Factory Ship

Overview

A factory ship is a fishing vessel that does not just catch fish but turns them into finished frozen product at sea. It hauls a trawl up a stern ramp, runs the catch through a processing line that heads, guts, and fillets it, freezes the product within hours, and stores it in a cold hold until landing weeks later. Waste from processing is reduced to fishmeal and oil rather than dumped. The ship is a floating factory with its own power plant, fresh water plant, accommodation for a large crew, and the navigation and fish-finding electronics of any modern trawler.

The hull is a large welded steel form, 80 to 145 m long, arranged on several decks: machinery and tanks low down, the processing factory and freezers on the working decks, the cold store in the cargo holds, and accommodation and the bridge above. Propulsion is usually diesel-electric, because the same generators that drive the propeller also run the heavy electrical loads of the factory and freezing plant.

Hull and trawl handling

The hull carries 10 to 20 mm shell plating over a dense grid of frames and deck girders, subdivided by watertight bulkheads. The defining feature aft is the stern trawl ramp, a wear-plated slope through the transom up which the cod end of the net is hauled by the trawl winches. Those winches store several kilometers of warp wire on large drums driven by hydraulic motors. Steering is by a spade rudder, and ballast tanks let the crew correct trim as the cold store fills with cargo over a voyage.

Propulsion

Diesel-electric drive decouples the propeller from the engines. The generators feed a switchboard, and a variable frequency drive supplies the propulsion motor at whatever speed the propeller needs. The motor turns the reduction gear and the shaft line to a controllable-pitch propeller, whose pitch actuator sets thrust without changing shaft speed, useful when trawling slowly against a heavy net. A bow thruster handles maneuvering in port.

Processing line

Catch lands in the receiving bin and flows along conveyors through the line. The grader sorts fish by size, then heading and gutting machines remove heads and viscera, filleting machines cut fillets from the backbone, and the skinning machine peels skin using a toothed grip roller against a fixed blade. A wash and chill system keeps the product clean and cold along the way, and the packing station weighs and trays it for freezing. Each machine runs on its own servo drives under a small controller, so the line speed can be matched to the catch rate.

Freezing and cold storage

Speed matters: product must freeze within hours of capture to hold quality. The freezing plant uses horizontal plate freezers that freeze blocks by direct contact between the product and refrigerant-filled aluminum plates, backed by a blast freezer where fans drive cold air over loose product. Ammonia compressors supply the cold and reject heat through the condenser. Frozen cartons move down to the cold store by the cargo elevator, where ceiling evaporators hold the hold at minus 25 C behind thick insulation.

Fishmeal plant and utilities

Heads, frames, and trimmings feed the fishmeal plant. The steam cooker coagulates protein, the screw press squeezes out liquid, the decanter centrifuge recovers fish oil, and the rotary dryer and mill turn the press cake into bagged meal. Living aboard for weeks is supported by the accommodation block with cabin modules, a galley, HVAC units, a reverse-osmosis fresh water plant, and a sewage treatment plant.

Power and bridge

Electrical demand is large and varies as the factory and freezers cycle, so the power plant runs four diesel generators onto a high-voltage switchboard, with transformers feeding low-voltage loads and an emergency generator for essentials. The integrated bridge carries dual radars, an ECDIS chart system, a fishing sonar, an autopilot, and a GMDSS radio suite, with propulsion and pitch controlled from the helm console.

Voyage and operation

A factory ship works a single fishing ground for weeks at a time, so its design is driven by endurance rather than speed. It carries enough fuel in the bunker tanks for 30 to 70 days at sea, enough stores for a crew of dozens, and enough cold store volume to fill before it must steam home. The fishing cycle repeats around the clock: the trawl is shot away over the stern, towed for an hour or more, and hauled back up the stern ramp by the trawl winches with the cod end heavy with fish. The catch empties into the receiving bin, and the processing line and freezing plant run continuously to clear it before the next haul arrives. Because the catch must be frozen within hours to hold its grade, the line speed, the number of freezers, and the refrigeration capacity are all matched to the trawl's expected yield. As the cold store fills over the voyage, the crew pumps the ballast tanks to keep the ship in trim, and the fishmeal plant turns what the processing line discards into a second saleable product rather than waste returned to the sea.