The expression "blowing for tugs" is one in common use with ex sailors.
In general it has come to mean that "I am out of breath," that's the way my doctor uses it.
But when used on the water by ships/boats how do or did a vessel call for assistance.
As a boy, over fifty years ago, I recall the river Mersey full of ship and tugs dashing all over the river competing for towing work. Tugs owned by companies like: Cock Tugs. Lamys Tugs. Rea Tugs. Alexandria Towing. How did they communicate with vessels and vessels communicate with them.