Both the Nautica RIB 18 Widebody 2011 and the Nautica RIB 20 Catamaran IO 2011 are rigid inflatable designs, both built in fibreglass, so the buying decision usually comes down to a handful of practical questions: how many people are you putting on the water, how far do you trailer, and what does your tow vehicle weigh?
On paper these two are close siblings in the size department - Nautica RIB 18 Widebody 2011 at 17,8 ft versus Nautica RIB 20 Catamaran IO 2011 at 19,5 ft. Weight tells a clearer story for trailering families: the Nautica RIB 18 Widebody 2011 tips the scales at 1 250 lbs - 200 lbs more than the Nautica RIB 20 Catamaran IO 2011 at 1 050 lbs. That difference is meaningful if you're working within a half-ton or three-quarter-ton truck's tow rating, especially once you factor in a motor, gear, and fuel.
Both boats share a closely matched power ceiling - 115 hp for the Nautica RIB 18 Widebody 2011 and 115 hp for the Nautica RIB 20 Catamaran IO 2011. Real-world performance will come down more to which motor is actually bolted on, its load at the time, and whether it's a 4-stroke or 2-stroke setup. Both carry nearly identical fuel loads - 50 gal and 48 gal - so range won't be a tiebreaker here.
For family outings this is probably the sharpest distinction between the two. The Nautica RIB 20 Catamaran IO 2011 is rated for 16 passengers, while the Nautica RIB 18 Widebody 2011 caps at 14. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Nautica RIB 20 Catamaran IO 2011 could be the deciding factor.
Bottom line: Choose the Nautica RIB 20 Catamaran IO 2011 if your priority is putting more people on the water - it handles 16 passengers and at 19,5 ft it has the deck room to back that rating up comfortably. The Nautica RIB 18 Widebody 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 14 that costs less to run day-to-day.