When two boats share the same hull type — in this case both the Duffy 16 Back Bay 2013 and the Duffy 21 Old Bay 2013 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 Duffy 21 Old Bay 2013 measures 21,0 feet overall (2013), giving it roughly 4,6 additional feet of deck space compared to the Duffy 16 Back Bay 2013 at 16,4 feet (2013). Weight tells a clearer story for trailering families: the Duffy 21 Old Bay 2013 tips the scales at 359 lbs — 338 lbs less than the Duffy 16 Back Bay 2013 at 21 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.
For family outings this is probably the sharpest distinction between the two. The Duffy 21 Old Bay 2013 is rated for 12 passengers, while the Duffy 16 Back Bay 2013 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Duffy 21 Old Bay 2013 could be the deciding factor.
Bottom line: Choose the Duffy 21 Old Bay 2013 if your priority is putting more people on the water — it handles 12 passengers and at 21,0 ft it has the deck room to back that rating up comfortably. The Duffy 16 Back Bay 2013 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 8 that costs less to run day-to-day.