The Original (1973) model of the 20 was a "miniature" 22, same interior (more or less), same proportions to the rig, but with a K/CB and only one port (window) on each side of the cabin. The 20 never had a gas tank locker as far as I remember (the 22 didn't have one until 1977 model).
Some changes to the 22 from 1972-83:
1) original interior had a settee to starboard and a small dinette to Port with no galley. Forward of main bulkhead was a V-berth with head to Port and some had a sink to starboard.
2) I think during that first year the interior was changed to have settees on both sides and the galley was added at the forward end of the Port settee, with a pedestal table that swiveled over the starboard settee.
3) Forward hatch was optional in 1972 but seems to have become standard by 1974-5? This hatch was raised above the to pof the cabin and probably snagged the jibsheets easily.
4) The deck was re-tooled for 1977 adding the fuel tank locker and a flush forward hatch.
5) The 1972-78 models had the shoal-draft keel (1'11" draft), in 1979 that was changed to the keel/centerboard design (1'3" CB up, 4'3" CB down). Strangely the rudder was kept and so the "sailing draft" really wasn't changed ,only the trailering draft.
6) 1972-79 models had the masthead rig, 1980-83 models had the taller, fractional rig.
7) Ballast was 600# of lead in the keel for 1972-78 models, 700# lead in hte keel for 1979, and 800# lead in the keel for 1980-83. The centerboard on the 1979-83 models was only lightly ballasted (total weight around 50#).
8) Mainsheet was originally a triangle design running to the aft corners of the cockpit, changed came around 1974-5 I believe ,when O'DAY "simplified" the mainsheet rigging on many models, after that it was attached to the backstay.
9) Original outboard bracket was a wood plate on an aluminum pipe that sort-of stuck out of the transom, height was fixed and horsepower was limited to about 6hp. Later models (mid 1973 and later?) had the lifting style bracket mounted to a wedge on the transom.
10) Spars were clear annodized for 1972, Gold annodized for 1973-75, clear annodized for 1977-78, then color-annodised 1979-1980 and painted 1981-83. I seem to recall a creamy-gold color for 1979 and black for 1980.
There were, I'm sure, other changes from 1972-83.....but those are what I remember seeing. I have attached a diagram of the older mainsheet rig, as well as a picture of a 1972 O'DAY 22 (Blue) and a 1973 O'DAY 20 (White) .
1976-78 models of the 20 had a taller, fractional rig, but the 1973-75 models had the masthead rig as shown.
