Page 210 - Introduction to Naval Architecture

196 RESISTANCE

Hence:

Making the same allowance of 0.0004 for roughness, yields:

/^ = 324 200 N

METHODICAL SERIES

Apart from tests of individual models a great deal of work has gone into
ascertaining the influence of hull form on resistance. The tests start with
a parent form and then vary systematically a number of form parameters
which are considered likely to be significant. Such a series of tests is
called a methodical series or a standard series. The results can show how
resistance varies with the form parameters used and are useful in
estimating power for new designs before the stage has been reached at
which a model can be run. To cover n values of m variables would
n
require m tests so the amount of work and time involved can be
enormous. In planning a methodical series great care is needed in
deciding the parameters and range of variables.
8
One methodical series is that carried out by Admiral D.W. Taylor. He
took as variables the prismatic coefficient, displacement to length ratio
and beam to draught ratio. With eight, five and two values of the variables
respectively he tested 80 models. Taylor standardized his results on a ship
length of 500ft (152m) and a wetted surface coefficient of 15.4. He
5
3
plotted contours of ^/A with V/L°~ and A/(I/100) as in Figure 8JO.
/if/A was in pounds per ton displacement. Taylor also presented
correction factors for length and contours for wetted surface area
correction. The residuary resistance, Rf, was plotted in a similar way but
5
with prismatic coefficient in place of V/L° as abscissa, see Figure 8.11.
9
Taylor's data was re-analysed using Q and C,, instead of resistance in
pounds per ton of displacement. Frictionai resistance was calculated
from the Schoenherr formula rather than being based on the Froude
data used by Taylor. A typical chart from the re-analysed data is given in
Figure 8.12.
More recent methodical series for merchant ships have been by
10 11
12
BSRA - and DTMB. The former varied block coefficient, length to
displacement ratio, breadth to draught ratio and longitudinal position
of the LCB. Data was presented in circular C form to a base of block