OK Bart,

I'll take a crack at the Self-tending jibs.
I do believe (I could be wrong) these jibs were used to reduce the size
of the Catboats sail.

The work boats, before the use of the gasoline engines, were single sail
vessels for ease of handling when used by water-men working by
themselves. An example would be the New England Catboat. As they got up
in size, the sail size became a problem. This was in the days of Gaff
Rigs.( the Marconni Rig didn't appear until after the advent of the
trans-Atlantic Radio antennas) The single sail's weakness grew. Two
heavy booms, weather helm/ with barn door rubber, increased beams to
maintain heeling and shallow draft.

These were the problems the were solved by the Jib ( The Friendship
Sloop) It allowed and increase in sail area without increasing the
main. Also, eased the pressure on the weather helm ( Rudder size)

As a working boat the extra lines for the jib weren't a welcome addition
to the Lobsterman, so the self-tending jib solved that problem. If the
mast was cantered back a little the boat would still turn into the wind
and wait as the traps were tended with hands off the helm.

This made a handy rig and was adopted by the day sailer design. That is
where, today you are likely to find the rig. In the knock abouts day
sailors.

Advantage; Increased sail area, less pressure aloft, Only one line to
trim and tack, Reduced beam, smaller rudders, Less crowded cockpits

Disadvantage; Size limit on jib (100%) A complicated foredeck

Ole Thom