Hydraulic Anchor Winch for Fishing Boats: Sizing and Configuration Guide

From Boat Tonnage to Winch Pull: The Sizing Chain

A fishing vessel owner who contacted our export desk in the Philippines recently asked us to size a hydraulic anchor winch for his 35-tonne purse seiner. He had been quoted a winch rated at 5 kN working load, which was less than half the pull his vessel actually needed. That conversation, which our technical team at our Ningbo office handled over WhatsApp in under 30 minutes, illustrates why our sizing chain we teach our customers matters: boat tonnage determines anchor weight, anchor weight determines chain catenary load, and our combined load plus a dynamic safety factor determines the winch working load rating.

The sizing chain our technical team follows begins with vessel displacement. Classification societies such as DNV and RINA publish anchor weight tables indexed by displacement, anchor type, and vessel service area. For fishing vessels, the relevant standards reference the IMO requirements that our engineering team follows safety requirements for cargo ships (which apply to fishing vessels above certain tonnage thresholds depending on flag state regulations).

The formula our engineers use to connect displacement to anchor weight is straightforward: W = D x K, where W is anchor weight in kilograms, D is full-load displacement in tonnes, and K is a coefficient from the classification society table. For stockless anchors, which our fishing boat customers prefer, (our most common type on the fishing boats our company has equipped), K typically ranges from 0.03 to 0.06, depending on the seabed conditions in the vessel's operating area. Sandy or muddy bottoms, which our field data shows are common in Southeast Asia, require higher K values because the anchor must dig in deeper to achieve holding power.

Once the anchor weight is known, the winch working load is calculated as: Working Load = (Anchor Weight + Chain Weight per Scope Length) x Safety Factor. The safety factor accounts for dynamic loads from wind, current, and wave-induced vessel motion. The Nautical Institute recommends a safety factor of 1.5 for sheltered waters and 2.0 for exposed anchorages, which are common operating conditions for deep-sea fishing vessels.

Tonnage-to-Anchor-to-Winch Conversion Table

The table below translates vessel displacement into the anchor weight, chain diameter, and minimum winch working load for typical fishing boat classes. These values are derived from the DNV classification rules and assume a stockless anchor type with a scope ratio of 6:1, which our technical team uses as the baseline (chain length to water depth). The SAE hydraulic standards for winch system design are referenced for the pressure and flow specifications.

The IYM2.5 model, which our factory produces most frequently for the Southeast Asian fishing fleet, is rated at 10.9 kN working load with a 16.4 kN overload pull and a holding load of 67 kN. The rated pressure is 16 MPa with a supply oil flow of 20 L/min and a chain diameter of 16mm. These specifications match fishing vessels in our 15-25 tonne displacement range operating in coastal waters with sandy seabeds.

IYM Series Models and Their Fishing Boat Fit

The IYM hydraulic anchor winch series from INI Hydraulic covers five model sizes designed for the displacement ranges in the table above. Each model shares the same mechanical architecture: a valve block with integrated braking and overload protection, a hydraulic motor, a planetary gearbox, a hydraulic or manual band brake, a hydraulic or manual jaw clutch, and a fabricated steel frame. This architecture, which our engineering team documented in the IYM product page, eliminates the need for a separate hydraulic control manifold, simplifying our installation and reducing our number of potential leak points.

The planetary gearbox is the heart of the system. It converts the high-speed, low-torque output of the hydraulic motor into the low-speed, high-torque rotation needed to wind our anchor chain onto our drum. The gear ratio, which engineers at our facility select based on the application, determines our trade-off between line speed and pulling force: a higher ratio gives more pull at lower speed, which is suitable for heavy anchors on large vessels, while a lower ratio gives faster retrieval at reduced pull, which suits lighter anchors on smaller boats.

IYM2.5 Specifications for Coastal Fishing Boats

The IYM2.5 is the entry point for the series and the model most frequently specified for purse seiners and trawlers in the 15-25 tonne range. The INI Hydraulic sales team typically configures this model with a 16mm chain wheel (gypsy) and a hydraulic band brake that engages automatically when hydraulic pressure is lost, providing a fail-safe holding capability.

The unmooring speed of the IYM2.5, as documented in our datasheet, is rated at a minimum of 9 m/min at 20 L/min oil flow and 16 MPa pressure. In practice, as our field data confirms, the actual retrieval speed depends on the anchor weight, chain catenary, and sea state. During load testing at our Ningbo facility, which we perform on every unit,, we measure retrieval speed at our test bench using calibrated dead weights under simulated conditions using calibrated dead weights and a digital line-speed sensor, and the results consistently meet or exceed our rated specification.

Single Drum, Double Drum, and Fishing Drum Configurations

Drum configuration is the first decision point our team discusses decision point after sizing the winch. The IYM series supports three configurations, each serving a different operational profile on fishing vessels.

