The Stanley Boats 16 Tiller 2011 is a modified-V design and the Stanley Boats Islander I/O 21 2011 is a deep-V design, so you're likely deciding between two noticeably 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 Stanley Boats Islander I/O 21 2011 measures 21,0 feet overall (2011), giving it roughly 5,0 additional feet of deck space compared to the Stanley Boats 16 Tiller 2011 at 16,0 feet (2011). Weight tells a clearer story for trailering families: the Stanley Boats Islander I/O 21 2011 tips the scales at 2 765 lbs - 2 240 lbs less than the Stanley Boats 16 Tiller 2011 at 525 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 220 hp, the Stanley Boats Islander I/O 21 2011 has a 180-hp advantage over the Stanley Boats 16 Tiller 2011's 40-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 Stanley Boats Islander I/O 21 2011 is rated for 6 passengers, while the Stanley Boats 16 Tiller 2011 caps at 2. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Stanley Boats Islander I/O 21 2011 could be the deciding factor.
Bottom line: Choose the Stanley Boats Islander I/O 21 2011 if your priority is putting more people on the water - it handles 6 passengers and at 21,0 ft it has the deck room to back that rating up comfortably. The Stanley Boats 16 Tiller 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 2 that costs less to run day-to-day.