The distinction between a ketch and a yawl is compounded of both the size and location of the mizzen sail. On a ketch, the area of the mizzen sail is generally between 30 % and 95 % of the area of the main. The mast is always stepped forward of the stern post. On a yawl, the mast is stepped aft of the rudder post, often on the after deck and the sail is less than 30 % of the main. Having sailed both, I also find that the mizzen on a yawl is used more as a trim tab than as a driving sail.

I believe the derivation of the term "jolly boat" is related to that of the "yawl boat." This would suggest a Scandahoovian derivation. The yawl boat would not only be hung astern, it would generally be the smallest boat on a ship, the purview of the junior officer aboard and the boat used when the captain did not wish to clear away one of the larger ship's boat. Many of the harbor craft derived from this, rather than the larger boats. Watermen would wish to use a smaller crew than a large vessel.

As I said above, I still do not know whether the yawl rig designation preceded the yawl boat or jolly boat designation. What I do know is that Steel's masting and rigging [1794] does not refer to either although it does refer to both "Dutch Hoys" and "French Shallops," which can be yawl rigged. There is no direct mention of ship's boats