Best Means of Propulsion.
The best method of propulsion was by the screw,
which acting in air was subject to much the same conditions
as obtained in marine work. Its efficiency depended
on its diameter and pits and on its
position,
whether in front of or behind the body propelled. From
this theory of dynamic support, Mr. Lanchester proceeded,
the efficiency of each element of a screw propeller
could be represented by curves such as were given
in his first lecture before the society, and from these
curves the over-all efficiency of any proposed propeller
could be computed, by mere inspection, with a fair degree
of accuracy. These curves showed that the tips of
long-bladed propellers were inefficient, as was also the
portion of the blade near the root. In actual marine
practice the blade from boss to tip was commonly of
such a length that the over-all efficiency was 95 per cent
of that of the most efficient element of it.
