Gilbert Park explains how and why he installed an OLAS Guardian wireless kill cord on his planing sports cruiser...

Lightweight, planing motorboats are very susceptible to being blown off course when not under power. This is can be awkward when coming up a channel to a mooring and there’s a need to put fenders and warps out. It’s manageable when you have crew, but by yourself you may need an autopilot to help you out.

The problem is that if you fall overboard the autopilot will just take the boat in the direction you’ve set until it hits something and you’ll be left in the water. Of course you can use a kill cord, but to get up to the bow or the stern you’ll need a very long kill cord that can easily snag.

The answer is a wireless kill cord, such as the OLAS Guardian (which is currently available via Amazon). You wear a Bluetooth transmitter which can be a wristband or attached to a lifejacket or belt loop. There is also a transmitter that features a small strobe light, and on the boat there’s a receiver.

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Once the transmitter is out of range the receiver shuts down the engine(s), sounds an alarm to alert any crew and can be programmed to send a SMS to a nominated number to say contact has been lost.

The OLAS Guardian seemed ideal for me, but the only problem was I have a twin outboard engine motorboat and until June 2020 OLAS would only work for a single engine boat. But there is now an additional wiring loom for up to three outboard engines.

If you only use two then you simply isolate the unused wires. The information online says it is easy to fit but is it? The kit comes complete with most things you will need, but be prepared to buy a fuse holder and have some additional connectors and wire ready. You’ll also need a 21mm hole saw.


The wiring for an OLAS Guardian is very straightforward. Click to enlarge

I started off by exploring where the current kill cord wiring was and working out how to connect into it. Then the search was on for space nearby for the pairing button and for the control unit.

The unit will flash a red light when the alarm goes off as well as sounding a very loud siren, but I chose to put mine out of sight inside the control area.

If I was alone there’d be nobody there to see the red light anyway! Installation was relatively easy and the instructions, while clear, were a bit small and reading the colour coding of the wires I needed a magnifying glass to be sure of the colours.

This was important because at times the wiring colours used can be confusing. For example, red and black wires are not connected to the 12V system, white and black are.

I also downloaded the app onto my smartphone that lets me check the wristband’s battery level, configure the alarm and set the telephone number for the SMS.


Once you’ve located the wiring for your physical kill cord system, the main installation challenge is drilling a 21mm hole for the sensor


All finished with the wristband looped around the pair of existing kill cord attachments. Guardian sensor is mounted just below. The ‘key’ from the kill cord device has to be left in place for the unit to work

In addition, it will also provide a script for a Mayday message that includes all the information about your boat and also gives the lat and long of where someone went overboard.

Useful, in a sailing boat with a crew but of limited use when alone!

The app can also be used with a transmitter as an MOB device.

I didn’t go for a swim to test it out, just started the engines and walked down the pontoon.

The engines stopped as predicted and could be restarted after a few seconds with or without the wristband, which means that if I do happen to have a crew member on board with me when I go over the side they can take control, restart the engine and recover me.

Buy the OLAS Guardian now on Amazon

OLAS Guardian alternatives


Mercury 1st Mate

Mercury 1st Mate is the only factory-fit wireless kill cord from a major engine builder, but it can also be retrofitted for other makes and models of engine. Two different kinds of fob are available: a crew fob which sounds the alert and marks the spot where they fell overboard; and a captain’s fob that also kills the engines and stops the boat.

Instead of a simple Bluetooth connection, it uses WiMEA technology (Wireless Marine Electronics Algorithm), which improves speed of reaction, reliability and reduces interference from other electronics.

Because it is linked to the boat’s NMEA network it can also display alerts on any connected chartplotter or MFD. This enables it to give an exact GPS location of where the wearer fell overboard.

The other big advantage is that it also acts as an effective anti-theft device. Mercury engines fitted with SmartCraft technology can’t be started without an unlock command first being sent from either the captain’s fob or their associated app.

Buy it now on Amazon



CoastKey uses a fob you can wear on a lanyard round your neck or clip to a belt loop or lifejacket.

The dash display provides reassurance of its status via coloured LEDs and a four-number keypad allows you to set your own code and restart the boat (without the code) if the fob wearer falls overboard.

You can add up to two other remote functions such as engine trim or an anchor windlass.

Buy it now from


Fell Marine MOB+

Fell Marine teamed up with Mercury to make 1st Mate, so MOB+ is their own base version of that system.

Choose alarm only or stop and alarm setting.

Buy it now from Amazon

Further reading

Fit an overboard tag and 7 more tips for sailing with cats

Family sailing safety gear: tested

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This feature appeared in the January 2021 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.

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