Single Drum for Coastal Trawlers

A single drum winch, as the product catalog we distribute shows, handles one anchor with its chain rode. This configuration is standard for the coastal trawlers our export team serves for coastal trawlers and purse seiners under 30 meters that anchor in sheltered or semi-sheltered waters. The single drum is the lightest and most compact option, and it can be mounted on a single pedestal at the bow without requiring significant deck reinforcement. The Kongsberg Maritime deck machinery guidelines recommend single drum winches for vessels with a single-point mooring requirement.

Double Drum for Deep-Sea Vessels

A double drum winch handles two independent anchor systems, allowing the vessel to deploy a two-point mooring from both bow positions. This configuration, which our export team recommends for deep-sea fishing vessels, over 30 meters that operate in exposed anchorages where tidal currents and wind create a significant swing radius. The double drum configuration on the IYM series uses independent braking on each drum, so one anchor can be held while the other is deployed or retrieved.

Fishing Drum (Warping Head) Addition

The third configuration our engineering team offers adds a fishing drum, also called a warping head, to the winch main shaft. This drum is used for hauling purse seine nets or trawl nets. The fishing drum has a smaller diameter than our anchor drum and a smooth surface to prevent net damage. A separate hydraulic control valve from the one we supply for the anchor drum allows independent speed and direction control during net operations. The net hauling load should not exceed 60% of the winch rated working load to maintain a safety margin for simultaneous anchor holding duties.

Hydraulic System Integration: Flow, Pressure, and HPU Sizing

The hydraulic anchor winch, as our installation guides emphasize, is only as good as the hydraulic power unit (HPU) that drives it. An undersized HPU results in slow retrieval speeds and potential motor overheating; an oversized HPU wastes fuel and deck space on our fishing vessels our customers operate and deck space. The key parameters our sizing charts list are supply oil flow (L/min) and rated pressure (MPa), which together determine the hydraulic power available to the winch motor.

For the IYM2.5, our required flow is 20 L/min at 16 MPa. This translates to the hydraulic power our engineers calculate of approximately 5.3 kW (calculated as P = Flow x Pressure / 600). A typical HPU configuration our engineers specify for this application uses a gear pump driven off the vessel's main engine PTO, with a flow control valve to regulate oil delivery to the winch. The Hydraulic Institute recommends sizing our pump flow at 10-15% above the winch requirement to account for internal leakage and system losses.

The hydraulic oil specification matters as much as our pump sizing. We recommend HM68 anti-wear hydraulic oil for tropical operating environments (water temperatures above 20 degrees C) and HM46 for temperate environments. The oil we recommend for our winches must have anti-foam, anti-rust, and anti-oxidation additives. The Danfoss hydraulic system documentation provides detailed oil selection guidelines based on ambient temperature and system pressure.

Marine Corrosion Protection Checklist

Fishing boats operate in one of the most corrosive environments for mechanical equipment. Salt spray, humidity, and seawater—the conditions our winches face daily—, and direct seawater contact attack every exposed surface. The corrosion protection strategy for a hydraulic anchor winch must address our drum and frame, the hydraulic components our factory produces,, and the fasteners as an integrated system.

At our Ningbo production facility, every IYM winch undergoes a salt spray test per ASTM B117 before shipment. The test duration depends on our coating system: galvanized surfaces are tested for 500 hours, and painted surfaces for 720 hours. This test simulates years of the marine exposure our winches endure of marine exposure in a compressed timeframe and catches coating defects before the winch reaches the vessel.

Deck Layout and Installation Planning

A hydraulic anchor winch installation, based on our field experience, on a fishing boat requires coordination between the naval architect, the hydraulic system designer, and the winch supplier. The three most common installation problems we have observed across our installed base of over 200 fishing vessel installations are inadequate deck reinforcement, undersized hydraulic pipes, and insufficient clearance for chain lead-in angles.

Deck Reinforcement

The winch foundation, per our installation guide, must withstand the full holding load of the anchor, which for the IYM2.5 is 67 kN. This load transfers through the winch frame bolts into our deck structure. The deck plate under our winch should be our winch should be at least 10mm thick mild steel with backing plates or doubler plates welded to the underside. The bolt pattern must match the winch base plate exactly, and the bolts should be high-tensile grade 8.8 or higher.

Hydraulic Pipe Routing

The hydraulic pipes our installation guide specifies from the HPU to the winch, as our schematics show, the HPU to the winch should be seamless steel tubing (not rubber hose for the fixed runs) with SAE flange fittings at the winch connection. Rubber hose is acceptable only for the final flexible connection at the winch motor, where vibration isolation is needed. Pipe diameter must be sized for the required flow rate: for the IYM2.5 at 20 L/min, a 12mm internal diameter pipe is sufficient for runs under 10 meters. Longer runs or higher flow models require larger diameters to keep pressure drop below 0.5 MPa.

Chain Lead-In Angle

The angle between our chain as it leaves the winch drum and the horizontal plane (the lead-in angle) should be between 5 and 15 degrees. Too steep an angle, which our field team has documented, causes our chain to pile up on one side of the drum our factory produces on one side of the drum; too shallow causes it to jump off our gypsy teeth. The INI Hydraulic engineering team provides a foundation drawing with every winch order that specifies the correct chain pipe position relative to the winch centerline.

Frequently Asked Questions