MOB Technology: Practicalities by Andrew Bray

Man over board (MOB) situations occur in a wide range of circumstances ‘ from a slip while boarding the dinghy, to being hurled into the sea during a knock down. Whatever the cause, the result can be fatal even in relatively benign situations, but particularly at sea.

Preventive measures are aspects of making a boat seaworthy ‘ lifelines, jackstays and attachments for harness tethers, non-skid surfaces, boom brakes, rigid boom vangs, netting and so on.
The ultimate preventative may be tethering at all times, but clipping on and off takes time, and a spare hand. So, in practice tethers are generally only used when the risk is perceived to be high, and we still need to be prepared to deal with a MOB.

The person faces many risks, but the main ones are drowning and hypothermia. For both reasons, it’s vital to get back to them quickly and retrieve them promptly from the water. If only it was that simple!

Some well-organised crews have plans where they actually practise a MOB reaction plan, based on the gear and number of people expected to be left on board. TyRapid reaction has saved many racing MOBs, and remains the best first option in suitable scenarios. But sailors know such plans won’t cover other foreseeable situations - such as when an absence isn’t noticed until later or if the MOB can’t swim; or is knocked unconscious. Other scenarios include: if insufficient crew remains, if it’s night or sight is lost in the waves, if the yacht is disabled, or if high freeboard or rough weather prevents recovery.
There’s no panacea for all such depressing scenarios, but gear exists that could improve the MOB’s chances in many of them. Before detailing some ‘optional extras’ it’s perhaps worth noting what’s generally regarded as basic.

Basic MOB kit

A Dan Buoy and associated flashing light, drogue, life-ring, and perhaps small radar reflector and maybe even a personal locater beacon (PLB) remains an essential bit of kit that provides a visual search reference, reveals current (compared with GPS) and flotation for the MOB if he can reach it. They’re required in some racing categories, but should be carried by most yachts, and certainly if they go to sea with more than a solo crew. Inflatable DanBuoy equivalents are lighter and easier to stow and deploy than rigid ones, but more easily knocked down by strong winds.

A floating throw line, and a second life-ring (eg LifeSling which can act as hoisting harness) on a long floating rope that can be thrown or towed within reach of a MOB should also be ever-ready. MOB recovery has failed in well-documented tragedies involving high freeboards. A dinghy or life raft could offer a lower obstacle, or a temporary haven. Special recovery modules are available (eg JonBuoy), but getting someone into hoisting gear could still prove impossible in rough conditions, or if the MOB is too exhausted or cold to co-operate.

An easy way for an able swimmer to re-board unaided under some conditions is a very basic but often overlooked precaution (eg a rolled-up ladder with a release lanyard) that also permits a tethered crewman to get to water level. Fortunately, modern yachts often have only short stern overhangs and incorporate stern boarding platforms or step-through transoms that allow a tethered crewman to directly grasp an MOB, with the possibility of dragging them back on board.

A retrieved MOB may be suffering from shock, exhaustion, and hypothermia, water inhalation, sunburn and physical injury. Prompt assessment and appropriate treatment and monitoring could prove vital, so crew should have first aid training and airway breathers, space blankets and a hot water bottle should be carried.

Latest developments
Recovery remains an intractable problem, but some general developments and specialised products may significantly improve a MOB’s chances. GPS is one area.
MOB buttons on GPS receivers allow a very quick recording of the initial location of the MOB. If the remaining crew can handle the yacht, their GPS provides a course and distance back to that position, and if for some reason they can’t return or relocate the MOB, the position can be used by others.

Although even a gentle one knot current carries a MOB away from a GPS position at 31 metres per minute, it remains a point from which systematic searches can be based, possibly taking currents (estimated, or revealed by DanBuoy drift) into account. Search patterns functions are built into some chart plotter software, for example. The MOB’s position can be passed to search and rescue or other vessels, even by crew who have no navigational knowledge, and other boats and aircraft can go straight to that position. Modern VHF radios can automatically include in their DSC MayDay alerting message the boat’s current GPS position, and that the emergency involves a MOB.

