2. OIL - FUEL TANKS

NOTE:

To obtain weight of the liquid contents of any compartment multiply "Tonnes at S.G.I.O" by the actual Specific Gravity of the liquid.

CAPACITIES, CENTRES OF GRAVITY AND FREE -SURFACE MOMENTS  ^

3. ENGINE - ROOM AND LUB-OIL TANKS

4. FRESH, FEED AND BALLAST WATER TANKS

NOTE:

To obtain weight of the liquid contents of any compartment multiply "Tonnes at S.G.I.O" by the actual Specific Gravity of the liquid.

EFFECT OF FREE SURFACE ON STABILITY ^

The effect of free surface in compartments containing fluids or fluid cargoes must be taken into account for all conditions of loading.

The maximum free surface moment in units of tonnes metres should be calculated for all tanks, based on the following table of specific weights:

EXAMPLE: Displacement of Vessel = 6,740 tonnes.

TANK	INERTIA(m)	SPECIFIC WEIGHT	FREE SURFACE MOMENT (Tonnes M)
Ballast Tank	1,000	1.025	1,025
Fresh Water Tank	850	1.000	850
Fuel 011 Tank	1,500	0.95	1,425
Lubricating 011 Tank	600	0.90	540
TOTAL F. S. MOMENT			3,840

Other methods of determining the effect of free surface of liquids may be acceptable and should be accompanied by detailed calculations.

EXAMPLE SHOWING USE OF CROSS CURVES (KN) ^

GZ calculations must be submitted for all sea going conditions. It is recommended that the following format be submitted for each condition included in the booklet:

Righting Lever GZ = KN - KG Sin Æ

where KN   =  Cross Curve ordinate
KG             =  Centre of Gravity above base (corrected for free surface effects)
and Æ        =  Angle of Inclination

Condition No.
Corresponding Displacement = tonnes

The Statical Stability curve may be drawn for each condition by using the GZ values calculated in the last column.

APPENDIX‘B’  ^

RECOMMENDED DATUM LINES FOR HYDROSTATIC
PROPERTIES AND CENTRES OF GRAVITY

STANDARD: STAB 2  ^

INCLINING EXPERIMENTS

CONTENTS

INTRODUCTION

APPENDIX A - Inclining experiment preparation and procedures

APPENDIX B - Determination of the ship’s metacentric height (GM) by means of the rolling period test

INTRODUCTION

Stability calculations depend upon an accurate determination of the centre of gravity of the ship and, unless the Inclining Experiment from which this determination is made is itself carried out with the greatest possible .accuracy, no really reliable calculation can be made.

Thus, the first determination of the centre of gravity, is basic, in that any alterations, additions of weight to, or removals of weight from, the ship during her life, are made relying upon figures obtained from the Inclining Experiment.

With the foregoing in mind, the preparations and procedures outlined in Appendix ‘A’ have been prepared to provide guidelines for the conduct of inclining experiments.

APPENDIX A ^

INCLINING EXPERIMENT - PREPARATIONS AND PROCEDURES

WEATHER CONDITIONS & MOORING ARRANGEMENTS .

1(i) The vessel should be moored in a sheltered area with bow or stern to the wind. The depth of water under the hull should be sufficient to allow the vessel to move freely. The breast ropes should be slackened right down and the remaining hawsers slackened each time a reading is taken. During the test the gangway should be removed.

(ii) If possible the test should not be conducted in wind conditions heavier than a light breeze. Excessive accumulations of rain, snow or ice should be removed before the test. Surveyors should ensure that the effect of wind and current does not adversely affect the test results.

CONDITION OF VESSEL, TRIM AND LIST

2(i) The vessel should be in as nearly a finished condition as possible and in a good state of readiness with shipyard gear and equipment, tool boxes, scaffolding, scrap and debris removed from the vessel. Weights capable of moving should be lashed in place.

(ii) During the test only the minimum number of people should be on board.

(iii) Bilges, decks and flats must be free of liquids.

(iv) Boilers, wet machinery and piping should be at operating level.

(v) Where possible all tanks should be empty. Tanks containing liquids should either be pressed full or at a level where the free surface effect can accurately be calculated. However, it is emphasized that empty tanks are preferred for an accurate test. It is advisable to remove manhole covers to verify that tanks are empty rather than relying on soundings. The viscosity of the liquid should be considered and the liquid heated if necessary to allow free movement. Care should be taken in pressing up tanks to ensure that there is no entrapped air.

(vi) In all cases the effect of free surface on the test results should be considered before proceeding with the test. Excessive free surface could .well lead to doubtful results and, in such cases, the surveyor should consider postponing the test.

(vii) All valves should be closed to prevent cross flooding or intercompartmental flooding.

(viii) The vessel should be as close to the design trim as possible and should not differ from this by more than 0.01 LBP. Unless the vessel is at the designed trim, soundings of tanks will not give true readings and the inclining stability calculation will require to be calculated for the trimmed waterline.

(ix) The vessel should be upright or within 1/2° from upright.

PENDULUMS

3(i) Two pendulums should be used, one at each end of the vessel. The length of each pendulum should be as long as possible and they should be located in an area protected from the wind. Pendulum weights should be suspended into a liquid such as oil to dampen excessive movement.

DRAUGHTS AND FREEBOARD

4(i) Draughts and/or freeboards should be read immediately before or immediately after the test. All persons required to be on board for the test should be in location during these readings. If the water is not perfectly calm a gauge glass may be used to ensure accuracy.

(ii) Draughts should be read forward and aft and draughts or freeboards lifted amidships to determine hog or sag. At the same time the density of the water should be recorded at various locations along the vessel.

TEST WEIGHTS

5(i) The weights used should be sufficient to give a total inclination of 1 1/2° to 3° on each side. It may be necessary to have a larger inclination in small vessels in order to get sufficient deflection of the pendulum. However, care should be taken to ensure:

1.  that the angle of heel does not exceed the angle at which GZ no longer equals GM sin Æ .
   
   
2.  that the deflection of the pendulum for each shift is sufficiently large to give meaningful readings, and
   
   
3.  that changes in the waterplane area during the shifts are kept as small as possible. In this regard vessels with appreciable flare at the waterline should be carefully considered and the angle of inclination should not exceed 1° . The test weights should be divided into four lots and arranged as close to amidships as possible. The accuracy of the test weights should be determined

WEIGHT MOVEMENTS

6(i) Eight (8) movements of the weights should normally be carried out. If the readings are not consistent for the initial four readings, the cause must be corrected and the number of movements repeated. At the time of the recording of the readings, the men on board should be allocated to their positions and not allowed to move.

