Cargo Work

Cargo Work

i. Bale capacity cubic capacity of a space when the breadth is taken from the inside of the cargo battens, the depth from the wood ceiling to the underside of the deck beams and the length from the inside of the bulkhead stiffeners.

ii. Grain capacity cubic capacity of a space when the lengths, breadths and depths are taken right to the plating. An allowance is made for the volume occupied by frames and beams.

iii. Stowage factors the volume occupied by unit weight of cargo. Usually expressed as cubic meters per tonne. It does not take into account any space which may be lost due to broken stowage.

iv. Broken stowage it is the space between packages which remains unfilled. The percentage that has to be allowed varies with the type of cargo and with the shape of the hold. It is greatest when large cases have to be stowed in an end hold

v. Measurement cargoes cargo on which freight is usually charged on the volume occupied by the cargo and this cargo is usually light, bulky cargo stowing at more than 1.2m3/tonne but may also be heavy castings of an awkward shape where a lot of space is occupied.

vi. Deadweight cargoes cargo on which freight is charged on its weight. Cargo stowing at less than 1.2m3/tonne is likely to be rated as deadweight cargoes.Cargo Handling Equipment:

Union purchase1. A speedy method of working cargo.

2. It should not be used for loads in excess of 2.55 tonnes or 1/3 of the SWL of the lowest rated derrick used, whichever is the least.

3. 2 derricks are used, one being positioned so as to plumb the hatch and the other to plumb overside.

4. The runners of the 2 derricks are joined by a union hook.

5. Schooner guy is fixed between 2 derricks to avoid them splaying apart as they rise. 2 derricks should be topped together

6. The 2 derricks are held in position by slewing guys. So the derricks do not move during operation. Only 2 cargo runners move. Preventer guys should be fitted in addition to slewing guys, passing over the derrick head once the derricks have been floated from crutches.

7. The derrick which plumbs the load first takes the weight and when the load has been lifted above gunwale height, the weight is gradually transferred to the second derrick.

8. When the second derrick has all the weight, its fall should be slacked away until the load is landed in the desired position.

9. It should be noted that if the angle between falls is 120 degree and the load is midway between the derricks, the tension on each fall is approximately equal to the weight lifted. This angle should not be exceeded.

10. When a load is suspended between 2 derricks, there is a considerable side-ways pull on each. This tends to bring the 2 derricks heads together, and for this reason, a preventer guy should always be rigged to back up the outboard guy on each derrick

Swing derrick1. Suitable for dealing with heavier lifts than the union purchase

2. The derrick may be swung to plumb the desired position

3. A deadman may be used instead of a winch to operate one of the guys.

4. This consists of a weight which is positioned on the offshore side of a vessel.

5. The derrick may then be swung in one direction by a guy led to a winch and in the other by the dropping of the dead man.

Single whip1. Used in conjunction with a bullrope for discharging light cargoes.

Heavy lift derrick / Jumbo derrick

1. Check the vessel is upright and on even keel

2. Clear away other rigging in the way of operation3. Clear away canvas covers

4. Rig preventer backstays to the mast

5. Ensure the topping lift in good condition, securely shackled

6. Engage 2 winches - port and starboard power guys. Check the leads and moving blocks clear

7. Engage 2 winches lifting purchase and topping lifting

8. Pass wire messenger about the derrick head and remove the clamp holding the derrick to the mast

9. Lower derrick to secure lifting purchase.

10. Check all winches are in double gear and all rigging is secured

Safe Working Load

1. Breaking strength divided by the safety coefficient

Safe Handling Practice for derricks

1. Derrick rigging should be regularly maintained with plan. Visually check before use

2. Before raise, lower and adjust a derrick, the hauling part of the topping life should be flaked down the deck clear of the operational area. All persons should stand clear

3. When topping lifts are secured to bitts, 3 complete turns should be taken before the 4 cross turns on top. Place a light lashing to prevent spring off of the wire.

4. When the rig is to be changed, the derrick head should be lowered to the crutch or to deck level for safety

5. The pawl of winch should be lifted to allow the derrick to be lowered. Seaman should pay attention when performing this duty and ready to release the pawl.

