A JACKASS was a kind of heavy utility
boat used in Newfoundland
in the 18th
and early 19th
The United States Navy during the same period used the term to describe a HAWSE-BAG, which was a canvas bag filled with OAKUM, old pieces of tarred and shredded rope, used to stop leaks, caulk the ship's seams and even to dress wounds.
The American Jackass plugged the HAWSE-HOLES, the two cylindrical openings at the ship's bow between which the anchor cables passed while the vessel was at sea. A sailor who "came in through the hawse-holes," had entered the service at the lowest level.
More colorful terms, and many more than one variety of jackass, can be found in author Patrick O'Brian's twenty volume series of novels on the Royal Navy during the Napoleonic Wars, beginning with Master and Commander, in paperback from W.W. Norton and Company, ISBN 0-393-30705-0.