i ©Copyright OCIMF 2010 Your Guide to Mooring Equipment and Operations 3rd Edition The OCIMF mission is to be the foremost authority on the safe and environmentally responsible operation of oil tankers and terminals, promoting continuous improvement in standards of design and operation Oil Companies International Marine Forum E?ective Mooring v ©Copyright OCIMF 2010 Contents Introduction iii Section 1 E?ective Mooring 1 1.1 What Does a Mooring System Do? 3 1.2 How Big are these Forces? 4 1.3 Mooring Layout 7 1.4 Wires or Synthetic Fibre Ropes 9 1.5 Elasticity 10 1.6 Vertical Angle (Dip) 13 1.7 Mixed Moorings 13 1.8 Synthetic Fibre Tails 13 1.9 Marine Loading Arms 15 1.10 Quick Release Hooks 16 Section 2 Mooring Winches 17 2.1 Winch Control Types 19 2.2 Winch Drums 21 2.3 Winch Brakes 21 2.4 Correct Layering 22 2.5 Split Drum Winches 23 2.6 Undivided Drum Winches 24 2.7 Correct Reeling 24 2.8 Brake Condition 25 2.9 Testing Brakes 26 2.10 Application of Brake 26 2.11 Incorrect Use of Brake 28 2.12 Exceptional Circumstances 28 2.13 Winch in Gear 29 2.14 Freezing Weather 29 2.15 Joining a New Ship 30 2.16 Safety Reminders 31 vi ©Copyright OCIMF 2010 Section 3 Wire Mooring Lines 33 3.1 Construction of Wire Mooring Lines 35 3.2 De?nitions 36 3.3 Typical Steel Wire Rope Constructions 37 3.4 Bend Radius 38 3.5 Advantages of Steel Wire Ropes 39 3.6 Certi?cation 40 3.7 Stoppers for Use with Steel Wires 40 3.8 Care of Wire 43 3.9 Maintenance of Steel Wire Mooring Ropes 44 3.10 Selection of Anchor Point for 1st Layer of Wire on a Drum 45 3.11 Splicing Wire 47 3.12 Safety Reminders 48 Section 4 Synthetic Fibre Ropes 49 4.1 Construction of Synthetic Fibre Ropes 51 4.2 Types of Material Used 53 4.3 Relative Minimum Breaking Loads of Synthetic Ropes 55 4.4 Certi?cation 55 4.5 Stoppers for Use with Synthetic Ropes 55 4.6 Belaying Synthetic Fibre Ropes on Bitts 56 4.7 Snap Back 57 4.8 Rope Care 59 4.9 Rope Inspection 60 4.10 Splicing 60 4.11 Safety Reminders 61 Section 5 O?shore Operations 63 5.1 Multi-Buoy Moorings 65 5.2 Single Point Moorings 69 5.3 Mooring to FPSOs and FSOs 72 5.4 Dedicated Shuttle Tankers 73 5.5 Conventional Tankers 74 5.6 Mooring Operation 75 5.7 Ship-to-Ship Transfer (STS) 76 vii ©Copyright OCIMF 2010 Section 6 Windlasses and Anchoring 81 6.1 Brakes 84 6.2 Cable Stoppers 84 6.3 Anchor Cables 85 6.4 Communication 85 6.5 Maintenance of Windlass Brakes 86 6.6 Adjustments 86 6.7 Prolonged Periods of Non-Use 87 6.8 Safety Reminders 87 Section 7 Personal Safety 89 7.1 Handling of Moorings 91 7.2 Safe Handling of Tug Lines 93 7.3 Gloves 95 7.4 Safety Reminders 96 19 ©Copyright OCIMF 2010 Section 2 Mooring Winches Mooring Winches Mooring winches can be categorised by their control type (automatic or manual tensioning), drive type (hydraulic, electric or steam), by the number of drums associated with each drive (single, double or triple), by the type of drums (split or undivided) and by brake type (band or disc) and method of brake application (mechanical screw or spring-applied). Each type has it own operational characteristics and precautions. It is important that personnel operating winches are familiar with the di?erent characteristics and have been trained in their operation. It should be noted that a winch’s heaving, or pulling, power is always less than the render force. Render force is that force required to turn the winch drum in the direction opposite its recover (heave in) direction. When a winch renders, some line will payout from the winch drum. Refer to section 2.12. 