design considerations for aluminum hull structures - Ship Structure ...

-71”(d)Welding ProceduresPreheatPostheatNoneNone - if area is smallThese propellers are of the built-up type with the blade palms boltedto the cast hub. The propeller blades and hub are cast stainless steel CF8alloy, while the studs for attaching the “bladesto the hub are monel 1%00(Kmonel) and the nuts for studs are Armco 17-@Hcondition H-11~0.The CHALLENGER propeller is presently a solid five-bladed of bronzematerial ad is 18 feet b-1/2 inches in diameter. An est~ated weight andcost comparison is shown in the following table:MaterialmFinishedWeight - Lbs. Cost Per ‘TotalApproximate Pound, $ cost, $Ni Al Bronze Solid 37,500 1.50 56,2S0CF8 - Cast Built-up L8,000 1.25 60,000Stainless SteelThe cast stainless steel propeller will weigh more since the hub has to belarger in diameter to accommodate the palms of the blades.13asedupon the foregoing, cast staitiess steel, CF8 alloy is recommendedfor the propeller of a large aluminum-hulledvessel.Shafting - The shafting for the CJIHJXNGER is presently made of AmericanBureau of Shipping Grade 2 steel and the diameters were based on the AmericanBureau of Shipping rules that were in existence at the time the vessel wasconstructed in 1965. ‘Thisship has an engine with a metric BHP of 9600 anda propeller RPM of 119. The diameter of the shafts are 16-3/4 inches (lineshaft) and 19-1/2 inches (tailshaft). The tailshaft has no liner since anoil lubricated stern tube bearing was installed.In this application it is suggested that the American WreauShipping Grade 2 steel material be retained for the shafting.ofStern Tube, Beari~ s and Seals - The existing steel hulled ship, hasa cast steel stern tube welded into the stern frame casting at the aft endand into the engine room aft watertight bulkhead at the forward end. Thearrangement is generally as shown on Figure 14.There are two stern tube bearings of the oil lubricated type (Waukeshatype), one long bearing 43-1/2 inches long at the aft end of the tube anda shorter one, 17-3/4 inches long, at the fcrward end of the tube.The materials of the existing assembly as installed in the steel hullship and the suggested materials for the aluminum hull ship are shown inthe table in Figure 14.All bolts, nuts and studs for the seals and glands exposed to seawater should be made of a combination of 304 or 316 stainless steels, inother words, if the studs or bolts are 304 then the nuts should be 316,or vice versa, to prevent galling.