Customs officers seized drugs with an estimated street value of £271,000 at Portsmouth Continental Ferry Port.
The 81kgs of cannabis were discovered during a routine check on vehicles coming off the P&O vessel Pride of Bilbao, which had travelled from its namesake city in northern Spain.
Two men were stopped as they arrived at the port.
Officers searched their blue Volvo estate, which was towing a boat on a trailer.
They said drugs were found in the hull of the boat.
The cannabis was then sent to an analytical laboratory where it would be weighed and checked before being stored in a secure warehouse.
Both men were interviewed by the Customs National Investigation Service and arrested.
Bob Gaiger, spokesman for Custom and Excise, said: ‘We have been busy at the port.’