That’s right Jonathan and you can also start the rest on land and interrupt it to drive onto the ferry (or a train) but that needs a bit more planning because you have to make sure you have taken enough rest before you drive off the ferry or train at the end of its journey. You can interrupt the daily rest period only once and you must increase your required rest by 2 hours, so 9 becomes 11 or 11 becomes 13.
Any interruption in rest must be as short as possible and no more than 1 hour including doing customs, immigration etc…
During both parts of the rest period, the driver must have access to a bunk or couchette, so it doesn’t apply on the Dover /Calais crossing or on the shuttle for instance.