6. Winch driver should take instructions from a single controller with a clear view of operation. The winch speed should be in consistent with the safe handling of the guys

7. Cargo runners should be secured to winch barrels by U bolts and minimum 3 turns should remain on the barrel when fully extended.

8. When dragging heavy cargo from tween deck, the runner should be used direct from the heel block via snatch blocks

Safe Handling Practice for Union Purchase Rig1. Safe working angle between married cargo runners should not exceed 90 degrees to avoid excessive tension

2. Cargo sling should be kept as short as possible to clear the hatch coaming

3. Derrick should be topped as high as possible

4. Derrick should be marked with the SWL when rigged for union purchase. Otherwise, the SWL should not be more than 1/3 of single derrick

5. Preventer guys of adequate strength should be rigged on the outboard side of each derrick, and secured to the deck with similar tension with slewing guys but to different eyes.

Safe Handling Practice for heavy lift (jumbo) derrick1. Officer to check the lift can be carried out safely and successfully. Ensure SWL of derrick adequate. Grease if need.

2. Give warning of expected list of ship to crew

3. Gangway lift clear of quayside, fore and aft moorings tended, ensure no damage will be incurred by heeling

4. Stability should be checked, concern the free surface effect, rise of G should not render unstable

5. Cast off any barge alongside our ship

6. Examine all rigging by officer. Secure all preventer backstays to the supporting mast. Use correct slings on the load with beam spreaders. Secure steadying lines on the 4 corners of the load to control oscillations during lifting

7. Rig and test steam guys and power guys to ensure correct leads. Winches should all be in double gear

8. Check the lugs on the load. Check the crate/container of the load is reinforced

9. All non-essential person clear away

10. Check no obstruction but enough dunnage on place to land

11. Rid fender as necessary

12. Take weight slowly then stop and inspect all round before proceed.

13. The ship may return sharply after landing the load. The offshore guy could be ease out as the load lands and lifting purchase veer smartly. Winch driver should be competent and under control of single person

Types of hatch covers in general use and their safe opening, closing, sealing and securing. Tank lids, trunkway doors, ventilation systems, hatches and other openings to cargo spaces.2. The stowage of general and mixed or unitized types of cargoes in general cargo ships. The making and use of cargo plans. Preparation of holds. Use of dunnage. Separation of cargoes. Loading and discharging processes and the securing of different types of cargo including heavy items. How to prevent or minimize cargo damage due to sweat and pilferage.i. Cargo plans

1. A cargo plan can help to prevent over-carrying, help the stevedores at the port of discharge

ii. Preparation of holds

iii. Use of Dunnage

1. Ship side spar ceiling/cargo battens. It consist of timber fit over the side frames horizontally into cleats on the frames. It may also be fit on the bulkheads at the end of the compartment

2. Tank top covered with a double layer of dunnage to ensure free drainage to the bilges.

3. Tween deck care to have a layer of dunnage at ship side over the stringer plate since water tends to accumulated there

4. Top of cargo protected by covering by matting, wood dunnage.

iv. Separation of Cargo

1. Method depends on type of cargo

Instance-bagged cargo by separation cloths made of burlap

Steel rails by chalk marks, water paint or strands of wire

Bulk cargo by old tarpaulins or separation cloths

Bales by rope yarns

Timber by water paints

2. Use polythene sheeting in various colour to separated cargo for different ports

3. Avoid mixing cargo by adequate vertical or horizontal separation

4. When cargo is packed in large containers, separation of small quantity is obviated and effort of handling can be reduced.

v. Loading and discharging processes

vi. Securing of cargo

vii. Sweat

1. Sweat is formed when the water vapour in the air condenses out into water droplets when the air is cooled below its dew point.

The water droplets may be deposited onto ships structure, it is known as ship sweat and this may run down onto the cargo.

The water droplets may be deposited onto the cargo, it is known as cargo sweat. It occurs when the cargo is cold and the incoming air is warm.

2. Prevention

Take the dry and wet bulb temperature of cargo compartments frequently.

