11 Stability

 11.1 All Vessels

11.1.1 General

11.1.1.1 The standard of stability to be achieved by a new vessel should be dependent on the maximum number of persons permitted to be carried and the intended area of operation. For the purposes of this code a person is taken to weigh 82.5Kg.

11.1.1.2 The following vessels are required to be provided with a stability information booklet which is approved by the Certifying Authority (and should refer to section 11.3):

• .1 vessels operating in Category 0 or 1; or

• .2 vessels carrying 16 or more persons; or

• .3 vessels carrying cargo greater than 1,000kg; or

• .4 vessels fitted with a lifting device as defined in 11.6; or

• .5 vessels towing where the towed object's displacement is greater than twice the displacement of the towing vessel. See section 11.7 (and 25.2); or

• .6 seagoing pilot boats;

• For guidelines on the minimum Form and Content of a stability book and guidance on the stability assessment see 11.8.4.

11.1.1.3 A vessel other than one for which 11.1.1.2 applies should either comply with section 11.3 or be subject to a simplified assessment of stability in 11.4, and is not required to be provided with approved stability information.

11.1.1.4 In winter there is a risk of icing up in more Northern waters, including the North Atlantic, the sea areas north of Europe, Asia, and the northern and north-eastern coasts of North America (as far south as 45^o North), The Bering and Okhost Seas and the Straits of Tartary, as well as the Southern Ocean south of 60^o South.

Vessels operating in these areas should either have stability booklets including conditions with icing allowances approved by the Certifying Authority, or avoid operating in these areas in winter (1 November to 30 April inclusive for northern areas, 15 April to 15 October for southern). Guidance on appropriate icing allowances may be found in MGN281 Annex 1 Part 1 section 21. Vessels that are not approved to operate in icing areas should have this noted in their approved stability booklet and certificates.

11.1.1.5 For stability requirements for an inflatable vessel or a vessel fitted with a buoyant collar, see section 11.5. For stability requirements for a decked vessel fitted with a lifting device, see section 11.6 and for a decked vessel engaged in towing, see section 11.7.

11.1.1.6 All vessels, other than those vessels deemed unsuitable for carriage of the booklet by the Certifying Authority (i.e. vessels with no cabin or shelter), are required to carry the relevant copy of the MCA Stability Guidance Booklet (Motor). Where a booklet is not carried on board a copy is to be made available to crew ashore. These booklets are available free of charge from the MCA or Certifying Authority. Although they contain generic safety advice, the stability and freeboard data already generated during the survey process should be appended to the booklet in the relevant section. It is the responsibility of the Certifying Authority to supply this information, and the owner/managing agent is to ensure this data is included.

11.2 Damage Survivability

11.2.1 This section applies to all vessels carrying 16 or more persons and those operating in Area Category 0 and 1, with 7 or more persons, subject to minimum safe manning levels being agreed by the Certifying Authority.

11.2.1.2 Multihull vessels should be fitted with engine rooms that are separated by a watertight bulkhead.

11.2.1.3 In assessing survivability, the following standard permeabilities should be used:-

Other methods of assessing floodable volume may be considered, to the satisfaction of the Certifying Authority.

11.2.1.4 In assessing survivability the vessel should meet the damage stability criteria for one of two methods. The first (denoted Option 1) considers minor hull damage scenarios with limited equilibrium trim and heel angles after damage. This has historically been used by monohulls and some catamarans. The second method (denoted Option 2) considers minimum length single compartment damage scenarios with more onerous residual stability, combined with increased allowable equilibrium angles after damage. This Option 2 has been developed to address particular stability issues raised by low waterplane area vessels with deep hulls which typically have large intact freeboards such as catamarans.

11.2.2 Damaged Stability, Option 1

11.2.2.1 Vessels should be so arranged that after minor hull damage or failure of any one hull fitting in any one watertight compartment, it will satisfy the residual stability criteria below. This may be achieved by fitting water-tight subdivision or alternative methods to the satisfaction of the Certifying Authority. Minor damage should be assumed to occur anywhere in the vessel but not on a watertight subdivision.