RESPONSIBILITIES

7(i) The responsibility for preparing the vessel for the test and conducting the test rests with the owner, shipbuilder or naval architect. The marine surveyor will assist only as necessary to obtain valid test results and will;

1.  check and record the adequacy of the vessel’s preparation by conducting a general inspection of the vessel prior to the inclining experiment,
   
   
2.  witness and record the soundings of tanks containing liquids and inspect all empty tanks prior to the test,
   
   
3.  verify the accuracy of the test data accumulated,
   
   
4.  verify weight and location of permanent ballast, if any, and
   
5.  submit a completed SI 35, "Report of an Inclining Experiment".The organization conducting the test shall:
   
   The organization conducting the test shall:
   
   
6.  accumulate a complete record of all test information,
   
   
7.  furnish the marine surveyor with accurate weight and centre of gravity information on weights to add, to deduct and to relocate to bring the vessel to lightship condition. This data should provide a clear accounting of the condition of the vessel as inclined and should be acceptable to the Surveyor,
   
   
8.  provide details as to weight and location of all permanent ballast on board the vessel, and
   
   
9.  prepare an inclining experiment report and submit the stability data as required by the regulations..

WAIVING OF AN INCLINING EXPERIMENT

8(i) Under certain circumstances the Approval Authority will consider an application from the owner for waiving an inclining experiment. See STAB 1, section 2.

APPENDIX ‘B’  ^

DETERMINATION OF SHIP’S METACENTRIC HEIGHT (GM)
BY MEANS OF THE ROLLING PERIOD TEST

INTRODUCTION

1(i) Subject to subsection (iv), this method of approximating a ship’s initial metacentric height (GM) may be used for vessels up to 24 metres in registered length, where it is not practicable to carry out an inclining experiment, or as a supplement to an inclining experiment.

(ii) If the following instructions are properly carried out, this method allows a reasonably quick estimation of the metacentric height, which is a measure of the ship’s stability.

(iii) The method depends upon the relationship between the metacentric height and the rolling period in terms of the extreme breadth of the vessel.

(iv) It should be noted that a roll test is not acceptable as a basis for determining a ship’s stability characteristics, where:

1.  an inclining experiment is required by Regulations;
   
   
2.  the vessel is of hard chine construction (i.e. of knuckled hull form) or is fitted with bilge keels, or
   
   
3.  reasonable doubt exists as to the adequacy of the intact stability characteristics of the ship, over its complete range of operating conditions.

TEST PROCEDURE

2(i) The rolling period required is the time for one complete oscillation of the vessel. To ensure the most accurate results in obtaining this value the following precautions should be observed:

1.  The test should be conducted with the vessel in harbour, in smooth water with the minimum interference from wind and tide.
2. 
    Starting with the vessel at the extreme end of a roll to one side (say port) and the vessel about to move towards the upright, one complete oscillation will have been made when the vessel has moved right across to the other extreme side (i.e. starboard) and returned to the original starting point and is about to commence the next roll.
3. 
    By means of a stop watch, the time should be taken for about five (5) of these complete oscillations; the counting of these oscillations should begin when the vessel is at the extreme end of a roll. After allowing the roll to completely fade away, this operation should be repeated at least twice more. If possible, in every case the same number of complete oscillations should be timed to establish that the readings are consistent, i.e. repeating themselves within reasonable limits. Knowing the total time for the total number of oscillations made, the time for one complete oscillation can be calculated.
4. 
    The vessel can be made to roll by rhythmically lifting up and putting down a weight as far off middle-line as possible; by pulling on the mast with a rope; by people running athwartships in unison; or by any other means. However, and this is most important, as soon as this forced rolling has commenced the means by which it has been induced must be stopped and the vessel allowed to roll freely and naturally. If rolling has been induced by lowering or raising a weight it is preferable that the weight is moved by a dockside crane. If the ship’s own derrick is used, the weight should be placed on the deck, at the middle-line, as soon as the rolling is established.
   
5. The timing and counting of the oscillations should only begin when it is judged that the vessel is rolling freely and naturally, and only as much as is necessary to accurately count these oscillations.
    
6. The mooring should be slack and the vessel "breasted off" to avoid making any contact during its rolling. To check this, and also to get some idea of the number of complete oscillations that can be reasonably counted and timed, a preliminary rolling test should be made before starting to record actual times.
    
7. Care should be taken to ensure that there is a reasonable clearance of water under the keel and at the sides of the vessel.
   
   
8. Weights of reasonable size which are liable to swing (e.g. a lifeboat), or liable to move (e.g. drum), should be secured against such movement. The free surface effects of slack tanks should be kept as small as is practicable during the test.
    
    

DETERMINATION OF THE INITIAL STABILITY

3(i) Having calculated the period for one complete oscillation, say T seconds, the metacentric height GM can be calculated from the following formula:

Where:
f = factor for the rolling period
B = breadth of the ship in metric units,
T = time for a full rolling period in seconds (i.e. for one oscillation ‘to and fro’ port-starboard-port, or vice versa).

ROLL FACTORS

4(i) The factor ‘f’ is of the greatest importance and data from a number of tests have been used in determining the following typical values:

1.  For unloaded fishing boats (but with fuel, stores, and equipment). f = 0.761
2.  For vessels of normal size (excluding tankers):

(a) empty ship or ship carrying ballast f = 0.88
(b) ship fully loaded and with liquids in tanks comprising the following percentage of the total load on board (i.e. cargo, liquids, stores, etc.)

The stated values are mean values. Generally, f - values are within ± 0.05 of those given above.

LIMITATIONS TO THE USE OF THIS METHOD

5(i) It must be noted that the greater the distance of masses from the rolling axis, the greater the rolling coefficient will be.

Therefore, it can be expected that:

•  the rolling coefficient for an unloaded ship, i.e. for a hollow body, will be higher than that for a loaded ship;
•  the rolling coefficient for a ship carrying a great amount of bunkers and ballast - both groups are usually located in the double bottom, i.e. far away from the rolling axis - will be higher than that of the same ship having an empty double bottom.

(ii) The above recommended rolling coefficients were determined by tests with vessels in port and with their consumable liquids at normal working levels; thus, the influences exerted by the vicinity of the quay, the limited depth of water and the free surface of liquids in service tanks are covered.

(iii) Experiments have shown that the results of the rolling test method get increasingly less reliable the nearer they approach GM-values of 0.20 metres and below.

(iv) For the following reasons, it is not generally recommended that results be obtained from rolling oscillations taken in a seaway:

1.  Exact coefficients for tests in open waters are not available.
2.  The rolling periods observed may not be free oscillations but forced oscillations due to seaway.
3.  Frequently, oscillations are either irregular or only regular for too short an interval of time to allow accurate measurements to be observed.
4.  Specialized recording equipment is necessary.

