Two "eagle eyed" sailors in the patrol boat HMAS Gladstone have potentially saved the lives of two fishermen clinging to an upturned tinny off far north Queensland.

LS Ben Harding and AB Perry Taylor were lookouts on the bridge of the 250 tonne patrol boat when at 9.10am on Thursday, August 16 they spotted a "speck" in the water 700 metres distant.

"They used binoculars to check and saw two men sitting on an upturned four metre tinny," the CO of Gladstone, LCDR Peter Ashen told Navy News by satphone.

"The pair alerted the officer of the watch LEUT Michelle Wheaton and we turned towards them.

"They were from one of four prawn trawlers moored beside Hagerstone Island south of Cape Grenville.

"The two men were trying to reach the mainland five miles away in a tinny when it sprung a leak, filled with water and overturned," LCDR Ashen said.

Gladstone came to the men, saw they were not injured and launched its RHIB.

"Our RHIB collected the men and took their tinny in tow," LCDR Ashen continued.

Meanwhile Gladstone had been able to raise the occupants of one of the trawlers by radio to tell of the rescue.

The young fishermen were taken to their own trawler without incident.

A large commercial ship was in the same channel and approaching the rescue scene and had its lookouts not been on the job, had the potential of running down the fishermen.

By Graham Davis