1969 O'Day Mariner 2+2 Advertisement
This advertisement, now in my own collection, features the "new Mariner 2+2". The original Mariner design (1963-1968) allowed for two to sleep on the V-berth. In 1969, O'Day enclosed the cabin, raised the cockpit floor and added two quarter-berths, thus allowing two more people to sleep in the cabin. Thus, the "2+2" was born.
Interestingly enough, this ad comes from the July, 1969 edition of the "Motor Boating" magazine.