11.2.2.2 In the damaged condition, the residual stability should be such that:

• .1 the angle of equilibrium does not exceed 7 degrees from the upright,

• .2 the resulting righting lever curve has a range to the downflooding angle of at least 15 degrees beyond the angle of equilibrium,

• .3 the maximum righting lever within that range is not less than 100mm,

• .4 the area under the curve is not less than 0.015 metre radians.

• .5 this damage should not cause the vessel to float at a waterline less than 75mm from the weatherdeck at any point.

11.2.3 Damaged Stability, Option 2 :

11.2.3.1 Damaged Stability should be calculated with any one compartment flooded. The extent of damage should be:

• .1 A damage length of 10% Length should be considered in the calculations. Where the distance between two transverse watertight bulkheads is less than the damage length, one or more bulkheads should be disregarded in the damage stability calculations, such that the compartment length considered is equal or above the damage length. The damage length given above need not be applied within the forepeak and aftpeak compartment/s.

• .2 The transverse extent of damage should be up to and including the centreline of the vessel. A catamaran need only be considered to have damaged the full extent of one hull, provided the two hulls are totally independent, and that there are not cross connections that, if damaged would flood the other hull and wet deck compartment. See Figure 11.2.3.1. Trimarans should be considered to have damaged wing and centre compartments up to the centre line of the vessel.

• .3 The vertical extent of damage should be taken for the full vertical extent of the vessel, and

• .4 The shape of the damage should be assumed to be a rectangular block.

• Watertight compartments aft of the transom that do not form part of the hull length and do not extend below the design waterline (such as overhangs and appendages) need not be considered in the damaged length assessment.

• If any damage of lesser extent than that required in 12.2.3 would result in a more severe condition, such damage shall be assumed.

• Figure 11.2.3.1

11.2.3.2 Spaces that are normally occupied at sea are to be provided with at least two independent means of escape preferably at opposite sides / ends of the superstructure that allow positive freeboard independent of its location.

11.2.3.3 Any weathertight doors or openings leading from undamaged spaces, that are normally occupied at sea, to the weatherdeck should be regarded as downflooding points for the purposes of the damage stability calculation.

11.2.3.4 A damage scenario which considers damage to all the forward compartments of each hull of a multihull that fall within 5%L from the forward extremity of the watertight hull measured on vessel centreline shall be assessed to ensure that these do not result in a more onerous damaged stability condition.

11.2.3.5 In the damaged condition, the residual stability and damaged waterline should be such that:

• 1. the angle of equilibrium (combined heel and trim) does not exceed 15 degrees from the upright, sufficient non-slip deck surfaces and suitable holding points e.g. rails, grab bars etc., are provided along escape routes and accessing escape routes. Additionally, practical consideration should be given to the means of accessing, launching and embarking liferafts (see also 13.2.1.1.4).

• 2. the resulting righting lever curve has a range to the downflooding angle of at least 20 degrees beyond the angle of equilibrium,

• 3. the maximum righting lever within that range is not less than 200mm, and

• 4. the area under the curve is not less than 0.045 metre radians.

• 5. the final equilibrium waterline should be below the lowest point of any opening which is not closed by an approved watertight closure. This includes air pipes, hatch covers, doors and any other weathertight closure.

• 6. this damage should not cause the vessel to float at a waterline less than 75mm from the weatherdeck. This may be relaxed on application to the Administration, provided that all of the following are met:

  • .1 the immersed portion of the weather deck is not a life saving appliance storage area;

  • .2 it is not part of an assembly station, evacuation point or part of an evacuation route; and

  • .3 that no more than 10% L of the deck edge on the damaged side is immersed in the process, and that negative freeboard measured from the deck edge is limited to a maximum of 300 mm.

11.3 Intact Stability: Vessels Requiring a Stability Information Booklet (see 11.1.1.2)

11.3.1 The lightship weight, vertical centre of gravity (KG) and longitudinal centre of gravity (LCG) of a monohull vessel should be determined from the results of an inclining experiment. Guidelines for the procedure on carrying out of an inclining experiment can be found in the Instructions for the Guidance of Surveyors on Load Line (MSIS 1), Part 6^footnote. Where it is considered impracticable to adopt the procedures given in MSIS1 any deviations to the number of pendulums should be agreed by the Certifying Authority and consideration should be given by the Certifying Authority to conducting the test more than once. There should be a minimum of 8 weight movements. The use of an electronic inclinometer^footnote is an acceptable alternative to the second pendulum if it is calibrated (where this provision exists) and readings are recorded.