(v) However, sometimes it may be desirable to use the vessel’s period of roll as a means of approximately judging the stability at sea. If this is done, care should be taken to discard readings which depart appreciably from the majority of other observations. For oscillations corresponding to the sea period and differing from the natural period at which the vessel seems to move should be disregarded. In order to obtain satisfactory results, it may be necessary to discard a considerable number of observations.

(vi) In view of the foregoing circumstances, it needs to be recognized that the determination of the stability by means of the rolling test in disturbed waters should only be regarded as a very approximate estimation.

GRAPHICAL METHOD

6(i) The initial stability may also be more easily determined graphically by using the sample nomogram on page 5.

1.  The values for B and f are marked in the relevant scales and connected by a straight line (1) . This straight line intersects the vertical line (mm) in the point (M).
   
   
2.  A second straight line (2) which connects this point (M) and the point on the, T scale corresponding with the determined rolling period, intersects the GM scale of the requested value.

METRIC UNIT

STANDARD: STAB 3
INTERIM STANDARD OF STABILITY FOR SHIPS BUILT OR CONVERTED FOR TOWING ^

1 As an interim measure while research is continuing, the following minimum intact stability criteria are to be used in the approval of stability data for the above vessels.

VESSELS BUILT OR CONVERTED FOR TOWING:

2(i) The area under the righting lever (GZ) curve should not be less than 0.055 metre-radians up to 30 degrees angle of heel and not less than 0.09 metre-radians up to 40 degrees or the angle of downflooding if this angle is less than 40 degrees.

Additionally, the area under the righting lever (GZ) curve between the angles of heel of 30 degrees and 40 degrees or between 30 degrees and the angle of downflooding, if this angle is less than 40 degrees, should not be less than 0.03 metre-radians.

(ii) The righting lever (GZ) should be at least 0.20 metres at an angle of heel equal to or greater than 30 degrees.
(iii) The maximum righting lever should occur at an angle of heel preferably exceeding 30 degrees but not less than 25 degrees.
(iv) The initial metacentric height (GM) should not be less than 0.55 metres.

3 With regard to the-Lightship condition specified in the Hull Construction Regulations, this condition is not considered to be an operating condition. Therefore, the above criteria are not applicable and the standard to be attained in this condition is a positive GM. (The Lightship condition is defined as the condition of a vessel ready for sea with no stores, consumables, fluid ballast, or crew on board).

STANDARD: STAB 4
STABILITY STANDARDS FOR FISHING VESSELS: ^

(a) subject to compliance with the Large Fishing Vessel Inspection Regulations, or
(b) required to submit stability data by the Small Fishing Vessel Inspection Regulations.

OPERATING CONDITIONS WITH NO ACCUMULATED ICE

1 The following minimum intact stability criteria are to be used in the approval of stability data for the above vessels:

(i) The area under the righting lever (GZ) curve should not be less than 0.055 metre-radians up to Æ = 30° angle of heel, and not less than 0.09 metre-radians up to Æ = 40° , or the angle or downflooding Æ _f if this angle is less than 40°
Additionally, the area under the righting lever (GZ) curve between the angles of heel of 30° and 40° or between 30° and Æ _f if this angle is less than 40° should not be less than 0.03 metre-radians.
(ii) The righting lever GZ should be at least 0.20 metres at an angle of heel equal to or greater than 30° .
(iii) The maximum righting arm should occur at an angle of heel preferably exceeding 30° but not less than 25° .
(iv) The initial metacentric height(GM) should not be less than 0.35 metres.

WORST OPERATING CONDITION WITH ACCUMULATED ICE

2 Using the ice accumulation weights and vertical centres of gravity requires by the appropriate fishing vessel inspection regulations:

1.  The area under the righting lever (GZ) curve should not be less than 0.04 metre-radians up to 30 degrees angle of heel and not less than 0.058 metre-radians up to 40 degrees or the angle of downflooding if this angle is ,.less than 40 degrees.
   Additionally, the area under the righting lever (GZ) curve between the angles of heel of 30 degrees and 40 degrees or between 30 degrees and the angle of downflooding, if this angle is less than 40 degrees, should not be less than 0.016 metre-radians.
2.  The righting lever (GZ) should be at least 0.15 metres at an angle of heel equal to or greater than 20 degrees.
3. The maximum righting lever (GZ) should occur at an angle of heel not less than 20 degrees.
4.  The initial metacentric height (GM) should not be less than 0.23 metres.

3 Hydrostatic and stability curves should normally be prepared on a designed trim basis. However, where the operating trim or the form and arrangement of the ship are such that change in trim has an appreciable effect on righting arms, such change of trim is to be taken into account.

4 The calculations may take into account the volume to the upper surface of the deck sheathing, if fitted. In the case of wood ships the dimensions should be taken to the outside of hull and deck planking.

5 Cross Curves of Stability may take the following into account and a note to this effect must be shown:

1.  Enclosed weathertight superstructures and enclosed weathertight deckhouses of similar construction,
2.  Weathertight trunks, and
3.  Hatchways having regard to the effectiveness of the closures.

6 Definitions for paragraph 5 are as follows:

SUPERSTRUCTURE means a decked structure on the bulkhead deck extending from side to side of the ship, or with the side plating not being inboard of the shell plating more than 4 per cent of the maximum moulded breadth of the vessel measured at mid-ships. A raised quarter deck is regarded as a superstructure.

WEATHERTIGHT means that in any sea conditions water will not penetrate into the ship.

7 In cases where a ship would flood through an opening, the stability curve is to be cut short at the corresponding angle of flooding and the ship is to be considered as having entirely lost her stability at that angle.

8 In the calculations for loading conditions an allowance is to be made for the weight of the wet fishing nets and tackle.

9 In all cases the cargo should be assumed to be homogenous unless this is inconsistent with practice.

10 The following conditions are not considered as operating conditions. Therefore the above criteria are not applicable and the standard to be obtained in these conditions is a positive.GM:

1.  Lightship
2.  Port after discharge of cargo with 10% of fuel, fresh water and stores remaining and accumulated ice on top-sides and rigging.
   (The lightship condition is defined as the condition of a vessel ready for sea with no stores, consumables, fluid ballast or crew on board).

APPENDIX ‘A’
DENSITIES AND STOWAGE RATES OF SOME FISHERY PRODUCTS ^

1(i) The following stowage rates may be used when approximate figures are required for stability calculations.

(ii) Other than the figures for redfish, the basic data is extracted from the British White Fish Authority Pamphlet Torry Advisory Note No. 17.

