828 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 77.12 



(lesiniblc, perhaps a dozen oi' more, especially 

 when the designer is allowed some latitude in 

 arranging the various principal units, the accom- 

 modations, and the service facilities. 



For craft over 25 ft or 30 ft in length the pre- 

 liminary space layouts may involve two or more 

 deck plans, one for the weather deck and another 

 for the space below deck. A boat-shaped hull 

 sketched around these spaces affords a rough idea 

 of the principal dimensions such as overall length, 

 beam, and depth of hull. Profiles based on these 

 hull sketches indicate the positions and sizes of 

 houses or other erections projecting above the 

 weather deck. Having the general size and shape, 

 or perhaps one might say the minimum size and 

 shape, the designer proceeds to incorporate 

 certain other features in the sketches such as 

 minimum freeboard and sheer, freeboard at or 

 near the bow, and profiles of the bow and stern. 

 He shows crew and passengers, as well as "cargo" 

 in the present case, in their proper or proposed 

 positions. 



Even though the powers and sizes of the en- 

 gine(s) are not yet known, the spaces for propelhng 

 machinery and auxiliaries can be roughed in, 

 leaving them oversize in case of doubt. The hull 

 structure usually presents no problem at this 

 stage, unless fire or subdivision bulkheads are 

 required. The buoyancy tanks or compartments 

 for flotation in an emergency can usually be 



worked into spaces not useful for anj^thiug else. 

 Their volumes should, if practicable, be so placed 

 that the swamped boat is supported at or about 

 zero trim. 



Fig. 77. B was drawn from the last of several 

 layout and arrangement sketches made for the 

 ABC planing-type tender. These indicated that a 

 craft 40 ft in overall length, with an estimated 

 displacement weight of 25,000 lb, was somewhat 

 larger than necessary. A smaller boat, 35 ft in 

 overall length and 32 ft long on the waterline, 

 appeared to be sufficiently roomy but with an 

 estimated weight of 18,000 lb its displacement- 

 length cjuotient of 245 was too high. The boat 

 shown in the figure, with a waterhne length of 

 35 ft, provides room enough to meet the require- 

 ments of Table 77. b and is not too heavy for its 

 length. The layout is nevertheless considered 

 purely preliminary. Its sole purpose is to show 

 that the spaces called for by the specifications 

 can be fitted into a craft of the minunum dimen- 

 sions represented by the sketch. It does not 

 necessarily represent the best arrangement pos- 

 sible within the limitations established by the 

 owner and operator. 



77.12 First Weight Estimate; Weight-Esti- 

 mating Procedure. The second step in the design 

 of the planing-type craft is to make a preliminary 

 weight estimate of the complete boat, in operating 

 condition and with the full useful load on board. 



Trace of De&iqned Waterline at rest 



Removable Sections to Permit Liftinq Out Enqmes 



In Second Arronqe- 

 ment Sketch T^^J 

 ^ \. L Movino Engines 

 '^ / ^ Forward and 



Passenqers Mt 



to Make Them 



More Comfortable 



and to Place 



Heavy 



Weiqhts 



Over 



FP Stotlons 



Fig. 77.B Sketch of Tentative Space Layout fok V-Bottom Tender for ABC Ship 



