When two boats share the same hull type — in this case both the Zodiac Cadet RIB 310 2011 and the Zodiac Pro 550 2011 are inflatable rigid designs with fiberglass construction — 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?
Size is the most obvious dividing line here. The Zodiac Pro 550 2011 measures 17,2 feet overall (2011), giving it roughly 7,0 additional feet of deck space compared to the Zodiac Cadet RIB 310 2011 at 10,2 feet (2011). Weight tells a clearer story for trailering families: the Zodiac Pro 550 2011 tips the scales at 695 lbs — 552 lbs less than the Zodiac Cadet RIB 310 2011 at 143 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.
The power gap is worth calling out. Rated to 90 hp, the Zodiac Pro 550 2011 has a 75-hp advantage over the Zodiac Cadet RIB 310 2011's 15-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load.
For family outings this is probably the sharpest distinction between the two. The Zodiac Pro 550 2011 is rated for 12 passengers, while the Zodiac Cadet RIB 310 2011 caps at 4. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac Pro 550 2011 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Zodiac Pro 550 2011 comes in at 8 lbs per hp versus 10 lbs per hp for the Zodiac Cadet RIB 310 2011. The lower the ratio the more explosive the acceleration — meaningful on a short RIB where bursts of speed, quick planing, and agility in surf or tight waterways define the experience.
Top speed is rated at 42 mph for the Zodiac Pro 550 2011 and 24 mph for the Zodiac Cadet RIB 310 2011.
Bottom line: Choose the Zodiac Pro 550 2011 if your priority is putting more people on the water — it handles 12 passengers and at 17,2 ft it has the deck room to back that rating up comfortably. The Zodiac Cadet RIB 310 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 4 that costs less to run day-to-day.