404 LOGGING 
times built on the ice and when nearing completion, a hole is 
cut large enough to permit the framework to be sunk. This 
method is not always as satisfactory as the first one described 
because ice may remain under the bottom of the crib and later 
cause it to settle unevenly. When the bottom is uneven, the 
crib must have some open pockets on the outer edge so that when 
it touches bottom enough rock ballast may be dropped down on 
the low side to make a level base. This may be done by setting 
spars at the corners of the crib and raising the low corners to a 
level by means of blocks and tackle. When cribs must be built 
in open water, they are constructed on inclined ways at some 
convenient point along the shore, and when they have reached 
a height sufficient to form a substantial raft, they are launched 
and then built up to a height slightly greater than the depth of 
water in which they are to be placed. They are then floated to the 
permanent site, loaded with stone and sunk to the stream bed. 
When the crib is to rest on a soft mud bottom, the load 
must be distributed over an area greater than the crib base. 
Stones are thrown on the bottom and when a sufficient quantity 
are in place the bed is roughly leveled and the crib sunk in position 
on top of it. 
The logs from which the crib framework is made should be 
notched where they cross each other and firmly drift bolted to- 
gether. The outward thrust of the rock ballast may be over- 
come by nailing round poles in the angle where poles cross or 
by quartering logs and nailing these pieces in the angle. 
In some cases the cribs are built rectangular in form above 
the water, but usually the upstream face is drawn in at an angle 
of from 30 to 40 degrees and planked over. The sloping face 
prevents ice and driftwood from forming a jam behind the crib 
and causing it to be carried away. A common method of attaching 
the boom sticks to the cribs is to drive a pile in the center of the 
crib. After a large iron ring has been loosely fitted over this 
pile the boom is fastened by a chain to the ring, and as the water 
rises and falls the ring slips up and down with the chain. When 
piling is used instead of cribs a nest of three or four piles are 
driven together and bound with chains or cable. 
Storage booms are usually taken in and the chains repaired 
after the drive is over. They are replaced early in the spring as 
soon as the ice leaves the stream. 
