-welded to the strongback.
The next step is to cut
slots in the transverse frames to accept the longitudinal frames
(sometimes called stringers). In this case, the longitudinal
frames are ¼” x 2” flat bar. The next progression is the shell
plating process that is the outside skin of the hull. On this
vessel, the plate that was used is ¼” Cor-ten®
steel plate.
Cor-ten®
steel is an alloy with primary elements of copper, nickel, and
chromium and is noted for its corrosion-resistance and high
tensile strength and thus is valued as a boat-building
material. For this purpose, the Cor-ten®
steel was welded with E8018W electrodes. The metal was
preheated to at least 80 degrees F. before welding to prevent
cold lapping and crater cracking. All of the plate seams were
backstep welded in sequence. This must be done to equalize
expansion and contraction to prevent distortion in every way
possible. The shell plating above the waterline is 3/16” A36
mild steel. The welding process on the distortion-prone,
thinner material was pulsed MIG welding with 0.35” solid wire
electrode.
After the hull is fully welded
inside and out, the next step is to fabricate the deck beams.
The deck beams are made from 3” x 2” x ¼” rolled angle iron.
The longitudinal piece connecting the deck beams in the fore and
aft direction were 1” x ¼” flat bar. The deck plating is then
cut, fitted, and welded using the same techniques previously
mentioned to prevent distortion. All plates were cut with a
motorized hand torch and a plasma torch. Fit up is critical.
Small weld joints are necessary to minimize distortion, the boat
builder’s worst enemy.
After the fabrication is
completely welded, all weld beads must be ground flush. Then
the boat must be properly sandblasted and primed with a marine
epoxy. Custom boat building is a lengthy process involving much
plate forming because of the compound curvature necessary to
attain the complex shape of a boat hull. My 30 years of welding
experience at Bethlehem Steel and my training at the
Hobart Institute of Welding
Technology have helped me greatly in my boat building
endeavors.
Terry may be contacted at:
5042 N. 200 E.
LaPorte, IN 46350
(219) 778-9310
bbuilder@netnitco.net
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