DENSITIES AND STOWAGE RATES

STANDARD: STAB 5
STANDARD FOR THE INTACT STABILITY OF PASSENGER VESSELS CARRYING MORE THAN 12 PASSENGERS ^

1 The provisions of this standard are not applicable to:

1.  Hydrofoils, air cushion vehicles, and high speed planing craft; and
2.  Ships built or converted before 1 June 1977, except where otherwise required by the Board.

DEFINITION

2 "Margin Line" - means an assumed line located 76.2 mm below and parallel to the upper surface of the bulkhead deck at side or, in the case of a vessel of open construction where the side shell is intact up to the gunwale, 305 mm below and parallel to the gunwale.

3 The owner of a vessel to which this standard applies, shall:

1.  arrange for an inclining experiment to be carried out in accordance with the requirements of STAB 2.
2.  provide stability data in accordance with the requirements of this standard and those of STAB 1, with the proviso that the cross curves required by STAB 1 are to include a curve at a 10^o angle of inclination; and
3.  provide a general arrangement drawing showing passenger seating arrangements and a ship profile view.

4 The owner shall submit for approval, stability data for each of the following conditions:

1.   Lightship Condition - ship completely outfitted for sea but with no passengers, crew cargo or stores and with all fuel, fresh water and water ballast tanks empty.
   
   
2.   Light Operating Condition - lightship condition, plus crew, full fuel, water and stores.
   
   
3.   Departure Condition - lightship condition, plus crew, full fuel, water and stores, cargo, full passenger complement, normally distributed.
   
   
4.   Arrival Condition - lightship condition, plus crew, 10% fuel, water and stores, full cargo and passenger complement, normally distributed.
   
   
5.   Worst Designed Operating Condition - any condition likely to be encountered in service in which the distribution and quantity of consumables, cargo, and passengers produce lower values of GZ and/or GM than conditions (ii), (iii) and (iv) above.

5 In addition to the conditions required in section 4; an emergency passenger heeling condition, as described in Section 6, shall be provided in all cases where the value of GZ at 10 degrees, in the Arrival Operating Condition, is equal to or less than metres where:

B = moulded breadth of vessel in metres.
N = total number of passengers carried.
D = displacement of vessels in tonnes.

6 Where an investigation of the effects of passenger crowding is indicated by the provisions of Section 5, the following shall apply:

(i) The passenger complement shall be restricted, in addition to any other criteria applicable, by the angle of heel due to passengers crowding to one side of the vessel. The certificate shall be endorsed to indicate the maximum number of passengers allowed on each deck and the Master shall be made aware that these numbers are not to be exceeded.

If the stability calculations reveal that, due to a disregard by passengers of deck capacity limiting notices, it would be possible to produce a passenger distribution which would create a dangerous situation, the Board may prescribe special measures, such as additional crew members or restricted areas, to control passenger distribution.

(ii) The maximum number of passengers on any deck shall be determined as follows:

Whether seats are provided or not, an allowance of two persons for each square metre of available deck area may be applied. The available deck area is considered to be the area of deck assigned to passengers including seating areas but excluding concessions stands, washrooms, stairwells, casings etc., and a minimum of 15% of the net area for passageways.

(iii) If required by Section 5, an Emergency Heeling Condition as described in this Section to be provided.

Superimposed upon the GZ curve for the Arrival Condition shall be shown a curve of passenger heeling arm, determined as follows:

1.  The assigned number of passengers on each deck shall be taken into account for the purpose of calculating the passenger heeling moment.
2.  On each deck, on the "down" side of the centerline, the passengers will be standing adjacent to their seats. The remainder of that deck’s total complement will move as far as possible to the "down" side to fill all available space on the basis of 4 persons per square metre. Should this area on the "down" side of the centerline not accommodate the required number, then credit in the heeling moment shall be allowed for the persons on the "up" side of the centerline. However, in such circumstances, an additional heeling condition will be required reflecting a partial passenger load such that the number of passengers on the deck or decks in question are crowded on the "down" side of the centerline only.
3.  The passenger heeling arm
4.    
5. where Æ = Æ for any angle of heel

7 In the development of the stability conditions required by Sections 4 and 6, the following standards will apply:

(i) In all conditions, except the Lightship Condition, calculations shall take into account the free surface effect of fluids in all slack tanks.
(ii) The weight of passengers shall be taken as follows:

1.  for vessels not carrying berthed passengers - 63.5 kg per person.
2.  for vessels carrying berthed passengers - 74.8 kg per person.

(iii) The height to the centre of gravity of passengers shall be assumed to be 1 metre above the deck level.

GENERAL CRITERIA FOR NORMAL OPERATING CONDITIONS

8(i) The following minimum criteria shall be used to assess the stability of the vessel in the conditions required by sub-sections 4(ii) to 4(v).

1.  The area under the righting lever (GZ) curve shall not be less than .055 metre radians up to 30° angle of heel, and not less than 0.09 metre radians up to 40° angle of heel or the angle of downflooding if it be less than 40.0° .
   
   
2.  Additionally, the area under the righting lever (GZ) curve between the angles of 30° and 40° , or between the angle of 30° and the angle of downflooding if that angle be less than 40° .shall not be less than 0.03 metre radians.

(ii) The righting lever (GZ) shall have a value of at least 0.20 metres at an angle of heel equal to or greater than 30° , except where otherwise provided in subsection (v).
(iii) The maximum value of the righting lever shall occur at an angle of heel preferably exceeding 30° but, except where otherwise provided in subsection (v), not less than 25° .
(iv) The initial fluid metacentric height (GM), shall not be less than 0.15 metres in the worst designed operating condition.
(v) For ferries and vessels of barge type hull form, on restricted service, where a limited range of stability may not permit compliance with subsections (ii) and (iii), the Board may accept a righting lever curve having its maximum GZ value at less than 25° and having a value at 30° of less than 0.20 metres provided that:

1.  the range of the righting lever (GZ) curve is not less than 40° .
2.  the area under the righting lever (GZ) curve within its range, or to the angle of downflooding if this be less, is not less than 0.18 metre radians.

Upon application to the Board. the criteria of this subsection may be modified for applicable vessels limited to voyages on sheltered waters.

GENERAL CRITERIA FOR ASSESSMENT OF EMERGENCY PASSENGER HEELING CONDITIONS

9(i) In addition to the criteria for normal operating conditions given in Section 8, the following criteria shall be used to assess the Emergency Passenger Heeling Condition required by Section 5.

(ii) Upon the righting lever (GZ) curve of the arrival condition, with an assigned distribution of passengers, shall be superimposed a curve of the passenger heeling arm, as determined from Section 6. The angle of static heel, determined from the intersection of the righting lever (GZ) curve and the heeling arm curve, shall neither exceed 10 nor immerse the margin line.
(iii) The residual area, between the curves of righting levers and passenger heeling arms shall be not less than 0.025 metre radians and the remaining righting lever must attain a value of at least 0.1 metres.
(iv) The criteria of this section are illustrated on the next page.

