Curving Steel Bulb Angles for Ships

What happens when a screw bearing for a 1200-foot freighter seizes in the mid-Atlantic, somewhere between the Panama Canal and the St. Lawrence Seaway?  The ship requires a tug to a shipbuilder in Sturgeon Bay Wisconsin, that’s been in the business since 1918.  Amazingly, within approximately a 2-week period, the freighter is dry docked there, repaired by an army of skilled marine craftsmen, and then sent back to Lake Michigan and onward to Alaska.

Damaged Screw Bearing

About a third of this remarkable company’s business is on the repair end; the other is design/build from the ground up of ships with modules in about 100 foot increments.  The modules are then assembled to create these rather impressive vessels.

Ships at Sturgeon Bay

What’s not seen from the exterior are rolled “bulb flat” steel stiffeners, running longitudinally along the hull on +/-30in centers.  Replacing hard-way rolled steel channels, these 10 to 12in wide, European-designed, bulb flats are rolled to precision radii.  The curved steel bulb angles basically eliminate one flange of a channel, thus reducing the weight of about 25,000 lineal feet.  When your business is hauling tremendous amounts of weight, physics dictates the results:  every pound saved in weight without compromising strength adds value to the ship.

Curved Bulb Angles Installed

On a smaller scale, the same bulb flats are also used in U.S. Coast Guard Cutters and personal/corporate yachts, measuring in at a mere 65 feet.  Again, using curved bulb angles might allow the ships to transport more goods including friends and family.  Let’s hope their propellers don’t seize up.

Repaired Screw Installed


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