When two boats share the same hull type — in this case both the Riviera Yachts 45 Open - Shaft Drive 2013 and the Riviera Yachts 51 Open Flybridge SII 2011 are deep vee 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 Riviera Yachts 51 Open Flybridge SII 2011 measures 54,7 feet overall (2011), giving it roughly 3,4 additional feet of deck space compared to the Riviera Yachts 45 Open - Shaft Drive 2013 at 51,3 feet (2013). Weight tells a clearer story for trailering families: the Riviera Yachts 51 Open Flybridge SII 2011 tips the scales at 4 806 lbs — 4 412 lbs less than the Riviera Yachts 45 Open - Shaft Drive 2013 at 394 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 825 hp, the Riviera Yachts 51 Open Flybridge SII 2011 has a 250-hp advantage over the Riviera Yachts 45 Open - Shaft Drive 2013's 575-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Riviera Yachts 51 Open Flybridge SII 2011 carries 977 gallons versus 608 gallons in the Riviera Yachts 45 Open - Shaft Drive 2013. 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 Riviera Yachts 51 Open Flybridge SII 2011 is rated for 16 passengers, while the Riviera Yachts 45 Open - Shaft Drive 2013 caps at 15. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Riviera Yachts 51 Open Flybridge SII 2011 could be the deciding factor.