APPENDIX ‘A’
SEATING ARRANGEMENTS FOR HIGH DENSITY PASSENGER VESSELS ^

Seats are to provide a minimum width per person of 450 mm and, where seats are arranged in rows, the horizontal clearance at seat level between the seat front of one row and the seat back of the next row shall not be less than 300 mm. Aisles between rows of seats or between a row of seating and adjacent structure shall, subject to the approval of the marine surveyor, have a minimum width of 750 mm.

APPENDIX ‘B’
ALTERNATIVE STANDARD FOR THE INTACT STABILITY OF SMALL PASSENGER VESSELS OF MULTIPLE-PONTOON CONFIGURATION AND RESTRICTED PASSENGER MOVEMENT ^

APPLICATION

1 The following criteria may be used as an alternative to those of STAB 5 to evaluate the intact stability and related characteristics of small passenger vessels:

(a) to which the Safety Convention does not apply,
(b) which are of multiple-pontoon configuration,
(c) which carry more than 12, but not more than 30 unberthed ..passengers on a single, open or partly-screened deck in fixed high-density seating, except that , upon request and with the Regional Manager’s favourable recommendations, the Board may consider accepting up to 49 passengers in individual cases,
(d) which do not exceed 18.3 metres in length or 40 gross tons, and
(e) which undertake short voyages, seasonally, in fine weather and .in sheltered waters within limits, specified in the Inspection Certificate not exceeding those appropriate to a Minor Waters Voyage, Class II.

2 This standard does not apply to:

(a) hydrofoils, air cushion vehicles, and high-speed planing craft, or
(b) ferries.

PREREQUISITES

3 For vessels to which this standard is to be applied, calculations are to be submitted to show that in the full load condition:

(a) the reserve buoyancy is not less than 100%, and
(b) the trim is not more than 50% of the mean hydrostatic draft.

4 Where practicable, means should be provided for verifying the watertight integrity of the pontoons and for periodic inspection of the internal structure. Also, the pontoons should be:

(a) filled with a suitable closed-cell buoyant material, or
(b) subdivided into watertight compartments in such a manner as to ensure that adequate reserves of buoyancy and of transverse and longitudinal stability remain after flooding of any one compartment.

5 The design of the platform and its supporting structure should ensure than no pockets or horizontal surfaces are formed in which water can accumulate.

MINIMUM INTACT STABILITY

6 The intact stability characteristics of the vessel will be considered to be acceptable if the following relationship is shown, by calculation, experiment or a combination of both, to be satisfied in the full load condition:

where:
GoM = initial metacentric height (metres) at displacement D as determined by calculation or experiment.

PASSENGER HEEL FACTOR

7 Passenger freedom of movement is governed by the seating and access arrangements and is represented by a passenger heel factor, p.

8 The heel factor is defined as the transverse shift of the passenger centre of gravity, expressed as a fraction of the breadth B, caused by a general movement of passengers as follows:

(a) With all seats initially occupied, passengers on one side of the centre line stand and move as far as possible to the other side to fill all available space at the rate of 4 persons per square metre. If the area available on the "down" side is not sufficient to accommodate the required number ,then the heeling moment calculation should take account of the number accommodated on the "up" side.
(b) Passengers initially seated on the "down" side do not move, but are assumed to be standing adjacent to their seats.
(c) For the purpose of the calculation, passengers should be assumed to weigh the equivalent of 14 per tonne. Their centre of gravity should be taken to be 1 metre above deck.
(d) The passenger heel factor should be calculated from:
or taken as 0.15 whichever is greater. B is as previously defined.

LIMITING HEEL ANGLE

9 Because of the variety of pontoon shapes and configurations which are possible, freeboard is defined in angular rather than linear terms as illustrated in Figure 1.

10 The angular freeboard, Æ _F, is determined as the angle of heel at which the righting lever, GZ, reaches its maximum value, normally the angle at which the pontoon on the "down" side is just completely immersed.

11 The limiting heel angle, Æ _L, is taken as half the value of Æ _F or as 10° , whichever is less.

HEEL & TRIM TEST

12 An experiment shall be conducted simulating the movement of passengers plus 10% overload both in the longitudinal and transverse directions. This experiment will demonstrate the reserve of freeboard in the worst anticipated heeling and trimming conditions to the complete satisfaction of a marine surveyor.

Figure 1

Freeboard & Limited Heel Angle

Where Æ = Æ

STAB-6
STANDARD FOR INTACT STABILITY OF NON-PASSENGER SHIPS AND PASSENGER SHIPS CARRYING NOT MORE THAN 12 PASSENGERS ^

1 The provisions of this standard do not apply to the following:

(i) Ships built or converted for towing, and
(ii) Fishing vessels.

2 The following intact stability criteria should be complied with for non-passenger ships and for passenger ships carrying not more than 12 passengers.

(i) The area under the righting lever (GZ) curve should not be less than 0.055 metre-radians up to 30 degrees angle of heel, and not less than 0.09 metre-radians up to 40 degrees or the angle of downflooding if this angle is less than 40 degrees. Additionally, the area under the righting lever (GZ) curve between the angle of heel of 30 degrees and 40 degrees, or between 30 degrees and the angle of downflooding if this angle is less than 40 degrees, should be not less than 0.03 metre-radians.
(ii) The righting lever GZ should be at least 0.20 metres at an angle of heel equal to or greater than 30 degrees.
(iii) The maximum righting lever (GZ) should occur at an angle of heel preferably exceeding 30 degrees but not less than 25 degrees.
(iv) The initial metacentric height (GM) should not be less than 0.15 metres.

3 The criteria mentioned in Section 2 give minimum values but no maximum values. However, it is advisable to avoid excessive values as these might lead to acceleration forces which could be prejudicial to the ship, it’s complement, or it’s equipment.

4 Regard is to be paid to the possible adverse effects on stability when certain bulk cargoes are carried. In this connection attention should be paid to the "Code of Safe Practice for Solid Bulk Cargoes", TP 5761.

5. Ships carrying grain in bulk are to comply with the criteria in .Section 2 in addition to the stability requirements contained in the "Grain Cargo Regulations".

6 For ships loaded with timber deck cargoes and provided that;

(i) The cargo extends longitudinally between superstructures or, where there is no limiting superstructure at the after end, it extends at least to the after end of the aftermost hatchway;
(ii) The cargo extends transversely for the full beam of the ship after due allowance for the rounded gunwhale and/or securing the supporting uprights, not exceeding 4 per cent of the breadth of the ship; and
(iii) The cargo remains securely fixed at large angles of heel.

