Section 2 Towing arrangements

2.1.1 All non-self-propelled units which are to be wet-towed to their operating location are to be fitted with adequate arrangements for towing.

2.1.2 Plans and full particulars of the unit’s towing facilities are to be submitted for approval, together with calculations or model test data supporting the assigned system design load. The maximum permitted static bollard pull for each towing arrangement is to be stated on the plans.

2.1.3 Oil storage units which may be towed in order to avoid hazards or extreme environmental conditions may require emergency towing arrangements in accordance with IMO Resolution MSC 35(63) for oil tankers when required by a National Administration. Where emergency towing arrangements are required, plans of the system and structural arrangements are to be submitted for approval. See also Pt 3, Ch 13, 9 Mooring of ships at single point moorings of the Rules and Regulations for the Classification of Ships.

2.2.1 Units are to be provided with a main towing system suitable for towing with one or two towing vessels and in addition it is recommended that an emergency towing system is provided.

2.2.2 The emergency towing system may be arranged by using the unit's anchor line or similar system.

2.2.3 The main towing system is to be suitable for the design load in accordance with Pt 4, Ch 9, 2.1 General 2.1.2 but is not to be taken less than 75 tonne-f.

2.2.4 The components of the towing system are to be manufactured and tested in accordance with Ch 10 Equipment for Mooring and Anchoring of the Rules for Materials.

2.2.6 Wire ropes are to have 'hard eyes' fitted at their ends.

2.2.7 Where towing bridles can be subjected to heavy wear due to chafing, chains are to be used.

2.2.8 The attachments to the unit are to be as far apart as practicable and on column-stabilised units the attachments are to be fitted to the lower hulls.

2.2.9 The length of the towing pendants attached to the unit is not to be less than the distance between the attachments.

2.2.10 The position and arrangement of the towing attachments are to be such that it is possible to change the chain/wire towing pendant connections quickly in calm water.

2.2.11 When towing with two towing vessels, each towline (weak link) is to be fitted between the unit's towing pendants and the towlines of the towing vessels. When towing with one towing vessel, the towline (weak link) is to be connected between the triangular plate or equivalent and the towline of the towing vessel.

2.2.12 The length of each towline (weak link) is, in general, not to be less than 50 m so that the connection to the towline of the towing vessel is at a safe distance from the unit.

2.3.1 Each towing pendant connected to the unit is to have a minimum breaking strength of three times the design load, see Pt 4, Ch 9, 2.2 Towing system 2.2.3.

2.3.2 The towline (weak link) is to have a breaking strength of approximately 85 per cent of the breaking strength of the towing pendant connected to the unit.

2.3.3 The towing pendant connections to the unit, triangular plate and shackles are to have a breaking strength greater than the strongest part of the towing system.

2.3.4 The attachments to the unit are to be designed for a towing direction of 0° to 90° off centreline port and starboard. Account is to be taken of the specified range of inclination angles.

2.3.5 Towing brackets or pad-eyes and their support structure are to be designed to the breaking strength of the attached towing pendant. The permissible stresses are to be in accordance with Pt 4, Ch 5, 2.1 General 2.1.1.

2.4.1 Means are to be provided to retrieve the unit's towing pendants or bridle in the event that the towing vessel's towline or the towline (weak link) should break.

2.5.1 It is recommended that an adequate number of spare parts for the towing system be provided on board during towing operations.