Cargo Gear and Rigging — Booms, Blocks, Wire, and Safe Working Load

What the rule requires

The marking and what it means

The safe working load for the assembled gear is marked on the heel of each cargo boom, crane, or derrick, in letters and figures of contrasting colour to the background and at least one inch in height 46 CFR §28.885. That marked figure is the load the gear is approved to lift and it does not include the weight of the gear. A boom marked 5 tons lifts five tons of cargo; the boom, runner, and blocks are not deducted from it.

Every wire rope, chain, ring, hook, link, shackle, swivel, block, and any other piece of loose gear used in loading or unloading must be commensurable with that SWL rating. The marking on a boom is the SWL for that boom's rigged configuration NAVEDTRA 14343 §9-1 — re-reeve the rig and the figure that was stencilled for the old configuration no longer describes what is in front of you.

The two inspection intervals

These are the values that decide questions, and candidates confuse them constantly.

Visual inspection of loose gear — by the vessel's captain or a designee, at frequent intervals and in any event not less than once in each operating month .
Thorough examination and proof load test — biennial, that is every second year, at a minimum of the SWL rating, performed and witnessed by competent personnel.

The proof load is not simply hung on the hook. It is lifted with the ship's normal tackle, with the boom or derrick at the lowest practicable angle, and once lifted it is swung as far as possible in both directions. The low angle and the swing are what load the guys, the topping lift, and the goosenecks — the parts that fail in service.

Results and notations of both the monthly inspections and the biennial test, with the date and location of each, are maintained aboard and available to Coast Guard representatives on request.

The mate tells you the derrick was proof tested nine months ago and asks whether anything is due. What do you check?

The proof test stands — it is biennial, so it is good for another fifteen months. The monthly visual inspection of the loose gear is a separate requirement and must have been carried out in each operating month since; you check the record for it and for the notations of date and location, which have to be available for the Coast Guard .

Safe working load, breaking strength, and the safety factor

Breaking strength is the load at which a piece of gear fails. Safe working load, also called the working load limit, is the maximum load it may carry in service. The safety factor is the ratio of breaking strength to safe working load, and it buys margin for shock loading, wear, and uncertainty NAVEDTRA 14343 §8-4. General rigging commonly runs about five to one; gear that lifts personnel or takes severe dynamic loading runs higher — six, eight, or ten to one. A diameter formula gives a rough field estimate of a rope's breaking strength, but the manufacturer's certificate governs.

Three consequences of that definition come up more often than the arithmetic:

The SWL of an assembled rig is set by its weakest component. A strong runner on a weak shackle is only as safe as the shackle.
Sling leg tension rises sharply as the legs spread from the vertical. Wide sling angles greatly increase the load on each leg and its fittings; the load is shared safely only at narrow angles.
Shock loading — a slack line snatched taut — can momentarily multiply the load far beyond the static weight, and it is a common cause of gear failure. Loads are taken up smoothly.

Gear is derated for the wear, corrosion, and damage found on inspection, and gear without a legible SWL marking or a current certificate is taken out of service NAVEDTRA 14343 §9-5. Each vessel keeps a register of its lifting appliances and loose gear recording SWL, test loads, and the dates of thorough examination and proof testing.

Mechanical advantage: count the parts at the moving block

A block is a pulley in a frame; a tackle is an assembly of blocks and rope, the rope being the fall, used to gain mechanical advantage or change the direction of pull NAVEDTRA 14343 §8-2. Its parts are the shell, the sheave, the pin, and the strap or hook by which it is secured, with the swallow admitting the rope and the becket as the fixed eye for the standing part. Blocks are classed single, double, triple, and so on by the number of sheaves in the shell NAVEDTRA 14256 — Blocks.

Theoretical mechanical advantage equals the number of parts of the fall supporting the moving block. Count the lines actually pulling on the moving block and nothing else. Applied:

Single whip (one fixed block) — no advantage at all, only a change of direction.
Gun tackle (two single blocks) — two or three, depending on which block moves.
Luff tackle (a double and a single) — three or four.

The two figures for the same pair of blocks are not a hedge; they are what the counting rule produces when the hauling part leads off the moving block instead of the standing one. Friction eats into the ideal figure, so allow roughly ten percent loss per sheave.

Blocks are sized to the rope: the groove must fit it and the sheave diameter must be large enough to avoid overbending wire. Mouse the hooks so they cannot jump off, and a snatch block, with its hinged shell, lets a rope be laid in on the bight without reeving from the end.

