Sec. 78.3 



MODEL-TESIINC; PROGRAM FOR A SI 1 1 1' 



8f)9 



(f) Shaft power required to drive the hull with 

 all appendages, rate of rotation of the propeller(s), 

 and other self-propulsion factors, first with stock 

 propellers (s), and then with propeller (s) designed 

 especially for the hull 



(g) Open-water and cavitation data on pro- 

 peller(s) designed specially for the hull 



(h) Determination of the proper neutral angles 

 for multiple rudders; observation of dynamic 

 stabihty of route and maneuvering character- 

 istics, Avith a free-running model; controllability 

 when backing 



(i) Wavegoing performance of the hull, when 

 meeting waves from ahead and being overtaken 

 by waves from astern 



( j ) Shallow-water and restricted-channel behavior 

 (k) Nature and magnitude of the periodic vibra- 

 tion forces imposed on the hull by the propeller. 



It is not always possible or advisable to conduct 

 all these tests or to make them in the order given. 

 For example, the preliminary design of roll- 

 resisting keels should not be completed nor the 

 keels be fitted to the model until after lines-of-flow 

 observations on the bare hull indicate their 

 proper positions. In the case of hull designs with 

 offset skegs and tunnels it should be known from 

 the flow tests that there is no cross flow under the 

 skegs, eddying alongside them, or separation and 

 eddying in the tunnel before shafts and struts 

 are fitted and self-propulsion tests are made. 



78.3 Model-Test Notes for Preliminary ABC 

 Designs. Rather than to give the preliminary 

 notes and to describe a detailed model-test 

 schedule in general terms, apphcable to any 

 case, the data prepared for model tests of the 

 prehminary designs of the ABC ship are quoted 

 in full in this section and in the sections following. 

 The wording is such as might be embodied in a 

 request for a complete set of model tests. 



There are two separate ABC hull forms to be 

 tested. Each has the same forebody, forward of 

 Sta. 10, but a different afterbody. These are 

 designated for convenience as: 



(1) Transom-stern, single-skeg; called transom 

 stern for short 



(2) Arch- or tunnel-stern, with double skegs; 

 called arch stern for short. 



Two separate models may be made or one bow 

 may be bolted to either of two sterns. So far as 

 can be determined at present, model tests at 

 displacements less than about 0.8 the designed 



displacement will not ix; oiilled for. Tiic; niinimiim 

 model weight for the partly loaded condition, 

 approximately 1,650 lb for a 20-ft model, should 

 be sufficient to care for the necessary midship 

 bulkheads and connecting bolts; see the last 

 paragraph of Sec. 78.5. 



The models may be made of wood or wax 

 provided they will be suitable for the entire test 

 schedule. 



As is customary at model-testing establish- 

 ments, the models are to be built to the molded 

 lines shown on the drawings, with no allowances 

 for shell plating. 



The appendages, only a part of which are shown 

 on the drawings available at this stage, are 

 expected to consist of: 



(a) Cutwater applied to the forward edge of the 

 stem. This is considered in the nature of an 

 appendage and is not to be in place during the 

 bare-hull tests. (Actually it was in place on the 

 ABC model bow) . 



(b) Roll-resisting keels, of shape, size, transverse 

 position, and fore-and-aft extent to be determined 

 only after lines of flow have been taken for both 

 hull shapes. In view of the contemplated width 

 of the roll-resisting keels, 3.5 ft on the ship and 

 0.1373 ft on the model, it is desired that the keel 

 trace on the hull be determined by flags or vanes 

 at a distance from the hull as well as by lines of 

 flow on the hull. These traces should extend at 

 least from Sta. 6 to Sta. 14. 



(c) Rudder horn and single rudder for the tran- 

 som-stern design. These latter are to have a 

 contra-shape, designed to recover rotational 

 losses in the propeller outflow jet, but they are to 

 be omitted in their entirety from the bare-hull 

 transom-stern model. Drawings showing these 

 appendages are to follow. 



(d) Double rudders for the arch-stern model. 

 The double rudders and the skegs on this model 

 are to be adapted for maneuvering tests to be 

 conducted subsequently, involving movable blades 

 with stocks that can be turned from the deck. 

 Only the unbalanced tails of these rudder blades, 

 above the level of the lower edges of the skegs, 

 are to be fitted to the bare hull; these may be in 

 dummy form. The balanced foils below the lower 

 edges of the skegs are to be added subsequently 

 as appendages, or else the dummy upper portions 

 are to be removed and the movable maneuvering 

 rudders fitted. 



(e) Bottom anchor and recess 



