E SUB-COMMITTEE ON CARRIAGE OF CARGOES AND CONTAINERS 3rd session Agenda item 10 CCC 3/10/4 30 June 2016 Original: ENGLISH UNIFIED INTERPRETATION OF PROVISIONS OF IMO SAFETY, SECURITY AND ENVIRONMENT-RELATED CONVENTIONS Cargo securing based on environmental conditions in annex 13 to the CSS Code (as amended) Submitted by the International Association of Classification Societies (IACS) SUMMARY Executive summary: This document provides in the annex, a copy of a draft IACS Unified Interpretation on Cargo securing based on environmental conditions (annex 13 to the CSS Code, as amended) Strategic direction: 1.1 High-level action: 1.1.2 Output: 1.1.2.3 Action to be taken: Paragraph 10 Related document: DSC 13/INF.9 Background 1 Cargo securing based on environmental conditions is permissible and widely used in shipping. The Code of Safe Practice for Cargo Stowage and Securing (CSS Code), annex 13, states: "7 Advanced calculation method 7.1 Assumption of external forces The basic acceleration data are to be considered as valid under the following operational conditions: 1. Operation in unrestricted area; 2. Operation during the whole year;
Page 2 3. Duration of the voyage is 25 days; 4. Length of ship is 100 m; 5. Service speed is 15 knots; 6. B/GM 13 (B = breadth of ship, GM = metacentric height). For operation in a restricted area, reduction of these figures may be considered, taking into account the season of the year and the duration of the voyage." 2 IACS also notes that the Code of Safe Practice for Ships Carrying Timber Deck Cargoes, 2011 (2011 TDC Code) (resolution A.1048(27)), introduces an acceleration reduction to assess the forces acting on cargo: "6.2 Accelerations and forces acting on the cargo 6.2.3 To take account of the factors mentioned in 2.13.4, the acceleration data calculated according to annex 13 of the CSS Code may be multiplied by a reduction factor ranging from 0 to 1, depending on expected maximum significant wave height during the intended voyage. The reduction factor is obtained by the following formula: 3 f R = H M 19.6 where H M is the maximum expected significant wave height in metres. (The value 19.6 is the assumed 20-year wave that will occur in the Northern Atlantic Ocean. Relevant significant wave heights for different sea areas and seasons can be obtained from "Ocean Wave Statistics".) 6.2.4 Reduced acceleration may be used for the design of securing arrangements for timber deck cargoes in any of the following ways:.1 Required securing arrangements are designed for different wave heights and the securing arrangement is selected according to the maximum expected wave height for each voyage..2 The maximum wave height that a particular securing arrangement can withstand is calculated and the vessel is limited to operate in wave heights up to the maximum calculated. Examples on such arrangements are unsecured transversely stowed timber deck cargoes in restricted sea areas..3 The required securing arrangement is calculated for the maximum expected twenty-year wave in a particular restricted area and the cargo is always secured according to the designed arrangement when operating in that area. 6.2.5 If one of the two first mentioned methods in 6.2.4 are used for a decision on securing arrangements, it is important that procedures for forecasting the maximum expected wave height on intended voyages is developed and followed and documented in the ship's approved cargo securing manual."
