STCW Sea Service & Career
Sea Time & Watchkeeping Calculator: STCW CoC Requirements Explained
Counting your qualifying sea service accurately is the first step before applying for an Notice of Eligibility (NOE), booking your Deck or Engine CoC oral exam, or revalidating your Certificate of Competency every five years. A miscalculated calendar month, an uncounted overlap day between contracts, or a missing 6-month supervised watchkeeping testimonial can delay your assessment by a full trip.
This guide explains how STCW 1978 (as amended) calculates sea service for Deck Officers (OOW, Chief Mate, Master), Engineers (EOOW, Second Engineer, Chief Engineer), ETOs and Tanker Endorsements, and how UK MCA, India DG Shipping, AMSA, USCG and MARINA verify your records.
Updated · Written by SeaReady in our own words. Not affiliated with OCIMF, RightShip, CDI, any MoU or any administration — always check the current official documents.
1. How STCW sea time is calculated (calendar months + 30-day rule)
Unlike tax-day counters (such as UK SED or India NRI 182-day rules) that count raw calendar days outside a country, maritime administrations assess sea service for Certificates of Competency in months and days:
- Step 1 — Full calendar months per contract: Count complete calendar months from your sign-on date to the day before the same date in the final full month (for example, signing on 10 March and signing off 24 July gives 4 full calendar months from 10 March to 9 July, regardless of whether individual months had 28, 30 or 31 days).
- Step 2 — Remaining days (inclusive of sign-on and sign-off): Count the leftover days from 10 July to 24 July inclusive (15 days). Across multiple contracts, add all the full calendar months together, sum all the leftover days, and divide the total leftover days by 30 to convert each 30-day block into 1 additional month.
- Step 3 — Overlap deduplication & Count-to-Today rule: Never count the same calendar day twice if you signed off one ship and signed on another on the same day, and never include future projected sign-off dates when submitting an official application — only service completed up to today counts.
2. STCW minimum sea-service requirements by rank (Deck, Engine & ETO)
The table below summarises the international minimum seagoing service required under the STCW Convention and Code (matched to SeaReady’s Next-Certificate eligibility checker):
| Target Certificate | STCW Regulation | Minimum Qualifying Sea Time | Watchkeeping, Tonnage & Propulsion Conditions |
|---|---|---|---|
| Officer of the Navigational Watch (OOW, ≥ 500 GT) | STCW Reg. II/1 | ≥ 12 months (approved cadet training programme + TRB) OR ≥ 36 months deck service | Must include at least 6 months of bridge watchkeeping duties under the supervision of the Master or a qualified OOW on ships ≥ 500 GT. |
| Chief Mate (≥ 3,000 GT) | STCW Reg. II/2 para 2.1.1 | ≥ 12 months approved seagoing service | Must be served while holding an STCW II/1 OOW Certificate of Competency on seagoing ships. |
| Master (≥ 3,000 GT) | STCW Reg. II/2 para 2.1.2 | ≥ 36 months as OOW OR ≥ 24 months (if ≥ 12 months as Chief Mate) | Approved seagoing service as an officer in charge of a navigational watch, reduced from 36 to 24 months when at least 12 months were served as Chief Mate. |
| Near-Coastal OOW & Master (< 500 GT) | STCW Reg. II/3 | OOW: ≥ 12 months (approved training) OR ≥ 36 months deck service; Master: ≥ 12 months as OOW | Applies to ships < 500 GT (and near-coastal thresholds ≥ 150 GT where set by the Administration) engaged on near-coastal voyages. |
| Engineer Officer of the Watch (EOOW, ≥ 750 kW) | STCW Reg. III/1 | ≥ 12 months combined workshop + seagoing service (≥ 6 months at sea in approved programme) OR ≥ 36 months (≥ 30 months in engine room) | Must include at least 6 months of engine-room watchkeeping duties under the supervision of the Chief Engineer or a qualified engineer officer. |
| Second Engineer Officer (≥ 3,000 kW) | STCW Reg. III/2 para 2.1.1 | ≥ 12 months approved seagoing service | Must be served as assistant engineer officer or engineer officer while holding an STCW III/1 EOOW Certificate of Competency. |
| Chief Engineer Officer (≥ 3,000 kW) | STCW Reg. III/2 para 2.1.2 | ≥ 36 months as EOOW OR ≥ 24 months (if ≥ 12 months as Second Engineer) | Approved seagoing service as a qualified engineer officer, reduced from 36 to 24 months when at least 12 months were served as Second Engineer Officer. |
| Second & Chief Engineer Officer (750 kW – 3,000 kW) | STCW Reg. III/3 | 2/E: ≥ 12 months as assistant/EOOW; C/E: ≥ 24 months (≥ 12 months while qualified as 2/E) | Applies to seagoing ships powered by main propulsion machinery between 750 kW and 3,000 kW propulsion power. |
| Electro-Technical Officer (ETO, ≥ 750 kW) | STCW Reg. III/6 | ≥ 12 months combined workshop + seagoing service (≥ 6 months at sea in approved programme) OR ≥ 36 months (≥ 30 months in engine room) | Documented in an approved Training Record Book (TRB) for trainees, plus high-voltage certification where required by the Administration. |
| CoC 5-Year Revalidation (Deck, Engine & ETO) | STCW Regs. I/2, I/9, I/11 & Section A-I/11 | ≥ 12 months in the last 5 years OR ≥ 3 months in the last 6 months | Approved seagoing service performing functions appropriate to the certificate held, plus a valid STCW Reg. I/9 medical fitness certificate and Reg. I/2 endorsement. |
3. Watchkeeping testimonials vs discharge book dates
A Discharge Book stamp or CDC entry proves you were on board the ship, but it does not by itself prove that you performed watchkeeping duties in accordance with STCW Code Section A-VIII/2 ( Watchkeeping Arrangements and Principles to be Observed), sailed on a vessel of qualifying tonnage/propulsion power, or stayed at sea rather than in lay-up. Before signing off every contract, obtain a signed Sea Service & Watchkeeping Testimonial on company letterhead (alongside your valid STCW Reg. I/2 certificate/endorsement and STCW Reg. I/9 medical certificate):
- Deck Cadets & Ratings upgrading to OOW (STCW II/1): The Master’s testimonial must state that you completed at least 6 months (180 days) of bridge watchkeeping duties under the direct supervision of the Master or a qualified OOW on ships of 500 GT or more, and your Training Record Book (TRB) tasks must be signed and dated during the voyage (never back-dated at sign-off).
