Why this trips people up
Ask most deckhands what counts towards their sea service and you'll get "days I was on the boat". That's not how the MCA counts it. Every day you're signed on is onboard yacht service, but only some of that time qualifies as the specific categories that unlock a certificate of competency (CoC): actual seagoing service, standby service, and yard service. Each has its own definition, and standby and yard time are both capped, so you can't pad a logbook with months tied up alongside a dock and expect it to count the same as time underway.
Getting this wrong is expensive. Testimonials that don't break out actual, standby and yard time get sent back by the MCA, and if you've been counting on a season of refit work to bridge the gap to your next CoC, discovering the cap too late can push your oral exam back by months.
This guide reflects MCA MSN 1858 (Amendment 2), "Training & Certification Guidance: UK Requirements for Deck Officers on Large Yachts (24m and over)" — the current notice covering yacht-restricted certificates. If you're converting towards an unlimited Merchant Navy CoC, the equivalent yacht sea-service rules sit in Annex F of MSN 1856 (Amendment 1), with different day caps noted below. MCA guidance is updated periodically. Always confirm the current version at gov.uk before submitting an application.
The five definitions, in the MCA's own words
These are the official service definitions from MSN 1858, section 5.2:
| Term | What it means |
|---|---|
| Onboard yacht service | The time spent signed on a yacht, irrespective of the vessel's activity. This is the broadest category and includes everything below. |
| Seagoing service | Time spent at sea, which may include time at anchor or river and canal transits associated with a passage. A minimum of 4 hours of working duty in 24 hours counts as 1 full day. |
| Standby service | Time immediately following a voyage while the vessel is under preparation for a subsequent voyage. Capped at 14 consecutive days per period, and can never exceed the length of the previous voyage. |
| Yard service | Time spent standing by a build, refit or repair. |
| Watchkeeping service | Actual seagoing service spent as a certificated watchkeeping officer in full charge of a navigational watch for not less than 4 out of every 24 hours while the vessel is on a voyage. |
Standby service: the two rules that matter
Standby service is the trickiest category because two limits apply at once, and the second one is the one people miss:
- The 14-day cap. No single period of standby can run longer than 14 consecutive days, even if the yard work or turnaround takes longer.
- The previous-voyage cap. A period of standby can never exceed the length of the voyage that came immediately before it. A 3-day passage followed by a 10-day turnaround only banks 3 days of standby, not 10.
Put together, the MCA states this plainly: under no circumstances can your total standby service exceed your total actual seagoing service. If most of your season was short hops between anchorages with long yard turnarounds in between, don't expect the standby time to make up the difference. It structurally can't.
What about time at anchor?
This is where the actual-vs-standby line gets drawn in practice. If the vessel anchors as part of a passage, for instance waiting briefly for a berth, or holding position to transit a canal or lock, that time counts as actual seagoing service (still capped at not exceeding the previous voyage). But if the vessel goes to anchor instead of a berth at the end of a passage, that time is standby service, not seagoing service. The distinction is whether the anchor is a stop mid-journey or the conclusion of one.
Yard service: two different caps depending on your route
Yard service, time standing by during a build, refit or repair, is allowed, but the cap depends on which certificate route you're on:
Yacht-restricted OOW (<3000 GT), per MSN 1858: since age 16 you need a minimum of 36 months' onboard yacht service, including at least 365 days seagoing service on vessels of 15 metres or more, made up of a minimum of 250 days' actual seagoing service and 115 days of any combination of seagoing, standby (still capped at 14 consecutive days per period) and yard service. Yard service within that 115-day pool is capped at 90 days, continuous or in separate periods.
Unlimited Merchant Navy route (OOW/Chief Mate/Master unlimited), per MSN 1856 Annex F: yard service is capped at a maximum total of 90 days for OOW and 30 days for Chief Mate or Master.
The takeaway either way: yard time helps, but it can't be your whole plan. If you're chasing an unlimited Chief Mate or Master CoC, the 30-day yard cap is tight, plan your seagoing time accordingly rather than assuming a long refit will cover the gap.
What you need to prove it
Onboard yacht service must be documented in a Merchant Navy discharge book, an MCA Certificate of Discharge, or a similar MCA-approved service record book, backed by testimonials. Your testimonial needs a breakdown of actual, standby and yard time separately, not just a total. It must be signed by the Master of the vessel (or, for service as Master yourself, by the owner or a responsible person from the yacht management company), and it should cover your conduct and ability for the last 12 months of service before you apply.
At least 6 months of your qualifying seagoing service must fall within the 5 years immediately before the MCA receives your application. A month is defined as a calendar month, or 30 days if it's made up of shorter periods.
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Frequently asked questions
What is standby service on a yacht?
Standby service is the time immediately following a voyage while the vessel is being prepared for the next one. A maximum of 14 consecutive days can be counted at any one time, and a period of standby service can never exceed the length of the voyage that preceded it. Because of that second rule, your total standby time across a career can never exceed your total actual seagoing time.
What is yard service?
Yard service is time spent standing by a yacht during a build, refit or repair. It counts towards qualifying sea service, but it's capped: on the yacht-restricted OOW route it forms part of a wider 115-day allowance alongside seagoing and standby time. On the unlimited Merchant Navy route, yard service is capped at 90 days total for OOW and 30 days for Chief Mate or Master.
Can standby service exceed my actual sea time?
No. The MCA is explicit: under no circumstances can your total standby service exceed your actual seagoing service. A period of standby also can't exceed the length of the voyage it follows, and no single period of standby can run longer than 14 consecutive days.
Does time at anchor count as sea service?
It depends why the vessel is at anchor. If the anchorage is part of a passage, for example a short wait for a berth or to transit a canal or lock, it counts as actual seagoing service. If the vessel goes to anchor at the conclusion of a passage rather than to a berth, that time counts as standby service instead.
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