If temperature of outside air is lower than dew point of the air in cargo hold, ship sweat occur (voyage from warm to cold place).

If temperature of air in cargo hold lower than the incoming air, cargo sweat occur (voyage from cold to warm place). For this case, ventilation from outside air should be stopped

viii. Prevent Pilferage

1. Cargo to be loaded into a lock-up, or overstowed quickly if in an open hold

2. Good lighting provided at night.

3. Provide watchman. Also, officer to visit the cargo space frequently

4. Cover ventilators by wire mesh

5. Check hatches are properly closed and locked after work finished for that hold

Ships' derricks should be properly rigged and employers and masters should ensure that rigging plans are available containing the following information:-

(1) position and size of deck eye-plates;(2) position of inboard and outboard booms;(3) maximum headroom (i.e. permissible height of cargo hook above hatch coaming);(4) maximum angle between runners;(5) position, size and safe working load of blocks;(6) length, size and safe working load of runners, topping lifts, guys and preventers;(7) safe working load of shackles;(8) position of derricks producing maximum forces(9) optimum position for guy and preventers to resist maximum forces as at (h);(10) combined load diagrams showing forces for a load of 1 tonne or the safe working load;(11) guidance on the maintenance of the derrick rig.

The operational guidance in the remainder of this section applies generally to the conventional type of ship's derrick. For other types, such as the "Hallen" and "Stulken" derricks, manufacturers' instructions should be followed.

Runner guides should be fitted to all derricks so that when the runner is slack, the bight is not a hazard to persons walking along the decks. Where rollers are fitted to runner guides, they should rotate freely.

Before a derrick is raised or lowered, all persons on deck in the vicinity should be warned so that no person stands in, or is in danger from, bights of wire and other ropes. All necessary wires should be flaked out.

When a single span derrick is being raised, lowered or adjusted, the hauling part of the topping lift or bull-wire (i.e. winch end whip) should be adequately secured to the drum end.

The winch driver should raise or lower the derrick at a speed consistent with the safe handling of the guys.

Before a derrick is raised, lowered or adjusted with a topping lift purchase, the hauling part of the span should be flaked out for its entire length in a safe manner. Someone should be available to assist the person controlling the wire on the drum and keeping the wire clear of turns and in making fast to the bitts or cleats. Where the hauling part of a topping lift purchase is led to a derrick span winch, the bull-wire should be handled in the same way.

To fasten the derrick in its final position, the topping lift purchase should be secured to bitts or cleats by first putting on three complete turns followed by four crossing turns and finally securing the whole with a lashing to prevent the turns jumping off due to the wire's natural springiness.

When a derrick is lowered on a topping lift purchase, someone should be detailed for lifting and holding the pawl bar, ready to release it should the need arise; the pawl should be fully engaged before the topping lift purchase or bull-wire is released. The person employed on this duty should not attempt or be given any other task until this operation is complete; in no circumstances should the pawl bar be wedged or lashed up.

A derrick with a topping winch, and particularly one that is self-powered, should not be topped hard against the mast, table or clamp in such a way that the initial heave required to free the pawl bar prior to lowering the derrick cannot be achieved without putting an undue strain on the topping lift purchase and its attachments.

A heel block should be secured additionally by means of a chain or wire so that the block will be pulled into position under load but does not drop when the load is released.

The derrick should be lowered to the deck or crutch and properly secured whenever repairs or changes to the rig are to be carried out.

If heavy cargo is to be dragged under deck with ship's winches, the runner should be led directly from the heel block to avoid overloading the derrick boom and rigging. Where a heavy load is to be removed, a snatch block or bull wire should be used to provide a fair-lead for the runner and to keep the load clear of obstructions.

Use of derricks in union purchase

When using union purchase the following precautions should be strictly taken to avoid excessive tensions:-

(i) the angle between the married runners should not normally exceed 90 and an angle of 120 should never be exceeded;

(ii) the cargo sling should be kept as short as possible so as to clear the bulwarks without the angle between the runners exceeding 90 (or 120 in special circumstances);

(iii) derricks should be topped as high as practicable consistent with safe working;

(iv) the derricks should not be rigged further apart than is absolutely necessary.