11.3.2 An inclining experiment may not produce satisfactory results for vessels such as multihulls where the VCG is less than one third of the GM over the range of standard operating conditions. In such cases the LCG should be obtained by displacement check or by weighing with two gauges (e.g. one fore and one aft). The lightship VCG may be obtained by an accurate weight estimate calculation with a suitable margin added, in no case should the lightship VCG be taken below main deck level. Details of the estimated lightship weight, LCG and VCG should be submitted to the Certifying Authority at an early stage for verification.

11.3.3 The lightship weight may include a margin for growth, up to 5% of the lightship weight at the discretion of the Certifying Authority, positioned at the LCG and vertical centre of the weather deck amidships or the lightship KG, whichever is higher. (The lightweight margin should not be used in practice to increase maximum cargo-deadweight.)

11.3.4 Curves of static stability (GZ curves) should be produced for:-

• .1 Loaded departure, 100% consumables;

• .2 Loaded arrival, 10% consumables;

• .3 Anticipated service conditions; and

• .4 Conditions involving lifting appliances (when appropriate).

11.3.5 In addition, where the vessel is approved to carry cargo more than 1,000 kg, simplified stability information in the form of Maximum KG data should be provided, including a worked example to illustrate its use.

11.3.6 Maximum free surface moments should be included within the Loaded Departure condition, and as a minimum, factored according to tank percentage fill for all other conditions.

11.3.7 Generally, buoyant structures intended to increase the range of positive stability should not be provided by fixtures to superstructures, deckhouse, masts or rigging.

11.3.8 The curves of static stability for the loaded conditions should meet the following criteria:

• .1 the area under the righting lever curve (GZ curve) should be not 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 angle of heel or the angle of downflooding if this angle is less;

• .2 the area under the GZ curve between the angles of heel of 30 and 40 degrees or between 30 degrees and the angle of downflooding if this less than 40 degrees, should be not less than 0.03 metre-radians;

• .3 the righting lever (GZ) should be at least 0.20 metres at an angle of heel equal to or greater than 30 degrees;

• .4 the maximum GZ should occur at an angle of heel of not less than 25 degrees; and

• .5 after correction for free surface effects, the initial metacentric height (GM) should not be less than 0.35 metres.

11.3.9 If a vessel with broad beam in relation to depth, such as a catamaran or multihull type does not meet the stability criteria given in section 11.3.8, the vessel should meet the following criteria:-

• .1 the area under the righting lever curve (GZ Curve) should not be less than 0.085 metre radians up to θ_GZmax when θ_GZmax = 15º and 0.055 metre-radians up to θ_GZmax when θ_GZmax = 30º.
• When the maximum righting lever, GZmax, occurs between θ = 15º and θ = 30º the required area under the GZ Curve up to θ_GZmax should not be less than:
• A = 0.055 + 0.002(30º - θ_GZmax) metre-radians
• where: θ_GZmax is the angle of heel in degrees at which the righting lever curve reaches its maximum.
• .2 the area under the righting lever curve between θ = 30º and θ = 40º or between θ = 30º and the angle of downflooding θf, if this angle is less than 40º, should not be less than 0.03 metre-radians;
• .3 the righting lever GZ should not be less than 0.2 metre at an angle of heel of 30 degrees;
• .4 the maximum righting lever should occur at an a angle not less than 15 degrees; and
• .5 the initial metacentric height GM_o should not be less than 0.35 metre.

11.3.10 Barges or pontoons with the following characteristics may use the stability criteria below (taken from the IMO International Code of Intact Stability, 2008) in lieu of either 11.3.8 or 11.3.9:

• a) Vessel is non self-propelled; and
• b) Vessel is un-manned; and
• c) Vessel is carrying deck cargo only; and
• d) Vessel had a block coefficient of 0.9 or greater; and
• e) Vessel has a breadth to depth ratio of more than 3; and
• f) Vessel has no hatchways in the deck except small manholes closed with gasketted covers.

