Cruisers are being advised to stow bags of sand to protect themselves when sailing off the coast of Spain and Portugal.

Fifteen orcas of the region’s 35-strong population are thought to be responsible for rudder damage, and whilst the cause of this learned behaviour is still not known, “sprinkling sand into the water around the rudder confuses the orca’s sonar” during an interaction, the Cruising Association has said.

“The orcas are coming in on sonar, not sight, we know that,” said John Burbeck, the Orca Project team leader at the Cruising Association. “And a few kilogrammes of sand around the rudder confuses that sonar picture they’re picking up.”

The aim is to hide the rudder behind a screen of sand, while preparing to reverse. Banging pots and pans on deck is also recommended.

No one has so far been seriously injured in the ‘interactions’ with the highly intelligent, social mammals that can travel up to 100 miles a day.

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“The thing that worries us is the time that an orca hits with such force, that someone is knocked over in the cockpit and fractures their skull. The whole dynamic of our relationship with this endangered population will change,” added Mr Burbeck.

The full webinar Orca and Yachts: Fact, Fiction and Fear, is available to watch now on the Cruising Association website.