The Beneteau First 34.7 2005 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.
The power gap is worth calling out. Rated to 80 hp, the Beneteau First 51 1986 has a 59-hp advantage over the Beneteau First 34.7 2005's 21-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 20 gallons in the Beneteau First 34.7 2005. 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 34.7 2005 caps at 10. 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.
The Beneteau First 51 1986 has a documented displacement of 28 660 lbs. Displacement data wasn't available for the other boat in this comparison.
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 6,7 ft for the Beneteau First 34.7 2005. That 2,5-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.
The Beneteau First 34.7 2005 uses Sloop rigging. Helm style differs too: the Beneteau First 34.7 2005 uses a 1 wheel versus a 2 wheels on the Beneteau First 51 1986. Wheel helms give better leverage and visibility on larger boats; tillers offer direct feedback and simplicity on smaller ones. For auxiliary power the Beneteau First 51 1986 carries a 80-hp engine against 21 hp on the Beneteau First 34.7 2005. Motoring range and ability to punch through a foul current or enter a tight marina under power will favour the more powerful installation.
Hull speed is rated at 8,8 knots for the Beneteau First 51 1986 and 7,2 knots for the Beneteau First 34.7 2005. For extended cruising, water capacity matters: the Beneteau First 51 1986 carries 74 gallons versus 26 gallons on the Beneteau First 34.7 2005 — a significant advantage on longer passages where watermaker or provisioning stops aren't guaranteed.
Bottom line: The Beneteau First 51 1986 at 51,4 ft offers more living space, greater range, and a more substantial offshore capability. The Beneteau First 34.7 2005 at 34,0 ft is the easier, lower-cost option — simpler to crew and a strong choice for coastal and day sailing.