Stability on board fishing vessels with RSW tanks

Purpose and scope

The purpose of this circular is to establish when seawater used in RSW tanks will be considered cargo and how this will affect any stability calculations. Conditions for the use of make-up water tanks, i.e. tanks for temporary storage of seawater to be used in RSW tanks, are also described.

This circular applies to Norwegian fishing vessels of 15 metres in overall length (LOA) and upwards where catch is stored, or intended to be stored, in RSW tanks.

Legislation

Regulations of 13 June 2000 No. 660 on the construction, operation, equipment and surveys of fishing vessels of 15 m in overall length (LOA) and upwards set out a requirement that ballast shall be permanently arranged. For vessels of more than 45 metres in length (L), the use of variable ballast may be permitted in order to satisfy the stability criteria.

The provision on variable ballast is not directed at the content and use of RSW tanks on fishing vessels built to transport and store catch in RSW tanks. With regard to this type of vessels, the Norwegian Maritime Authority will consider all content of the RSW tanks as cargo, and the weight of the content of the RSW tanks can be taken into account in all loading conditions.

Regulations of 8 September 2017 No. 1368 on ballast water management on ships and mobile offshore units specify requirements for ballast water management on all Norwegian ships certified to call at foreign ports. This means that all fishing vessels certified for a greater trade area than in-shore fishing shall meet the requirements for ballast water management. In accordance with the Regulations on ballast water management, ballast water is defined as water taken on board in ballast tanks to control trim, list, draught, stability or stresses. Based on the conditions and terms stated in the paragraph on make-up water tanks, the water in make-up tanks can be considered not to be ballast water.

Considerations

The interpretation of the legislation is based on the fact that the Norwegian Maritime Authority does not regard the content, or parts of the content, of RSW tanks as water ballast, provided that the intention is to use the tanks for catch storage.

Due to the way these vessels are operated, a minimum catch is not required to claim that all content is cargo, since these vessels always have seawater as a part of the cargo. Moreover, the amount of seawater will always vary. The specific weight of the cargo will be approximately the same and is not significant for the immersion and stability of the vessel. Seawater is always accessible and does not depend on the amount of fish that is caught.

The seawater in RSW tanks differs significantly from water ballast. Firstly, it has another purpose, and secondly, it is factor of production that is important to the end product (the catch). A large amount of energy is required to process and cool the water, thus creating an added value. This is regarded as a production factor in the same way as ice, packaging, salt, etc. Therefore, seawater in RSW tanks is considered cargo.

Stability calculations

The vessel's stability documents shall provide information on stability for loading conditions covering the entire range of operation, including i.a. returning to shore without a catch, as well as returning with a maximum catch. Section 3-7 first paragraph of the Regulations describes conditions that shall be calculated as a minimum.

Where the term catch is used in relation to requirements for stability calculations, this does not include seawater in RSW tanks that are loaded on board and intended for catch storage. Empty cargo holds mean cargo holds without any catch. This does not exclude the fact that there may be seawater in the RSW tank(s) that are loaded on board intended for storage of catch.

The content of the RSW tanks may therefore be considered for all required conditions when making calculations for vessel stability.

Make-up water tanks

Some vessels use a forepeak tank as a make-up water tank. The tank is not a cargo tank or a ballast water tank. However, it is used for storing fresh or refrigerated (sea) water which will be used in the cargo tanks at a later stage. The make-up water in the forepeak tank will not to be considered as ballast water if the vessel complies with all stability requirements without a filled forepeak tank. This means that the stability calculations must be approved with an empty tank in all loading conditions. Unfavourable conditions must also be considered, and documentary evidence of freeboard and stability when using the tanks must be provided. Instructions for use on board shall also apply to the use of make-up water tanks.

These tanks shall only be used for refrigerating water or adding fresh water to the RSW tanks. This means, among other things, that the water shall only be pumped out from the RSW tanks. Filling water from a port, storing it in a make-up water tank and then discharging it at another port is not accepted. Forepeak tanks used for ballast operations are covered by the BWM Convention. In connection with approval of the vessel's stability, the company must submit a description of the intended use of such tanks, including stability calculations and tank plan, describing the relevant tanks that will be used as make-up water tanks.