Wire rope condition and rigging fittings

Wire rope is used where high strength and low stretch are wanted — standing rigging, boat falls, cargo runners, towing gear NAVEDTRA 14067 §3-4. A kink pulled taut permanently distorts and weakens it, so wire is unreeled and coiled without forcing turns in or out, kept off sharp edges and small-radius bends, and kept clean and lubricated against internal corrosion. Retire running wire for broken wires counted in one lay length against the limit, reduction in diameter from wear or a wasting core, corrosion and pitting, birdcaging, kinks, crushing, or heat damage. Before cutting, put seizings on both sides of the cut so the strands cannot fly apart. Wire is stronger than fibre of the same size but gives less warning before it goes.

Cargo runners and falls are running wire that fatigues quickly, so they are inspected far more often than standing rigging and renewed on wear criteria rather than on a calendar .

Wire-rope clips are the fitting most often rigged wrong, and the yard's own reminder is the one to carry into the exam room: "never saddle a dead horse." The saddle, the base of the clip, goes on the live standing part and the U-bolt on the dead end, in the correct number and torque NAVEDTRA 14343 §8-3. The rest of the fitting inspection is cracked or distorted shackles, bent pins, worn thimbles, seized turnbuckles, loose or wrongly fitted clips, and corroded end terminations. Moused shackle pins and turnbuckles locked against turning keep gear from working loose under vibration and load reversal.

Telling it apart

The criterion that separates the rigs is how the load is moved athwartships — and each answer carries a different SWL consequence.

Single swinging boom — the boom itself is slewed for every lift, by slacking one guy and heaving the other or by a slewing winch NAVEDTRA 14343 §9-2. Flexible, because the boom can spot a load anywhere in its swing, but slow, and the guys take a heavy side load whenever the load hangs off the boom head. Most often misfiled: candidates credit it with the speed of the two-boom rig.
Yard-and-stay (burtoning, married falls) — neither boom slews. One is topped and guyed to plumb the hatch, the other to plumb over the side, and the two runners are shackled to a single cargo hook NAVEDTRA 14343 §9-3. Fast, because the booms are fixed and cargo cycles continuously, but the combined pull on the married falls with the load midway between the booms can be very high, and the SWL of the yard-and-stay rig is lower than the SWL of a single boom used alone. Coordination between the two winch drivers is the whole job; out-of-step heaving overloads the union guy and the guys.
Deck crane — one operator hoists, luffs, and slews from the cab with no re-rigging, the machinery housed on a slew ring NAVEDTRA 14343 §9-4. Cranes are designed to handle 150 percent of rated load at no specified speed and to withstand a static suspended load of 200 percent of rated load without damage or distortion NAVEDTRA 14104 Ch. 10 — Cranes. Those are design figures, not permission to lift them.

Crane and winch safety devices are examinable in their own right: brakes must hold the rated load automatically when power or control is lost, limit switches stop the hook before two-blocking and stop luffing and slewing at the ends of travel, and a load indicator or cut-out prevents lifting beyond the SWL . Never override a cut-out to force a lift.

Working a question

You are rigging a single swinging boom to land a 3,600 lb crate on the pier. The boom heel is marked SWL 5 tons. The runner is rove as a luff tackle, hauling part off the moving block. The shackle at the cargo hook is stamped 4,000 lb; the sling tag is legible and rated well above the load.

Find the governing figure, not the biggest one. The 5-ton boom marking is irrelevant to whether this lift is safe, because the SWL of an assembled rig is that of its weakest component NAVEDTRA 14343 §8-4. The 4,000 lb shackle governs.
Compare load to that figure. 3,600 lb against 4,000 lb. The lift is within the rig, with 400 lb of margin and no more. Nothing gets added to the load to reach the shackle's limit — no water in the crate, no ice, no dunnage.
Check the sling legs. Widen the legs to clear the crate's corners and the tension in each leg climbs above 1,800 lb, and that tension is what the shackle and the hook see. Narrow the angle or use a longer sling.
Work out the pull on the winch. A luff tackle is a double and a single, so with the hauling part off the moving block there are four parts at the moving block: theoretical advantage four, ideal pull 900 lb. Three sheaves at roughly ten percent each adds about 270 lb, so allow about 1,170 lb at the drum NAVEDTRA 14343 §8-2.
Take the strain smoothly. Snatching the runner taut can momentarily put a multiple of 3,600 lb through that 4,000 lb shackle. This is where gear at 90 percent of SWL fails.
Set the deck before hoisting. Guys rove and made fast to rated points, gooseneck sound, blocks turning freely, hooks moused, winch brake tested, and the boom's SWL and guy leads suited to the working angle NAVEDTRA 14343 §9-1. Nobody under the load, nobody in the bight of a runner or guy under tension, and a signalman if the winch operator cannot see the landing spot NAVEDTRA 14343 §9-5.

