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freeboard assignment





All ships (with certain exceptions) are required to be surveyed and marked with permanent load line markings in accordance with the International Convention on Load Lines, 1966 as modified 1988. The principle purpose of load line assignment is to ensure that the ship always has sufficient reserve buoyancy and intact stability when proceeding to sea.


International Convention on Load Lines is an International Convention on Load Lines (CLL), signed in London on 5 April 1966, amended by the 1988 Protocol and further revised in 2003. The 1988 Protocol was adopted in order to harmonize the survey and certification requirement of the 1966 Convention with those contained in the International Convention for the Safety of Life at Sea(SOLAS) and MARPOL 73/78.


This Convention provides for the terms of ship's surveys, issuance, duration, validity and acceptance of International Load Line Certificates, as well as relevant State control measures, agreed exemptions and exceptions.


Annexes to the Convention contain various regulations for determining load lines, including details of marking and verification of marks, conditions of assignment of freeboard, freeboard tables and corrections, special provisions for ships intended for the carriage of timber and the prescribed form of International Load Line Certificates.


also taken into account are the potential hazards present in different zones and different seasons and additional safety measures concerning doors, hatchways etc.


The following ships are not required to have load lines assigned:

* warships;

* new ships of less than 24 metres in length;

* existing ships of less than 150 tons gross;

* pleasure yachts not engaged in trade, and;

* fishing vessels.

(Annex A – Article 5)


Purpose of F/B assignment

* Reserve buoyancy

* Water on deck

* Not overloaded (Hull markings)

* Maintain Conditions (Inspections)

Conditionof F/B assignment

* Stability

* Strength of Hull

* Water/ Weather tightness

* Protection of crew


Consideration for F/B assignment

*Dimensions and form of the ship

* Means of freeing water on deck

* Means of closing/opening (doors/sills)

* Structural strength (hull, deckhouse, hatches)

* Hull penetrations ( piping inlets & discharges)

* Cargoes (oil, timber, GC)

* routes, weather and seas likely to be found


The seasonal zones, areas and periods that determine the appropriate load line in a particular sea area at a given time of year are set out in Annex II


The Tropical, Summer and Winter freeboard zones are based upon the following weather criteria:

Summer Zones – Regions where not more than 10% of wind speeds exceed force 8 Beaufort (34 knots).


Tropical Zones – Regions where not more than 1% of wind speeds exceed force 8 Beaufort (34 knots) and not more than one tropical storm in a ten-year period occurs in an area of 5º

latitude/longitude square in any one separate calendar month.

Winter Zones – Are all other regions


It is a criminal offence for the Master and/or shipowner to allow a vessel to be operated in a zone, when in the upright condition, the relevant amidships zone load line would be below the still load waterline. Such an action would immediately invalidate all Classification Society and Load Linecertification and will lead to criminal prosecution.


Length (L)

This is taken as 96% of the total length on a waterline at 85% of the least moulded depth, or, as the length from the fore side of the stem to the axis of the rudder stock on that waterline, if greater.


Perpendiculars (FP, AP)

is a line drawn perpendicularly to the load line through the after side of the rudder post or through the axis of the rudder stock. T



Amidships is at the middle of the length


Breadth (B)

Unless expressly provided otherwise, the breadth (B) is the maximum breadth of the ship, measured amidships to the moulded line of the frame in a ship with a metal shell and to the outer surface of the hull in a ship with a shell of any other material.


Moulded depth

is the height above baseline of the intersection of the underside of the deck plate with the ship side.

When there are several decks, it is necessary to specify to which one refers the depth.


Depth for freeboard (D)

This is the moulded depth amidships, plus the thickness of the freeboard deck stringer plate, where fitted, plus T(L – S)/L if the exposed freeboard deck is sheathed, where:

T is the mean thickness of the exposed sheathing clear of deck openings, and S is the total length of superstructures.

The depth for freeboard (D) in a ship having a rounded gunwale with a radiusgreater than 4% of the breadth (B) or having topsides of unusual form is the depth for freeboard of a ship having a

midship section with vertical topsides and with the same round of beam and area of topside section equal to that provided by the actual midship section.


Block Coefficient (Cb)

Cb = Volume of displacement at draught 0.85D/ ((Length* ´ Breadth* ´ draught (at 85% of least moulded depth))

(* as previously defined)

(in no case shall the block coefficient (Cb) be taken to be less than 0.68.)



The freeboard assigned is the distance measured vertically downwards amidships from the upper edge of the deck line to the upper edge of the related load line.


Freeboard Deck

This is normally the uppermost continuous deck exposed to weather and sea, which has permanent means of closing all openings in the weather part thereof, and below which all openings in the sides of the ship are fitted with permanent means of watertight arrangement.


Deck line

The deck line is a horizontal line marked

amidships on each side of the ship. Its upper

edge shall normally pass through the point

where the continuation outwards of the upper

surface of the freeboard deck intersects the

outer surface of the shell plating.

However, the deck line may be placed with

reference to another fixed point on the ship on condition that the freeboard is correspondingly corrected and that the reference point location and the identification of the freeboard deck is clearly indicated on the International Load Line Certificate.


