Load Lines, Draft Marks and Freeboard

What the rule requires

The load line test is three gates, and all three must open

46 CFR §175.122 subjects a vessel to load line assignment, certification, and marking under subchapter E (Load Lines) when, and only when, every one of the following is true:

• Length — 24 meters (79 feet) in length or more.
• Keel date — the keel was laid, or the vessel was at a similar stage of construction, on or after July 21, 1968.
• Voyage — she is on a voyage other than a domestic voyage.

Read the sentence in the regulation and you will see the conditions strung together with "and", not "or". That is the whole architecture of the rule, and it is what exam questions turn on. A 92-foot vessel built in 1990 running a domestic voyage clears two gates and fails the third, so she is not subject to load line assignment.

Notice what does not appear in the trigger: tonnage. There is no gross-ton threshold in §175.122. Length in meters and feet, a construction date, and the character of the voyage are the only variables. A candidate holding a 100 GT ticket has spent his career thinking in gross tons and will reach for a tonnage figure here; the rule does not offer one.

The consequence of clearing all three gates is threefold and worth keeping straight, because it is more than paint: assignment of the load line, certification, and marking.

The marks every vessel carries

46 CFR §185.602 is the hull marking rule, and it operates independently of whether a load line was ever assigned. Paragraph (a) requires each vessel to be marked as required by part 67, subpart I. Paragraphs (c) through (g) then apply to each vessel that does not demonstrate compliance in accordance with §178.310(c).

Paragraph (c) is a choice of two, and the word to fix on is "or". A vessel must either:

1. Have permanent draft marks at each end of the vessel; or
2. Have permanent loading marks placed on each side of the vessel forward and aft to indicate the maximum allowable trim, and amidships to indicate the maximum allowable draft.

Take the second option and the dimensions become specific. A loading mark must be a horizontal line at least 205 millimeters (8 inches) long and 25 millimeters (1 inch) high, with its upper edge passing through the point of maximum draft, painted in a contrasting color to the sideshell paint. The upper edge is the operative surface; the line has thickness, and the limit lives at its top.

Two more provisions carry real inspection weight. Where draft marks are obscured by operational constraints or by protrusions, the vessel must be fitted with a reliable draft indicating system from which the bow and stern drafts can be determined — the requirement to know your drafts survives the loss of the marks. And on a vessel whose permitted number of passengers on upper decks is limited by stability criteria as indicated by her stability letter, the maximum number allowed on that deck must be marked durably in numbers and letters at least 25 millimeters (1 inch) high at the entranceway to the deck.

Where the two regimes meet

The single link between load lines and the Subchapter marking rule is paragraph (e): on a vessel that has a load line, the amidships marks required by paragraph (c)(2) must be those required by the International Convention on Load Lines, 1966. So the amidships mark changes character depending on the outcome of the §175.122 test. No load line, and the amidships mark is simply the maximum allowable draft under §185.602. Load line assigned, and the amidships mark is the Convention mark.

An 84-foot small passenger vessel, keel laid 1996, runs charters entirely within U.S. waters. Is she subject to load line assignment?

No. She clears the length gate (24 meters / 79 feet or more) and the keel-date gate (on or after July 21, 1968), but also requires that she be on a voyage other than a domestic voyage. Two out of three is not the test. She still requires hull marking under , and because she has no load line, her amidships mark is not the Convention mark.

Freeboard, draft, and reserve buoyancy

The physical quantity a load line protects is reserve buoyancy: the volume of the watertight portion of the ship above the waterline. It can be stated as a volume in cubic feet, as a ratio or percentage of the above-water body to the underwater body, or as an equivalent weight of seawater in tons, where the tonnage figure is 1/35 of the above-water volume in cubic feet, per NAVEDTRA 14057 Ch. 12 — Base Line.

