The frictional resistance is caused by tangential
stresses due to the drag of the water moving parallel
to the surface of the vesseL.
The residual resistance is caused by the distribution
of pressure which develops about the hull
because of the waves and eddies occasioned by the
ship's motion.
Froude (9, 10) found experimentally that the
frictional resistance, R¡, of towed planks could be
expressed by the relation