May be this is motor is a 2-strokes. Is not clear what it is and my Italian is not that great. But I just think that Mariner do not make 4-strokes engines.

Odessea Raid 2004 Italy to Turkey via Greece

RIB 6-6.5 mtrs
Mariner 150 4-strokes

Total Miles 2420
Total hours 143
Total Consumption 5120
Average speed 23 miles

5120 / 2420 = 2.115 ltrs/mile!!