HYDRODYNAMICS IN SHIP DESIGN 



Sec. 6S.5 



liner Oranje of 1939 [Prius, H. N., and Ijssel- 

 muiden, A. H., De Ingenieur, The Hague, Holland, 

 23 Jun 1939, p. 50; 30 Jun 1939, p. 74; WRH, 15 

 Oct 1939, pp. 316-323; TMB Transl. 128, Nov 

 1939]. The tumble home amidships is 8.75 ft in 

 a height of about four decks above the DWL, for a 

 waterline beam of 83.5 ft. This is so extreme that 

 the lifeboats can not be launched clear of the 

 ship's side. 



Tumble home is not called for by the particular 

 requirements of the ABC ship. It is incorporated, 

 however, in the body plans of Figs. 66. P and 67. L, 

 in an effort to provide parallel sides and constant 

 beam in that portion of the ship set aside for 

 passenger accommodations. Laying out, building, 

 and equipping staterooms and similar rooms is 

 greatly simpUfied if the region has parallel straight 

 sides, practically zero sheer, and no deck camber, 

 corresponding to a building on shore [Watsuji, 

 H., SBSR, 2 Aug 1934, p. 118]. 



Tumble home is usually, but not necessarily 

 confined to the abovewater hull. It may be 

 extended below the DWL in order to achieve a 

 reduction in C/r , to modify the rolUng charac- 

 teristics in some respect, or to take care of a 

 sHght list when the vessel is in light condition 

 [SNAME, 1905, PI. 119]. 



It is often desired, for wavegoing, to incor- 

 porate flare in the abovewater sections forward 

 for a considerable distance above the DWL. To 

 avoid the excessive top weights and volumes 

 involved by carrying that flare all the way to 

 the weather deck, a compound-flare section of the 

 type sketched at E in Fig. 26. B is useful. 



Compound flare built into the bows of British 

 cruisers for the past forty years has proved its 

 worth in service. More recently it has been 

 worked into the cargo vessels of the British 

 Windsor class, both forward and aft [MESR, 

 Jul 1952, pp. 89-90]. It is often of advantage, 

 with no appreciable impairment of wavegoing 

 behavior, to widen the deck below the weather 

 deck so as to get more useful room there. This is 

 because internal space lying above a ship's side 

 with excessive flare is difficult to utihze. 



The following method of working a compound 

 flare into the abovewater entrance is adapted 

 from that employed by the Naval Construction 

 Department of the British Admiralty and is 

 pubhshed with the kind permission of the Director 

 of Naval Construction, Sir Victor G. Shepheard: 



(a) The shape and position of the weather deck 

 at the side is determined from operational and 



other requirements and is faired in the usual 

 way, in all three planes. The section lines forward 

 are faired into this deck edge and completed as 

 though there were to be no compound flare. 



(b) A fair knuckle Une is then drawn on the out- 

 board profile (sheer drawing) in the position 

 desired for the lower edge of the diminished-flare 

 region. Its vertical position, shape, and curvature 

 depend upon the position of the internal decks 

 below the weather deck, the anchor-stowage 

 positions selected, and other factors. The line of 

 the knuckle runs more-or-less parallel to the 

 weather deck, or at a slope to it, either up aft 

 or down aft, depending partly on appearance and 

 the aesthetic sense of the designer. 



(c) At two selected stations, about 1/3 and 2/3 

 the length of the knuckle from the bow, two 

 level lines are drawn on the body plan, represent- 

 ing the height of the knuckle line at those stations, 

 as taken from the outboard profile 



(d) Two partial-section lines are projected down 

 on the body plan from the weather deck edge, at 

 the stations in question, to the knuckle level 

 lines at those stations, giving the knuckle half- 

 breadths. A suitable flare slope above the knuckle 

 is about 80 deg (with reference to the horizontal). 

 It is not necessary that the flare slope be constant 

 for all stations; appearance and room inside the 

 ship may determine this. 



(e) Laying out the knuckle half-breadths at the 

 two selected stations, and the fore-and-aft position 

 of the knuckle line at the stem, a fair line is 

 drawn on the half-breadth plan, giving the half- 

 breadths of the knuckle at all stations along its 

 length 



(f) Level lines for the remaining stations are 

 then added to the body plan, whereupon the 

 knuckle half-breadths for these stations are laid 

 off on them 



(g) With the points thus determined the knuckle 

 line projection is completed on the body plan, 

 and the straight section-line segments above the 

 knuckle are drawn in between the weather deck 

 and the knuckle 



(h) The original section lines below the knuckle 

 are now flared out in easy curves to meet the 

 knuckle intersections at the respective stations, 

 after which the section-line segments above and 

 below the knuckle, and the knuckle itself, are 

 check-faired 



(i) Adjustments may be necessary if the resulting 

 flare below the knuckle is too great to avoid 

 objectionable pounding or slamming 