- Engine Cadets & Assistants upgrading to EOOW (STCW III/1): The Chief Engineer’s and Master’s testimonials must confirm at least 6 months of supervised engine-room watchkeeping duties on ships with main propulsion machinery of 750 kW or more, alongside your completed engineering TRB and workshop skills record.
- OOW / EOOW upgrading to Chief Mate, Master, 2/E or C/E (STCW II/2 & III/2): Ensure each testimonial records the ship’s IMO number, Gross Tonnage (≥ 500 GT or ≥ 3,000 GT), Main Engine propulsion power in kilowatts (kW) (≥ 750 kW or ≥ 3,000 kW), exact rank served (distinguishing Chief Mate from OOW and Second Engineer from 3/E or 4/E for the 24-month reduced route), and UMS / watchkeeping hours.
4. Flag administration differences (UK MCA, DG Shipping, AMSA, USCG & MARINA)
While STCW sets the international baseline, every national administration applies its own verification rules when issuing a Notice of Eligibility (NOE) or assessment approval:
| Administration | Primary Guidance / Rules | How Sea Time & Testimonials Are Assessed |
|---|---|---|
| UK MCA | MSN 1856 (Deck), MSN 1857 (Engine), MSN 1861 (Revalidation) | Requires Discharge Book / Sea Service Testimonials signed by the Master (and Chief Engineer for engine dept), including actual days at sea vs shipyard/lay-up allowances and bridge/engine watchkeeping testimonials. |
| India DG Shipping | MS (STCW) Rules & DGS E-Governance / TAR Book Circulars | Requires Continuous Discharge Certificate (CDC) entries, company sea-service letters, e-Governance Master Checker verification and completed Onboard Training Record Book (TAR) before booking MMD assessments/orals. |
| Australia AMSA | Marine Order 70, Marine Order 71 (Deck) & Marine Order 72 (Engine) | Qualifying sea service assessed by vessel size (≥ 500 GT / ≥ 3,000 GT) and propulsion power (≥ 750 kW / ≥ 3,000 kW), with specific watchkeeping letters from the Master or Chief Engineer. |
| USA USCG (NMC) | 46 CFR Part 11 (Officer Endorsements) & 46 CFR § 10.107 | Counts service in days rather than calendar months (1 year = 360 days; 1 month = 30 days; 1.5x credit up to 12-hour watch systems on certain vessels where authorized under 46 CFR § 10.402). |
| Philippines MARINA | MARINA STCW Circulars & MISMO Online System | Requires SIRB (Seafarer’s Identification and Record Book) stamps, Certificate of Sea Service uploaded to MISMO, and COP/CoC revalidation evidence. |
Questions seafarers ask
How are calendar months and leftover days calculated for STCW sea service?
Most maritime administrations (including UK MCA, India DG Shipping and AMSA) calculate each contract by counting full calendar months from the sign-on date to the corresponding day in the last full month, then summing the remaining odd days across all contracts and dividing by 30 to convert leftover days into additional months (with both sign-on and sign-off dates counted inclusively unless Two contracts overlap on the same calendar day).
What happens if two sea-service contracts overlap on the same date?
If you sign off one vessel and sign on another vessel on the same calendar day (or if two logged periods overlap), that calendar day can only be counted once toward your qualifying sea time. SeaReady’s Sea Service calculator automatically detects overlapping contracts, flags them in amber and deduplicates the overlapping days so your total never overstates your sea time.
Does yard time, dry-dock or lay-up count toward my next Certificate of Competency?
Under STCW Section A-I/1, "seagoing service" means service on board a ship relevant to the issue or revalidation of a certificate. Most administrations (such as UK MCA under MSN 1856/1857) restrict the amount of shipyard, dry-dock or prolonged lay-up time that can count toward initial OOW/EOOW or senior CoCs, and require the Master’s Sea Service Testimonial to state actual days at sea, days on watchkeeping duties and days in port or dry-dock separately.
How much tanker sea time is required for Basic and Advanced Oil, Chemical or Liquefied Gas Tanker endorsements?
Under STCW Regulation V/1-1 (Oil and Chemical Tankers) and Regulation V/1-2 (Liquefied Gas Tankers): Basic Tanker training requires either 3 months of approved seagoing service on the relevant tanker type OR an approved Basic Tanker fire-fighting and cargo course. Advanced Tanker certification (required for Masters, Chief Engineers, Chief Mates, Second Engineers and anyone with immediate responsibility for cargo operations) requires an approved Advanced course PLUS at least 3 months of approved seagoing service on that tanker type (or at least 1 month as a supernumerary with at least 3 loading and 3 unloading operations documented in an approved training record book).
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