The RNLI's D-class lifeboat at Penarth was called out to two incidents in quick succession on Friday evening.
The RNLI said its volunteers were called out at around 7.15pm to help two people who were cut off by the tide nearby.
Having contacted the coastguard by mobile phone, the pair were able to give a What3Words location which made it easier to locate them.
They were taken aboard the lifeboat and returned safely to the lifeboat slipway.
During the first shout, the coastugard received a call about a boat that needed help a couple of miles off Cardiff.
The 12ft vessel was found at anchor near the River Rhymney and taken safely by tow into the Cardiff Bay Barrage.
An RNLI Penarth spokesperson said in both cases, the casaulties involved had mobile phones to call 999 and ask for the coastguard.

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