A speedboat from Brighton Marina ran aground close to the Portobello sewage treatment works at Telscombe Cliffs yesterday.
The 16ft boat had beached and came close to smashing into a big concrete groyne there.
It was 10 yards off the groyne when it was refloated by the RNLI Brighton lifeboat crew who towed it back to the marina at lunchtime yesterday.
Crew member Kieron Lawlor swam ashore where the two people who had been in the speedboat were trying to keep the vessel from harm by holding on to it with mooring lines.
A coastguard drove one of the two shaken speedboat crew members back to the marina.
RNLI crewman Lawlor joined the other in the stricken vessel while it was towed by the lifeboat.