The essence is a two conductor ("sensing") wire, say #22 gauge, that runs through a loop on each item to be secured (gas tank handle, dinghy eye, and ends through a connector to a pigtail connected to the inside of the dinghy motor where the two ends are simply tied together). One side of the wire is connected to +12V the boat, the other to the coil of a simple relay (Radio Shack 275-005, e.g.) and then to ground. When the alarm is activated, the relay is operated ("On"). The relay contacts are wired to sound an alarm buzzer or other device (Radio Shack 49-490 or 273-068, e.g.) if the relay is DEactivated, as would occur if the sensing wire were cut or unplugged from the motor. The power for the buzzer should come from inside the boat, where it cannot be interrupted by a thief, only by the owner.
You can add a few other bells and whistles: The connector to the dinghy motor was a magnetic reed switch activated by a magnet attached to the motor, so that Tom needed only to remove the wire rather than unplugging it to disconnect the alarm. Or plan to use a connector plug from NAPA that is rubber covered -- a type used to connect dinghy lights to the motor -- it has held up well and is easily unplugged. You could also have a blinking light operated by the sensing wire so that you (and prospective thieves) knew that there was an alarm activated.
If, for convenience, there were 2 sensing wires -- one run forward, e.g., and one run aft, they should be connected in series, so that if either one were cut, the relay would be deactivated, sounding the alarm.
The relay could operate a 12V heavy duty truck-type flasher (from NAPA) to flash the spreader lights. Just make sure the alarm relay contacts had enough current capacity to operate all the devices connected to it.
NOTE: The alarm, buzzer, flashing light, etc., are wired on the side of the relay that is normally "off/open". If the wire through the relay (normally "on/closed") is disconnected, the circuit is then through the normally "off" portion of the relay, thereby activating alarms. All alarms, relays, switches, etc. should be concealed on the yacht, with only wires and plug visible on the dinghy.
Wiring should be properly fused based upon the draw of the alarm devices.
You can add a few other bells and whistles: The connector to the dinghy motor was a magnetic reed switch activated by a magnet attached to the motor, so that Tom needed only to remove the wire rather than unplugging it to disconnect the alarm. Or plan to use a connector plug from NAPA that is rubber covered -- a type used to connect dinghy lights to the motor -- it has held up well and is easily unplugged. You could also have a blinking light operated by the sensing wire so that you (and prospective thieves) knew that there was an alarm activated.
If, for convenience, there were 2 sensing wires -- one run forward, e.g., and one run aft, they should be connected in series, so that if either one were cut, the relay would be deactivated, sounding the alarm.
The relay could operate a 12V heavy duty truck-type flasher (from NAPA) to flash the spreader lights. Just make sure the alarm relay contacts had enough current capacity to operate all the devices connected to it.
NOTE: The alarm, buzzer, flashing light, etc., are wired on the side of the relay that is normally "off/open". If the wire through the relay (normally "on/closed") is disconnected, the circuit is then through the normally "off" portion of the relay, thereby activating alarms. All alarms, relays, switches, etc. should be concealed on the yacht, with only wires and plug visible on the dinghy.
Wiring should be properly fused based upon the draw of the alarm devices.
