When two boats share the same hull type — in this case both the Mariah FS20 2009 and the Mariah SX18 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 Mariah SX18 2009 measures 18,0 feet overall (2009), giving it roughly 16,0 additional feet of deck space compared to the Mariah FS20 2009 at 2,0 feet (2009). Weight tells a clearer story for trailering families: the Mariah FS20 2009 tips the scales at 355 lbs — 352 lbs more than the Mariah SX18 2009 at 3 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 2009 has a 70-hp advantage over the Mariah SX18 2009'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 FS20 2009 carries 38 gallons versus 22 gallons in the Mariah SX18 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 Mariah SX18 2009 is rated for 8 passengers, while the Mariah FS20 2009 caps at 1. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Mariah SX18 2009 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Mariah SX18 2009 comes in at 0 lbs per hp versus 1 lbs per hp for the Mariah FS20 2009. The lower the ratio the more explosive the acceleration — meaningful on a short RIB where bursts of speed, quick planing, and agility in surf or tight waterways define the experience.
Top speed is rated at 41 mph for the Mariah FS20 2009 and 40 mph for the Mariah SX18 2009.
Bottom line: Choose the Mariah SX18 2009 if your priority is putting more people on the water — it handles 8 passengers and at 18,0 ft it has the deck room to back that rating up comfortably. The Mariah FS20 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 1 that costs less to run day-to-day.