When two boats share the same hull type — in this case both the Achilles LS4-RU 2009 and the Achilles SU-18 2012 are inflatable non rigid designs with inflatable 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 Achilles SU-18 2012 measures 18,0 feet overall (2012), giving it roughly 9,3 additional feet of deck space compared to the Achilles LS4-RU 2009 at 8,7 feet (2009). Weight tells a clearer story for trailering families: the Achilles SU-18 2012 tips the scales at 433 lbs — 370 lbs less than the Achilles LS4-RU 2009 at 63 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 90 hp, the Achilles SU-18 2012 has a 84-hp advantage over the Achilles LS4-RU 2009's 6-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load.
For family outings this is probably the sharpest distinction between the two. The Achilles SU-18 2012 is rated for 11 passengers, while the Achilles LS4-RU 2009 caps at 4. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Achilles SU-18 2012 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Achilles SU-18 2012 comes in at 5 lbs per hp versus 11 lbs per hp for the Achilles LS4-RU 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.
The Achilles SU-18 2012 is an inflatable design — lighter, easier to store, and quicker to launch from a beach or dock without a slipway. The Achilles LS4-RU 2009 is a rigid hull, which typically offers a more confident ride in chop and easier maintenance over the long term.
Bottom line: Choose the Achilles SU-18 2012 if your priority is putting more people on the water — it handles 11 passengers and at 18,0 ft it has the deck room to back that rating up comfortably. The Achilles LS4-RU 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 4 that costs less to run day-to-day.