Shaft Coupling Saves Time And Money For Northwest Boatbuilder
The marine industry is now successfully using an "unconventional" shaft coupling combining a high torque-carrying capability with ease-of-mounting and dismounting. Classified by Lloyd's, ABS, and DNV, among others, SKF OK couplings prove to be a simple, safe and fast way of connecting two shafts. OK couplings are manufactured by the Coupling Division of SKF Steel, Inc., whose U.S. headquarters are in Avon, Conn. The coupling's range includes more than 100 standard sizes for shaft dimensions from 25 mm to 1,000 mm; torque transmission capacities range from 350 Nm to 26,000,000 Nm.
Located on the Guemes Channel, Port of Anacortes, Wash., Dakota Creek Industries, Inc. uses ASK OK170HB couplings in the manufacturing of their commercial marine vessels. According to Dakota Creek president Dick Nelson: "We presently save 50 percent of our machinist's time during installation because the couplings have no flanges, don't need bolts, nuts, or keyways, and eliminate the need for thrust rings." Because split bearings are unnecessary and the coupling uses less space than a flange, machinery room layout is simpler.
Dakota Creek was founded in 1977 by a group of boatbuilding veterans. Coached by their fathers and grandfathers, they learned their crafts in Northwest shipyards. Their boats fish the waters from the Puget Sound north to the Bering Sea; their tugs work on the North Slope and berth tankers.
The Dakota Creek Industries' production yard comprises facilities for new construction and repair. It is equipped with platens, 250-foot building grids, mobile cranes, backup outfitting, repair piers, and marine railways. The yard has built 21 hulls, among them, the 123-foot crabber/trawler Morning Star, the 100-foot bowpicker Alliance, and the 95-foot harbor tug Philip W. "We accommodate the owner's design wishes when laying out the vessel," says Mr. Nelson. "We take pride in our work, and that pride shows up in out boats." Built for Alyeska Ocean, Inc. and launched recently for its maiden voyage to Alaska, was the 131-foot trawler Aldebaran, which is the brightest star in the constellation Taurus. Aldebaran's diesel engine propeller shaft is low in the hull to leave more cargo room topside. Used in constructing the Aldebaran were three SKF OK170HB couplings, interconnecting the line and tail shafts and one OKF170HB coupling at the reduction gear box and C.P. unit. The whole shaft-line was installed through the stern-tube. Elimination of keyways meant a reduced shaft diameter and as much as 25 percent savings in machining costs.
The ASK OK170HB coupling has a thin inner sleeve with an external taper; the tough outer casing has a correspondingly tapered bore. The bore diameter of the inner sleeve is larger than the diameter of the shafts, allowing the coupling to slide easily over the shaft joint. Actual connection is made when the outer sleeve is pressed up over the tapered sleeve with the aid of oil under pressure; oil injected between the tapered surfaces eliminates friction when mounting. The oil is drained away when the outer sleeve reaches its correct position, and a powerful interference fit grips the shafts. Torque transmission capacity is 128,000 Nm.
The yard stated they first used the SKF coupling in 1981, and it is low maintenance, dependable, effective and trouble free. In spite of the fact that the OK coupling is more expensive to purchase than some conventional couplings, Mr. Nelson stated he looked forward to saving 25 percent in the long run and to continue increased production because of decreased installation time.
A free color brochure is available describing the SKF170HB coupling in full detail. For a copy,