The so-called "Hydrographer's trousers" date back to the mid- 1960s and have been passed on from one hydrographer to the next as a slightly unusual tradition.

"What do you do when you hand over command?" Commodore Nairn said. "To mark continuity this pair of trousers was handed over from one to the next."

"I wore them once to a special dinner just to say I wore them." As well as the pants, Commodore Nairn yesterday handed over the leadership of the Australian Hydrographic Office after eight years in the top job.

That made him Australia's longest-serving hydrographer. He started in the hydrographic service in 1980, working in North Sydney - which is where he met his wife Sue. He started his tenure as Hydrographer of Australia on December 22, 2004 and he said that he was leaving because of the Navy's rotation policy.

"The routine is that the hydrographer position gets handed over after five years," he said.

"I did eight years at the pleasure of the chief of the navy. There were significant projects under way and it was good that I was to stay until they were finished."

One of those projects he considered his greatest achievement while working there - overseeing the full electronic charting of Australia, computerising maps that let ships navigate safely.

He will be leaving the navy in April ahead of taking up a six-month position as acting CEO of Shipping Australia.

Commodore Brace said he felt like he had big shoes to fill because "Rod has done a tremendous amount of work here".

Having worked in the Wollongong office four times before, Commodore Brace feels his "passion for hydrography" will stand him in good stead.