Hydraulik Brattvaag M6300  //  Low-Speed Vane Hydraulic Motor Rotor Assembly

Hydraulik Brattvaag M6300: Restoration of Trawl Winch Torque Through Rotor Group Re-Engineering

A technical case study documenting the recovery of operational pulling force on a stern trawl winch system equipped with a Hydraulik Brattvaag M6300 low-speed vane hydraulic motor. The investigation revealed severe internal leakage and rotor-stator wear causing a collapse in volumetric efficiency under hauling load conditions. The repair strategy included reverse-engineering of rotor vanes, precision restoration of the cam ring geometry, and upgrading of wear-resistant materials within the hydraulic motor assembly.

FAILURE MODE Severe vane edge wear, internal hydraulic leakage, cam ring pitting, side plate scoring, volumetric efficiency collapse, and thermal overload during full trawl hauling operations
DOWNTIME 6 days
COST ESTIMATE ~€9,000 including vane reverse-engineering, stator profile grinding, sealing system overhaul, and hydraulic recommissioning
ROOT CAUSE Long-term operation under cyclic overload conditions combined with progressive vane edge degradation caused excessive internal leakage between high-pressure and low-pressure chambers. Loss of hydraulic sealing integrity destabilized the oil film inside the rotor-stator interface, generating localized thermal loading, accelerated cam ring surface fatigue, and a severe reduction in volumetric efficiency.

Operational Symptoms During Trawl Hauling

During full-load trawl hauling operations, the vessel crew observed a progressive loss of pulling force on the stern trawl winch system. Under peak wire tension conditions, the hydraulic motor was unable to maintain stable rotational torque, resulting in intermittent wire speed fluctuations and unstable trawl handling characteristics. Simultaneously, return-line hydraulic oil temperature increased to 68°C during continuous operation, indicating substantial internal hydraulic losses within the motor assembly.

Inspection Findings and Hydraulic Wear Mechanisms

Disassembly of the Hydraulik Brattvaag M6300 vane motor revealed significant wear of the vane working edges, extensive scoring on the side sealing plates, and wave-pattern pitting damage along the cam ring running profile. Dimensional inspection confirmed excessive rotor chamber leakage paths between high-pressure and low-pressure zones. The degraded sealing geometry destabilized the hydraulic oil film within the rotor assembly, accelerating internal recirculation losses and reducing volumetric efficiency to approximately 58%.

Rotor Group Re-Engineering and Component Manufacturing

A decision was made to perform a full engineering reconstruction of the rotor group rather than a standard component replacement. Using unworn reference vanes as dimensional templates, a new vane set was manufactured from upgraded alloy steel with enhanced wear resistance characteristics. The replacement vanes underwent controlled heat treatment and volumetric hardening to 58–60 HRC, followed by precision grinding of the working edges to restore the original rotor-stator sealing geometry. Simultaneously, the cam ring profile was restored through precision CNC grinding to eliminate pitting damage and recover the designed vane travel contour.

Hydraulic System Restoration and Operational Results

The hydraulic motor assembly was rebuilt with newly manufactured side distribution plates and a complete replacement of high-temperature sealing elements and O-rings. Rotor axial clearances were adjusted to minimize internal end leakage under operational load conditions. Following recommissioning and sea-trial verification, volumetric efficiency recovered to approximately 92% of the original design specification. Return-line hydraulic oil temperature stabilized at 44°C during continuous hauling operations, while pulling force and trawl winch load stability were fully restored. Dynamic load fluctuations during wire tension changes were also significantly reduced due to improved vane guidance and restored hydraulic chamber sealing integrity.

Prevention

Implementation of scheduled vane wear dimensional inspections, continuous hydraulic oil contamination monitoring, periodic thermal trending of return-line temperatures, and maintaining rotor axial clearance within OEM tolerances during overhaul procedures.

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