The load line mark: ring, lines and their spacing
1The lesson in plain words
The ring and its lines show how deep you may load in each zone and in fresh water. Read the upper edge, and know where each line sits.
The mark
Amidships on both sides, below the deck line, is the load line mark: a ring 300 mm in outside diameter and 25 mm wide, crossed by a horizontal line 450 mm long and 25 mm wide whose upper edge passes through the ring’s centre. The centre lies the summer freeboard below the deck line. Beside the ring are the letters of the assigning authority, about 115 mm high.
The lines
A vertical line 25 mm wide stands 540 mm forward of the ring’s centre. From it run horizontal lines 230 mm long and 25 mm wide. Always read the upper edge. Pointing forward: S, summer, level with the ring’s line; T, tropical, above it; W, winter, below it; WNA, winter North Atlantic, below W. Pointing aft, towards the ring: F, fresh water summer, and TF, tropical fresh water.
The spacing
Let dS be the assigned summer draught. Tropical freeboard is summer freeboard minus dS/48; winter freeboard is summer plus dS/48. T is dS/48 above S on the hull, and W is dS/48 below S. For ships of 100 m or less, WNA is 50 mm below W; for longer ships the WNA freeboard equals the winter one. F is the fresh water allowance (FWA) above S, and TF is the FWA above T.
Fresh water allowance
In fresh water, the same ship floats deeper because it displaces a larger volume of less dense water. The fresh water allowance (FWA) is the extra immersion permitted. Use FWA = Δ ÷ (4 × TPC) mm, where Δ is the summer displacement in tonnes and TPC is the tonnes needed to increase draught by 1 cm at the summer waterline. Hydrostatics explains the derivation.
Example
Use Hydrostatics’ ship: summer Δ 16,500 t and sea-water TPC 25.3 t/cm. FWA = 16,500 ÷ (4 × 25.3) ≈ 163 mm. Draughts are T = dS + dS/48, W = dS − dS/48, F ≈ dS + 0.163 m and TF ≈ dS + dS/48 + 0.163 m. These are draughts from the keel; freeboard is measured down from the deck line.
Timber and paint
Ships assigned timber freeboards carry a vertical line 540 mm abaft (aft of) the ring’s centre. LT, LS, LW and LWNA extend aft; LF and LTF extend forward. L identifies timber lines; the other letters name the same seasons and water types as ordinary lines. Marks must be permanent and clearly visible: white or yellow on dark plating, or black on light plating. Check that they match the certificate.
2Key data
- Ring
- 300 mm outside diameter, 25 mm wide
- Line through the ring
- 450 mm × 25 mm, upper edge through the centre
- Load lines
- 230 mm × 25 mm, from a vertical line 540 mm forward of the centre
- T and W
- dS/48 above and below S (dS = assigned summer draught)
- WNA (ships ≤ 100 m)
- 50 mm below W
- FWA
- FWA = Δ ÷ (4 × TPC) mm, using summer sea-water values
3Key points
- 1
Ring 300 mm, line through it 450 mm, load lines 230 mm; all 25 mm wide. Read the upper edge.
- 2
Forward of the vertical line: T, S, W, WNA. Aft of it: F and TF.
- 3
T is dS/48 above S, W is dS/48 below S; WNA is 50 mm below W for ships of 100 m or less.
- 4
F is FWA above S and TF is FWA above T; FWA = Δ ÷ (4 × TPC) mm.
- 5
Timber: vertical line 540 mm abaft the ring; LT, LS, LW, LWNA run aft, LF and LTF forward.
4Frequent mistakes
Wrong: Read the centre or lower edge of the line.
Right: Every load line is its upper edge, as are the deck line and the line through the ring.
Wrong: FWA is about 16.3 mm for summer Δ 16,500 t and TPC 25.3 t/cm.
Right: FWA = 16,500 ÷ (4 × 25.3) ≈ 163 mm. Keep the formula’s millimetre units.
Wrong: Winter is above summer because winter is the bigger freeboard.
Right: A bigger freeboard means less draught, so W is below S on the hull, and T is above it.
5Practice case & exam keys
The shared ship has a length between perpendiculars (LBP) of 140 m and assigned summer draught dS. A cadet says departure for the winter North Atlantic must be delayed because no separate WNA line is painted. What do you check?
Show the answer
Check the marks against the certificate. For this 140 m ship, winter North Atlantic freeboard equals winter freeboard, so a separate WNA line is unnecessary. W draught = dS − dS/48. Verify the assigned W mark and the applicable zone and season before accepting the loading.
Exam keys
- Ring 300 mm OD, line 450 mm, lines 230 mm, 540 mm from the centre; upper edges.
- T draught = dS + dS/48; W = dS − dS/48; WNA = W − 50 mm for ships ≤ 100 m.
- F draught = dS + FWA; TF = T + FWA (matching units); FWA = Δ ÷ (4 × TPC) mm.
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