https://help.gosimpletax.com/hc/en-gb/articles/115000668024-Seafarers-Earnings-Deductions
If you’re an employee and work at sea, you may be able to reduce your tax bill by getting the Seafarers’ Earnings Deduction.
To make the claim;
Click on Other Income & Losses
Click on Expenses
Click on ADD Group
Select Seafarers and patent reliefs
Choose a Category from the Drop Down List
Enter the Required Details
In the Additional Information Box, you must include the names of all the ships that you worked on during the Tax Year.
Click on SAVE