The Jersey Lifeboat Association and RNLI first launched their all-weather vessels at about 8 am on Monday after the crew of the Condor Rapide spotted a capsized yacht near the Minquiers reef while returning from St Malo.
The Channel Islands Air Search plane and a French military helicopter also scoured the area.
No-one was on board the vessel or in the immediate area, and the operation was called off about two hours later.
French authorities later made contact with the owner of the vessel, which was identified as a five to seven-metre long motorboat and believed to have come from Paimpol in Brittany. Attempts were made to tow it back to St Helier Harbour, but it broke up and sank.
The Condor Rapide, which stayed on the scene until the search and rescue teams arrived, eventually made it into St Helier Harbour at 9.50am, about an hour and a half later than scheduled.
Minutes after the first incident ended, the Coastguard received reports of an empty kayak drifting near the Demie des Pas lighthouse off Jersey’s south coast.
The Channel Islands Air Search plane and the JLA’s Sir Max Aitken III were diverted to the scene and were joined by the St Helier inshore lifeboat and one of the Fire and Rescue Service’s RIBS.
The teams were stood down following an extensive search of the coast. The owner of the kayak later came forward to report that the craft had gone missing from Dicq area.
Another abandoned kayak was spotted near La Rocque a short time later, but was retrieved by its owners.
Harbourmaster Captain Bill Sadler praised the search teams and the crew of the Rapide and also urged Islanders to ensure their water craft were registered through the free Jersey Coastguard Safety Identification Scheme.
For more information visit ports.je/jerseycoastguard.