g a line stretched perpendicularly from the deck to the
keelson, accurately to the edge of the square: the lower point of the line
where it touches the keelson will be immediately beneath the marks made
upon the deck. If this point does not come in the centre of the keelson, it
will be better to shift it a little, so as to bring it to the centre,
altering the mark upon the deck correspondingly, provided either paddle
shaft will admit of this being done--one of the paddle brackets being
packed behind with wood, to give it an additional projection from the side
of the paddle bearer. Continue the line fore and aft upon the keelson as
nearly as can be judged in the centre of the ship; stretch another line
fore and aft through the mark upon the deck, and look it out of winding
with the line upon the keelson. Fix upon any two points equally distant
from the centre, in the line stretched transversely in the direction of the
shaft; and from those points, as centres, and with any convenient radius,
sweep across the fore and aft line to see that the two are at right angles;
and, if not, shift the transverse line a little to make them so. From the
transverse line next let fall a line upon each outside keelson, bringing
the edge of the square to the line, the other edge resting on the keelson.
A point will thus be got on each outside keelson, perpendicularly beneath
the transverse line running in the direction of the shaft, and a line drawn
between those two points will be directly below the shaft. To this line the
line of the shaft marked on the sole plate has to be brought, care being
taken, at the same time, that the right distance is preserved between the
fore and aft line upon the sole plate, and the fore and aft line upon the
central keelson.

489. _Q._--Of course the keelsons have first to be properly prepared?

_A._--In a wooden vessel, before any part of the machinery is put in, the
keelsons should be dubbed fair and straight, and be looked out of winding
by means of two straight edges. The art of placing engines in a ship is
more a piece of plain common sense than any other feat in engineering, and
every man of intelligence may easily settle a method of procedure for
himself. Plumb lines and spirit levels, it is obvious, cannot be employed
on board a vessel, and the problem consists in so placing the sole plates,
without these aids, that the paddle shaft will not stand awry across the
vessel, nor be carried forward beyond