A 55-year-old man from Kent who was sailing on a tug that was towing a 60ft motor cruiser from Dover to Brighton is still missing despite a nine-hour search by lifeboats.
The crewman, one of two sailing in a tug called Endurance, fell into the water five miles south of Sovereign Harbour near Eastbourne on the East Sussex coast in gale force winds. He had been trying to re-establish the tow when he fell overboard.
Rescue services were alerted when the crewman's colleague sent out a Mayday distress call.
The RNLI said an all-weather lifeboat from Eastbourne was launched at around half past midnight on Tuesday morning.
A lifeboat from Newhaven joined the search as well as a coastguard helicopter and mobile units from HM Coastguard but the search was abandoned at just after 9am without success.
Rescue teams also searched along the shoreline for signs of anyone coming ashore but by 2pm the search was abandoned.
The cruiser was towed into Sovereign Harbour by the Newhaven Lifeboat after drifting away from the scene.