Trawl Winch Product

Overview

Trawl winches are the mechanical hearts of bottom-fishing vessels, managing hundreds of tonnes of rope and net in coordinated motions across multiple drums. Unlike specialized haulers (e.g., Longline Hauler) that serve a single line, a trawl winch orchestrates:

1. Net drum: Spooling the trawl net and separating bridles (legs that extend bottom contact width).
2. Warp drum: Managing towing warps (heavy cables pulling the net along the seabed).
3. Optional tertiary drum: Handling auxiliary lines (dandies, sweep lines, acoustic pingers).

A typical trawler deploys a 30-40 m net, towing it 50–100 m behind the vessel at 2–4 knots for 4–6 hours per tow. A single haul may involve 200–400 tonnes of rope and net, requiring coordinated winch control to prevent fouling, line breakage, or crew injury.

Dual Drum Architecture

The Drum Assembly (One Unit) consists of two massive spools (2 m diameter × 1.5 m face width each), side-by-side on a common shaft or independent shafts. Primary drum (net) and secondary drum (warp) are both driven by a single Hydraulic Motor through a Gearbox Reducer 5:1 reducer, but can be engaged/disengaged independently via clutch mechanisms or separate solenoid control.

The dual arrangement allows operators to manage asymmetric loads: during tow-out, the warp drum might be slipping (paying out rope slowly), while the net drum holds steady. During haul-back, both drums work together at matched speeds to prevent net twisting.

Load Management and Spooling

A critical problem in rope winches is uneven rope distribution. If the operator doesn't consciously manage the rope across the drum face, it piles in one area, creating high local stress and rope kinking. The Spooling Gear (also called a line equalizer) is a mechanical solution:

An adjustable Spooling Nut (threaded collar on the drum shaft) provides a gradually increasing lead angle, causing rope to corkscrew across the drum as it spools. A spring-loaded Spring-Loaded Guide maintains constant tension on this guide rope, ensuring smooth distribution.

Modern winches also integrate Pressure Sensor feedback: if one drum tension rises 15% above the other, the proportional Proportional Control Valve automatically throttles that motor, re-balancing load. This "soft-stop" prevents sudden rope breakage and allows operators to detect snagging early.

Proportional Control and Safety

The Control Panel features dual joysticks (one per drum) and a Load Limit Dial that sets maximum allowable tension. As tension rises (measured via Pressure Sensor feedback on motor discharge), the PLC gradually reduces proportional solenoid opening, softening hoist speed before hard limit is reached.

Example: If an operator sets load-limit to 200 bar (equivalent to ~50 tonne net tension), and snagging is encountered, the winch automatically reduces speed at 180 bar, alerting the operator to slow down before hitting the 200 bar cutoff. If 200 bar is reached (rope about to break), the solenoid closes fully and the Brake System engages, holding the load.

An emergency Emergency Stop button de-energizes all solenoids and hydraulically releases the brake, dropping the load safely if operator incapacity occurs.

Braking System

The Brake System is a spring-set, hydraulic-release disc brake rated 2500 Nm holding torque. At rest, powerful springs clamp three Brake Disc sintered bronze discs, preventing any rope drift. When hauling is required, the Brake Release Solenoid pilot-pressurizes the Brake Piston, forcing springs back and releasing friction.

This fail-safe design is critical in fisheries: if hydraulic power is lost during a haul-back, the brake automatically engages, holding the catch safely suspended. A Manual Release Pump (hand-operated) is carried by crew for emergency brake release if pressure loss occurs.

Rope Types and Wear

Trawl warps are typically:

• Natural fiber: Manila or sisal (cheap, low cost of loss, high stretch = shock absorption).
• Synthetic: Polypropylene or polyamide (lighter, higher strength, lower stretch = sharper load transients).
• Steel wire rope: Ultra-high-strength (14–22 mm wire, 200+ tonne break load), used in deep-water bottom trawling where rope weight becomes a limiting factor.

Steel warps require Rope Lagging (grooved metal guides) to prevent wire cutting into softer materials and to provide grip. Rope lagging wears at ~5 mm per season and requires annual replacement.

Operational Envelope

A typical bottom-trawl sequence:

1. Tow-out (15 min): Warp drum pays out 50–100 m rope at controlled speed (0.3 m/sec), net drum holding. Current shear on extended warps creates lateral forces; operator uses gentle tension to maintain course.

2. Tow (4–6 hours): Both drums locked at cruise tension (50–100 tonne), vessel making 2.5 knots. Autopilot holds course. Acoustic net monitoring relays data to wheelhouse: contact height, spread width, catch biomass.

3. Haul-back (30–45 min): Both drums engage at matched speed (1.0–1.5 m/sec). Net comes up first (lighter), then warps (heavier). Load rises from 50 tonne (net alone) to 200+ tonne (full rigging) as net approaches surface. Proportional solenoids reduce speed as load increases, preventing shock to structure.

4. Deck ops (20–30 min): Net swung aboard via deck crane. Catch sorted by species and size. Net and rigging inspected for damage.

Reliability and Maintenance

Trawl winches operate in extreme conditions: constant saltwater spray, sand/grit ingestion via rope, thermal cycling (sun exposure → nighttime cooling). Critical maintenance items:

• Rope lagging replacement: Annually, ~200 kg per winch.
• Gearbox oil analysis: Monthly, detects bearing wear and metallic contamination.
• Brake disc replacement: Every 18 months, ~$5000 parts+labor.
• Motor seal service: Annually, prevents oil degradation and loss of control response.

A well-maintained trawl winch lasts 15–20 years. Common failure modes include brake piston stiction (salt deposits jam hydraulic release) and gearbox bearing spalling (oscillating shock loads from tow-out snagging). Modern winches integrate redundant brake pilots and sealed gearbox sumps to mitigate these risks.

Variants

Single-drum winches simplify design but reduce operational flexibility; used on smaller demersal (bottom-dwelling) fisheries.

Three-drum systems add a tertiary drum for auxiliary lines (sweep cables, dandies), permitting wider net spread and directional control.

Hydraulic-hybrid winches use accumulator energy recovery: during haul-back deceleration, the winch motor acts as a pump, storing energy in accumulators. On tow-out, accumulators release stored energy, reducing main pump demand and fuel consumption by 15–25%.