Freeboard is the rough measure of it: the distance in feet from the waterline to the weather deck edge, calculated at the midship section, and freeboard plus draft always equals the depth of the hull in feet NAVEDTRA 14057 Ch. 12 — Waterline Displacement. That identity is the engine behind most numerical questions on this topic. Given any two of the three, you have the third.

Add weight and four things move at once, in a fixed pattern: draft and displacement increase by the same amount, while freeboard and reserve buoyancy decrease. Retaining a substantial amount of reserve buoyancy is essential to seaworthiness; some ships can take more than their own weight in flooding water aboard without sinking on account of it.

Displacement itself is the weight of the volume of water the hull displaces, and at rest it equals the weight of the ship. The conversion the exam uses is V = 35W, where V is the volume of displaced seawater in cubic feet, W is weight in tons, and 35 is the cubic feet of seawater per ton — the long ton of 2,240 pounds. Displacement varies with draft, and the relationship is read off a displacement curve: enter with mean draft on the vertical scale, cross to the curve, drop to the displacement scale. On the sample curve, a mean draft of 26 feet gives approximately 16,300 tons.

Telling it apart

Three marks on the same hull

The criterion that separates them is what the mark tells you — a reading, a limit under the Subchapter, or a limit under the Convention.

• Draft marks — a reading. Fitted at each end of the vessel, they tell you the actual draft forward and aft, and they satisfy §185.602(c) on their own with no loading marks at all.
• Loading marks — a limit set by the vessel's own permitted loading. On each side, forward and aft they indicate maximum allowable trim; amidships indicates maximum allowable draft. Specified at 8 inches by 1 inch, contrasting color, upper edge through the point of maximum draft.
• Load line (Convention) mark — the amidships mark required by the International Convention on Load Lines, 1966, which replaces the plain amidships maximum-draft mark on a vessel that has a load line, and appears only where the §175.122 test was met.

Draft against freeboard

Both are vertical measurements at the midship section, and the criterion separating them is which side of the waterline they occupy.

• Draft — the depth of the ship's keel below the waterline. As it increases, displacement increases.
• Freeboard — waterline up to the weather deck edge. This is the answer to the classic multiple-choice item on the term, where "distance in feet from the keel to the waterline" sits in the option list as the trap NAVEDTRA 14057 Ch. 12 — Review Questions.
• Depth of hull — the two added together.

Working a question

The situation. You are master of a 26-meter passenger vessel, keel laid in 1998. Depth of hull at the midship section is 13 feet 0 inches. She is floating at a mean draft of 8 feet 3 inches. You are ordered to load 20 long tons of stores and equipment, and you must report her freeboard afterward and state which marks govern.

1. Settle the load line question first, because it decides which amidships mark applies. Length is 26 meters, so the first gate opens. Keel laid 1998 is on or after July 21, 1968, so the second opens. The third gate is the voyage, and the question has not put her on a voyage other than a domestic voyage — so on these facts she is not subject to load line assignment under 46 CFR §175.122. Do not supply the missing fact yourself; if an exam question intends a foreign voyage it will say so.
2. Establish present freeboard from the identity. Freeboard plus draft equals depth of hull, so freeboard is 13 feet 0 inches minus 8 feet 3 inches, or 4 feet 9 inches, taken at the midship section and nowhere else NAVEDTRA 14057 Ch. 12 — Waterline Displacement.
3. Apply the direction of change before touching any arithmetic. Weight added increases draft and displacement by the same amount and decreases freeboard and reserve buoyancy. Any answer option showing freeboard increasing after loading is out at this point, without computation.
4. Convert the added weight to volume of displacement if the question asks for it. V = 35W gives 20 × 35 = 700 cubic feet of additional displaced seawater NAVEDTRA 14057 Ch. 12 — Base Line. Displacement after loading is the original displacement plus 20 long tons.
5. Find the new draft from the displacement curve, not by guesswork. Enter the curve with the new displacement, read across to the curve, and read the mean draft. Suppose it comes out at 8 feet 9 inches.
6. Return to the identity for the answer. Freeboard is 13 feet 0 inches minus 8 feet 9 inches, or 4 feet 3 inches. Reserve buoyancy has decreased by the volume of hull now submerged that was watertight above water before.
7. Name the governing marks. Under 46 CFR §185.602 she must carry either permanent draft marks at each end or loading marks on each side; with no load line assigned, her amidships loading mark indicates maximum allowable draft rather than the Convention mark.