2.1 Winch Control Types Some ships are equipped with self-tensioning winches with the intention of eliminating the need for line tending. These 20 ©Copyright OCIMF 2010 E?ective Mooring are designed so that a speci?ed line tension can be pre-set. The winch will render (pay out) when tension in the line exceeds this value and will recover (heave in) when it is less than this value. However, experience has shown that the use of such winches while the ship is alongside is not a safe practice because the winch restraint is limited to its render load. This is small compared to what it can hold on the brake. It is possible for the winches at opposite ends of the ship to work against each other when an external force, caused by either wind or current or both, is applied to one end so that the ship could ‘walk’ along the jetty. In the simple illustration given in Figure 8, a ship is shown moored by one line at each end. Hose Fig. 8 Possible E?ect of Winch Operating in Self-Tensioning Mode Should the bow winch render a little for any reason (i.e. a change in direction of force of wind or current) some rope will pay out. The ship will move astern a little and the after mooring will slacken. The aft winch will heave in the slack and re-tension the line. If the disturbance is repeated or continuous, the ship will be moved progressively astern. Mooring winches should not be left in automatic self-tensioning mode once the ship is secured alongside. On completion of mooring, the winch should be left with the brake on and out of gear. 21 ©Copyright OCIMF 2010 Section 2 Mooring Winches 2.2 Winch Drums Winch drums may be either split or undivided. The split drum is comprised of a tension section and a line storage section. On heaving in, the mooring line is transferred from the storage section to the tension section to provide a su?cient number of turns on the tension section to hold the tension of the line on that section only and to provide su?cient extra turns to allow for line tending. When using split drum winches, the following should be borne in mind: • Manhandling the line from storage drum to the tension drum may be di?cult and requires care and su?cient personnel • regular attention should be paid to ensure that the appropriate number of turns is maintained on the tension drum throughout the time the ship is alongside. No more than one layer of line should be maintained on the tension drum when the line is under load. The advantage of the split drum is that it can maintain a constant brake holding capacity and heaving force as the mooring line is always run o? the ?rst layer of the tension drum. The undivided drum has the advantage that it avoids the need to manhandle the mooring line from section to section, as may be required with the split drum. However, it is more di?cult to correctly spool and stow the mooring line on the undivided drum and, as a result, the mooring line may be damaged when tension is applied. 2.3 Winch Brakes The holding capacity of winch brakes varies from ship to ship, but brakes should always be set to render at 60% of the minimum breaking load (MBL) of the mooring line to permit slippage before the line breaks. 22 ©Copyright OCIMF 2010 E?ective Mooring As brakes may deteriorate in service, they should be designed to hold 80% of the line’s MBL, but have the capability to be adjusted down to 60% in service. The value of the brake holding capacity in relation to the size of line is important. There would be little point in a mooring system where lines part at loads less than the brake holding capacity. This factor should be considered when renewing lines. Brake holding capacity is dependent upon several factors, some of which are discussed below. 2.4 Correct Layering The number of layers of line on the drum a?ects the brake holding capacity. The force at which the brake will render will vary dependent upon the number of layers of line left on the drum. The more layers of line on the drum the greater will be the reduction of brake holding capacity. This is illustrated in Figure 9. Brake holding power reduced to 40 tonnes as radius R2 increases to 4th layer Brake holding capacity 55 tonnes RB = Brake Radius 4th LayerR2 RB R1 RB 1st Layer Fig. 9 Impact of Increased Layers on Brake Holding Capacity