Mercury 300XXL SeaPro Commercial DTS CMS

The new Mercury 300XXL SeaPro Commercial DTS CMS follows the same low-rpm, high-torque calibration as the rest of the SeaPro line, letting operators lean on it without piling extra stress on the engine. It carries a 30-inch shaft, the longest offered in this SeaPro family, for deep-transom commercial hulls.

Why a 30-inch leg

This length suits taller commercial boats where a shorter shaft would leave the gearcase running too shallow; the measurement is fixed once the engine ships, so confirm transom height first. The 4.6-liter, 279 cid V8 tops out at 4800-5600 rpm, matching the rest of the SeaPro range.

Controls and build details

Steering is hydraulic or power here, both optional rather than fitted, while digital throttle and shift is available through its own separately purchased control box. The V8's 32 valves sit on dual-cam heads, idle charge keeps the 85-amp alternator useful at low rpm, and this SeaPro tips the scale at 527 lbs dry.

Is the digital control box part of the purchase? No, it ships apart from the powerhead.

Why choose this over a shorter SeaPro? Only if your hull's transom specifically needs the extra shaft length.

It ships new, with no prior hours, built for repeated commercial duty rather than occasional recreational trips on the water. Buyers moving a boat between SeaPro shaft lengths within a fleet should note that rigging, not just the powerhead, needs to match the 30-inch measurement here.