VII. NAVAL ARCHITECTURE,. ETC. 417 



VII. SHIPPING, NAVAL ARCHITECTURE, AND 

 MARINE ENGINEERING. 



2147. Models made of hard paraffin for ascertaining the 

 Resistance of Ships by measuring the resistance of their models. 



W. Froude, F.R.S. 



The models from 6 to 16 feet in length are made of hard paraffin. The 

 experimental apparatus employed in working the model includes appliances? 

 for designing, moulding, and casting the models, shaping them by automatic 

 machinery, moving them through the water at the required speeds, and auto- 

 matically recording the leading phenomena />f the trial, namely, the speed, 

 the resistance, and the change of level induced by the speed at each end of the 

 model. 



The several processes are illustrated by the accompanying series of seven 

 photographs and two specimens, which may be explained as follows : 



No. 1. The designer. 



This consists of a pile of adjustable templates, the thicknesses of which 

 represent the horizontal intervals between the successive water-lines of the 

 intended models shown on a reduced scale. One edge of each template is an 

 elastic steel band held to a wooden base-piece by adjustable ordinates hinged 

 to the band and sliding through mortices in the base-piece fitted with hinged 

 metal clamps. One of these templates (No. 8) set up as for use is sent to aid 

 this explanation. 



The photograph shows them in combination, and represents the intended 

 small scale model by a series of water-lines in steps, which, if either filled up 

 solid and fair to the salient angle of each, or trimmed off fair to the re-en- 

 tering angle, would constitute the finished form. 



No. 2. a. The moulding box ; 6. The mould ; and c. The core. 

 L. B. D. 



a. A rectangular wooden box 16'- x 2' 9" x I' 10". 



In this the external form of the full sized model (that is (6) the mould) is 

 shaped by help of a series of rough cross sections deduced from the small scale 

 designer, and into the mould is fitted the core (c), which constitutes the figure 

 of the inside of the model, c is framed on a series of internal cross sections 

 made good to a surface and rendered coherent, first by a series of laths nailed to 

 them externally, and, secondly, by a skin of calico drawn tight over the lathed 

 surface, and then coated with plaster-of-paris and clay. Between this "core" 

 and the " mould " there is, of course, a space, equal to the intended thickness 

 of the model, into which space the melted paraffin is] run, and there allowed 

 to remain until by cooling it has become solid enough to bear removal. 



Nos. 3 and 4, the shaping machine. 



This is what has sometimes been termed in technical phrase a " copying 

 machine." The model, bottom upwards, and adjusted successively to a series 

 of different levels, travels longitudinally between a pair of revolving cutters, 

 which are caused by means of a hand lever to so recede and approach one 

 another, as the model passes, as to cut upon the model the horizontal section 

 or " water-line," correctly appropriate to the level at which the model is set. 

 At the side of the machine, in full view of the operator, there is a vertical 

 board, which carries either a drawing of the intended model, showing the series 

 of water-lines to be cut, or one of the " designer " templates already described. 

 In front of this board is a " tracer," and the board and the " tracer" severally 

 imitate upon the appropriate scales (the former by longitudinal motion, the 

 latter by vertical motion) the longitudinal motion of the model and the lateral 

 motion of the cutters. Thus the drawing (or template) passing along beneath 

 the tracer is practically a small scale picture of the model travelling past the 



39508. D d 