Same lift, but the shackle's stamping is corroded to the point that you cannot read the figure. What do you do?

Take it out of service and get a shackle with a legible SWL mark or a current certificate. Loose gear without either is not used, and an unreadable mark is not an invitation to estimate from the pin diameter .

Where candidates lose the point

Answers "annually" for the proof load test. The word in the regulation is biennial, and it is defined in the text as every second year. The annual-sounding interval on this topic is the monthly visual inspection of loose gear, which is the other distractor pair in the same question.
Treats the marked SWL as including the boom, runner, and blocks, then deducts gear weight from the figure before comparing it to the cargo. The SWL excludes the weight of the gear; the whole marked figure is available for the load.
Counts every part of the fall. A three-sheave rig looks like a mechanical advantage of six until you count only the parts supporting the moving block. The single whip is the clean test of whether a candidate has this: one fixed block, no advantage, change of direction only.
Gives the yard-and-stay rig the SWL of one of its booms. The married-falls rig is rated lower than a single boom working alone, and the pull at the union guy with the load midway between the boom heads is what does the damage.
Saddles the dead end when fitting wire clips. The U-bolt goes on the dead end, the saddle on the live part.
Answers that a wide sling angle spreads the load and is therefore safer. Leg tension rises sharply as the legs spread from vertical.
Overrides a load cut-out or limit switch to complete a lift, or trusts a brake that has not been tested at the start of the watch.

Check yourself

A crane's rated load is 10 tons. Your lift is 14 tons and the crane is stated to handle 150 percent of rated load. Do you lift it?

No. The 150 percent figure is a design criterion the crane is built to meet at no specified speed, and 200 percent is a static suspended load it must withstand without damage or distortion NAVEDTRA 14104 Ch. 10 — Cranes. Neither figure raises the SWL, and the load indicator or cut-out is there to prevent exactly this lift NAVEDTRA 14343 §9-4.

Where must the SWL be marked on a cargo boom, and to what standard?

On the heel of the boom, in letters and figures of contrasting colour to the background, at least one inch in height 46 CFR §28.885.

A runner has a certified breaking strength of 40,000 lb and is used for general cargo rigging. What SWL do you work to, and what changes if the same wire is used to hoist a stage with men on it?

At a factor of about five to one, SWL is 8,000 lb. Gear lifting personnel takes a higher factor — six, eight, or ten to one — so the same wire would be worked to a substantially lower limit NAVEDTRA 14343 §8-4.

You are hoisting with a gun tackle and the load will not start. A shipmate suggests re-reeving so the hauling part comes off the other block. Can that help?

Yes. A gun tackle gives an advantage of two or three depending on which block moves, so re-reeving so that an additional part of the fall supports the moving block gains one increment of advantage NAVEDTRA 14343 §8-2. Confirm the block and its hook are rated for the load either way.

Inspecting a cargo runner before working cargo, you find the strands sprung apart over about a foot of its length. Is this a defect you can dress and keep working?

No. Birdcaging is cause to retire the rope, as are broken wires beyond the limit in one lay length, reduction in diameter, corrosion and pitting, kinks, crushing, and heat damage NAVEDTRA 14067 §3-4.

Your vessel's booms were thoroughly examined and proof tested last year and the shackles, hooks, and blocks look sound. What are you still required to do this month?

Carry out the visual inspection of all wire rope, chains, rings, hooks, links, shackles, swivels, blocks, and other loose gear — the captain or a designee, not less than once in each operating month — and record the result with its date and location .

How is the biennial proof load applied, and why at that boom angle?

With the ship's normal tackle, at a minimum of the SWL rating, with the boom or derrick at the lowest practicable angle, and once lifted it is swung as far as possible in both directions . The low angle and the swing put the strain into the topping lift, guys, and gooseneck rather than testing the hoist alone.