560 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. riR.12 



It is recognized that the under-the-bottom 

 anchor scheme for the ABC ship has several 

 disadvantages of major proportions: 



(1) Greater weight of mushroom anchor, con- 

 servatively estimated as 64,000 lb, compared to 

 22,500 lb for a stockless anchor, or 13,000 lb 

 for an LWT anchor. Slightly greater weight of 

 chain, due to the extra-heavy 6.5-fathom shot 

 just above the anchor. 



(2) Greater power required in the anchor windlass 

 to hoist the heavier anchor and adjacent shot of 

 heavy chain. Inasmuch as the holding power 

 calculated for the ABC ship is 160,000 lb, a 

 standard windlass might be adequate for the 

 purpose if not required to hoist both anchors 

 simultaneously. 



(3) Greater hawsepipe and chainpipe weights 



(4) Lost buoyancy due to water around anchor 

 and chain in hawsepipe and lower part of chain- 

 pipe, amounting to about 5 tons in the ABC 

 design. Sufficient volume is left above the cup of 

 the anchor to clear stones, clay, and mud caught 

 in the cup, as well as to permit the anchor to 

 drop clear in the river below Port Correo, where 

 there may be less than 4 ft bed clearance above 

 the mud. 



(5) Difficulty of buoying the bottom anchor when 

 dropped 



(6) Impossibihty, except in clear tropical waters 

 in dayfight, of noting the direction in which the 

 anchor chain leads from the hawsepipe. However, 

 with a bottom anchor and a short scope, this 

 information is not really necessary. 



Although the proposed under-the-bottom anchor 

 installation has by no means proved itself suffi- 

 ciently to warrant working it into the design of a 

 ship to be built, it is carried through here as 

 part of the ABC preliminary design because it 

 permits the use of a moderate bulb and a fore- 

 castle that is not too wide and blunt. 



68.12 Knuckles and Other Longitudinal Dis- 

 continuities. Flaring sides, projections, recesses, 

 and other discontinuities of considerable fore-and- 

 aft extent often have to be worked into the above- 

 water form to meet service or utilitarian needs. 

 For smooth-water conditions, with relatively small 

 waves, these discontinuities have little or no ad- 

 verse effect provided they are kept clear of the 

 ship-wave profile along the free surface under any 

 conditions of load, trim, heel, and speed fikely 

 to be encountered. Even for wavegoing, the 



Bulqed Fender Stroke 

 of Constant Rodius 



Forms Port of the Shelf 

 Plotinq 



Fig. 68.J Bulged Fender Strake for a Small Vessel 



external knuckle of the compound-flare tj'pe of 

 section proves quite acceptable. 



The projecting edges of thick fenders or fender 

 strakes rec[uire chamfering in a transverse plane 

 to prevent their hanging up on similar projections 

 along docks, especially when the tide level rises 

 and falls. This chamfering should also be sufficient 

 to prevent the fender from throwing objectionable 

 spray, although the offending surfaces need to be 

 nearly vertical to eliminate all spray. 



A neat solution to the problem of the above- 

 water fender is offered by the heavy, bulged 

 fender strake of Fig. 68. J, forming a part of the 

 main hull. In addition to satisfying all the hydro- 

 dynamic requirements this construction has 

 great inherent stiffness as a fender because of its 

 shape and it requires no care and preservation in 

 service, other than that afforded to the hull 

 proper. The ship designer is cautioned, however, 

 not to place a bulge of this kind where the water 

 can climb up around its convex surfaces in normal 

 running. 



Reentrant discontinuities or coves, near the 

 designed waterline, are to be avoided where 



Internal Coves 

 and External 

 Chines Need Not 

 ie Filleted or Rounded 

 if The-y Lie Generollij 

 Porallel to The Lines of Flow 



Fig. 68.K Projecting Blisters and Sponsons 



