When two boats share the same hull type — in this case both the Zodiac Medline II 2008 and the Zodiac Pro Open 550 2012 are inflatable rigid designs with rigid inflatable 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?
On paper these two are close siblings in the size department — Zodiac Medline II 2008 at 19,0 ft versus Zodiac Pro Open 550 2012 at 18,1 ft. Weight tells a clearer story for trailering families: the Zodiac Medline II 2008 tips the scales at 1 432 lbs — 550 lbs more than the Zodiac Pro Open 550 2012 at 882 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 150 hp, the Zodiac Medline II 2008 has a 30-hp advantage over the Zodiac Pro Open 550 2012's 120-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 Open 550 2012 is rated for 11 passengers, while the Zodiac Medline II 2008 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac Pro Open 550 2012 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Zodiac Pro Open 550 2012 comes in at 7 lbs per hp versus 10 lbs per hp for the Zodiac Medline II 2008. 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 46 mph for the Zodiac Medline II 2008 and 45 mph for the Zodiac Pro Open 550 2012.
The Zodiac Pro Open 550 2012 is an inflatable design — lighter, easier to store, and quicker to launch from a beach or dock without a slipway. The Zodiac Medline II 2008 is a rigid hull, which typically offers a more confident ride in chop and easier maintenance over the long term.
Bottom line: Choose the Zodiac Pro Open 550 2012 if your priority is putting more people on the water — it handles 11 passengers and at 18,1 ft it has the deck room to back that rating up comfortably. The Zodiac Medline II 2008 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.