• (i) The area under the righting lever curve up to the angle of maximum righting lever should not be less than 0.08 metre-radians.
• (ii) The static angle of heel due to a uniformly distributed wind load of 540 Pa (wind speed 30 m/s) should not exceed an angle corresponding to half the freeboard for the relevant loading condition, where the lever of the wind heeling moment is measured from the centroid of the windage area to half the draft.
• (iii) The maximum range of stability should be at least 20 degrees.

11.3.11 For any newly built ship with known differences from a sister ship, a detailed weights and centres calculation to adjust the lead ship’s lightship properties should be carried out.

The lightship properties for the new ship may be assessed by carrying out a lightweight check. The deviation in lightship displacement should not exceed 2% of the lightship displacement of the sister ship. In addition, the deviation in lightship LCG should not exceed 1% of the LBP of the sister ship LCG. Where the deviation is within these limits the actual lightship weight and LCG derived from the lightship check should be used in conjunction with the higher of either the lead ship’s VCG or the calculated value.

Subject to the agreement of the Certifying Authority, the requirement for an inclining test may be dispensed with in cases where the margins on intact and damage stability are sufficient to permit minor changes in VCG, e.g. a minimum of 10% margin on intact and damage stability criteria requirements, and the weight difference can be accurately assessed to the satisfaction of the Certifying Authority. In addition the vessel must be similar in all respects and the Certifying Authority must be satisfied with the procedure and accuracy of the original inclining. Small modifications, for which an accurate assessment by calculation may be taken into account, are acceptable. Where lightship particulars of a vessel are based on a lightship check the inclining report for the ‘lead’ sister vessel should be included in the stability information of the subsequent sister/s.

Where the deviation exceeds either of these limits, an inclining test should be carried out.

A sister ship is defined as a ship built under the survey of a Certifying Authority, by the same yard from the same plans and within five years of the new ship.

11.4 Intact Stability: Vessels Complying with Simplified Stability Assessment (see 11.1.1.3)

11.4.1 A vessel should be tested in the fully loaded conditions (which should correspond to the freeboard assigned) to ascertain the angle of heel and the position of the waterline which results when all persons which the vessel is to be certificated to carry are assembled along one side of the vessel (the helmsman may be assumed to be at the helm). Each person may be substituted by a mass of 82.5kg for the purpose of the test.

11.4.2 The vessel will be judged to have an acceptable standard of stability if the test shows that;

• .1 the angle of heel does not exceed 7 degrees and in the case of a vessel with a watertight weather deck extending from stem to stern, as described in section 4.1.1, the freeboard to deck is not less than 75mm at any point; or

• .2 if unable to meet the criteria in 11.4.2.1 the angle of heel may exceed 7 degrees, but should not exceed 10 degrees, if the freeboard in the heeled condition is in accordance with that required by section 12 in the upright condition.

11.4.3 Additionally for vessels over 15 metres in length the heeling moment applied during the test described in 11.4.1 should be calculated. Using the formula below the vessel should attain a value of initial GM not less than 0.5m if using an estimated displacement or 0.35m if the displacement of the vessel is known and can be verified by the Certifying Authority.

11.4.3.1 Where displacement of the vessel is known and can be verified:

• where HM = No. of persons x weight per person (kg) x distance from CL (m)

• θ = heel angle (degrees) obtained from the test defined in 11.4.1 and 11.4.2

• Δ = full displacement including passengers, industrial personnel, crew, equipment and cargo (kg)

• GM must exceed 0.35m

• Note: Weight per person must be taken as no less than 82.5 kg Cargo weight must not exceed 1,000 kg

11.4.3.2 Where displacement of the vessel is estimated:

• where HM = No. of persons x weight per person (kg) x distance from CL (m)

• θ = heel angle (degrees) obtained from the test defined in 11.4.1 and 11.4.2

• Δ = full displacement including passengers, industrial personnel, crew, equipment and cargo (kg)

• Δ = C_B x LOA x Moulded Beam x Load Draught x 1.025

• The Certifying Authority is to approve the value of C_B used; in the case of doubt C_B of 0.9 can be used (for pontoons etc.) or 0.67 for others.