The following examples will show how rapidly loads increase on derricks, runners and attachments as the angle between runners increases:

a) At 60 included angle, the tension in each runner would be just over half the load;

b) At 90 the tension would be nearly three-quarters of the load;

c) At 195 the tension would be nearly 12 times the load.

When using union purchase, winch operators should wind in and pay out in step, otherwise dangerous tensions may develop in the rig.

An adequate preventer guy should always be rigged on the outboard side of each derrick when used in union purchase. The preventer guy should be looped over the head of the derrick, and as close to and parallel with the outboard guy as available fittings permit. Each guy should be secured to individual and adequate deck or other fastenings.

Narrow angles between derricks and outboard guys and between outboard guys and the vertical should be avoided in union purchase as these materially increase the loading on the guys. The angle between the outboard derrick and its outboard guy and preventer should not be too large and may cause the outboard derrick to jack-knife. In general, the inboard derrick guys and preventer should be secured as nearly as possible at an angle of 90 to the derrick.

Use of stoppers

Where fitted, mechanical topping lift stoppers should be used. Where chain stoppers are used, they should ALWAYS be applied by two half-hitches in the form of a cow hitch suitably spaced with the remaining chain and rope tail backed round the wire and held taut to the wire.

A chain stopper should be shackled as near as possible in line with the span downhaul and always to an eye plate, not passed round on a bight which would induce bending stresses similar to those in a knotted chain.

No stopper should be shackled to the same eye plate as the lead block for the span downhaul; this is particularly hazardous when the lead block has to be turned to take the downhaul to the winch or secure it to bitts or cleats.

The span downhaul should always be eased to a stopper and the stopper should take the weight before turns are removed from the winch, bitts or cleats.

Overhaul of cargo gear

When a cargo block or shackle is replaced, care should be taken to ensure that the replacement is of the correct type, size and safe working load necessary for its intended use.

All shackles should have their pins effectively secured or seized with wire.

A special check should be made on completion of the work to ensure that all the split pins in blocks etc. have been replaced and secured.

On completion of the gear overhaul, all working places should be cleaned of oil or grease.

Derricks are long hollow steel booms rotating on swivels (heel), they each have a part rope guy and a steel pendant which is used for heaving and positioning the derrick and also to keep the derrick in place. The rope is used in a tackle and can absorb sudden shocks, which come on the derrick while in operation. On the opposite side to the cargo being worked a preventer guy made of wire rope is fitted which is kept slightly slack than the rope guy, This enables the rope guy to stretch before any load comes on the preventer guy. This preventer is the last shock and strain absorber, if the preventer is weak or is damaged it can part with disastrous consequences. So maintaining the preventer and fixing it right is of utmost importance.

When the two derricks are used together such that one derrick is positioned just above the loading area on the jetty and the other is positioned above the un loading area within the hold, and the gynfall (load lifting) wires are joined together, the arrangement is called a UNION PURCHASE. This is the fastest method of working cargo, however the loads that this arrangement can lift are less than the individual SWL of the derrick. Additionally there is a risk of the angle subtended at the hook point between the two-gynfall wires going beyond 120degrees when the gynfall wires together act as a pulling force on the derricks laterally and can part the rope guys and or the preventer wire.

Thus while the Union Purchase may be the fastest method it requires careful rigging of the derricks as well as experienced winch men to handle the operation together with the duty officer keeping an alert watch on the working of the same.

Mechanical advantage

The mechanical advantage of a block and tackle is equal to the number of parts in the line, that either attach to or run through the moving block, or the number of supporting ropes. For example, take a block and tackle with 2 sheaves on both the moving block and the fixed block. If one compares the blocks, one will see one block will have 4 lines running through its sheaves. The other will have 4 lines running through its sheaves (including the part of the line being pulled or hauled), with a 5th line attached to a secure point on the block. If the hauling part is coming out of the fixed block, the block and tackle will have a mechanical advantage of 4. If the tackle is reversed, so that the hauling part is coming from the moving block, the mechanical advantage is now 5.

