Section 1 Omission of Hatch Covers on General Cargo Ships

1.1.1 This Guidance Note outlines the aspects to be considered for general cargo ships which have loading conditions where one or more of the hatch covers are required to be omitted, see also Pt 3, Ch 9, 10 Omission of hatch covers of Rules and Regulations for the Classification of Ships, July 2022.

1.1.2 Any proposals for the omission of hatch covers are to be agreed by both the National Authority (in order to obtain an exemption from the Load Line Convention requirements for hatch covers) and from LR where the Class notation Hatch Covers omitted in Hold (No(s) ...) will be assigned.

Guidance is provided in this document on how to consider the above aspects, which can be used as a basis for discussions with the Flag Administration, particularly where the Flag Administration does not have its own requirements.

Note that the above aspects are dependent on the quantity of water ingress to be considered, which is to be agreed by the Flag Administration. Hence, the Class notation will not be assigned unless agreement by the Flag Administration has been obtained in writing.

1.1.5 Note that the transport of solid bulk cargoes is not normally permitted without weathertight steel hatch covers.

1.2.1 Open-top cargo ship means a general cargo ship where one or more of the cargo holds needs to have hatch covers removed in one or more loading patterns.

1.2.2 Freeboard is the distance between the assigned load line and freeboard deck.

1.2.3 Freeboard deck, for the purposes of Chapters I and II of Annex I of the International Convention on Load Lines, 1966 (hereinafter referred to as the Load Line Convention, 1966), is the freeboard deck according to the Load Line Convention, 1966, as if hatch covers are fitted on top of the hatch coamings.

1.2.4 Maximum sustained speed is defined as the maximum service speed, taking into account speed loss due to resistance increase in regular waves. Voluntary speed loss is not taken into consideration.

1.2.5 Minimum ship manoeuvring speed is defined to be the minimum speed which maintains directional control and is consistent with the operating characteristics of the ship.

1.2.6 Green water is sea water other than spray shipped aboard the ship under normal operational conditions.

1.3.1 Model experiments should be carried out in long-crested, irregular waves. It is recommended that the Pierson-Moskovitz, JONSWAP, or Bretschneider wave spectrum generated, for the purpose of these experiments, has a significant wave height of approximately 8,5 m at the most unfavourable realistic wave period (zero crossing) as determined by calculation or previous testing experience.

1.3.2 For ships operating in restricted areas only, other spectra may be used.

1.3.3 The effect of wind generated spray need not be simulated during the tests.

1.3.6 Additional tests may be required.

1.3.7 The model experiments should be carried out with a self-propelled, unrestrained model without the necessity to change course. The time period of each experiment is to correspond to at least one-hour real time.

1.3.8 The loading condition used for the tests should correspond to at least the maximum loaded draught with level trim. If operational trim values differ substantially from level trim, additional trim values may need to be included in the model test programme.

1.3.9 The KG value selected for the test in all wave directions given in Ch 1, 1.3 Procedure of model tests 1.3.4 should lead to ship’s natural roll period which is in resonance with the wave peak period in beam seas. Additional runs with the three worst wave directions (obtained from the full test) should also be performed with the KG value corresponding to limit GM curve valid for the open top condition, see Ch 1, 1.3 Procedure of model tests 1.3.8.

1.3.10 For each test condition, the cargo holds required to have their hatch covers omitted should be considered as having no cargo. Cargo on deck or in other cargo holds should not be used as a means to prevent shipping of water into an empty hold, e.g. stowed on deck outboard of the open hold. Rain covers for the open hold should not be simulated in the model test.

1.3.11 In additional to the usual parameters measured (ship motions, ship speed, relative motions, rudder angles, etc.) the volume of water entering all open cargo holds should be measured for each experiment. The quantities of water taken aboard the model should be removed and measured after each test run so that the metacentric height, moment of inertia and displacement are not appreciably disturbed by any accumulation of water during the testing programme.

1.3.12 Where freeing ports are fitted, an additional model test, see Ch 1, 1.4 Freeboard 1.4.1.(b), should be conducted at a draught which corresponds to the condition of the ship fully loaded with cargo, and with open holds flooded to the static equilibrium level with freeing ports open. A hold permeability of 0,9 should be assumed. Tests should be conducted at zero speed in beam seas at the wave peak period that corresponds to the resonance with the natural roll period of the ship.

1.3.13 The said test may be required to be Witnessed. A comprehensive report of the same should be submitted.

1.4.2 It is recommended that the maximum hourly rate of ingress of green water in any one open hold determined from model testing should not exceed the hatch opening area multiplied by 400 mm/hour.

1.4.3 A conventional geometrical freeboard and minimum bow height should be calculated assuming that hatch covers are fitted. Note that the freeboard requirements given in the Load Line Convention, 1966 as amended will still need to be complied with, i.e. the freeboard and bow height assigned to an open-top cargo ship should not be less than the equivalent geometrical freeboard determined from the Load Line Convention, 1966 as amended.