• GM must exceed 0.50m

• Note: Weight per person must be taken as no less than 82.5 kg

  Cargo weight must not exceed 1,000 kg

11.4.4 For vessels carrying a combination of passengers, industrial personnel, activity related equipment and cargo, for which the cargo element does not exceed 1000kg (see definitions), the test defined in section 11.4.1 should be carried out with the maximum permissible weight, and additionally with passenger plus industrial personnel weight only. For the purposes of these tests the cargo and activity related equipment may be assumed to be retained at its normal stowage position.

11.4.5 In all cases, the maximum permissible weight derived from the tests conducted should be recorded on the certificate. Vessel loading will be restricted by the position of the freeboard mark and the maximum permissible weight, and thus for the purposes of this test, attention should be paid to any activity related equipment where this may be significant, e.g. diving equipment.

11.4.6 Vessels complying with ISO 12217 Part 1 ‘Small craft - Stability and buoyancy assessment and categorisation - Non-sailing boats of hull length greater than or equal to 6 metres’ (see Appendix 13), assessed using any Option of section 5.3 – `Test and calculations to be applied’, may as an alternative, after verification of the stability assessment by the Certifying Authority, be assigned an area of operation in accordance with the following Table 11.4:

Table 11.4

11.5 Stability and Survivability of Open Boats, Inflatable Boats, Rigid Inflatable Boats or Boats Fitted With a Buoyant Collar

11.5.1 General

11.5.1 These requirements apply to an open boat, inflatable boat, rigid inflatable boat or those vessels with a buoyant collar. Unless a boat to which the Code applies is completely in accordance with a standard production type, for which the Certifying Authority is provided with a certificate of approval for the tests which are detailed below, the tests required to be carried out on a boat floating in still water are shown below. In all cases, the maximum permissible weight derived from the tests conducted should be recorded on the certificate. Vessel loading will be restricted by the maximum permissible weight, and thus for the purposes of this test, attention should be paid to any activity related equipment where this may be significant, e.g. diving equipment.

11.5.2 Stability Tests

11.5.2.1 The tests should be carried out with all the vessel’s equipment, fuel, cargo, activity related equipment (e.g. diving equipment) and number of persons for which it is to be certificated, on-board. The engine, equipment and cargo may be replaced by an equivalent mass. Each person may be substituted by a mass of 82.5kg for the purpose of the tests.

11.5.2.2 The maximum number of persons for which a boat is certified should be crowded to one side, with half this number seated on the buoyancy tube / gunwale. This procedure should be repeated with the persons seated on the other side and at each end of the open boat, inflatable boat, rigid inflatable boat or vessel with a buoyant collar. For the purposes of these tests the cargo, or equivalent alternative mass, should be retained at its normal stowage position. In each case the freeboard to the top of the buoyancy tube / gunwale should be recorded. Under these conditions the freeboard should be positive around the entire periphery of the boat.

11.5.3 Damage Tests – Inflatable Boats

11.5.3.1 The tests should be carried out with all of the vessel’s equipment, fuel, cargo, activity related equipment (e.g. diving equipment) and the number of persons for which it is to be certificated, on board. The engine, equipment and cargo may be replaced by an equivalent mass. Each person may be substituted by a mass of 82.5kg for the purpose of the tests.

11.5.3.2 The tests will be successful if, for each condition of simulated damage, the persons for which the inflatable boat or rigid inflatable boat is to be certificated are supported within the inflatable boat or rigid inflatable boat. The conditions are:

• .1 With forward buoyancy compartment deflated (both sides if appropriate);

• .2 With the entire buoyancy compartment, from the centreline at the stem to the transom, on one side of the inflatable boat or rigid inflatable boat deflated.

11.5.4 Swamp Test

11.5.4.1 It should be demonstrated by test or by calculation that a vessel, when fully swamped, is capable of supporting its full outfit of equipment, cargo and activity related equipment, the total number of persons and equivalent mass of cargo for which it is to be certificated, and a mass equivalent to its engine and a full tank of fuel, with a reserve of buoyancy of 10%.

11.5.4.2 In the swamped condition the open boat, inflatable boat, rigid inflatable boat or vessel with a buoyant collar, should not be seriously deformed.

