£850,000 is to be spent repairing X berth which is used by the inter island ferries.
X berth was built in the mid-1990s and handles mid-sized passenger boats.
It is estimated that around 40,000 passengers have used the facility so far this year, but Ports say that it is now past its design life.
Two new pontoons and a gangway have already arrived in Guernsey, with a third due to arrive this week.
Some parts are being fabricated on island.
Acting harbour master James Way says the design has been developed with operators to ensure it fits current and future needs:
“The replacement of the X berth has given us the opportunity to review how the current arrangements can be improved.
"In addition to better access for passengers and crew, the new facilities will provide on-shore power for berthed vessels, and the installation
of a new turnstile gate, making the berth available for superyachts to come alongside.”
Work to replace the main pontoons and gangways will begin in November after the final Islands Unlimited sailing of the season.
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