1.4.4 Seasonal freeboards should be omitted (all seasons freeboard assignment should be used) unless the minimum geometrical freeboard and corresponding seasonal freeboards for which the ship is eligible (assuming hatch covers are fitted) are greater than the freeboard for which the model tests were satisfactorily carried out. In such cases, the minimum geometrical freeboard and the corresponding seasonal freeboards greater than the freeboard for which the model tests were carried out should be assigned.

1.4.5 The minimum freeboard and minimum bow height assigned to the ship should not be less than those corresponding to the model test conditions.

1.5.1 The longitudinal and local strength is to comply with the requirements of Pt 3, Ch 9, 10 Omission of hatch covers of Rules and Regulations for the Classification of Ships, July 2022.

1.5.2 The longitudinal strength is to be assessed against the seagoing limits in order for the ship to have unrestricted service for conditions where hatch covers are omitted.

1.5.3 Where it is not possible to meet the seagoing strength limits, a service factor of 0,8 may be applied to calculate increased limits provided that a wave height limitation is assigned to the ship for hatch coverless conditions. This wave height limitation is to correspond to the wave height assumed in the model tests. Note that the seagoing limits will still be applicable to conditions where all hatch covers are fitted.

1.6.1 The stability of the ship in all conditions of loading (without water ingress) should meet the provisions of the Code of Intact Stability for All Types of Ships Covered by IMO Instruments.

1.6.2 The stability of the ship in intact flooded condition should meet the survival criterial (with factor s=1) of Chap. II-1 Part B-1 of SOLAS 1974 as amended under the conditions given in Ch 1, 1.6 Intact stability 1.6.3 to Ch 1, 1.6 Intact stability 1.6.6.

1.6.3 Where cargo hold freeing ports are fitted, they should be considered closed for the purpose of determining the flooding angle, provided that they are reliable and effective.

1.6.4 The ship in the intact condition before water ingress should be assumed to be loaded at the maximum draught for the open-top condition taking into account the maximum allowable VCG resulting from intact and damage stability criteria.

1.6.5 The cargo hold(s) should be considered empty and filled with water (permeability of 0,9 for cargo hold) on the tank top. It is recommended that the maximum hourly rate of green water (in m³/hour) shipped in seagoing conditions, as established by the comprehensive model testing and converted in (mm/hour), be added to 100 mm/hour (max tropical rainfall) and the sum multiplied by 3 hours, see also Ch 1, 1.4 Freeboard 1.4.2.

1.6.7 Where tween decks are fitted, ample provisions should be made for rapidly freeing the tween decks from water and for draining them through evenly distributed openings. The minimum freeing port area on the tween decks fitted along the holds should be calculated in accordance with ILLC 1966 as amended.

1.6.8 Calculations should be performed for intermediate phases of hold flooding with each phase comprising of an accumulated height of water of 0,5 m until the height of the assumed accumulated water in Ch 1, 1.6 Intact stability 1.6.5 above is reached.

1.7.1 Damage stability assessments should be carried out as required by the relevant statutory instrument with the hatch coaming of the open top hold(s) considered as downflooding area(s).

1.8.1 The bilge pumping system is to comply with the requirements of Pt 5, Ch 13, 3.8 Ships where hatch covers are omitted.

1.8.2 If fitted, freeing ports are to comply with the requirements of Pt 3, Ch 9,10.6 Freeing ports.

1.9.1 In the open-top condition a vessel’s fixed gas fire-extinguishing system will not be effective and the fire protection arrangements will need to be specially considered.

1.9.2 An equivalent arrangement for open-top container ships is given in MSC. Circ.608 Rev.1; this requires a fixed water spray system to be provided so that any fire can be contained in the bay of origin and adjacent areas can be cooled to prevent structural damage. Such an arrangement is considered to be an acceptable approach for general cargo ships.

1.9.3 As an alternative to a fixed water spray system and subject to Flag acceptance an equivalent arrangement applying fire-fighting monitors based on MSC.1/Circular 1472 can also be considered.

1.9.4 In accordance with MSC/Circ.1120, the water spray system required in paragraphs 9.2, 9.3 and 9.4 of MSC/Circ.608/Rev.1 will also satisfy the requirement for dangerous goods.

1.9.5 A fixed fire detection and alarm system should be provided when carrying dangerous goods in the open top condition. The system should be designed and arranged to take account of the specific hold configuration and ventilation arrangement.

1.9.6 If an equivalent arrangement is not provided, then no dangerous goods or combustible cargoes (as defined in the FTP Code 2010, Annex 2, paragraph 1) should be carried when cargo hatch covers are not fitted.

1.10.1 Dangerous goods for which ‘stowage on deck only’ is specified in the IMDG Code should not be carried in or vertically above the open top hold.

1.10.2 Dangerous goods other than those described in Ch 1, 1.10 Dangerous goods 1.10.1 should not be carried in or vertically above open top holds unless such holds are in full compliance with SOLAS II-2, Regulation 19.

1.10.3 Fire protection arrangements should be in accordance with Ch 1, 1.9 Fire protection 1.9.4 to Ch 1, 1.9 Fire protection 1.9.6.