Yantai Raffles' big gamble

Dockside shipbuilding cranes seem to primarily take two shapes. There are balance cranes, which resemble luffing-jib tower cranes, and hang a counterweight at height that helps them raise heavy loads. And there are very large gantry cranes: horizontal beams sitting on a pair of travelling or stationary uprights.

Probably the biggest-ever gantry crane, with a maximum capacity of 20,000t, was tested with full load in April at the Yantai Raffles shipyard in Yantai, Shandong province, China. Named after a mountain, the Tai Sun crane is suitably huge. Built into a 380m by 120m dry dock, it resembles a pair of asymmetric bars used by gymnasts. The top bar is 114 m above ground, the second bar 89m. The crane is intended for huge offshore platforms: the largest production units, accommodation modules, and deck boxes placed high on vessels.

"Big projects need big solutions," Brian Chang, executive chairman of Yantai Raffles Shipyard, tells Cranes Today. "To build major projects worth several hundred million dollars, which are sequential processes, you need to have a crane handle units as it handles a 50t block."

This manufacturing method saves shipbuilders weight and time, he argues. "If they can design their 15,000t module in one integrated piece instead of 30 blocks, they can reduce their structure weight, piping, cabling, by perhaps 25% of the total weight.

"If you can handle the larger blocks, 15,000t-16,000t, you can chop up a semi-submersible offshore platform into two pieces: lower pontoon columns and an upper deck box.

"When you do that, you end up being able to outsource deck boxes to partners with lesser facilities than you; you are scalable, you can handle multiple projects, and these deck boxes, although 15,000t, can be built in more facilities, not only in your own, and the erection time would be only a few days to lift it up, put it on [the pontoons] and then do some welding.

"This operation brings all the work down to the ground. Bringing this work to the ground means that we have a better turnaround time, better safety, better quality, and of course lower cost. Then you are able to do multiple projects without incurring the full infrastructure costs to do everything in your own yard. In this way we say that we are emulating automotive and aeronautics industry, the business is reduced to assembly and not full manufacturing."

Chang founded the Yantai Raffles Shipyard Ltd in 1994 in Singapore. Over his 40-year career, the Singapore native has overseen 600 projects and pioneered construction of Singapore’s first jack-up drilling rig at Far East Levingston Shipbuilding (now Keppel FELS). The company converted the existing Yantai shipbuilding and repair facility into a much larger facility specialising in offshore platforms. It has a large land-based pedestal crane and two 370t-capacity gantry cranes.

The Tai Sun crane has been engineered to reduce risk, Chang says. "Cranes are unsafe in so many ways. In the shipyard cranes are one of the major causes of accidents. When it rotates it presents a problem. Slings of all types present major problems. Hooks and pad-eyes [lifting brackets] present many problems. Now, generally speaking, pad-eyes cannot be tested. The only time they are tested is when they are lifted, so they have that risk.

"If you are doing lifting with floating cranes, the only cranes with sufficient capacity, of approximately 3,000t-4,000t, have limited reach and limited height. These cranes will sway with the waves and the wind.

“Our crane is 120m wide. It has sufficient reach. And it has sufficient height: one beam is nearly 120m above the bottom of the dry dock. The load is inside a dry dock, so it is safe from waves. And it is fast. In two hours it can lift a deck box up, and lower it down faster. So we can react in an instant to weather changes. We do not use slings, we do not use pad-eyes in our lifting operation.

“We have a patented device that puts even loading at every sling right across the deck box. Our single point loading is 52t, so this evens out all the load along the whole deck box or whatever module we lift. This means that we do not put any stress into the deck box."

The two parallel steel beams, 126m long, rest on four concrete columns. The seaward gantry is 114m high to accommodate semisubmersible derricks; the other is 84m high. Fully outfitted with six winches each, wires, controls, transformers, each steel beam weighs 4,800t. The lower beam sits on a wider pair of concrete columns that can be raised on hydraulic jacks and rolled back and forth on a 10m-long track to change the distance between the two from a minimum of 35.5m to a maximum of 45.5m. He expects the dry dock water to be about 11m deep.

The winches can be synchronised to work together and operated individually. They all have variable-speed drive, and have a safety factor of four to five times. Each winch has a 2,000t capacity, and there are six on each beam.

The rigging

Each winch spools more than 3,100m (1,400ft) of 2in (51mm) diameter wire rope into four pulley blocks reeved with 10 falls of rope. Each pulley block terminates in a triangle. On each corner hangs another triangle. Suspended from these are more triangles, each corner of which has two C-shaped connectors. This rigging arrangement divides a 20,000t load by a total of 384 lifting points (12 winches, each with 4 pulley blocks, each with 8 connectors), yielding a single point loading of 52t.

At the end of the crane's wire rope hangs a C-shape circular clamp. The crane rigging has been arranged so that when they are at rest, the C clamp openings hang down. To attach the deck to the crane, riggers pick up and rotate the clamps, and slip them over a 3-inch bar welded to the side of the load.

Brian Chang outlines the lift process. "If you have a deck load that is 20,000t, and you want this thing lifted, we study it, and see if it is liftable. Some things are not liftable: they break under their own weight.

“If you present two lines on the module that can carry 20,000t, we will weld a 30mm section right on to the module, 80m long, and on top of the plate is a 3in diameter round bar, like a handrail. You deliver this to me afloat. I put it into dry dock, and it takes us a few hours to get C clamps right on the rail. Then after that, you don't have to wait for the tide, or anything, we can start lifting it out of the water. We can achieve a 10m per hour lifting rate."

Chang points out that the single lift would be in the middle of a week-long turnaround project, which would mainly involve welding the load so that it is stable enough to sail away.

The shipyard's current pressing problem is finding customers to use the crane, which cost $40m, excluding the infrastructure and dry dock. Chang estimates a payback period of three to four years. But he says that the crane's first lift, a 12,500t deckbox for a semi-submersible drilling rig the yard is building for Awilco Offshore Semi ASA, will not be raised until August or September this year. He says that full utilisation would be 10-15 lifts a year, leaving plenty of excess capacity. "I don't think that it will ever be fully booked. There aren't 50 of these projects a year in the world."

"At this time there are a lot of projects using small crane assembly, looking at putting small blocks together at great heights. None have planned a big lift, because there were no such cranes until now. Now we are talking with customers on this basis."