The following stability criteria should be complied with:

(a) the area under the righting lever (GZ) curve should not be less than 0.08 metre-radians up to 40 degrees or the angle of downflooding if this angle is less than 40 degrees.
(b) the maximum value of the righting lever (GZ) should be at least 0.25 metres..
(c) at all times during a voyage the metacentric height (GM) should be positive after correction for the free surface effects of liquids in tanks and, where appropriate, the absorption of water by the deck cargo and/or ice accretion on the exposed surfaces.
Additionally, in the departure condition the metacentric height (GM) should be not less than 0.10 metres.
(d) The conditions of loading should take account of:

1. in the arrival condition it should be assumed that the weight of the deck cargo has increased by 10 per cent due to water absorption, and
2. where it is anticipated that some formation of ice will take place an allowance should be made in the arrival condition for additional weight.

STAB-7
STABILITY CRITERIA FOR OFFSHORE SUPPLY VESSELS ^

CONTENTS

GENERAL

1 APPLICATION

2 DEFINITIONS

3 OPERATIONAL PRECAUTIONS AGAINST CAPSIZING

INTACT STABILITY

1 CALCULATION OF STABILITY CURVES

2 DOWNFLOODING POINT

3 STABILITY CRITERIA

4 LOADING CONDITIONS

5 ENVIRONMENTAL FACTORS

(a) Pipe Entrapped Water
(b) Ice Accretion

6 STABILIZING TANKS AND TRANSFER OF LIQUIDS

7 FREE SURFACE EFFECTS

8 SIMPLIFIED STABILITY INFORMATION

VESSELS ENGAGED IN TOWING

GENERAL ^

APPLICATION

1(i) Every new offshore supply vessel of 24 metres and over but not more than 100 metres in length is to comply with the provisions of this Standard.

(ii) An existing vessel which is modified to such an extent that, in the opinion of the Board, its stability has been adversely affected shall comply with the provisions of this Standard as far as is reasonable and practicable.

(iii) Where a ship other than an offshore supply vessel as referred in (i) is employed on similar services, the extent of compliance with the provisions of this Standard will be determined on the basis of hull forms, ship design and type of operation.

(iv) Provisions for offshore supply vessels carrying more than 12 industrial personnel are not included in this Standard.

(v) Offshore supply vessels used for specialized services such as diving, research, surveys, "stand-by purposes" etc., are to be considered by the Board on an individual basis taking into account the design and size of the ship, the number of personnel carried and the operational characteristics.

DEFINITIONS ^

2(i) "New ship" means a ship the keel of which is laid or construction of the hull of which is commenced, or a ship transferred from foreign registry to Canadian registry on or after September 1, 1985.

(ii) "Offshore supply vessel" means a vessel:

(a) which is primarily engaged in the transport of stores, materials and equipment for offshore installations; and
(b) which is designed with accommodation and bridge erections in the forward part of the vessel and an exposed cargo deck in the after part of the handling of cargo at sea.

(iii) "Offshore Installation" means a marine structure located at an offshore site.

OPERATIONAL PRECAUTIONS AGAINST CAPSIZING ^

3 In addition to the guidance data contained in Stability Standard STAB 1, the following notes to the master are to be included in the Stability Booklet as appropriate:

(i) Compliance with the stability criteria does not ensure immunity against capsizing regardless of the circumstances or absolve the master from his responsibilities. The master should therefore exercise prudence and good seamanship having regard to the season of the year, weather forecasts and the navigational zone and should take the appropriate action as to speed and course warranted by the prevailing circumstances.

(ii) Care should be taken to ensure that the cargo allocated to the vessel is capable of being stowed in such a way that compliance with the stability criteria can be achieved and if necessary the amount of cargo should be limited so as to allow any required ballast water to be taken.

(iii) Before a voyage commences care should be taken to ensure that the cargo and sizeable pieces of equipment have been properly stowed or lashed so as to minimize the possibility of both longitudinal and lateral shifting while at sea, under the effect of acceleration caused by rolling and pitching.

(iv) The arrangement of cargo stowed on deck should be such as to avoid any obstruction of the freeing ports or the areas necessary for the drainage of pipe stowage positions to the freeing ports. Freeing ports are not to be fitted with covers.

(v) The number of tanks containing slack liquids should be kept to a minimum.

(vi) Having regard to anticipated weather conditions, the adjustment in port loading is to be carried out at the discretion of the master to compensate for the likelihood of ice accretion/water on deck in accordance with Subsection 2(5) - Environmental Factors.

(vii) When the danger of ice formation arises immediate steps should be taken to remove the ice from large surfaces of the vessel, beginning with the upper structures. All the means for combating ice formation should be ready for use.

(viii) Hatches, doors, etc., which give access to the cargo deck should be kept closed during navigation, except when necessarily opened for the working of the vessel, and should always be ready for immediate closure and be clearly marked to indicate that these fittings are to be kept closed except .for access.

(ix) Shipowners bear the responsibility to ensure that adequate, accurate and up-to-date stability information for the master’s use is provided.

INTACT STABILITY ^

CALCULATION OF STABILITY CURVES

1(i) Because of the unique design characteristics of offshore supply vessels the conventional method of investigation of stability using Cross Curves which assume level trim and no change in trim during heeling over-estimates the results. Therefore, the Cross Curves of stability are to be prepared:

(a) taking into account the change of trim due to heel, i.e., on the basis of free trim during heeling;
(b) for a range of heeling angles at close intervals to enable the accurate calculation of the maximum righting lever; and
(c) for the design level. keel trim and for additional trimmed conditions where the operational range of trim is in the order of 0.01L or more.

(ii) Hydrostatic curves need only be prepared at design level keel trim unless the operational trim would have an adverse effect on stability.

(iii) The stability data are to clearly identify any of the following superstructures, deckhouses, etc., which may be taken into account in the calculations:

(a) enclosed superstructures complying with Schedule I, Section 3(9)(b) of the Load Line Regulations (Sea);
(b) the second tier of similarly enclosed superstuctures; and
(c) deckhouses on the freeboard deck, provided that they comply with the conditions for enclosed superstructures as referred to in (a).

(iv) Where deckhouses comply with the above conditions, except that no additional exit is provided to a deck above, such deckhouses should not be taken into account; however, any deck openings inside such deckhouses should be considered as closed even where no means of closure is provided.

(v) Deckhouses, the doors of which do not comply with the requirements of Schedule I, Section 12 of the Load Line Regulations (Sea) should not be taken into account; however, any deck openings inside the deckhouse are regarded as closed when their means of closure comply with the requirements of Schedule I, Sections 15, 17, or 18 of that Regulation.

(vi) Deckhouses on decks above the freeboard deck should not be taken into account but openings within them may be regarded as closed.

