Section 8 Fittings for masts and derrick booms

8.1.1 The application of fixed fittings, ropes and loose gear in derrick systems is to comply with the requirements of this Section. The items themselves are to be manufactured in accordance with the requirements given in Ch 8 Fittings, Loose Gear and Ropes.

8.1.2 Effective continuity of materials is to be maintained in the bearing brackets for fittings and abrupt changes of plate thickness are to be avoided. Care is to be taken to avoid pockets in which water may collect. The connection to the mast or derrick boom is to provide an easy transfer of load into the surrounding structure and to minimise hard spots and sources of stress concentration.

8.1.3 All welds are to be sound, uniform and free from undercutting or other defects. Care is to be taken to ensure adequate weld penetration. Effective arrangements are to be made for the inspection of finished welds. The extent of examination by non-destructive methods is to be to the Surveyor’s satisfaction.

8.1.4 All bearing surfaces are to be machined to ensure a smooth finish and a good fit. Adequate and accessible means of lubrication are to be provided.

8.2.1 The gooseneck bearing assembly is to be such that:

1. The gooseneck pin is secured in position to prevent displacement under normal operating conditions.

2. Brackets and supporting structure are adequate to support the forces from the derrick boom operating at the maximum and minimum angles. Edges of brackets are to be stiffened as necessary to resist distortion.

3. Where the gooseneck is supported by a mast, a diaphragm or equivalent stiffening is fitted, or the width of brackets or other attachments is not less than two thirds of the diameter of the mast at that level.

8.2.2 Derrick heel fittings are to be such that:

1. The axis of the derrick heel crosspin cuts the axis of the derrick boom. Design incorporating a small offset will be specially considered.

2. The derrick heel crosspin is secured to prevent displacement under normal operating conditions.

8.2.3 Trunnions and other alternatives to goosenecks will be specially considered.

8.2.4 Adequate means are to be provided for the lubrication of all bearing surfaces and their protection from contamination by dirt or excessive water. Such protection is not to make inspection of the assembly unreasonably difficult.

8.3.1 The cargo runner is to be of sufficient length to ensure that with the derrick rigged for lifting, the maximum safe working load is to be that at least two turns remain on the winch barrel when the derrick is at either:

1. its highest working position and lifting from the tank top or lowest level from which it can be operated;

2. its maximum overside position and lifting from a lighter with the ship at its light waterline.

The cargo runner is to be securely attached to the winch barrel.

8.3.2 The length of the span tackles is to be such that at least two turns remain on the winch barrel when the derrick is at its position of maximum outreach, or one turn when the derrick is in its stowed position. Where single rope spans are fitted, the span rope may be led to a topping winch or be fitted with a span chain securely attached to the deck eyeplates by a shackle or screw pin. Where span chains are fitted, the links are to be of sufficient size that the eye of a shackle can be passed through. Where the span rope is more than one part, it is to be led to a winch barrel or topping winch and securely attached to it.

8.4.1 In general, each derrick boom is to be provided with two slewing guys where the SWL of the derrick does not exceed 20 tonnes or three guys for derricks with higher safe working loads. The safe working load of each guy is to be not less than that required by Table 2.8.1 SWL of derrick boom slewing guys. Where three guys are required, deck fittings are to be provided so that two guys can be used on each side of the ship. For slewing guys used with derrick cranes, see Ch 2, 5.3 Slewing guys 5.3.3.

8.4.2 Where the angle of the heel or trim in the operating condition exceeds 5° or 2° respectively, the requirements for slewing guys will be considered.

8.4.3 Alternative arrangements of slewing guys and proposals for reduced slewing guys where cargo slewing guys are fitted will be specially considered. Such arrangements are to be capable of operating at 5° heel and 2° trim or at greater angles where specified.

8.4.4 Natural or man-made fibre ropes may be used in the guy tackle (but not the guy pendant) provided the SWL of the guy does not exceed 4 t.

