Matching a inflatable rigid Achilles HB-315LX 2008 against a inflatable non rigid Achilles SU-18 2009 means you're likely deciding between two genuinely different on-water experiences. Hull type shapes everything from ride quality and fuel burn to dock handling and resale trajectory.
Size is the most obvious dividing line here. The Achilles SU-18 2009 measures 18,0 feet overall (2009), giving it roughly 17,0 additional feet of deck space compared to the Achilles HB-315LX 2008 at 1,0 feet (2008). At 128 lbs and 44 lbs respectively, both sit in a similar weight class — either should pair comfortably with most mid-size SUVs and half-ton trucks, though always confirm your specific tow rating with the motor added.
The power gap is worth calling out. Rated to 90 hp, the Achilles SU-18 2009 has a 75-hp advantage over the Achilles HB-315LX 2008's 15-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 2009 is rated for 11 passengers, while the Achilles HB-315LX 2008 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Achilles SU-18 2009 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Achilles SU-18 2009 comes in at 1 lbs per hp versus 9 lbs per hp for the Achilles HB-315LX 2008. 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.
Bottom line: Choose the Achilles SU-18 2009 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 HB-315LX 2008 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.