Both the Mariah FS20 2010 and the Mariah R18.9 2010 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 FS20 2010 at 20,0 ft versus Mariah R18.9 2010 at 18,3 ft. Weight tells a clearer story for trailering families: the Mariah FS20 2010 tips the scales at 3 550 lbs - 250 lbs more than the Mariah R18.9 2010 at 3 300 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 260 hp, the Mariah FS20 2010 has a 35-hp advantage over the Mariah R18.9 2010's 225-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 FS20 2010 carries 38 gallons versus 22 gallons in the Mariah R18.9 2010. 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 FS20 2010 is rated for 10 passengers, while the Mariah R18.9 2010 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Mariah FS20 2010 could be the deciding factor.
Bottom line: Choose the Mariah FS20 2010 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 R18.9 2010 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 8 that costs less to run day-to-day.