When two boats share the same hull type — in this case both the Achilles SG-156 2011 and the Achilles SU-18 Commercial 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?
On paper these two are close siblings in the size department — Achilles SG-156 2011 at 15,5 ft versus Achilles SU-18 Commercial 2012 at 18,0 ft. Weight tells a clearer story for trailering families: the Achilles SU-18 Commercial 2012 tips the scales at 433 lbs — 161 lbs less than the Achilles SG-156 2011 at 272 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 Commercial 2012 has a 35-hp advantage over the Achilles SG-156 2011's 55-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 Commercial 2012 is rated for 11 passengers, while the Achilles SG-156 2011 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Achilles SU-18 Commercial 2012 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Achilles SU-18 Commercial 2012 comes in at 5 lbs per hp versus 5 lbs per hp for the Achilles SG-156 2011. 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.
Both are inflatable designs, which means they pack down for compact storage, can be carried in a bag, and are dramatically lighter than equivalent rigid hulls. The trade-off is setup time and the need to monitor tube pressure regularly. Tube diameter differs: 20 in. (50 cm) on the Achilles SG-156 2011 vs 24 in. (60 cm) on the Achilles SU-18 Commercial 2012 — larger tubes generally mean more buoyancy and a drier, more stable ride.
Bottom line: Choose the Achilles SU-18 Commercial 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 SG-156 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 8 that costs less to run day-to-day.