128 
NATURE 
[JUNE 5, 1902 
THE PROPOSED EXPERIMENTAL TANK 
FOR TESTING SHIP MODELS FOR RESIST- 
ANCE. 
| pee recent opening of the National Physical Labo- 
ratory, as described in NATURE on March 27, 
marked an epoch in the advance of science into the 
commercial development of this country. Equipped as 
the Laboratory will be with the best appliances for testing 
materials and instruments of precision, for fixing 
standards of measurement and comparison, it will 
supply that which, in other countries, has already been 
recognised as a vital necessity to national commercial 
prosperity. 
There is, however, a branch of scientific investigation 
not contemplated in the original scheme for the Physical 
Laboratory and which it is now proposed to include in it, 
namely, an experimental tank for testing, by means of 
models, the resistance of vessels either already in exist- 
ence or only in the stage of design. 
The system followed in the practical application of 
theory to the solution of these problems of naval archi- 
Fic. 1.—View of Washington Tank, north end, showing Wave Breaker. 
tecture was devised by the late Mr. Wm. Froude. In 
his first experimental tank, erected at Torquay more than 
thirty years ago, Mr. Froude carried out the researches 
which led to his well-known discovery of the laws which 
govern the resistance offered by water to the propulsion 
of ships. 
Although the method pursued has often been de- 
scribed in NATURE and elsewhere, a brief outline of it, 
by way of reminder to our readers, may not be out of 
place. 
A model of the vessel the resistance of which is to 
be tested is made either of wood or, preferably, of 
paraffin. If the latter material is used, the block is 
cast roughly to the shape of the proposed hull and then 
placed in a cutting machine, where it is planed down to 
the exact shape required, by a cutting tool, the movements 
of which are controlled by the operator. The latter guides 
the instrument by following with a pointer the lines of 
the hull on a drawing, the connection between the pointer 
and the cutting tool being so exact that the contour lines 
of the design are faithfully reproduced on the hull of 
the model. The final touches are done by hand, and 
NO. 1701, VOL. 66] 
the trim of the model, when placed in the water, serves 
as a check on the accuracy of the workmanship. 
The model, when ready for testing, is placed in the 
tank and attached to a travelling framework or “ carriage” 
which spans the width of the tank and is propelled 
either by a self-contained motor or by a stationary engine 
and cable. The travelling carriage is fitted with a 
dynamometer and registering apparatus, which records 
automatically the pullor resistance of the model and the 
speed at every point of the course traversed. Thus, at 
the conclusion of a series of trial runs at different 
speeds, accurate diagrams are obtained, from which the 
curves of resistance can be plotted for the various speeds 
considered, and, by interpolation, for any intermediate 
speed. Ina similar way, the effect of alteration of trim 
and displacement can be easily determined, and the most 
interesting and useful experiments on the effect of 
alterations to existing vessels, on the efficiency of various 
forms of screw propellers, on the relative oscillations of 
different types of hull, and many other problems that are 
met with in naval architecture can be carried out with 
results that approximate closely enough for all practical 
requirements to those actually obtained 
on full-sized ships. The economy in 
using models instead of full-sized vessels 
for obtaining such experimental data is 
sufficiently obvious, and need not be 
insisted upon. 
It is to Mr. Froude also that we are 
indebted for establishing the exact rela- 
tions that subsist between the model and 
the full-sized vessel, upon which depends 
the success of the experimental method. 
This relation or law of “ corresponding 
speeds” is to the effect that, comparing 
ship and model, “the resistance is in 
proportion to the cube of the linear 
dimension at speeds proportional to the 
square root of the linear dimension.” 
The practical value of Mr. Froude’s 
labours was recognised by the Govern- 
ment at an early period, and his tank 
at Torquay was established under 
Admiralty supervision in 1870. Fifteen 
years later, the Government decided to 
build and equip a much larger tank at 
Haslar, near Portsmouth, where models 
14 feet long could be run over a course 
of 4oo feet. This tank is under the 
direction of Mr. R. E. Froude, whose 
valuable researches by means of model 
experiments have greatly added to our 
knowledge ot the laws relating to fluid resistance, 
oscillation of ships, propeller efficiency, and other 
problems of naval architecture. 
The tank at Haslar, erected at Government expense, 
has been devoted purely to Admiralty work, and it is 
not found possible to extend its use to the testing of 
models for private shipbuilders. 
The only other tank of this kind in the kingdom is 
that constructed by Messrs. Denny at Dumbarton, and 
this is only employed upon the work of that firm. 
Recognising the need for a tank where private ship- 
builders could at any time send a model to be tested, 
the Institution of Naval Architects, at their summer 
meeting in Glasgow last year, passed a resolution to the 
effect that such a tank ought to be established, and the 
council of that Institution has since been considering 
how this proposal could best be carried out. 
The two chief difficulties were the selection of a site 
suitable for the purpose and the raising of the necessary 
funds to carry the scheme out. As regards the latter 
requirement, it was felt that those interested in the 
welfare of the shipowning and shipbuilding interests of 
