Matching a deep vee Zodiac Medline 500 2013 against a inflatable rigid Zodiac Pro Open 550 2012 means you're likely deciding between two genuinely different on-water experiences. Hull type shapes everything from ride quality and fuel burn to dock handling and resale trajectory.
On paper these two are close siblings in the size department — Zodiac Medline 500 2013 at 16,4 ft versus Zodiac Pro Open 550 2012 at 18,1 ft. Weight tells a clearer story for trailering families: the Zodiac Pro Open 550 2012 tips the scales at 882 lbs — 104 lbs less than the Zodiac Medline 500 2013 at 778 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 120 hp, the Zodiac Pro Open 550 2012 has a 80-hp advantage over the Zodiac Medline 500 2013's 40-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Both carry nearly identical fuel loads — 23 gal and 22 gal — so range won't be a tiebreaker here.
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 500 2013 caps at 9. 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 19 lbs per hp for the Zodiac Medline 500 2013. 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.
The Zodiac Pro Open 550 2012 has a documented top speed of 45 mph. Speed data wasn't available for the other model.
Both are inflatable designs, which means they pack down for compact storage, can be carried in a bag, and are dramatically lighter than equivalent rigid hulls. The trade-off is setup time and the need to monitor tube pressure regularly. Tube diameter differs: 1 ft. 8 in. (0.5 m) on the Zodiac Medline 500 2013 vs 1 ft. 11 in. (0.575 m) on the Zodiac Pro Open 550 2012 — larger tubes generally mean more buoyancy and a drier, more stable ride.
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 500 2013 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 9 that costs less to run day-to-day.