While sailing with a small crew, it was noticed that, contrary to appearances, it is very easy to lose a person overboard in good weather. In our first voyages, we didn't use harnesses when there was almost no wave, the sun was shining, and a light wind was blowing. However, when the yacht is on autopilot in such conditions, and the other person is sleeping or occupied below deck, a mere stumble could cause someone to fall overboard and not be able to catch up with the yacht by swimming. Therefore, we started to practically always clip onto the lifeline.
As additional protection, we devised a system we called Man Overboard (MOB). Such systems exist, but at that time they were beyond our budget. So, we constructed a system where "tags," worn by every crew member, send a radio signal to a base station. When such a signal disappears, the system triggers a loud alarm.
The system can also have an additional feature enabled, which we call in two ways - "all's well" (from the shout used by watchmen on defensive walls in one of the places we visited in ancient times to inform each other) or "watchdog," a term borrowed from electronic systems. This feature is activated by holding down a waterproof button available from the cockpit for a few seconds. When it is activated, this button must be pressed at least every 15 minutes. Otherwise, the system will trigger an alarm to prevent the tired helmsman from napping.
The tags each have two buttons. These can be used to manually trigger an alarm or turn off the tag (simultaneously unregistering it from the base station, so it does not trigger an alarm).
Our MOB was built based on ready-made tags and a base station from Texas Instruments (CC1350STK and LAUNCHXL-1350). Necessary modifications included adding waterproof housings (for both the tags and the base station) and the ability to use two AAA rechargeable batteries in the tags (instead of the original small batteries, which provided too short a runtime). Besides that, a power regulator powered the base station from the yacht's battery, an antenna for the base station, a waterproof button, and a loud siren. We have no overall schematic. We assume that building such a system is likely only for hobbyist electronics enthusiasts who can independently select and connect all elements (as was the case with us). However, we share the software's source code, which can save time if someone wants to build such a system.
Our system does not look very aesthetically pleasing (it was built on the yacht) but has been working satisfactorily for many years.
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WARNING! The software code posted here may serve as a reference source for sailors planning to build a similar system. However, it may contain errors, so it should be used solely at one's own risk, by individuals with the appropriate education to verify, develop, and modify it themselves!
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