Where candidates lose the point

Reaching for a tonnage threshold. The distractor reads something like "vessels of 100 gross tons or more" and it looks right to anyone who thinks about vessels in tons all day. §175.122 sets no tonnage condition; the gates are length, keel date and voyage.

Stopping at the length gate. Given an 80-foot vessel, the candidate confirms 79 feet or more and picks "subject to load line". The keel date and the voyage still have to be satisfied, and on domestic runs the third gate is shut.

Answering "freeboard" as keel to waterline. That is draft. Freeboard runs from the waterline to the weather deck edge, and the two appear side by side in the option list precisely because the swap is so common.

Treating draft marks and loading marks as both required. Paragraph (c) is an either/or. A vessel with permanent draft marks at each end and no loading marks anywhere is compliant with (c).

Measuring freeboard at the bow or the stern. It is calculated at the midship section. Bow and stern figures belong to trim, which is what the forward and aft loading marks address.

Assuming obscured draft marks excuse the requirement. Where protrusions or operational constraints hide the marks, §185.602(f) requires a reliable draft indicating system from which bow and stern drafts can be determined. The obligation to know the drafts does not lapse.

Calling every amidships mark a Convention mark. The 1966 Convention marks are required amidships only on a vessel that has a load line.

Check yourself

Your vessel is 25 meters in length, keel laid in 1961, and departs on an international voyage. Is she subject to load line assignment under 46 CFR §175.122?

No. She meets the length condition and is on a voyage other than a domestic voyage, but her keel was laid before July 21, 1968, so the second condition fails. All three conditions in 46 CFR §175.122 must be met.

Depth of hull at midships is 11 feet 6 inches and the vessel floats at a mean draft of 7 feet 0 inches. What is her freeboard, and what happens to it if 15 long tons of gear are struck below?

Freeboard is 4 feet 6 inches, since freeboard plus draft equals the depth of the hull. Loading 15 long tons increases draft and displacement, so freeboard and reserve buoyancy both decrease NAVEDTRA 14057 Ch. 12 — Waterline Displacement.

A vessel carries permanent loading marks rather than draft marks. What does the mark on each side forward and aft indicate, and what does the amidships mark indicate?

Forward and aft marks indicate the maximum allowable trim; the amidships mark indicates the maximum allowable draft, per 46 CFR §185.602. If the vessel has a load line, that amidships mark must instead be the one required by the International Convention on Load Lines, 1966.

An inspector questions a loading mark you have had painted 6 inches long and 1 inch high. Is it acceptable?

No. The mark must be a horizontal line at least 205 millimeters (8 inches) in length and 25 millimeters (1 inch) in height, in a color contrasting with the sideshell paint, with its upper edge passing through the point of maximum draft.

Your vessel displaces 90 long tons. What volume of seawater does she displace, and what weight is a long ton?

Using V = 35W, 90 × 35 = 3,150 cubic feet, at 35 cubic feet of seawater per ton. The long ton used for ships is 2,240 pounds NAVEDTRA 14057 Ch. 12 — Base Line.

Your vessel's stability letter limits the number of passengers permitted on the upper deck. What marking does that require, and where?

The maximum number of passengers allowed on that deck must be shown by a durable marking in numbers and letters at least 25 millimeters (1 inch) high, at the entranceway to that deck.

Guards and a rubbing strake obscure the draft marks aft. What is required?

A reliable draft indicating system from which the bow and stern drafts can be determined, under §185.602(f). Painting the marks elsewhere on a whim is not the remedy the regulation names.