When two boats share the same hull type — in this case both the Seaway Boats 18 Sportsman 2011 and the Seaway Boats 21 Coastal Hardtop 2011 are deep 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?
On paper these two are close siblings in the size department — Seaway Boats 18 Sportsman 2011 at 18,0 ft versus Seaway Boats 21 Coastal Hardtop 2011 at 21,0 ft. At 11 lbs and 18 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 Seaway Boats 21 Coastal Hardtop 2011 tops out at 140 hp. Engine specs for the Seaway Boats 18 Sportsman 2011 aren't listed — confirm with a dealer before selecting an outboard.Both carry nearly identical fuel loads — 4 gal and 4 gal — so range won't be a tiebreaker here.
For family outings this is probably the sharpest distinction between the two. The Seaway Boats 21 Coastal Hardtop 2011 is rated for 6 passengers, while the Seaway Boats 18 Sportsman 2011 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Seaway Boats 21 Coastal Hardtop 2011 could be the deciding factor.
Bottom line: Choose the Seaway Boats 21 Coastal Hardtop 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 Seaway Boats 18 Sportsman 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.