(vii) The stability data submitted are to clearly indicate the allowances for appendages such as shell thickness, bossings, the exclusion of thruster tunnels, diving pools, etc., considered in the calculations.

(viii) It is recommended that tabular data for stability curves be also included for reference.

DOWNFLOODING POINTS ^

2(i) A diagram, to be included in the Stability Booklet, is to indicate the downflooding points. That is, the position of openings which cannot be closed weathertight at sea, such as funnel exhaust and vents and other openings leading below deck or to enclosed superstructures.

(ii) The angle of immersion of these openings under free trim should be in excess of 30 degrees and such that the minimum criteria are met before immersion takes place.

(iii) Small openings such as those for passing wires or chains, tackle anchors and also holes of scuppers, discharge and sanitary pipes should not be considered as open if they submerge at an angle of inclination more than 30° ; but if they submerge at an angle of 30° or less; these openings should be assumed open if significant progressive flooding could occur.

STABILITY CRITERIA ^

3(i) The following are the stability criteria:

(a) the area under the righting lever (GZ) curve should not be less than 0.055 metre-radians up to Æ = 30° angle of heel and not less than 0.09 metre-radians up to Æ _f* if this angle is less than 40° . Additionally, the area under the righting lever (GZ) curve between the angles of heel of 30° and 40° or between 30° and Æ _f, if this angle is less than 40° , should not be less than 0.03 metre-radians;
(b) the righting lever GZ should be at least 0.20 m at an angle of heel equal to or greater than 30° ;
(c) the maximum righting arm should occur at an angle of heel preferably exceeding 30° but not less than 25° ; and
(d) the initial metacentric height GM_o should not be less than 0.15 m.

Where Æ = Æ

(ii) The following equivalent criteria are acceptable where a vessel’s characteristics render compliance with (a) impracticable:

(a) the area under the righting lever (GZ) curve should not be less than 0.070 metre-radians up to an angle of 15° when the maximum righting lever (GZ) occurs at 15° and 0.055 metre-radians up to angle of 30° when the maximum righting lever (GZ) occurs at 30° or above. ‘Where the maximum righting lever (GZ) occurs at angles of between 15° and 30° , the corresponding area under the righting lever curve should be:
0.055 + 0.001 (30° - Æ _max**) metre-radians;
(b) the area under the righting lever (GZ) curve between the angles of heel of 30° and 40° , or between 30 and Æ _f if this angle is less than 40° , should not be less than 0.03 metre-radians;
* Æ _f is the angle of heel in degrees at which openings in the hull, superstructure or deckhouse which cannot be closed weathertight immerse. In applying this criterion, small openings through which progressive flooding cannot take place need not be considered as open. (See Subsection 2(c).)
** Æ _max is the angle of heel in degrees at which the righting lever curve reaches its maximum.
(c) the righting lever (GZ) should be at least 0.20 m at an angle of heel equal to or greater than 30° ;
(d) the maximum righting lever (GZ) should occur at an angle of heel equal to not less than 15° ; and
(e) the initial transverse metacentric height (GMo) should not be less than 0.15 m. .

Where Æ = Æ

(iii) The minimum freeboard at the stern in all operating conditions shall not be less than 0.01L or the assigned summer freeboard, whichever is less.

(iv) The stability criteria mentioned above are minimum values; no maximum values are recommended but it is advisable to avoid excessive values, since these might lead to acceleration forces which could be prejudicial to the vessel, its complement, its equipment and the safe carriage of the cargo.

(v) The applicable stability criteria used is to be included in the Stability Booklet for reference.

LOADING CONDITIONS ^

4(i) For the purpose of assessing in general whether the stability criteria are met, stability data are to be submitted for the main loading conditions intended by the owner in respect of the vessel’s operations. As a minimum, in addition to the lightship condition, the following loading conditions are to be submitted:

(a) vessel in fully loaded departure condition with cargo distributed below deck and with cargo specified by position and weight on deck, with 100% stores and fuel, corresponding to the worst service condition in which all the relevant stability criteria are met;
(b) vessel in fully loaded arrival condition with cargo as specified in (a), but with 10% stores and fuel;
(c) vessel in ballast departure condition, without cargo but with 100% stores and fuel;
(d) vessel in ballast arrival condition without cargo and with 10% stores and fuel remaining; and
(e) vessel in the worst anticipated operating condition or conditions.

(ii) The assumptions for calculating the loading conditions are to be as follows:

(a) if the vessel is fitted with cargo tanks, the fully loaded conditions of (i)(a) and (i)(b) are to be modified, assuming first the cargo tanks full and then the cargo tanks empty;
(b) if in any loading condition water ballast is necessary, additional diagrams should be calculated, taking into account the water ballast, the quantity and disposition of which should be stated in the stability information; and
(c) in all cases when deck cargo is carried a realistic stowage weight should be assumed and stated in the stability information, including the height of the cargo and its centre of gravity.

(iii) A diagram showing the maximum permissible deck load (tonnes/m²) along the cargo deck is to be included in the Stability Booklet.

ENVIRONMENTAL FACTORS ^

5(i) Because of the adverse effect on stability, due allowances are to be made in the loading conditions for the anticipated additional weight as a result of water entrapped in and around pipe deck cargo; and considering the season of the year and the navigational zone where the vessel may operate, the additional weight from ice accretion is to be similarly treated.

(ii) In addition to the minimum loading conditions, the worst operating conditions are to be evaluated as follows:

(a) included in the Stability Booklet:

1. Case No. 1
Operating conditions representing the vessel loaded such that where pipe deck cargo water entrapment is encountered, seasonal load line marks will not be submerged.

2. Case No. 2
Operating conditions representing the vessel loaded such that where ice accretion is encountered, seasonal load line marks will not be submerged.

(b) not included in Stability Booklet but submitted for review:

1. Case No. 3
Non-operating conditions representing the vessel fully loaded to the seasonal load line mark and the additional weight (overload) from pipe deck cargo water entrapment.

2. Case No. 4
Non-operating conditions representing the vessel fully loaded to the seasonal load line mark and the additional weight (overload) from ice accretion.

