Both the Mariah R20.9 2009 and the Mariah RX181 Bow Rider 2008 are modified-V designs, both built in fibreglass, so 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?
On paper these two are close siblings in the size department - Mariah R20.9 2009 at 20,0 ft versus Mariah RX181 Bow Rider 2008 at 18,0 ft. Weight tells a clearer story for trailering families: the Mariah R20.9 2009 tips the scales at 3 700 lbs - 1 250 lbs more than the Mariah RX181 Bow Rider 2008 at 2 450 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 270 hp, the Mariah R20.9 2009 has a 80-hp advantage over the Mariah RX181 Bow Rider 2008's 190-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Mariah R20.9 2009 carries 38 gallons versus 22 gallons in the Mariah RX181 Bow Rider 2008. 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 Mariah R20.9 2009 is rated for 10 passengers, while the Mariah RX181 Bow Rider 2008 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Mariah R20.9 2009 could be the deciding factor.
Bottom line: Choose the Mariah R20.9 2009 if your priority is putting more people on the water - it handles 10 passengers and at 20,0 ft it has the deck room to back that rating up comfortably. The Mariah RX181 Bow Rider 2008 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 8 that costs less to run day-to-day.