The mechanical advantage of a tackle is relevant, because it dictates how much easier it is to haul or lift your load. A tackle with a mechanical advantage of 4 (a double tackle) will be able to lift 100 lbs with only 25 lbs of tension on the hauling part of the line. In the diagram on the right the mechanical advantage of the tackles shown is as follows:

Gun Tackle = 2

Luff Tackle = 3

Double Tackle = 4

Gyn Tackle = 5

Threefold purchase = 6

The formula used to find the effort required to raise a given weight is:

S * P =W +(nW)/(10)

Where: S is the power in the hauling part. P is the power gained by the purchase (this is the same as the number of parts at the moving block). n is the number of sheaves in the purchase. W is the weight lifted. 10 is the denominator of the fraction for friction. An arbitrary 10% is used for each sheave.

Mechanical advantage correlates directly with velocity ratio. The velocity ratio of a tackle refers to the relative velocities of the hauling line to the hauled load. A line with a mechanical advantage of 4 has a velocity ratio of 4:1. In other words, to raise a load at 1 meter per second, 4 meters of line per second must be pulled from the hauling part of the rope.

Friction The increased force produced by a tackle is offset by both the increased length of rope needed and the friction in the system. In order to raise a block and tackle with a mechanical advantage of 6 a distance of 1 meter, it is necessary to pull 6 metres of rope through the blocks. Frictional losses also mean there is a practical point at which the benefit of adding a further sheave is offset by the incremental increase in friction which would require additional force to be applied in order to lift the load. Too much friction may result in the tackle not allowing the load to be released easily or by the reduction in force needed to move the load being judged insufficient because undue friction has to be overcome as well.

Rigging methods A tackle may be

"Rigged to advantage" - where the pull on the rope is in the same direction as that in which the load is to be moved. The hauling part is pulled from the moving block.

"Rigged to disadvantage" - where the pull on the rope is in the opposite direction to that in which the load is to be moved. The hauling part is pulled from the fixed block.

While rigging to advantage is obviously the most efficient use of equipment and resources, there are several reasons why rigging to disadvantage may be more desirable. The decision of which to use depends on pragmatic considerations for the total ergonomics of working with a particular situation. Lifting from a fixed point overhead is an obvious example of such a situation. Pawl

A winch mechanism that is capable of sustained, heavy load operation comprises a frame, a ratchet, and a pawl for cooperative engagement with a pinion and a drum gear. The frame includes a plurality of apertures positioned proximate to the pawl axle, one aperture for each mode of operation of the winch mechanism. Pawl position relative to the pinion is defined by the position of a ratchet plug and the apertures in the frame. The winch mechanism includes a forward-engaged mode, a reverse-engaged mode, and a free-spooling mode. A wave washer urges the ratchet plug into one of the apertures once the ratchet mode is determined

Pawl Pawl pinA 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 it and over its top with a hook on the end, like with a crane. It is commonly used in docksand onboard ships. Some large derricks are mounted on dedicated vessels, and are often known as "floating derricks".

The device was named for its resemblance to a type of gallowsfrom which a hangman's noosehangs. The derrick type of gallows in turn got its name from Thomas Derrick, an English executionerfrom the Elizabethan era.

Oil derrick

Another kind of derrick is used over oil wellsand other drilled holes. This is generally called an oil derrick and is a complex set of machines specifically designed for optimum efficiency, safety and low cost. This is used on some offshore oil and gas rigs.

The centerpiece is the archetypical derrick tower, used for lifting and positioning the drilling string and piping above the well bore, and containing the machinery for turning the drilling bit around in the hole. As the drill string goes deeper into the underlying soil or rock, new piping has to be added to the top of the drill to keep the connection between drill bit and turning machinery intact, to create a filler to keep the hole from caving in, and to create a conduitfor the drilling mud. The drilling mud is used to cool the drilling bit and to blow rock debris clear from the drill bit and the bottom of the well. The piping jointssections -- usually each about 10 meters (30 ft) long -- have threaded ends, so they can be screwed together. The piping is hollow to allow for the mud to be pumped down into the drilling hole, where it flushes out at the drilling bit. The mud then proceeds upwards towards the surface on the outside of the piping, carrying the debris with it. ..

