Maritime Academy
Load Lines — Summer, Winter and Seasonal Zones
Plan by certificate and the zones/dates throughout the voyage, not weather at the loading port.
Assess assigned marks, density, stability and structural limits together. The diagram is not a loading calculation.
Rules and bulletins may change. Before operation or voyage, verify the latest official source and ship-specific applicability. This page is not permission, certification or a real-time risk notice.
Read the mark; verify the zone separately
Use the upper edge of the applicable mark. S: Summer; W: Winter; T: Tropical; F: Summer Fresh Water; TF: Tropical Fresh Water. A lower mark means greater freeboard and less permitted draught. F/TF are not seasonal zones.
WNA: regulation 40(6) adds 50 mm to Winter freeboard for ships not exceeding 100 m within regulation 52 areas during winter. For other ships WNA freeboard equals Winter. Do not automatically substitute LOA for the regulatory length; check the certificate and definition.
Reg.6 / 40 — Marking and WNA reference ↗Official zone chart and key seasonal distinctions
IMO — Chart of Zones and Seasonal Areas ↗2023 corrigendum; PDF page 4 for the 1988 Protocol text. Includes southern winter-zone coordinate corrections.
| Zone | Winter | Summer |
|---|---|---|
| North Atlantic Zone I | 16 Oct – 15 Apr | 16 Apr – 15 Oct |
| North Atlantic Zone II | 1 Nov – 31 Mar | 1 Apr – 31 Oct |
| North Atlantic Seasonal Area · L > 100 m | 16 Dec – 15 Feb | 16 Feb – 15 Dec |
| North Atlantic Seasonal Area · L ≤ 100 m | 1 Nov – 31 Mar | 1 Apr – 31 Oct |
| North Pacific Winter Seasonal Zone | 16 Oct – 15 Apr | 16 Apr – 15 Oct |
| Southern Winter Seasonal Zone | 16 Apr – 15 Oct | 16 Oct – 15 Apr |
Selected periods, not a worldwide table. Zone I, Zone II and Seasonal Area are distinct. The chart omits ≤100 m exceptions for the Baltic, Black Sea, Gulf of Lion, Sea of Japan and the US coastal corridor; read Annex II as well.
Boundary-crossing planning record
- Record certificate assignment and applicable zone/date.
- Use approved tools to project consumption, ballast, cargo and density changes to the crossing.
- Compare crossing draught with the assigned limit; separately complete trim, stability, strength and UKC checks.
FOUR-STAGE TOPIC OVERVIEW
Establish applicability, then verify the operation
Assigned certificate
Zone/crossing date
Voyage draught/density
Stability/final review
1 · Read the assigned certificate
Compare International Load Line Certificate, marks and conditions. Summer (S), Winter (W), Tropical (T), Fresh Water/TF and applicable WNA/timber assignments are not interchangeable. Do not invent unassigned marks or allowances.
Reference: IMO — International Convention on Load Lines ↗2 · Position and seasonal dates
Convention Annex II defines zones, seasonal areas and periods. Local summer does not itself authorise the Summer mark. Check each route crossing/date, regional periods and applicable WNA conditions against official text/corrected charts.
Reference: IMO — Load Lines 2021 edition: December 2023 chart corrigendum ↗3 · Maintain compliance throughout the voyage
Project loading, departure and entry draught into more restrictive areas. Assess actual water density, assigned freshwater allowance, trim/list, fuel/water consumption and approved calculation method. Separately check whether a summer departure becomes excessive at winter-zone entry.
Reference: UK MCA — Stability guidance and load lines ↗4 · Marks are not the only limit
Load-line compliance does not remove stability, longitudinal strength, local load, port/canal draught, UKC or conditions-of-assignment requirements. Preserve hatch/opening integrity. Final planning rests on the master’s assessment and approved ship loading/stability tools.
Reference: IMO — International Convention on Load Lines ↗MASTER • RESPONSIBLE OFFICER • COMPANY
Six field checks
- Verify certificate, marks and conditions.
- List every seasonal-zone crossing and date.
- Confirm applicable S/W/T/F/TF/WNA conditions from documents.
- Calculate departure/crossing draught, density and trim.
- Check stability, strength, port draught and UKC separately.
- Preserve plan, calculations, consumption assumptions and master confirmation.
Educational checklist. Completion is not operational/compliance approval; use the relevant vessel permits/forms separately.
Documents to have available
- International Load Line Certificate
- Current Annex II and corrected zone/season chart
- Approved stability/loading-computer output
- Draught, density, consumption and cargo-plan records
Onboard scenarios
Summer-compliant departure; Winter applies mid-voyage.
Calculate draught at the boundary/date against the assigned Winter limit.
Calm weather: may Summer replace Winter?
No. Weather appearance does not change zone/season/certificate requirements.
LEARNING CHECK
Think of your answer, then reveal the explanation
Is freshwater allowance identical for every ship?
No. Use the assigned value and actual density in ship-specific calculations.
Does load-line compliance establish UKC compliance?
No. Port/channel depth, squat and UKC need separate assessment.
Self-assessment only; no exam result, personnel record or competence certificate is generated.
Open the official sources
IMO — International Convention on Load Lines
IMO convention overview
Open source ↗WWWCDN.IMO.ORGIMO — Load Lines 2021 edition: December 2023 chart corrigendum
Official chart corrigendum; not a standalone voyage chart
Open source ↗WWW.GOV.UKUK MCA — Stability guidance and load lines
Maritime authority guidance
Open source ↗Legal instruments, explanatory guidance and operational bulletins have different roles. Check later amendments and consolidated texts where needed. Access and external documents remain under the publisher’s control.