11.5.4.3 An adequate means of draining the boat should be demonstrated at the conclusion of this test.

11.5.5 Person Recovery Stability Test

11.5.5.1 Two persons should recover a third person from the water into the vessel. The third person should feign to be unconscious and be back towards the inflatable boat or rigid inflatable boat so as not to assist the rescuers. The third person should also, where the water temperature in the operating region requires it, wear suitable anti-exposure clothing (e.g. dry suit or immersion suit). Each person involved should wear an approved lifejacket. The vessel should remain stable throughout the operation, and should not capsize.

11.6 Stability of Vessels Fitted with a Deck Crane or Other Lifting Device

11.6.1 For the purposes of section 11 only, a lifting device does not include a person retrieval system, the vessel’s own anchor handling equipment, or davits for tenders, where judged by the Certifying Authority not to have a detrimental effect on the stability of the vessel.

11.6.2 Reference should be made to section 25.4 for requirements for safety standards other than stability for a vessel fitted with a deck crane or other lifting device.

11.6.3 A vessel fitted with a deck crane or other lifting device should be a decked vessel (or assessed in accordance with section 4.1.3.2) and comply with the general requirements of section 11, which are appropriate to it.

11.6.4 In addition, with the vessel in the worst anticipated service condition for lifting operations, compliance with the following criteria should be demonstrated by a practical test or by calculations:

• .1 With the crane or other lifting device operating at its maximum load and heeling moments, with respect to the vessel, the angle of heel generally should not exceed 7 degrees or that angle of heel which results in a freeboard to deck edge anywhere on the periphery of the vessel of 250mm, whichever is the lesser angle (consideration should be given to the operating performance of cranes or other lifting devices of the variable load-radius type and the load moment with respect to the vessel for lifting devices situated off centreline).

• .2 When an angle of heel greater than 7 degrees but not exceeding 10 degrees occurs, the Certifying Authority may accept the lifting condition providing that all the following criteria are satisfied when the crane or other lifting device is operating at its maximum load moment;

  • .1 the range of stability from the angle of static equilibrium to downflooding or angle of vanishing stability, whichever is the lesser, is equal to or greater than 20 degrees;

  • .2 the area under the curve of residual righting lever, up to 40 degrees from the angle of static equilibrium or the downflooding angle, if this is less than 40 degrees, is equal to or greater than 0.1 metre-radians;

  • .3 the minimum freeboard to deck edge at side , measured at A.P. and F.P. throughout the lifting operations should not be less than half the assigned freeboard to deck edge at side amidships. For vessels with less than 1000mm assigned freeboard to deck edge amidships the freeboard at A.P. or F.P. at deck edge should not be less than 500mm; and

  • .4 the freeboard to deck edge anywhere on the periphery of the vessel is at least 250mm.

11.6.5 Information and instructions to the Master on vessel safety when using a deck crane or other lifting device should be included in the Stability Information Booklet. The information and instructions should include;

• .1 the maximum permitted load and outreach which satisfy the requirements of section 11.6.2, or the Safe Working Load (SWL), whichever is the lesser (operating performance data for a crane or other lifting device of variable load-radius type should be included as appropriate);

• .2 details of all openings leading below deck which should be secured weathertight; and

• .3 the need for all personnel to be above deck before lifting operations commence.

11.6.6 Requirements for a lifting system which incorporates counterbalance weight(s), counter ballasting or a vessel that cannot comply with the requirements of section 11.6.4 but is otherwise deemed to have adequate residual stability may be specially considered by the Administration. See also 25.4.1.8.

11.6.7 Vessels fitted with stern (or bow) gantries or fitted with lifting devices over the ship’s side are not required to have a stability book, having consideration for the exclusions in 11.6.1, provided it can be demonstrated to the satisfaction of the Certifying Authority that:

• .1 The lifting device is not of a variable load radius type (e.g. knuckle boom crane), and

• .2 The SWL of the lifting device does not exceed 1% of the vessel’s displacement, or 200 kg whichever is the greater. Where the displacement of the vessel is not known it may be estimated from the following formula:

• Δ = C_B x LOA x Moulded Beam x Load Draught x 1.025

• The Certifying Authority is to approve the value of C_B used; in the case of doubt C_B of 0.9 can be used (for pontoons etc.) or 0.67 for others, and

• .3 A practical test is conducted with the gantry/lifting device at the maximum rated load/radius, when the crew are represented in their operational positions to operate the crane to handle the load, which demonstrates the maximum heel angle of 4 degrees and minimum heeled freeboard of 250mm around the periphery of the vessel are achieved.

