48Te AHC Launch and Recovery System


Denith Engineering has designed and manufactured this 48Te AHC Launch and Recovery System. The client  requested that the system be certified and to that end Denith Engineering engaged Lloyds Register to appraise the structural components, to survey the manufacture and attend the assembly and factory testing.


A drum manufactured from steel plate and arranged to accept the ring gear, split LeBus grooving and with stub shaft on both ends. Two band brakes manufactured from rolled steel flat bar complete with bonded and bolted brake linings.

The winch is powered by ten drives, each comprising a pinion, hydraulic motor and disc brake. The pinions engage with ring gears that are bolted to the drum side plates.

The winch is actuated from side to side using through rod travel cylinders fitted to the winch base to control rope fleeting angle during spooling. The rod ends are pinned to deck mounted supports aligned with the ships frames.

Guards are fitted to the drive components of the winch.


The A-Frame has two bases suitable for deck mounting and arranged to accept the cylinders and arms. A pair of legs arranged to pivot in the bases and to accept the two pairs of actuation cylinders and manifolds which are arranged to actuate the A-frame through its working arc. Change over control is achieved by linear transducers.

A cross beam was designed to bolt onto the A frame arms and to accept the docking head components and umbilical sheave.

Catching System

The Docking Head is designed to hold the full trencher weight during overboarding and inboarding. The docking head can rotate the Trencher to its inboarding orientation and to damp its motion whilst docked and inboarding. 

A dampening device is fitted to the system to dampen the roll and pitch movements. The overboarding sheave runs on spherical roller bearings on a stationary Load Cell shaft and is fitted with pay-in/pay-out sensors. 

The sheave design features an induction hardened rope groove, bolted side plates and a forged inner housing with spherical roller bearings. The docking head is fitted with a walkway for A-Frame access.

Hydraulic Power Unit

The HPUs and MCCs are mounted within two high cube 6 meter containers. The main hydraulic system comprises of 3x250kW electric motors per HPU, each driving a variable displacement hydraulic pump with mechanical and proportional pressure controllers. Together these pump sets supply the hydraulic energy that operates the winch motors and all cylinders on the A-frame.

A single 22kW electric motor per HPU drives a variable displacement pressure control pump that supplies pilot pressure to the control system.

Control of the A-frame cylinders is through proportional control valves that allow for smooth and fluent operation. The two primary cylinders are fitted with LVDTs and work in a master/slave configuration. To ensure the A-frame cylinders always operate together and at the same speed, each cylinder will be controlled from a separate proportional control valve.

The winch is driven by dual-displacement radial piston motors. These motors are high-torque low-speed motors with a small moment of inertia, ideal for AHC winch operations. Servo solenoid valves controls the hydraulic motors and mounted in close proximity to the motors for better control and response. An accumulator ensures that there is a constant source of hydraulic energy for high frequency of operation during AHC mode.


  • The Control desk is suitable for marine applications and is manufactured from sheet steel 1.6 mm sections with enclosure protection class IP65. The Operator control console is equipped with the following control items:
  • Control equipment consisting of Joysticks for control of the main hoist and umbilical winches, cylinders, and hydraulic motors
  • HMI system for the Operators to monitor the status of the system variables
  • Push buttons, selectors and warning pilot lights for operation and control of the system
  • Dedicated climate-control environment

The motor control panels suitable for marine applications is manufactured from sheet steel 1.6 mm sections assembled with enclosure protection class IP54.  The panel is complete with doors and with internal cooling for the control and power distribution equipment.

The Motion Reference Unit is a dedicated Kongsberg MRU and is mounted adjacent to the equipment, under deck at ship’s side on LARS centerline.

Denith developed its own software for the AHC control. 

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