The single-hander’s last chance
If a single hander goes overboard and clears the vessel, with or without a harness, they are effectively lost. Even if they are attached with a safety harness a self steered vessel forging ahead will exert too much drag for the solo sailor to pull themselves back aboard.
A system to easily retrieve a man-over-board
Once a crew member has fallen overboard it can be very difficult to retrieve them even when the yacht is alongside. They are often exhausted or cold and completely unable to pull their own weight, plus the weight of water in their clothing, over the topsides and once again aboard. In the perfect conditions this is a near impossible feat. This can lead to a very difficult situation especially so if the crew are unequal in strength and disposition. A typical cruising couple with a burley man and a lithe lady is a perfect example of this, where the latter is trying to recover the man in a MOB situation.
Increasing the visibility of a man overboard with a Dan Buoy
It is very difficult to spot the head of a crew member in the water in a man overboard (MOB) situation. The crisis will be compounded if the vessel has only two people aboard. With one gone overboard the other has to deal with the boat whilst maintaining a bearing on the MOB position. The chances of them being lost in a challenging seaway are very high.