Page 3 3 There are no formal requirements and procedures given in the CSS Code on how reduction of the acceleration figures may be considered taking into account the season of the year and the duration of the voyage when operating in a restricted area as mentioned in paragraph 7.1 of annex 13 to the CSS Code. Discussion 4 The joint industry research project Lashing@Sea that was led by the Maritime Research Institute Netherlands (MARIN) was conducted from 2006 until 2009. IMO was first advised of this project in document DSC 13/INF.9. 5 IACS was requested by the project participants to investigate and develop a unified interpretation for cargo securing based on environmental conditions. 6 IACS conducted a validation exercise by comparing full-scale measurements from the Lashing@Sea project and seakeeping computations, and undertook a review of the text in annex 13 to the CSS Code and the acceleration reduction method given in the 2011 TDC Code in correlation to long-term measurement results and respective hydrodynamic simulation results. IACS concluded that requirements for cargo securing based on environmental conditions should be specified by a method that is slightly different from the method in the 2011 TDC Code. 7 A linear acceleration reduction factor has been developed by IACS. This starts at a minimum allowable reduction factor of 0.3 at 0 m significant wave height. The reduction factor then increases linearly until reaching 1 at 7 m significant wave height. 8 IACS is aware that the method as shown in the 2011 TDC Code has been taken from Swedish regulations developed in 1993. IACS re-evaluated the Lashing@Sea project report in that regard as well as the technical background of the Swedish acceleration reduction approach (which is based on a probability of occurrence of 10-8 for the maximum significant wave height expected in a sea area within 20 years). As the reduction method is based on weather forecasts for the actual voyage with a probability of about 1 for encountering the predicted wave height, the 2011 TDC Code method does not appear to be consistent and therefore is not considered applicable for such an approach. Furthermore, IACS understands from the technical background on which the Swedish method was founded, that it was based on very limited available acceleration data from measurements and simulations, and that further verification was recognized as being necessary. Due to the lack of verified data, in particular at increased significant wave height, and also taking into account its own investigation results, IACS concluded that introducing a linear reduction curve up to 7 m significant wave height is pragmatic and prudently conservative. 9 Based on the above discussion, IACS has developed a draft Unified Interpretation (UI) on Cargo securing based on environmental conditions, a copy of which is provided in the annex to this document. Action requested of the Sub-Committee 10 The Sub-Committee is invited to consider the foregoing and, in particular:.1 the draft UI set out in the annex;
Page 4.2 the possible consequences on the acceleration reduction method in the 2011 TDC Code in the event the Sub-Committee agrees with the attached draft UI; and.3 take action as appropriate. ***
Annex, page 1 ANNEX DRAFT IACS UNIFIED INTERPRETATION SC XX (June 2016) CARGO SECURING BASED ON ENVIRONMENTAL CONDITIONS CSS Code Annex 13 (as amended) Regulations CSS Code Annex 13, paragraph 7: 7 ADVANCED CALCULATION METHOD 7.1 Assumption of external forces The basic acceleration data are to be considered as valid under the following operational conditions: 1. Operation in unrestricted area 2. Operation during the whole year 3. Duration of the voyage is 25 days 4. Length of the ship is 100 m 5. Service speed is 15 knots 6. B/GM 13 (B: breadth of ship, GM: metacentric height). For operation in a restricted area, reduction of these figures may be considered, taking into account the season of the year and the duration of the voyage. External forces to a cargo unit in longitudinal, transverse and vertical direction should be obtained using the formula: F(x,y,z) = m a(x,y,z ) + Fw(x,y) + Fs(x,y) F(x,y,z) = longitudinal, transverse and vertical forces m = mass of the unit a(x,y,z) = longitudinal, transverse and vertical acceleration (see table 2) Fw(x,y) = longitudinal and transverse force by wind pressure Fs(x,y) = longitudinal and transverse force by sea sloshing. The basic acceleration data are presented in table 2. Table 2: Basic acceleration data
Annex, page 2 Remarks: The given transverse acceleration figures include components of gravity, pitch and heave parallel to the deck. The given vertical acceleration figures do not include the static weight component. Interpretations 1. CSS Code, Annex 13 Cargo securing based on environmental conditions An acceptable method to account for an operation in a restricted area is to apply the reduced acceleration factors plotted below to the acceleration values listed in table 2 of annex 13. It is the operator's responsibility to ensure that the significant wave heights associated with the reduced acceleration factors will not be exceeded during the voyage. The reduction factor, fr, depends on the significant wave height H M : For H M = 0 m, fr = 0.3 For H M > 7 m, fr = 1.0 For 0 < H M 7.0 m, fr depends linearly on H M and can be calculated according to following formula: fr = 0.3+0.1H M