Load line mark and accompanying load lines (Regulations 5 to 8)

The Load Line Mark consists of a ring 300 mm in outside diameter and 25 mm thick which is intersected by a horizontal line 450 mm in length and 25 mm thick, the upper edge of which passes through the centre of the ring. The centre of the ring is placed amidships and at a distance equal to the assigned summer freeboard measured vertically below the upper edge of the deck line.


Conditions of assignment of freeboard

1. Information to the master.

Master to be supplied information for the loading and ballasting of the ship avoiding unacceptable stresses of the ship’s structure.

Also, to be provided with ship’s stability guidance for all condition of service.


2. Superstructure end bulkheads

3. Doors

4. Position of hatchways, doorways and ventilators

5. Cargo and other hatchways

6. Hatchways closed by portable covers and secured by tarpaulins ..

7. Hatchways closed by weathertight covers of steel …

8. Machinery space openings


9. Miscellaneous openings in freeboard and superstructure decks

  • 10. Ventilators
  • Air pipes
  • 12. Cargo ports and other similar openings
  • 13. Scuppers, inlets and discharges
  • 14. Sidescuttles
  • 15. Freeing ports
  • 16. Protection of the crew

Types of ships

  • Type “A” ships
  • Tankers, tank barges, & similar designs, only to carry liquid cargoes in bulk
  • High integrity of exposed deck, cargo tanks with only small access openings closed by watertight gasketed steel (or equivalent) covers
  • Low permeability of loaded cargo tanks

Type "B" ships Ships that are not Type A

Type B ships are assigned bigger freeboards (less favourable).

However, certain Type "B" ships may qualify for reduced freeboards (more favourable).


Type "B reductions: (B – 60; B – 100)

If L > 100 m, loaded, will be afloat after flooding of any compartment/s, excluding the machinery spaces

If L > 150 m, same, but including machinery spaces

In such cases, freeboard. may be reduced up to 60% of the difference between Type " A " and Type “B” freeboards

Under certain conditions, the Freeboard may be reduced up to 100% of the difference between Type " A " and Type “B” freeboards


Freeboard tables.

For Type A and Type B ships (Entering with Length)

corrections to the tabular freeboards
Corrections to the tabular Freeboards

Length: If 24 < L < 100 m, for type B ships, freeboard may be increased.

Block coefficient: If Cb> 0.68, the freeboard must be increased (less favourable)

Depth: If D > L/15, more draught, freeboard increased

If D < L/15, freeboard may be reduced (subject to conditions).


Superstructure: Superstructure can provide additional righting energy during

extreme rolls where deck edge is immersed. Freeboard may be reduced if the superstructure meets certain requirements.

Trunks: Deckhouses which are < 92% of beam are trunks, not superstructures”

A trunk is  60 % of beam.

Structurally as strong as a superstructure

Under conditions trunks can contribute to the superstructure correction


Sheer: The deck sheer provides more buoyancy at bow & stem (i.e., pitching

response), reduces deck wetness; Ships with a particular sheer profiles may have its freeboard reduced or increased

Bow Height: Ships must have a minimum bow height (to ensure reserve buoyancy at bow). Ships with smaller bow height have its freeboard increased, but no freeboard reduction is given for excessive bow height.

preparation for a load line survey
Preparation For A Load Line Survey

Ensure particulars in the conditions of assignment of L/L have been incorporated into the Planned Maintenance schedule.


The detailed preparations should commence three months before the expected date of survey.


1. Check that all access openings at ends of enclosed structures are in good condition. All dogs, clamps and hinges should be free and well greased. All gaskets and water tight seals should be crack free. Ensure that the doors open from both sides.


2. Check all cargo hatches and access to holds for water tightness especially battening devices such as cleats and wedges.


3. Inspect all machinery space openings on exposed decks.

4. Check that any manholes and flush scuttles are capable of being made water-tight.

5. Check that all ventilator openings are provided with efficient weather-tight closing appliances and repair any defects.


6. All airpipes must be provided with permanently attached satisfactory means for closing openings.

7. Inspect any cargo ports below the freeboard deck and ensure that all of them are watertight.

8. Ensure that the non return valves on board discharge are operating in a satisfactory manner.


9. Side scuttles below the freeboard deck or to spaces within enclosed superstructures must have efficient internal watertight deadlights. Inspect the deadlight ‘rubbers’.

10. Check that all freeing ports are in a satisfactory condition e.g. shutters are not jammed, hinges are free and that pins are of non corroding material.


11. All guard rails and bulwarks should be in satisfactory condition, e.g. all fractured rails should be re-welded.

12. If the life lines are required to be fitted in certain areas, rig the lines and overhaul as necessary.


13. De-rust and paint the deck line, load line mark, load lines and the draught marks.

In brief ensure that the hull is water-tight below the freeboard deck and watertight above the freeboard deck.


14. On the day of the survey have the certificate and record ready for the surveyor’s inspection.

15. The master should have sufficient stability information to show that the vessel can be loaded and ballasted correctly. ( If having approved loading computer program, print out test pages to submit to surveyor)


16. Have all the necessary key to areas which surveyor may want to inspect e.g. store rooms

17. Sufficient men should be available for work such as opening cargo hatches, and ladders and stages should be ready for the surveyors to view the load line marks.