When two boats share the same hull type — in this case both the Zodiac Pro Open 550 2011 and the Zodiac Pro Open 850 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 Open 850 2011 measures 27,9 feet overall (2011), giving it roughly 9,8 additional feet of deck space compared to the Zodiac Pro Open 550 2011 at 18,1 feet (2011). Weight tells a clearer story for trailering families: the Zodiac Pro Open 850 2011 tips the scales at 3 307 lbs — 2 425 lbs less than the Zodiac Pro Open 550 2011 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 350 hp, the Zodiac Pro Open 850 2011 has a 230-hp advantage over the Zodiac Pro Open 550 2011's 120-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Zodiac Pro Open 850 2011 carries 106 gallons versus 22 gallons in the Zodiac Pro Open 550 2011. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.

For family outings this is probably the sharpest distinction between the two. The Zodiac Pro Open 550 2011 is rated for 11 passengers, while the Zodiac Pro Open 850 2011 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac Pro Open 550 2011 could be the deciding factor.