11.6.8 Vessels that are fitted with a stern (or bow) gantry / centre line lift that are required to have a stability booklet (e.g. those not excluded by 11.6.7) should meet the following criteria. All the following criteria should be satisfied when the A frame or other lifting device is operating at its maximum vertical moment;

• .1 the range of stability from the angle of static equilibrium to downflooding or angle of vanishing stability, whichever is the lesser, is equal to or greater than 15 degrees;

• .2 the area under the curve of residual righting lever, up to 40 degrees or the downflooding angle, if this is less than 40 degrees, is equal to or greater than 0.10 metre-radians;

• .3 GM should be positive and greater than or equal to 0.05m.

• .4 the minimum freeboard to deck edge at bow, side or transom, measured at A.P. and F.P. throughout the lifting operations should not be less than half the assigned freeboard to deck edge at side amidships or at the transom. For vessels with less than 1000mm assigned freeboard to deck edge amidships the freeboard at A.P. or F.P. at deck edge should not be less than 500mm; and

• .5 the freeboard to deck edge anywhere on the periphery of the vessel is at least 250mm.

11.7 Stability of Vessels Engaged in Towing

11.7.1 Vessels engaged in towing that are not required to have a stability information booklet (section 11.1.1.2.5) and those that are required to have a stability information booklet should meet the requirements of this section. Reference should be made to section 25.2 for requirements for safety standards other than stability for a vessel engaged in towing.

11.7.2 Generally, a vessel engaged in towing should be a decked vessel (or assessed in accordance with section 4.1.2.2) and comply with the general requirements of section 11 which are appropriate to the vessel.

11.7.3 The danger to safety of deck edge immersion makes an open boat (other than those assessed in accordance with section 4.1.2.2) unsuitable for towing other vessels or floating objects. Open boats may only tow vessels of less than twice their displacement in harbour areas and in area categories 5 and 6, in favourable weather.

11.7.4 For vessels with stability information booklets, the book should include loading conditions for towing.

11.7.5 Stability for towing conditions may be deemed satisfactory if the heeling lever (defined below) does not exceed 0.5 times the maximum GZ for the most critical loading condition.

• Heeling Lever =

  (0.6 x Max. Bollard Pull x Vertical Distance between Hawser and Centre of the Propeller(s))

  Displacement

• The height of the hawser should be measured at:

• the fixed gog, or the side rails if higher, if a fixed gog is always used; or

• the top of the winch drum (with no towline deployed), or the side rails if higher, if a fixed gog is not always used.

• If the maximum GZ occurs at an angle greater than 30 degrees of heel then the GZ value for 30 degrees of heel should be used instead of the angle of maximum GZ

11.7.6 In lieu of compliance with 11.7.5 the vessel should be shown to comply with section 2.8 of Part B of the IMO’s amended Intact Stability Code^footnote (2008 IS Code) in its entirety.

11.7.7 The stability of vessels without stability information booklets can be deemed satisfactory if –

• • in the normal working condition, the freeboard is such that the deck edge is not immersed at an angle of less than 10 degrees; and

• • The results of the heel test indicate that –

• wd	≥	0.076 K
  LBTρtan(θ)		f

• Where: K = 1.524 + 0.08L - 0.45r

  • L = Length of vessel between perpendiculars (metres)

  • r = Length of radial arm of towing hook (metres)

  • f = Freeboard (metres)

  • ρ = Density of sea water

  • θ = Heel angle from heel test

  • w = Weight moved for heel test

  • d = transverse distance moved by weight for heel test.

11.7.8 Where the simplified stability calculation for vessels without stability information booklets described in 11.7.7 is not appropriate for the vessel then a more comprehensive stability analysis should be completed using appropriate criteria to satisfy the owners’ responsibility to provide a safe working environment under Health and Safety general duties.

11.7.9 The heel test should be carried out in small increments in both directions, and the average resultant heel angle noted for the average heeling moment wd.

