When two boats share the same hull type — in this case both the Riviera Yachts 51 Open Flybridge SII 2010 and the Riviera Yachts M470 Sport Cruiser 2009 are modified 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 2010 measures 54,7 feet overall (2010), giving it roughly 7,7 additional feet of deck space compared to the Riviera Yachts M470 Sport Cruiser 2009 at 47,0 feet (2009). Weight tells a clearer story for trailering families: the Riviera Yachts 51 Open Flybridge SII 2010 tips the scales at 4 806 lbs — 4 784 lbs more than the Riviera Yachts M470 Sport Cruiser 2009 at 22 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 2010 has a 400-hp advantage over the Riviera Yachts M470 Sport Cruiser 2009's 425-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 2010 carries 977 gallons versus 325 gallons in the Riviera Yachts M470 Sport Cruiser 2009. 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 2010 is rated for 16 passengers, while the Riviera Yachts M470 Sport Cruiser 2009 caps at 14. 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 2010 could be the deciding factor.