Outside assistance
If a search does become necessary, the more participants the better, but SAR professionals with aircraft can cover more water quickly, and may also be better equipped to retrieve the MOB or drop a life raft. A flare may attract attention from nearby small craft that aren’t monitoring the distress channel, but with modern VHF, HF, mobile phone, and even satellite phones, in many coastal waters there’s reasonable prospect of assistance from other small craft. TyIn remote areas, timely assistance is less likely. But SAR communications is now well organised internationally, and if authorities become aware of the situation promptly, know they’re looking for a MOB, and have a position, even on the high seas they may be able to organise help from ships, fishing boats, or even long range aircraft.

Inflatable PFDs
In most conceivable circumstances an MOB has a far better chance if wearing a personal flotation device (PFD). Even in cold water, it prolongs life, and in general allows far more time for searches and recovery. They usually incorporate a lifting strop, although not all standards also specify a crotch strap, without which the PFD may simply be lifted off a helpless MOB. Lights are often optional extras too, but without them locating a MOB at night involves a searchlight, and is hit-and-miss. A brightly coloured PFD with reflective patches is much easier to see than a bobbing head, day or night.

As reinforced plastic fabrics replaced rubberised ones, inflatable PFDs have become cheaper, lighter, more flexible, and less bulky. They are far less encumbering than permanently buoyant PFDs, and in the water they can be fully or partially deflated for faster swimming or easier clambering. Many cruising parents kit their children with automatic inflating PFDs (they may incorporate a harness too), but very few adult sailors currently wear PFDs routinely, even at sea.

There are moves by Australian State and Federal authorities towards requiring that PFDs be worn in apparently ‘safe’ situations. The idea that adults on an anchored yacht, for example, should all wear PFDs will be derided by many, but given time and better styled gear, it’s possible enough sailors would comply to progressively change attitudes. It would help if manufacturers and regulators get away from the idea that PFDs are safety gear for emergency use only, towards making them comfortable, durable, light, and unobtrusive. A standard that allows for oral-only inflation bladders to be built into clothing would make this easier. PFDs are already being built into more general purpose clothing. The British SeaSafe system (www.seasafe.co.uk), for example, has auto-inflation built into stylish wet weather gear.

MOB alarms
Even on racing yachts, but especially on cruisers, it’s quite possible that someone goes overboard without being noticed, while other crew are distracted, below decks, or even asleep. Back-tracking and searching just might find someone, especially if wearing a PFD, but an already life-threatening situation has been made much worse. This is a nightmare scenario for cruising couples and yachts with children on board. Systems that sound an alarm if someone goes overboard are potentially lifesaving ‘ even in port, let alone at sea. All MOB alerting systems involve the MOB carrying a small radio transmitter. There are two basis types.

Missing crew alert
The newest, smallest and cheapest systems broadcast an individual identity number every second or so. A receiver monitors all the transmitters on board, and alarms if one of them is no longer heard. The transmissions are very weak and don’t propagate far, or through water at all, so the alarm should sound within a few seconds of someone falling in. MOBi-lert and Lifetag are two currently available products of this type. Both are quite small and no encumbrance to wear routinely. LifeTag is wrist mounted and uses a user replaceable Lithium camera battery (at least 200 hours operation), while MOBi-lert can be belt or neck-mounted with rechargeable batteries lasting about two days. The alarms are freestanding, and can trigger other responses, such as creating a waypoint, or via a relay, stopping engines, releasing a Dan Buoy or whatever ‘ even a single-hander could benefit from an automated reaction.

There are related products such as Coastkey (www.coastkey.com) which is designed to stop an outboard if the driver falls out ‘ conventional dead-man wrist clips restrict movement and are not widely used. McMurdo have a fishing boat tracking system (Guardian) with an associated MOB tag that in UK waters reports the incident position automatically to SAR via Iridium satellite.

PLB alerting
The older approach involves crew routinely carrying a waterproof transmitter known as a Personal Locator Beacon. The PLB only begins transmitting when activated by water contact or manually by the MOB. The transmission is detected by a dedicated receiver on the yacht, which alarms and may initiate other responses via a relay. SeaMarshall’s water-activated PLBs claims a response in 15 seconds, but the reliable MOB to yacht range may be less than a mile, so a manually activated PLB needs to be deployed quickly.

