Both the Sea Hunt Ultra 186 2010 and the Sea Hunt XP 21 2013 are modified-V designs, both built in fibreglass, so 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 - Sea Hunt Ultra 186 2010 at 18,5 ft versus Sea Hunt XP 21 2013 at 21,2 ft. Weight tells a clearer story for trailering families: the Sea Hunt XP 21 2013 tips the scales at 2 150 lbs - 350 lbs less than the Sea Hunt Ultra 186 2010 at 1 800 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 Sea Hunt XP 21 2013 has a 50-hp advantage over the Sea Hunt Ultra 186 2010'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 Sea Hunt Ultra 186 2010 carries 58 gallons versus 50 gallons in the Sea Hunt XP 21 2013. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.
For family outings this is probably the sharpest distinction between the two. The Sea Hunt XP 21 2013 is rated for 6 passengers, while the Sea Hunt Ultra 186 2010 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Sea Hunt XP 21 2013 could be the deciding factor.
Bottom line: Choose the Sea Hunt XP 21 2013 if your priority is putting more people on the water - it handles 6 passengers and at 21,2 ft it has the deck room to back that rating up comfortably. The Sea Hunt Ultra 186 2010 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.