When two boats share the same hull type — in this case both the Zodiac Pro 850 2011 and the Zodiac Pro Open 550 2008 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 850 2011 measures 27,9 feet overall (2011), giving it roughly 9,9 additional feet of deck space compared to the Zodiac Pro Open 550 2008 at 18,0 feet (2008). Weight tells a clearer story for trailering families: the Zodiac Pro 850 2011 tips the scales at 2 976 lbs — 2 879 lbs more than the Zodiac Pro Open 550 2008 at 97 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 300 hp, the Zodiac Pro 850 2011 has a 180-hp advantage over the Zodiac Pro Open 550 2008'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 2008 is rated for 11 passengers, while the Zodiac Pro 850 2011 caps at 10. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac Pro Open 550 2008 could be the deciding factor.