2000

Radar interferes with ship steering gear, nearly causing collision           

Two navy warships nearly collided when the radar beams of one disabled the steering of another. The minehunter HMAS Huon went out of control and veered across the bow of the frigate HMAS Anzac.

Huon – the first of six state-of-the-art coastal minehunters for the Australian Navy – lost its steering as a result of electromagnetic interference (EMI) from Anzac and passed ahead of the frigate “at close range” . The incident occurred in June 2000 while the warships were sailing to Singapore.

The near-collision was used in the Australian National Audit Office report to highlight shortcomings in the testing and evaluation of new defence equipment, especially in the navy, leading to installation of only partially tested systems. "The incident prompts questions concerning the adequacy of EMI testing during developmental testing and evaluation (T&E) and whether the services should complete more extensive T&E before integrating new platforms into defence exercises", the report stated.

The report on the incident rejected Defence Department claims that EMI testing was expensive and not necessarily cost-effective and said that T&E should be conducted as early as possible in order that risks could be reduced before they became dangerous. “In extreme cases, inadequate T&E could have tragic consequences,” the report said.

1994

Commercial computers interfere with radiocomms on a small vessel

The experiences of the crew of the research vessel (R/V) Deep Scan, a privately owned research and recovery ship, offer some insight into the complexities of integrating commercial off-the-shelf (COTS) computing equipment into a shipboard electromagnetic environment. R/V Deep Scan is constructed as a commercial vessel with many of the electrical characteristics of military mine-clearing ships. Its hull and deck structures are constructed from wood, closed cell foam and fibreglass, and it shares EMI/EMC problems common to non-metallic ships.

Computing equipment on board is said to be compliant with FCC Part 15 for radiated emissions. A commercial workstation processes sonar and navigation track data from multiple transducers. A 386 PC processes both electromagnetic survey data from multiple detection transducers and data for navigation. Navigation data is provided by COTS GPS (Global Positioning System) and LORAN-C receiver systems. Depth information is provided by COTS depth sounding equipment. Heading data is provided by a COTS fluxgate compass.

Operating the marine VHF transmitter at more than 1W begins to corrupt collected data, and any use of HF SSB transmission causes the COTS computing equipment used for magnetic data collection and navigation to enter states that challenge rational explanation.

FCC rules limit the levels of unintentional electromagnetic radiation, but the close proximity of COTS computing equipment (the vessel is under 60 feet long) to the antennas used for data collection and communications is largely responsible for disruption of operations due to the EMI the COTS equipment generates.

EMI generated by the switching power supplies in the COTS equipment slightly degrades the LORAN-C signal-to-noise ratio through radiated coupling. COTS computing equipment generates sufficient radiated interference on the HF bands to render HF communications impractical. Broadband interference and harmonics from COTS computing equipment interfere with communications reception on selected VHF channels, in some cases enough to prevent useful communications.

Daily operations on board R/V Deep Scan are influenced by the EMI and susceptibility problems associated with the use of COTS computing equipment. Responding to a call on the VHF radio presently requires the crew to wait for a logical break in survey operations, or requires termination of survey operations. During survey operations, monitoring some VHF channels is not possible, HF transmission is impossible and HF reception is seriously degraded.

Vessel collisions, capsizes, and unintended movement of an offshore platform

There was a minor collision between a supply vessel servicing a semi-submersible offshore oil and gas installation. The vessel experienced a sudden power increase brought on because of interaction between radio signals from a portable VHF radio and the joystick control. This caused the joystick to execute commands not requested by the operator and resulted in contact between the vessel and the installation. The interaction caused minor damage (though it could have been far worse).

The incident occurred outside UK waters and was reported in a safety notice issued by an offshore operator. The safety notice was seen by an HSE inspector on a bulletin board on an offshore installation, dated 30 September 1999, which referred to the incident as having happened 'recently'.

The case in the Rotterdam harbour is an 'old case' of about 15 years ago: we have installed X-band (1 kW) radars for Vessel Traffic Control and due to one of these transmitters the steering machine of a small towing ship was influenced in such a way that the ship hit the quay.

Capsizes

There is some evidence that EMI may have contributed to two boat capsizes, via autopilot malfunctions. One was the 16 metre fishing vessel the “Dalewood Provider” which capsized on August 17 1989, the other was the 64 tons “Martin N” which sank on April 25th 1987. In the latter case three lives were lost. In both cases the concern is that the on-board VHF radiotelephone system interfered with the autopilot sufficiently to turn the rudder hard over.

Staff at the Centre report that erratic alterations in a boat’s course when autopilot is engaged and VHF radio used is commonplace, generally due to insufficient EMI suppression at the autopilot’s interface and control cables. This interference problem is apparently so common that it is routine on some fishing vessels for the crew to turn off the autopilot when operating the vessel’s radio equipment.

Oil platform movement

A platform was anchored to the sea bottom, but its exact position was adjusted by thrusters, i.e. large electric motors driving propellers. The position of the platform was controlled by a computer system. The power and control cables, all screened, were routed from the control room on the bridge at the top of the platform, all the way down to the engine rooms far below. However, the cable feedthroughs were not protected against electromagnetic disturbances. Communication radios were used both on board the platform and for communication with land.

When a technician tried to use his com radio in the engine room, the connection was continually bad. By letting the radio antenna touch a cable harness, the connection became much better: the radio got a much improved “antenna”. Unfortunately, the energy in the cable screens also went elsewhere. It went via the cable screens to the thruster control equipment, which interpreted the energy as a signal for adjusting the position of the platform.