When two boats share the same hull type — in this case both the Shoalwater 21 Cat 2013 and the Shoalwater 23 Cat 2013 are catamaran 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 — Shoalwater 21 Cat 2013 at 21,0 ft versus Shoalwater 23 Cat 2013 at 23,7 ft. Weight tells a clearer story for trailering families: the Shoalwater 23 Cat 2013 tips the scales at 165 lbs — 151 lbs less than the Shoalwater 21 Cat 2013 at 14 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 300 hp, the Shoalwater 23 Cat 2013 has a 50-hp advantage over the Shoalwater 21 Cat 2013's 250-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. 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 Shoalwater 23 Cat 2013 is rated for 9 passengers, while the Shoalwater 21 Cat 2013 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Shoalwater 23 Cat 2013 could be the deciding factor.
Bottom line: Choose the Shoalwater 23 Cat 2013 if your priority is putting more people on the water — it handles 9 passengers and at 23,7 ft it has the deck room to back that rating up comfortably. The Shoalwater 21 Cat 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.