The UK Coastguard first received an emergency call from a 24ft motor boat Maverick, which reported engine failure, and the skipper gave his position as three miles south west of the lifeboat station.
However, as the lifeboat was departing the harbour after dealing with this situation at 6.43pm, the coastguard then received reports of an 18ft speed boat with three people on board had 'broken down' inside the harbour and 'they could see the lifeboat'.
A Selsey RNLI statement read: "The all-weather Shannon class lifeboat Denise and Eric launched at 3.00pm on Wednesday August 29 and quickly arrived on scene at 3.12pm.
"As soon as a tow was established between the lifeboat and Maverick a course was set for Chichester Harbour.
"At 5.03pm Chichester Harbour entrance was reached. The Maverick was taken to Itchenor jetty and safely berthed alongside at 6.15pm with the lifeboat departing at 6.30pm."
Upon then receiving the call from a speed boat in trouble, the Selsey crew then called for assistance from the Hayling RNLI.
The Selsey RNLI statement added: "Selsey lifeboat was asked to assist the speed boat and took the boat under tow at 6.48pm.
"With the ebbing tide the lifeboat could not tow the vessel to their home berth so Hayling RNLI lifeboat was requested to take over the tow.
"The tow was passed to Hayling lifeboat at 7.23pm and the Selsey lifeboat continued the passage back to Selsey.
"The station was reached at 8.00pm and the lifeboat was rehoused, washed down refuelled and made ready for service by 9.00pm."