(iii) The criteria and assumptions taking into account the environmental factors are to be as follows:

(a) Pipe entrapped water

Where pipes are carried on deck, a quantity of trapped water equal to a certain percentage of the net volume of the pipe deck cargo should be assumed in and around the pipes:

1. the net volume should be taken as the internal volume of the pipes, plus the volume between the pipes;
2. this percentage of the net volume should be 30 if the freeboard amidships is equal to or less than 0.015L and 10 percent if the freeboard amidships is equal to or greater than 0.03L;
3. for intermediate values of freeboard amidships the percentage may be obtained by linear interpolation; and
4. for the purpose of calculation of the percentage of net volume, the summer freeboard amidships should be used.
5. Plugged pipes are not to be accepted as a means of reducing the amount of entrapped water.
6. No free surface allowance need be made for water entrapped in pipe deck cargo.
7. A sample calculation should be provided to confirm the amount of entrapped water shown in the loading condition. Where pipe deck cargoes of various types and diameters may be carried, information should be provided in the form of calculations, curves or tables to indicate the quantity of entrapped water to be assumed in each case.
8. Relevant conditions should be clearly marked ‘pipe deck cargo

(b) Ice Accretion

For vessels operating in areas where severe ice accretion may be expected - the areas North of latitude 43° N bounded in the West by the North American Coast and the East by the rhumb line running from latitude 43° N longitude 48° W to latitude 63° N longitude 28° W and hence along longitude 28° W - the following ice accretion loads are to be used in the stability calculations:

1. 54 kg/m² of total deck area, including the superstructure and deckhouse tops that are exposed to the weather;
2. 37 kg/m² of area exposed to the weather in the case of the superstructure and deckhouse fronts, and the deckhouse sides and bulwarks including the area of the deckhouse sides and bulwarks on both sides of the vessel except that only the inboard surfaces shall be included in computing the bulwark areas;
3. 78 kg/m² of area, taking into consideration overall block dimensions, in the case of the guardrails and stanchions, hatch coamings, companionways and ship fittings exposed to the weather; and
4. 48 kg/m² in the case of rigging, masts, derricks and similar high objects measured to a height of 6.1 m above the main weatherdeck.
5. Relevant conditions should be clearly marked ‘ice accretion’.

For vessels operating in the "north" - all sea areas North of the North American continent, West of the area defined above - a reduced ice accretion load may be considered by the Board where the owner demonstrates that lesser loads are encountered.

STABILIZING TANKS AND TRANSFER OF LIQUIDS ^

6(i) Limitations on the use of stabilizing tanks (when fitted) are to be observed:

(a) loading conditions where the stabilizing tank is in use should be included;
(b) guidance should be given concerning the operation of the stabilizing tank including appropriate liquid levels and any restrictions on its use in certain sea conditions;
(c) the free surface of the liquid in the tank should be taken into account unless the particular condition is marked ‘Stabilizing tank empty’ (or ‘pressed up’);
(d) the free surface used should be that corresponding to the inertia of the maximum water plane of the tank with the ship upright; and
(e) the operating position of the dump valves or other means of emptying the tank(s) should be clearly indicated.

(ii) Where, due to burning of fuel oil, it is essential to add water ballast during a voyage to maintain an adequate standard of stability, attention should be drawn to this in the appropriate condition.

(iii) The liquid ballast used in an oil tank must be discharged in accordance with the Oil Pollution Prevention Regulations or the Arctic Shipping Pollution Prevention Regulations.

FREE SURFACE EFFECTS ^

7(i) For all loading conditions, the initial metacentric height and the statical stability curves are to be corrected for the effect of liquids in tanks.

(ii) When liquid cargo is to be discharged or a tank is to be ballasted at sea, as soon as pumping commences a full free surface will exist on those tanks being pumped and the effect of this on the stability is to be taken into account.

(iii) Tanks which are taken into consideration when determining the effect of liquids on the stability at all angles of inclination should include single tanks or combinations of tanks for each kind of liquid (including those for water ballast) which according to the service conditions can simultaneously have free surfaces.

SIMPLIFIED STABILITY INFORMATION ^

8(i) To enable the master to assess the stability of the vessel and verify whether the stability is sufficient in all loading conditions differing from loading conditions specified elsewhere, information in the form of tables or diagrams is to be provided as follows:

(a) the data may take the form of a diagram or tables giving maximum KG, minimum GM or maximum deadweight moment values relative to draught or displacement, according to the owner’s general practice. In company fleets it is recommended that a single method be utilized throughout;
(b) the scale of draughts or displacements in the diagram or tables should be extended to take account of the addition of entrapped water to the full load displacement where pipe deck cargoes may be carried or of the effect of ice accretion;
(c) particular effort should be made to facilitate the use of this information by clear and straight-forward presentation; and
(d) a sample calculation showing the use of the deadweight moment diagram or equivalent should be provided, including the treatment of free surface. Derivation of the effective deadweight moment or equivalent should also be shown on each condition sheet.

VESSELS ENGAGED IN TOWING ^

1(i) Where a vessel is also engaged in towing operations, the additional stability requirements specified in Part VIII, Section 104 of the Hull Construction Regulations are to be complied with.

(ii) The stability criteria in Standard STAB 3 or as stated in this Standard may be used, provided the initial metacentric height GM_O for any particular towing condition is not less than 0.55 m.

(iii) A vessel engaged in towing operations should not carry deck cargo, except that a limited amount, properly secured, which would neither endanger the safe working of the crew on deck nor impede the proper functioning of the towing equipment, may be accepted.

(iv) While towing is underway the vessel must carry only the crew normally assigned for such operations.

STANDARD: STAB 8
INTERIM STANDARD FOR THE INTACT STABILITY OF UNMANNED CARGO BARGES^

1 The provisions of this standard are applicable to unmanned cargo barges that:

(i) are required by standard LOAD 2 to be assigned load lines; and
(ii) are constructed after 1 September 1977.

2 This standard does not apply to Crane, Derrick or Hopper Barges.

3 Except where otherwise exempted by the Board, the owner of a new barge shall:

(i) arrange to have an inclining experiment carried out in the presence of and to the satisfaction of a marine surveyor;
(ii) submit to the Board the developed stability data for the operating conditions of the barge, including the light, loaded and worst operating conditions; and
(iii) include in the stability submission the basic data required by Section 1 of standard STAB 1.

4 Except where otherwise provided in Section 5 of this standard, the intact transverse stability of the barge shall be based upon a minimum area under the GZ curve up to the angle of maximum GZ, or to the angle of downflooding if this be less, of not less than 0.08 metre-radians.

5 Where the vertical centre of gravity of the cargo is below the deck at side, the required transverse stability may be determined in terms of the metacentric height in metres. The initial metacentric height (GM) at any draft must not be less than that given by the following formula:

where
k = .15
B = Beam in metres
f_e = Effective freeboard (f + f_a) in metres, where

f = freeboard to the deck at side in metres;
f_a = additional freeboard allowance for barges having a structural watertight trunk.

l = length of trunk in metres
L = overall length of barge in metres
b = breadth of trunk in metres
h = trunk height at side in metres

6 The intact longitudinal stability of the barge is to be determined in terms of the minimum longitudinal metacentric height (GM₁) within the range of operating drafts and is not to be less than that given by the following formula:

where
L = overall length of barge in metres
d = draft in metres.

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