PLB direction finding
Both SeaMarshall and Vectra2 PLB alerting systems have an associated direction finding systems. Similar over-water range limitation apply, but this could greatly improve the chances of relocating the MOB by searching or back-tracking. Sea Marshall’s system is often fitted to yachts visiting the Southern Ocean, for example, where sight of the MOB may be lost within seconds and water temperatures fatal within less than 30 minutes. Both systems transmit on the 121.5MHz SAR homing frequency, so in warmer water, or in a survival suit, the MOB also has improved chances of being located by aircraft.
Some 121.5MHz PLBs are capable of detection by the COSPAS/SARSAT polar orbiting satellites. However, this old system is slow, imprecise, geographically restricted, unreliable, and ceases on February 2009, leaving 406MHz as the prime satellite alerting frequency.

406 MHz PLBs
The 406 MHz PLBs have shorter durations than EPIRBS, and aren’t required to operate while floating, but they still provide a direct connection into the Global Maritime Distress and Safety System, under which countries like Australia provide around-the- clock SAR services over wide areas. SAR should learn the serial number of an activated 406 PLB within minutes via the geostationary satellite system, but extracting approximate positional information from the Dopplered signal via polar orbiting satellites may take several hours.

The 406 beacons simultaneously transmit a 121.5MHz homing signal, so should be compatible with existing PLB alerting and direction finding. A greater MOB/yacht range and better directional sensitivity should result from larger antennae than SeaMarshall and Vectra2 use, and if one didn’t need their PLB alerting functions, ( if MOBi-lert was carried for example) one might instead consider something like the Titley 121.5 MHz directional receiver, which are used by some SAR in Australia.

GPS Reporting PLBs
A significant recent development are 406Mz PLBs that contain a GPS receiver, and broadcast their own position via a Geostationary satellite every 20 minutes. If an MOB has one of these there is a good chance in many coastal waters that SAR will be actively looking within an hour (even if their yacht is not aware they are missing!) and can home-in on the PLB’s 121.5MHz signal.

GPS-PLBs have the potential to revolutionise survival chances in many situations. Currently, the smallest is the GME MT410G - compact enough to be carried routinely, either on a belt or within the outer covering of an inflatable PFD. It’s waterproof and floats, but only broadcasts efficiently to the distant geostationary satellite if the antenna is clear of the water, and reasonably vertical. A person treading water can’t achieve this for very long so would really need the buoyancy of a PFD as well. A yacht may be able to obtain their MOB’s latest GPS-PLB position from SAR, and it seems logical that communications satellites such as BGAN will eventually be used to do this automatically by SMS.

Real life scenario
A recent incident (January 2007) near where I live illustrated the reality of many cruising MOB situations, and the potential impact of radio, PFDs, and personal lights on the outcome. A 70-year-old sailor fell overboard at night in rough weather a mile offshore. His family couldn’t sail the yacht, and a rope fouled the propeller, but they promptly radioed their GPS position to a local volunteer coast station. A helicopter was soon in the air, and a police boat put to sea. The man was wearing a PFD and yellow clothing so he was visible, and still alive when the helicopter located him using a searchlight. After 90 minutes in seas too rough for the chopper to hoist from, he was rescued by the police, homing in on a strobe dropped by the chopper.

The following table is based on US Coastguard data, relating water temperature to survival times.

WATER TEMP Degrees Celsius (soft conversion from Fahrenheit)
EXHAUSTION/
UNCONSCIOUSNESS
EXPECTED TIME
OF SURVIVAL
(if wearing PFD )

Less than 15 mins
15 to 45 mins
0.28°C to 4.4°C
15 to 30 mins
30 to 90 mins
4.4°C to 10.0°C
30 to 60 mins
1 to 3 hours
10.0°C to 15.6°C
1 to 2 hours
1 to 6 hours
15.6°C to 21.1°C
2 to 7 hours
2 to 40 hours
21.1°C to 26.6°C
3 to 12 hours
3 hours to indefinite
26.6°C