Eesistance  =  Length  x  Breadth  x  Coefficient  of  Friction
X  (Speed)*  X  (1 +4  sin*  if>  +  sin*<^).
The  last  term  was  styled  the  "  coefficient  of  augmentation."
Hence

Besistance  =  Coefficient  of  Friction  x  (Speed)*
X  "  Augmented  Surface."

And  his  supposition  was  that  for  ships  of  good  forms  a  similar
expression  would  hold,  within  the  limits  of  speed  usually  attained.
For  clean-painted  iron  ships  the  formula  was  very  simply  stated :

Besistance  =  Length  x  Mean  Girth  of  Wetted  Surface  x  Coeffi-
cient of  Augmentation  x  (Speed  in  knots)  *  -^  100
_  Augmented  Surface  x  (Speed  in  knots)*
100

{This  method  of  estimating  the  probable  resistances  of  ships
has  been  extensively  employed  by  some  shipbuilders,  and  is  un-
doubtedly of  use  when  the  speeds  to  be  attained  are  comparatively
moderate.  As  the  speeds  increase,  and  the  wave-making  resistance
assimies  importance,  the  method  necessarily  £eu1s;  the  total
resistance  then  varies  with  a  higher  power  of  speed.
Mr.  Froude  investigated  the  frictional  resistances  of  ship-shaped
models,  and  as  the  result  of  a  series  of  experiments  came  to  a


448  NAVAL  ARCHITECTURE.  chap.  xi.
