CHAPTER 68 



Layout of the Abovewater Form 



68 . 1 General Design Features, Exclusive of Wave- 



going 546 



68.2 Reserve-Buoyancy Requirements 546 



68 . 3 Freeboard and Sheer for Protected Waters . 547 



68 . 4 Freeboard and Sheer for General Service . 547 



68.5 Design of Abovewater Section Shapes; 



Tumble Home; Compound Flare .... 551 



68.6 Check of Range of StabiUty and Dynamic 



Metacentric Stability 553 



68.7 Abovewater Profile and Deck Details . . . 553 



68 . 8 Selection of Deck Camber 553 



68.9 Bulwarks and Breakwaters 554 



68.10 Design of Anchor Recesses 556 



68.11 Proposed Under-the-Bottom Anchor In- 



stallation for Ships with Bulb Bows . . . 558 

 68.12 Knuckles and Other Longitudinal Discon- 

 tinuities 560 



68 . 13 Transverse Discontinuities 561 



68 . 14 Shaping and Positioning of Superstructure 



and Upper Works 561 



68.15 Design of Facilities for Abovewater Smoke 



and Gas Discharge 563 



68 . 16 Reducing the Wind Drag of the Masts, Spars, 



and Rigging 566 



68.17 Consideration of Increased Draft Through 



the Years 566 



68.18 Preparation of Hull Lines for Model Tests . 566 



68.1 General Design Features, Exclusive of freeboard, just mentioned, plus a rise of the 



Wavegoing. Were it not for wavegoing require- 

 ments the abovewater portions of a ship down to 

 the ship-wave profile at designed speed could be 

 given a strictly utilitarian shape. This shape 

 might even be found adequate to meet damage- 

 control and floodability requirements. Actually it 

 is done with many ferryboats, day-service pas- 

 senger vessels for inland waters, river and harbor 

 craft, and canal boats. Since the abovewater 

 shape of the average seagoing vessel is so inti- 

 mately related to wavegoing, a considerable part 

 of the discussion pertaining to it is found in 

 Part 6 of Volume III. The design rules in this 

 chapter therefore apply principally to ships of 

 aU types operating in protected waters, as well 

 as to those features covered by the general service 

 of every vessel. 



68.2 Reserve-Buoyancy Requirements. Re- 

 serve buoyancy in the form of intact or waterti^it 

 volume of the main hull above the designed 

 waterplane, a rather important feature of sub- 

 mersible and submarine vessels, is rarely set 

 down as a design item for a surface ship. It is 

 not to be found in the requirements of Chap. 64 

 for the ABC ship. It appears partly as the cus- 

 tomary specification for minimum freeboard to 

 some specified deck, when the ship is designed to 

 remain afloat with one, two, or three compart- 

 ments flooded. It also appears as a requirement 

 for an adequate range of transverse metacentric 

 stabiUty, although rarely stated in so many 

 words. Wavegoing requirements are not forgotten 

 but they generally take the form of a minimum 



weather-deck line forward and aft in the form of 

 sheer. 



For the heeling and change-of-trim conditions 

 to be expected in service, assuming that the 

 situations represented by them are essentially 

 static, a certain margin of buoyancy or freeboard 

 is necessary, particularly in the form of a limiting 

 distance above the heeled waterplane. This takes 

 care, among other things, of the overshoot action 

 accompanying a relatively sudden list, or of 

 incidental waves. The margin may take the form 

 of a corresponding distance above the waterplane 

 when trimmed, to give protection against the 

 water in the crests of waves made by the ship's 

 own motion or by passing vessels. Certain types 

 of craft acquire temporary and unexpected lists, 

 Kke the heel of a tug when a heavy towline tension 

 is exerted transversely or the heel of a small 

 day-service passenger vessel when a great many 

 passengers crowd suddenly to one rail or the other. 

 All craft may at times be subject to unsymmetrical 

 loading and may have to run at the corresponding 

 lists or trims for uncomfortably long periods. 



The reserve-buoyancy volume could well be 

 reckoned, not from the designed waterplane with 

 the vessel at rest, but from the actual wave 

 profile when the ship is running at its designed 

 speed. For example, both the buoyant volume 

 and the reserve-buoyancy volume of a small, 

 fast tug have an appreciably different shape in 

 way of the surface when the tug is running free 

 than when it is pulling and standing almost still. 

 It can be argued that a vessel will never be 



546 



