MAKING A BT LOWERING 
The BT is designed for lowering from a ship underway 
at speeds up to 18 knots. Best results, however, are 
obtained when the speed is not in excess of 12 knots. 
At higher speeds, unless the sea is very smooth, only 
an experienced operator should attempt to operate 
the winch. New operators should practice lowerings 
and recoveries with a dummy BT, before undertaking 
the operation with an actual instrument. Operation 
of the BT winch cannot be learned from reading a 
description any more readily than one can learn to 
pitch a baseball or bowl 300 by reading a manual. 
Nevertheless, the essential steps, together with some 
useful hints, are outlined below. 
PUT THE SLIDE IN THE BT 
Hold the slide by the edges and inspect it to be 
sure that it has a well-smoked surface. Then, insert 
it into its bracket. The edge with the bevelled corner 
goes in first, the bevel toward the nose of the BT. 
Push the slide all the way home against the stop pin. 
It is important to be sure that the slide is fully pushed 
in; otherwise the temperatures recorded will be fic- 
titiously low. With the slide fully in, the stylus will be 
brought against the smoked surface when the sleeve 
is moved back to cover the slide opening. To reduce 
extraneous scratches on the slide, do not move the 
sleeve back until the BT is ready to be put over 
the side. 
EXAMINE 
THE WIRE AND CONNECTION TO THE BT 
If the connection is frayed, rusted, or in any way 
doubtful, or if the wire is kinked, cut the faulty con- 
nection and make a new one. Check the swivel care- 
fully, particularly the swivel pin. More BT’s are lost 
by poor wire connections than from any other cause. 
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