Rock depth readings were taken at 44 locations in the harbour

The date for the completion of a marina development at St Sampson's is now expected to be July, although most of the major work will be finished in May.

Problems with determining rock depth have meant changes are needed to the installation of pontoons.

A problem with a drill has also added to delays.

However, harbourmaster Captain Robert Barton said the difficulties with the depth and distribution of the rock bed are not the result of surveyors getting it wrong.

He said: "We did 44 trial holes across the harbour.

"The only way you can be completely sure where all the rocks are is to remove all the material on top of them, so it's not a question of errors being made."

"It's not an exact science and you will always find in marine civil engineering works of this sort that the survey isn't 100% accurate."