8.4.5 Where derricks are rigged for use in union purchase, preventer guys are to be fitted in addition to slewing guys. Preventer guys are to have a safe working load not less than the maximum guy tension derived from Ch 2, 4.3 Calculation of forces. Fibre rope is not to be used for preventer guys.

8.4.6 Boom head or schooner guys used for crossconnecting the heads of derricks in union purchase are to have a safe working load not less than 20 per cent of the SWL of the union purchase system, and not less than 1,0 t. These guys may be of steel wire or of fibre rope.

8.4.7 The hauling end of wire rope slewing guys is to be securely attached to a winch barrel when the derrick is being slewed under load.

8.4.8 Slewing guys are to be attached to the derrick boom and the deck eyeplate by a link, shackle or similar device so designed as to permit the guy to take up its varying positions while maintaining a straight lead. Leads are to be such that the guys will not foul rails, bulwarks or other obstructions when under load. Fairleads may be used.

8.4.9 Preventer guys are to be shackled on, or looped over the derrick head and shackled, or equivalent, to eyeplates on the deck or bulwark.

8.5.1 Swivelling eyeplates are to be used for the attachment of span tackle and cargo runner lead blocks to the mast for all derricks where the safe working load is 3,0 t or more or where the load in the span tackle exceeds 5,0 t. They may also be used elsewhere.

8.5.2 Fixed eyeplates at the derrick head may be of the ’sword-fitting’ type, providing a pair of eyeplates on opposite sides of the derrick tube, or the fitting may penetrate one side of the tube and be securely attached to internal structure.

8.6.1 Swivels are to be arranged, as necessary, to ensure that blocks maintain their correct alignment.

8.6.2 The cargo runner lead block at the derrick heel is to have a duckbill or similar head fitting which prevents the block falling when the cargo runner is slack. This is to be arranged so as to allow the heel block to clear the derrick tube when the derrick tube is in its stowed position.

8.6.3 Snatch blocks may only be used as deck lead blocks.

8.6.4 Wood blocks may only be used with fibre ropes.

8.7.1 Cargo hooks are to be of such construction or shape, or are to be provided with an efficient device, so as to prevent displacement of the sling or load from the hook.

8.7.2 In general, ‘C’, (or Liverpool) type hooks may be used where the SWL of the derrick rig does not exceed 25 t. Cargo hooks of the Ramshorn type may be used in rigs of any SWL. Proposals to use other designs of hook will be considered.

8.8.1 Where built-in sheaves are fitted to the derrick boom, the design of the sheave slot is to be such as to maintain continuity of strength of the boom tube. A typical arrangement is shown in Figure 2.8.1 Built-in sheaves but alternative arrangements will be considered.

Figure 2.8.1 Built-in sheaves

8.8.2 Where cargo runner roller guides are fitted to the derrick boom, they are to be such that:

1. They are of adequate strength to resist distortion.

2. Any tendency for the runner to chafe or jam in or between the rollers and their supports is minimised.

3. There is adequate means of lubrication.

8.8.3 Where it is intended to loop preventer guys over the end of a derrick boom, a preventer safety catch is to be securely welded or otherwise fixed to the boom. This safety catch can take the form of the boom end sealing plate being extended, over part of its circumference, beyond the outer surface of the boom tube, or alternatively, a separate fitting can be used. Edges are to be smoothed.

8.9.1 Sufficient eyeplates or equivalent attachments are to be provided for the safe operation of the derrick system and they are to be of suitable design and safe working load.

8.9.2 Eyeplates are not to be welded to the upper edge of the sheerstrake nor, in general, are they to penetrate the strength deck plating. Deck, bulwark or other plating is to be of sufficient thickness to withstand any shear forces that may be incurred in way of eyeplates due to asymmetrical loading of the eyeplate, and such plating is to be stiffened as necessary to prevent deformation under direct eyeplate loadings. The attachment of eyeplates and the adequacy of the supporting structure are to be to the Surveyor’s satisfaction.