You can find a PDF copy of the Neptune datasheet on our Downloads page.

Neptune 20M Personnel Access System

The Neptune system enables transfer of personnel with equipment or cargo, from a vessel via a gondola, to a fixed, or floating, offshore structure with full (6DoF) motion-compensation to remove wave-induced motions.

If the target is fixed and stationary, vessel induced motion is removed from the gondola, and it is said to be “space stabilised”. If the target is floating and also subject to wave action, the gondola and target motions are matched, and it is said to be “synchronised”.

PRINCIPLE:

A stand-alone system that can be installed on any suitable vessel and operates without requiring any vessel services or data, except for the optional use of ship-generated electrical power.

DESCRIPTION:

The system has five ‘joints’ and these are highlighted in Figure 1. The foundation, is fixed to the vessel deck and therefore moves with the vessel.

Annotated drawing of the Neptune 20M System highlighting the five joints
Figure 1: Overview of the Neptune 20M System
Slew:Rotates the entire Neptune system around the vertical axis.
Gimbal:Keeps the arms in a vertical plane as the vessel rolls and pitches.
Shoulder:Rotates the upper arm relative to the gimbal top frame.
Elbow:Rotates the forearm relative to the upper arm.
Wrist:Rotates the gondola relative to the forearm to keep the floor horizontal.
The function of each joint is described in the table above.

MOTION MEASUREMENT:

When in space-stabilised mode, the vessel deck movement is measured in real time using an integral Position and Attitude Sensing System (PASS). This obtains position from Global Navigation Satellite System (GNSS) satellites using Real Time Kinematic (RTK) techniques to enhance precision. This position, along with data from an Inertial Navigation System (INS), is used to generate a PASS output that the Neptune controllers use to calculate joint angles to space-stabilise the gondola.

In synchronised mode (i.e. gondola motion matched with a moving target) a Remote Sensing System (RSS) measures the motion of the floating target. The Neptune controllers use RSS data to derive the joint angles needed to synchronise gondola and moving target motions.

OPERATING WINDOW:

Simulations (Figure 2), and sea trials (Figure 3) have proven Neptune capable of operating at Significant Wave Heights (Hs) up to 2m even on smaller vessels, for example on a 54m mono hull and a 36m catamaran.

SPECIFICATION:

Height capability above deck:20.4m when on a standard mounting frame
Typical transfer height:17m above sea level
The operating height can be increased by mounting the unit on a pedestal.
Reach from centre of slew axis:greater than 21m
Vessel stand-off:greater than 10m (typically 14 to 17m)
Slewing capability:295° (typically limited to 233º depending on installation)
Motion compensation accuracy:Better than ± 10 cm
  
Maximum system individual motion compensation ability:
Heave:5 m
Roll:± 10°
Pitch:± 10°
Yaw:± 147.5°
Sway:± 2 m        Sway and Surge: in addition to
Surge:± 2 m        a 3m diameter watch keeping circle
  
Weight11.3 t (excluding hydraulic power unit)
Foundation footprint2.5 m x 3 m
Hydraulic power unit2 x 120 kW (diesel or electric)
Gondola capacity3 people including PPE and tools
Payload in personnel mode300kg maximum
Payload in crane mode700kg maximum

NOTES:

1. Motion compensation figures can be achieved with wave periods as short as 5 seconds.

2. Computer modelling, with ship-motion predictions, can be carried out to determine performance limits for a specific vessel if required.

3D computer simulation of Neptune 20M mounted on a mono-hull vessel.
Figure 2: Neptune 20M Simulation and Modelling
Neptune 20M prototype during sea trials on the MHO Esbjerg Fast Crew Transfer Vessel (FCTV).
Figure 3: Neptune 20M prototype during sea trials

PRINCIPAL DIMENSIONS:

Figure 4 shows a typical installation on a Fast Crew Transfer Vessel with an aluminium hull. The components shown in blue are the deck mounting frame and stowage cradle.

Dimensioned drawing of Neptune 20M Stowed On Deck
Figure 4: Principal Dimensions of a Typical Installation

FEATURES:

  • Low weight and a small footprint means the Neptune System can be easily accommodated on smaller vessels meaning savings in cost and CO2 emissions
  • The Neptune System can easily be retrofitted. Typically a mounting frame picks up on existing deck mounting points that are normally reserved for standard shipping containers
  • The purchase cost is a fraction of traditional stabilised gangways
  • The Neptune System exerts no pressure on the target structure. The personnel carrying gondola hovers near the target with only the passive ramp making sliding contact

SAFETY:

Design for safety is a key principle and is achieved in the following ways:

  • No single failure causes a hazardous situation
  • All critical components are duplicated with automatic switch-over (redundancy)
  • At the landing point, the stand off position is controlled by proximity sensors which keep the gondola at a safe distance from the landing platform
  • Personnel in gondola are seated with safety harnesses
  • No dependence on ship’s systems or data beyond vessel station-keeping

CERTIFICATION:

Designed to the requirements of DNV-ST-0358 Standard for Offshore Gangways and

DNV-ST-0378 Standard for Offshore and Platform Lifting Appliances.

Certification available to this or other equivalent classification society standards.

Conforms to HSE recommended ± 10 cm movement envelope.

OPERATING ENVELOPE:

Neptune 20M Operating Envelope
Figure 5: Neptune 20M Operating Envelope