When two boats share the same hull type — in this case both the Stanley Boats Islander 19 ft. 2012 and the Stanley Boats Islander I/O 21 2012 are deep vee designs with aluminum 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 — Stanley Boats Islander 19 ft. 2012 at 19,3 ft versus Stanley Boats Islander I/O 21 2012 at 21,7 ft. Weight tells a clearer story for trailering families: the Stanley Boats Islander I/O 21 2012 tips the scales at 2 765 lbs — 1 040 lbs less than the Stanley Boats Islander 19 ft. 2012 at 1 725 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 200 hp, the Stanley Boats Islander I/O 21 2012 has a 50-hp advantage over the Stanley Boats Islander 19 ft. 2012's 150-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Stanley Boats Islander I/O 21 2012 carries 33 gallons versus 24 gallons in the Stanley Boats Islander 19 ft. 2012. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.
Both boats are rated for 8 passengers — a good fit for a family of four or five plus guests. Comfort at capacity is another matter; the longer hull typically means more seat options and better weight distribution.
Bottom line: The Stanley Boats Islander I/O 21 2012 at 21,7 ft is the right call if deck space, comfort, and entertaining are top of your list. The Stanley Boats Islander 19 ft. 2012 at 19,3 ft wins on trailering ease, likely lower purchase price, and simpler docking — a solid choice for a buyer who wants more boat for less money.