This is an example log. The voyages below are made up, to show how the cut-off dates are worked out. Start your own log and they disappear.
Plan your next trip
Try a date for going back to work and see whether your run holds.
Only nights outside the UK at midnight count. On a trip between UK ports, that means nights beyond the 12-mile limit.
AIS tracking
Your ship’s position from AIS, checked every hour while you’re near the coast.
Voyage log
Vessels
Save each ship once, then pick it when you log a voyage.
Ports
Save ports once. Picking one on a voyage sets UK or outside UK for you.
Project types
Save the kinds of work you do. Only these show when you pick a project type on a voyage.
Equipment
Save equipment here once, then pick it from a list when you log a voyage.
Set-ups
Group equipment you use together, e.g. an ROV and everything on it. Pick the set-up on a voyage to add it all at once.
Software
Save the software you use, then pick it on a voyage. It fills the Software column of your CV table.
Software bundles
Group software you always run together. Pick the bundle on a voyage to add it all at once.
Nights at a glance
Each square is one day, judged by where you were at midnight.
Tax years
6 April – 5 April
How it's worked out
A day abroad is a night abroad
A day counts as absent only if you're outside the UK at midnight. On a voyage that starts or ends at a foreign port, every midnight on board counts, including the day you sail from a UK port.
365-day eligible period
You need an unbroken run of at least 365 days that starts and ends with a day abroad. Time at home can sit inside the run as long as the next two rules hold.
183-day rule
No single stay in the UK inside the run may be longer than 183 days.
Half rule
At the end of each trip abroad, your UK days so far must be no more than half of all the days in the run so far, as on HMRC’s working sheet for box 11 (below).
The 12-mile limit
UK waters end 12 nautical miles offshore. On a voyage between UK ports, a night counts only if the ship was beyond that limit at midnight, so log the date of each crossing (and the position, if you have it) from the deck log.
What doesn't count
Nights inside UK waters on a voyage between UK ports, and work on an offshore installation (rigs, FPSOs on station). The Channel Islands and the Isle of Man count as outside the UK.
Working sheet
HMRC’s box 11 working sheet, filled in from your log. H must say “No” on every row for the run to continue.
This log works out your days from what you enter; it isn't tax advice and HMRC makes the final decision. Keep your discharge book, sign-on/off letters, payslips and flight tickets as evidence. Claim the deduction on your Self Assessment return (the Seafarers' Earnings Deduction boxes on the Additional information pages, SA101), due online by 31 January after the tax year ends. The UK 12-mile limit used to check positions comes from Marine Regions (VLIZ, CC BY 4.0), simplified to about 200 m, and excludes the Channel Islands and the Isle of Man.