DOCKING SYSTEMS FOR PILOTS

 

Benefit versus Cost

       -   A comparison of shore-based and portable docking systems

DGPS Portable Pilot Unit

Differential GPS applies a secondary source of correction data to raw GPS signals.
This improves the accuracy of the position from a typical PPU by about three to four metres. 

Navicom Dynamics’ newest GPS receivers are accurate to 2.5m in raw GPS, and with differential
corrections applied they achieve an accuracy of 50-60cm and often better than this.

DGPS corrections are freely available through the WAAS and EGNOS systems (covering parts of
Northern Hemisphere only), or via free-to-air MF beacons operating in the300kHz band in many
countries.  Where neither is available, it is possible to set up a dedicated DGPS base station at a port.

Level of accuracy:

• Less than 60cm, often better.  (Higher accuracy  is often not noticeable on PPU
  software or laptop screens)
• ± 2cm/sec (0.05 Kn) for velocity

Equipment needed:

• PPU (with dual antennas for heading calculation)
• DGPS reference station where free-to-air DGPS is not available (range 30 – 40km)

Disadvantages:  

Free DGPS corrections are not available in some areas of the world

Advantages:  

• A DGPS PPU can be used at every berth in the port
• Can be used for the entire pilotage
• Real-time heading, regardless of  whether DGPS corrections are available or not
• Data is consistently available
• Lowest cost solution

Summary:  

DGPS-based PPUs have proved accurate enough for all pilotage situations, including docking.
In most cases, no shore-based infrastructure is required.  The technology is consistent, stable
and can be operated anywhere there is an available chart and GPS satellite visibility. Where
DGPS is unavailable, the PPU is very often accurate enough working from raw GPS.

DGPS systems are the most flexible, as well as the cheapest, option and will capably
perform all pilotage requirements.

 

 

 

RTK Portable Pilot Unit

PPUs based on RTK technology need an RTK base station, which has a reliable radius of 5-10km. 
RTK systems give centimetre accuracy, making them the highest-precision PPUs.

Level of accuracy:

• 1-40cmdepending on whether RTK Lock is achieved.  2.5m if 'Float' is also lost 
• ±1cm/sec for velocity

Equipment needed:

• PPU (with dual antennas for heading calculation) and UHF receiver for correction signals
• At least one RTK base station. (Extra stations for use beyond approx 10km radius)

Advantages:

• Very accurate distances and velocities
• Can be used at every berth in the port and for channel navigation
• Real-time headnig

Disadvantages: 

• Laptop resolution limits ability to view centimetre accuracy
• Use limited by range of base station

Summary:

RTK is the most accurate PPU technology.

 

 

Laser Docking System

This consists of two laser sensors, with monitoring units located in a control room ashore. 
Vessel movement data can be displayed on a jetty-mounted monitor, and/or or transmitted
wirelessly to the ship’s display, or a laptop on board the ship.

Laser docking is the most accurate docking solution, but only works for the last 300 or so metres
of the docking procedure, and then only when the vessel is immediately opposite the lasers. 
It is unable to measure speeds in any direction except at right angles to the berth.    It does not
perform any other functions, such as channel navigation or swinging assistance, and it only
operates on a single berth.

Level of accuracy:  

• 1cm
• ±1cm/sec for velocity

Equipment needed:

• Two laser sensors with monitoring units, a control PC and jetty interface
• A large jetty display and/or wireless link to on-board display
• Speed warning lights

Disadvantages:                                                                

• Does nothing but aid in final docking manoeuvre on a single berth 
• May not work on dark-hulled, non-reflective ships
• Jetty display may be hard to see in some conditions
• Very expensive
  

Advantages:

• Very accurate and stable
• Berthing operation monitored from on shore 

Approximate cost:

Upwards of USD 250,000

TOTAL SOLUTION PRICE:  More than USD 0.25million

Summary:

Unless used in conjunction with other purposes such as mooring load monitoring, the benefits are
limited..  A major premium is being paid for a minor increase in accuracy.  This extra accuracy is
unlikely to give any actual operational advantage over a PPU, and the system cannot be used for
navigation outside the immediate vicinity of a single berth.

 

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