The Seafarer 31 Mark II is a recreational keelboat, built predominantly of fiberglass, with a balsa-cored deck and with wood trim. It has a masthead sloop rig; a raked stem; a raised counter, reverse transom; a skeg-mounted rudder controlled by a wheel and a fixed fin keel. It displaces 10,300 lb (4,672 kg) and carries 4,850 lb (2,200 kg) of lead ballast.[1][3]
The boat has a draft of 5.25 ft (1.60 m) with the standard keel.[1][3]
The boat is fitted with a Universal Atomic 4 30 hp (22 kW) gasoline engine or optionally a Palmer M-60 gasoline engine for docking and maneuvering. The fuel tank holds 20 U.S. gallons (76 L; 17 imp gal) and the fresh water tank has a capacity of 45 U.S. gallons (170 L; 37 imp gal).[1][3]
The design has sleeping accommodation for five people, with a double "V"-berth in the bow cabin, an L-shaped or optional U-shaped settee around a drop-down table and a straight settee in the main cabin. The galley is located on the port side just forward of the companionway ladder. The galley is U-shaped and is equipped with a three-burner stove, an ice box and a sink. A navigation station is opposite the galley, on the starboard side. The head is located just aft of the bow cabin on the both sides.[1][3]
The design has a hull speed of 6.71 kn (12.43 km/h).[3]