The derrick also controls the weight on the drilling bit, because the drill bit works at an optimum rate only when it is pushed with a precise degree of pressure relative to the rock beneath it. Too much weight can break the drilling bit, and not enough weight will prolong drilling time. At the start of drilling extra heavy piping collarsare used to create enough weight to drill. Since the weight of the pipes above the drill bit will increase the pressure on it as it goes deeper, the derrick will apply less pressure as piping sections are added. It will eventually lift the nearly entire drill string-and-piping complex to prevent too much weight as the well goes deeper.

Because of all these different requirements, done under high cost and time pressures, in any climate and virtually any place in the world, combined with the fact that the purpose is to find flammable or explosive fossil fuels, oil drilling is a complex and dangerous business.

The people who do this hard work do so under dangerous circumstances and often in considerable isolation, especially when on offshore drilling platforms.

Patent Derrick Systems

Hallen Derrick

The 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. In a Hallen Universal derrick, which has no Hallen D-Frame, the halyard has an extended length since it runs through further blocks on the centerline. The Universal Hallen derrick, replacing the D-Frame option, is a kind of traditional topping lift. The Hallen D-Frame is a steel bracket welded on the mast in the centerline. For an observer standing abeam, the frame has a D-shape. The D-Frame supersedes the outriggers and provides a good controlling angle on the guys. The Hallen derrick has a good purpose for e.g. containers, logs, steel rail, sawn timber and heavy lifts and doesn't lend itself for small, general cargo. It keeps the deck clear of guy ropes and preventors. Only one winchman is needed and within a few minutes the Hallen is brought into use. It is less expensive than a crane. A disadvantage is the low working range of the Hallen Derrick, it is able to swing 75 from the centerline and can work against a list of up to 15.

Velle Derrick

The 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.

Stlcken Derrick

The patent Stlcken derrick is used for very heavy cargo. It stems from the German shipyard Blohm + Voss GmbH. This derrick can handle up to 300 tonnes. The Stlcken can be made ready in few minutes, which is a lot faster than a traditional heavy derrick, doesn't require lots of space and is operated by four winches. Between two v-shaped, unstayed Samson-posts is the Stlcken secured. This makes it possible to let the derrick swing through the posts to reach another hatch. For each post is a hoisting winch, a span winch and a lever that is run by one man only. Bearings, swivels, sheaves and the gooseneck can be unattended for up to four years and create only a friction of about 2%. The span tackles are independent and the halyard is endless. With the revolving suspension heads on the posts it takes ten minutes to swing all the way through. In the double-pendulum block type, half of the cargo tackle can be anchored to the base of the boom. In order to double the hook speed, the halyard passes through the purchases since one end is secured which reduces the SWL to its half. Typical dimensions of a 275 tonne Stlcken are: 25.5 m length, 0.97 m diameter, 1.5m to 3.4m diameter of posts, 18m apart the posts (upper end) and 8.4m apart the posts (lower end). The hook of a full-loaded 275tonne Stlcken can move 2.3m per minute. If only one purchase is secured and the derrick is loaded with 137tonnes the hook gains velocity to 4.6m per min. Even more speed can be gained when the winch ratios are reduced to 100tonnes (triple speed) and 68tonnes (quadruple speed). Detaching the union table the double-pendulum block type of Stlcken is able to swing through which allows the lower blocks to swing freely to each side of the boom. In this way the derrick reaches a vertical position. A bullrope easily pulls the derrick to the other side until the weight of the cargo tips the derrick over. The span tackles now have the weight on the other side. The union table is fixed again and the derrick can start its work on the other side. There are also Stlcken with single-pendulum blocks. At this type the cargo hook is detached and the lower and upper cargo block are hauled into the center of the Stlcken. To tip the derrick over the gravity is here used again. A derrick helps pump oil in most offshore rigs.

Limber boards - Gutters or conduits on each side of the keelson to afford a passage for water to the pump well.Limber boards (Naut) short pieces of plank forming part of the lining of a ship's floor immediately above the timbers, so as to prevent the limbers from becoming clogged