The Beneteau First 21.7 S 2004 vs Beneteau First 51 1986 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 Beneteau First 51 1986 measures 51,4 feet overall (1986), giving it roughly 31,3 additional feet of deck space compared to the Beneteau First 21.7 S 2004 at 20,1 feet (2004). Weight tells a clearer story for trailering families: the Beneteau First 51 1986 tips the scales at 28 660 lbs — 25 916 lbs less than the Beneteau First 21.7 S 2004 at 2 744 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 80 hp, the Beneteau First 51 1986 has a 60-hp advantage over the Beneteau First 21.7 S 2004's 20-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Beneteau First 51 1986 carries 185 gallons versus 8 gallons in the Beneteau First 21.7 S 2004. 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 Beneteau First 51 1986 is rated for 15 passengers, while the Beneteau First 21.7 S 2004 caps at 6. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Beneteau First 51 1986 could be the deciding factor.

Displacement is where these two sailboats genuinely part ways. The Beneteau First 51 1986 displaces 28 660 lbs — a 25 916-lb difference over the Beneteau First 21.7 S 2004 at 2 744 lbs. That gap separates two entirely different categories of sailing: the heavier boat is built for offshore passage-making and load-carrying, while the lighter hull rewards performance sailing and easier handling in lighter air.

Draft is a practical consideration that many buyers underestimate until they're already at the marina. The Beneteau First 51 1986 draws 9,2 ft, compared to 6,0 ft for the Beneteau First 21.7 S 2004. That 3,2-foot difference affects which anchorages you can access, which haul-out facilities will take you, and how carefully you need to read the tide tables in shallower cruising grounds.

For auxiliary power the Beneteau First 51 1986 carries a 80-hp engine against 20 hp on the Beneteau First 21.7 S 2004. Motoring range and ability to punch through a foul current or enter a tight marina under power will favour the more powerful installation.

For extended cruising, water capacity matters: the Beneteau First 51 1986 carries 74 gallons versus 11 gallons on the Beneteau First 21.7 S 2004 — a significant advantage on longer passages where watermaker or provisioning stops aren't guaranteed.