11.8 Approval and Carriage of Stability Information

11.8.1 A Vessel Not Required to have an Approved Stability Information Booklet.

A vessel for which stability is assessed on the basis of practical tests or simplified methods, defined in section 11 of the Code, conducted by a competent person(s), should be approved by the Certifying Authority. In order to give approval, the Certifying Authority should be satisfied that the requirements have been met, accepting the results obtained and keeping a detailed record of the procedure of the tests or calculations and the results which were accepted.

The Certifying Authority should retain the details in the records maintained for the vessel, and these details are to be entered on the certificate. See section 11.1.1.6 for requirements for the carriage of a Stability Guidance Booklet.

11.8.2 A Vessel Required to have an Approved Stability Information Booklet.

11.8.2.1 The owner(s) should be responsible for the inclining test of a vessel to be undertaken by competent persons and for the calculation of the lightship particulars, which are used in the stability calculations.

11.8.2.2 A person, independent of the owner / managing agent, competent to the satisfaction of the Certifying Authority should witness the inclining test of a vessel and be satisfied as to conditions and the manner in which the test is conducted.

11.8.2.3 The owner(s) of a vessel should be responsible for the submission of the Stability Information Booklet, based on the Administration’s model booklet prepared by a competent person(s), the content and form in which stability information is presented, its accuracy and its compliance with the requirements of section 11 for the standard required for the vessel. The owner(s) should either submit three (3) hard copies of the booklet to the Certifying Authority for approval or an electronic copy as agreed with the Certifying Authority.

11.8.2.4 When satisfied with the form and content of the Stability Information Booklet (including satisfaction with the competency of the person(s) who produced the booklet, methods and procedures used for calculations, the stability standard achieved and instructions which may be given to the Master but excluding accuracy of hull form data), the Certifying Authority should stamp the booklet with an official stamp which contains the name of the Certifying Authority, the date of approval, a file (or record) reference, number of pages in the booklet and "APPROVED FORM AND CONTENT".

Two (2) copies of the approved booklet should be returned to the owner(s). The owners should be instructed to confirm that one (1) copy has been placed on the vessel and will be retained on the vessel at all times for use by the Master. The second booklet is for the record of the owner(s).

The Certifying Authority should retain the third copy of the approved booklet in the records kept for the vessel.

11.8.2.5 It will be necessary to keep a hard copy of the approved Stability Information Booklet on board the vessel for use and reference, however any electronic stability software (which has been validated, to the satisfaction of the Certifying Authority, against the approved Stability Information Booklet) may additionally be used.

11.8.2.6 Seagoing Pilot Boats should have a simplified set of guidance, based on the approved stability information booklet, available for the coxswain to use. The guidance shall include information on permitted loading conditions which consider the condition of tanks, number of persons on board and where they may be seated and the position and mass of any cargo carried. Conditions of operation which are not permitted shall also be clearly included in the guidance.

11.8.3 A Vessel Required to Have Approved Damage Stability Information

11.8.3.1 The owner(s) of a vessel should be responsible for the submission of the damage stability calculations prepared by a competent person(s), their accuracy (including methods and procedures used for calculations) and compliance with the requirements of section 11.2.

The owner(s) should submit two (2) copies of the calculations to the Certifying Authority for approval.

11.8.3.2 The Certifying Authority should approve the results of the damage stability cases provided that the results meet the standard defined in section 11.2.

Approval (of the results but not the accuracy of the calculations) should be given in a formal letter from the Certifying Authority to the owner(s) and a copy of the calculations returned marked with the name of the Certifying Authority, the date and "RESULTS APPROVED".

11.8.4 Guidance on Stability Assessment

Guidelines on the minimum Form and Content of a stability book and guidance on minimum levels of checking for Certifying Authorities leading to approval are contained in Appendix 11.

It should be noted that the Certifying Authority may require a full stability analysis for a vessel which has been modified from the original design, particularly if the freeboard has been significantly reduced or the modification has involved the addition of an item of equipment which may have caused the position of the vertical centre of gravity to be situated at a higher level than that intended by the designer.

A full assessment, as opposed to a form and content check (see Appendix 11), may be requested by the Certifying Authority for any vessel where there is concern with regard to the vessel’s stability.