A danbuoy is an important part of any vessel’s safety kit. For sailing yachts in particular it’s a very effective way of marking the location that a casualty entered the water.
Most danbuoys consist of a fibreglass whip, approximately 2 metres long, attached to a bright orange, weighted vertical can buoy. The danbuoy whip has an orange flag on its end and, ideally, reflective tape along its length. Many danbuoys have a light on them or they are attached to a horseshoe buoy by a length of bright orange floating polypropylene line. The horseshoe buoy itself may have a light and a whistle attached.
More and more offshore vessels on long passages are now carrying danbuoys with small personal AIS transponders attached to them. If you decide to do this (which I think is very sensible if you are going well offshore) make sure you choose an AIS that is self-activating or, at the very least, train all your crew to turn it on before they deploy the danbuoy! Of course, they also need to be trained on how to use the AIS receiver too.
On smaller vessels a telescopic danbuoy is carried. This has the advantage of being more compact and can be extended before deployment or, ideally, it extends itself on deployment. Inflatable danbuoys also exist, although they are generally less robust and lighter, making leeway effect significant.
To stop a danbuoy being deployed and then blowing off downwind, away from the casualty whose position it is supposed to be marking, most are fitted with a small conical sack known as a drogue. This should be allowed to deploy automatically when the danbuoy is released so that it fills with water and helps to anchor the danbuoy to the sea.
Finally, whilst the danbuoy is an extremely useful piece of safety kit, it is critical that all crew know how to use it, stow it properly and deploy it. I have lost track of the number of times I’ve joined a boat and, on my deck walk, noticed that some well-meaning crew member has securely tied the danbuoy to the pushpit effectively making it almost useless in the case of a real emergency. Once you’ve bought your danbuoy, make sure it can be quickly released and deployed in an emergency!