of water having the surface struck as a base, and for its altitude twice
the height due to the velocity with which the board moves through the
water. If the board strike the water obliquely, the resistance will be
less, but no very reliable law has yet been discovered to determine its
amount.

535. _Q._--Will not the resistance of a vessel in moving through the water
be much less than that of a flat board of the area of the cross section?

_A._--It will be very much less, as is manifest from the comparatively
small area of paddle board, and the small area of the circle described by
the screw, relatively with the area of the immersed midship section of the
vessel. The absolute speed of a vessel, with any given amount of power,
will depend very much upon her shape.

536. _Q._--In what way is it that the shape of a vessel influences her
speed, since the vessels of the same sectional area must manifestly put in
motion a column of water of the same magnitude, and with the same velocity?

_A._--A vessel will not strike the water with the same velocity when the
bow lines are sharp as when they are otherwise; for a very sharp bow has
the effect of enabling the vessel to move through a great distance, while
the particles of water are moved aside but a small distance, or in other
words, it causes the velocity with which the water is moved to be very
small relatively with the velocity of the vessel; and as the resistance
increases as the square of the velocity with which the water is moved, it
is conceivable enough in what way a sharp bow may diminish the resistance.

537. _Q._--Is the whole power expended in the propulsion of a vessel
consumed in moving aside the water to enable the vessel to pass?

_A._--By no means; only a portion, and in well-formed vessels only a small
portion, of the power is thus consumed. In the majority of cases, the
greater part of the power is expended in overcoming the friction of the
water upon the bottom of the vessel; and the problem chiefly claiming
consideration is, in what way we may diminish the friction.

538. _Q._--Does the resistance produced by this friction increase with the
velocity?

_A._--It increases nearly as the square of the velocity. At two nautical
miles per hour, the thrust necessary to overcome the friction varies as the
1.823 power of the velocity; and at eight nautical miles per hour, the
thrust necessary to overcome the friction varies as the 1.713 power of the
velocit