Slide 1

DERRICKS AND CRANES

Single swinging derricksA derrick is a lifting device composed of one mast or pole which is hinged freely at the bottom. It is controlled by lines (usually four of them) powered by some means such as man-hauling or motors, so that the pole can move in all four directions. A line runs up and over its top with a hook on the end to lift cargoThe conventional derrick was initially evolved as a single hoist operation for loading and discharging of weights. It was the basic concept as an aid which became popular when combined within a union rig

Union purchaseThe union purchase method of rigging is perhaps the most common with conventional derrick rigs. With this operation, one of the two derricks plumbs the hatch and the other derrick plumbs overside. The two runner falls of the two derricks are joined together at the cargo by a union hook. The load is lifted by the fall which plumbs the load, when the load has been lifted above the height of the bulwark or ships rail, or hatch coaming, the load is gradually transferred to the fall from the second derrick.Cargo movement is achieved by heaving on on one derrick runner and slacking on the other.The safe working angle between the runners is 90 deg and should never be allowed to exceed 120 degThere is a danger from overstressing the gear if unskilled winch drivers are employed or if winch drivers do not have an unobstructed view of the lifting/lowering operations.Union purchase

Yo yo gearWith two derricksThe rig uses the two inshore derricks . Each derrick has been rigged with a gun tackle, and the moving blocks have been joined by a heavy strop supporting a floating block with cargo hook attached.The operation of loading or discharge is carried out by slewing both derricks towards the quayside, trying to keep both the derrick heads as close together as practacable Yo yo gear

Yo yo gearWith four derricksThis is probably the most popular of the two yo yo gearThe two derricks once rigged for union purchase do not have to be adjusted.The two cargo runners of the inboard derricks are passed through a cargo block and two outboard derricks are passed through second cargo block. The separate pairs of runners are shackled together, as are the floating blocksYo yo gear

Heavy lift derrick

Heavy lift derricksSpecial multiple blocks of appropriate safe load are provided for the topping lifts, purchases, and guys of these derricks. Wires of larger size, both in circumference and length are provided. Additional stays are fitted to the mast or samson post and besides the necessary guys. Unless special heavy winches are provided, the ordinary winches must be put into double gear when working heavy lift derrick.Swinging of a derrickSwinging a derrick is done with the help of guy pendant and guy tackle which can be heaved/slacked by winch or manually. Careful supervision is required when swinging a derrickBefore swinging a derrick the load is to be lifted over to make a wide clearance with the side railingsThe outboard guy is placed well aft to move the derrick boom outThe inboard guy is led horizontally from the derrick head near the hatch coaming.Vessel should be upright while swinging the derrick.Some prefer to keep a slight list to the inboard side to bring the derrick back easily after discharging Simple derrick

Types of heavy lift derricksThe hallen derrickThe Velle derrickThe Stuelcken derrickThe hallen derrick

Hallen Derrick

Hallen DerrickThe boom is connected with the lower part of the mast which is shaped like a Y or a bipod and therefore it is a single swinging derrick. On the cross trees, two guys are fastened using swivel outriggers which are stayed vertically and horizontally. In order to maintain a good controlling angle between guys and derrick, the outriggers cannot pass the inboard parallel of the centerline. Looking at the illustration, one can easily see that the right outrigger stays in the centerline and the left outrigger has moved outboard. This derrick will lower or heave cargo as both guys are veered or hauled. Three winches, controlled by joystick, are necessary to operate the Hallen Derrick; two for the guys and one for the purchase. To avoid an over-topping or over-swinging limit-switches are used. However, the limits can be modified if a different working range or a special vertical stowage is required. The safe working load (SWL) of the Hallen is between 10 and 80 tonnes.

Velle derrick

Velle DerrickThe Velle derrick is quite similar to the Hallen but without use of outriggers. On top of the boom is a T-shaped yoke assembled. Also here, the guys serve for topping and lowering the boom but they are fastened on the yoke with four short, steel-wire hanger-ropes. The ends of the topping and lowering ends of the halyard are secured to half-barrels on one winch. In this way the boom moves in the same speed as the winch veers the topping end of the halyard and hauls the lowering end of the halyard, and vice versa. The slewing ends are also wound on to another half-barrel. For hoisting the cargo, there is a third winch to hoist to cargo on the yoke. Runners decrease swing and rotation of the cargo. A joystick duplex controller steers the Velle derrick.

cranesShips cranes are versatile and have become increasingly popular since their conception. This is because of advanced designs and flexible features.Operator cabins are positioned with aerial viewing and provide crane drivers with clear views of lifting and hoist/ ground areas.The hoist and topping lift wires are accommodated on the winch barrels found in the base of the crane beneath the cab position.

Gantry cranesGantry rigs operate on track ways which tend to travel the length of the cargo deck in order to service each cargo holdAlso used for moving the pontoon hatch coversGantry structure tends to be a dominant feature and is subject to extensive maintenance attention.Gantry cranes are suitably employed with outreach capability for working cargo to the quayside.STRESS ES ON CARGO GEARWhatever the arrangement of cargo gear, it is essential to pre calculate the loads and tensions imposed at various parts in order to determine that blocks, wires, shackles and all ancillary gear are of safe working load before being used.The parallelogram of forces may be stated as follows:if two forces acting upon a point be represented, both in amount and direction, by two sides of a parallelogram, the resultant force may be measured as the diagonal of the parallelogram, drawn from the point of application

Two forces of 10 tons and 7 tons are acting upon a shackle. One force is vertically downward and the other at a direction of 36 deg fro the vertical. What is the total force the shackle?By laying off the forces as shown and completing the parallelogram it can be seen that the total force acting upon the shackle is 15.5 tons

7 t 10 t 15.5 t

Weight = 12 tons3 fold purchase to advantage VR = 6Friction is 60%60% of 12 tons = 7.2 tonsTotal load to overcome is 12 + 7.2 = 19.2 tEffort = load/VR = 19.2/6 = 3.2 tons

By completing the parallelogram, A the diagonal of the parallelogram, represents the stress upon the shackle 14.8 tons.A1 is the force projected to form the resultant of another parallelogramB represents the thrust on the derrick 16.8 tonsC represents the stress or tension on the span 10 tons bsi