The Sea Ray Express Cruiser 340 1988 vs Sea Ray Fly 510 2015 comparison sits squarely in the category of decisions where specs alone won't tell the whole story — intended use, storage, and long-term ownership costs all factor in.
Size is the most obvious dividing line here. The Sea Ray Fly 510 2015 measures 51,0 feet overall (2015), giving it roughly 17,0 additional feet of deck space compared to the Sea Ray Express Cruiser 340 1988 at 34,0 feet (1988). Weight tells a clearer story for trailering families: the Sea Ray Fly 510 2015 tips the scales at 46 800 lbs — 36 700 lbs less than the Sea Ray Express Cruiser 340 1988 at 10 100 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 600 hp, the Sea Ray Fly 510 2015 has a 260-hp advantage over the Sea Ray Express Cruiser 340 1988's 340-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 Ray Express Cruiser 340 1988 carries 25 gallons versus 5 gallons in the Sea Ray Fly 510 2015. 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 Ray Fly 510 2015 is rated for 15 passengers, while the Sea Ray Express Cruiser 340 1988 caps at 10. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Sea Ray Fly 510 2015 could be the deciding factor.
Bottom line: Choose the Sea Ray Fly 510 2015 if your priority is putting more people on the water — it handles 15 passengers and at 51,0 ft it has the deck room to back that rating up comfortably. The Sea Ray Express Cruiser 340 1988 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 10 that costs less to run day-to-day.