SPOTCHECKSAFETY
• Rolling the crane on/off using multi- wheel trailers, dollies or jack bogies,
• Skidding the crane on/off using skid shoes sliding over skid tracks
• Lifting the crane on/off using a large floating crane or sheerleg. All loading methods require a careful
ballasting of the vessel or barge during the actual operation to ensure the deck remains level with the quay during the load transfer, while also compensating for any tide changes. If conditions at the discharge location are
favourable, the crane is unloaded in the same fashion. If not, an alternative offloading method has to be used, resulting in for instance a roll-on/skid-off operation, or a lift-on/roll-off operation.
Design criteria Using risk-based criteria, a slow towed barge with a long exposure window will see a higher design wave height compared with a faster ship-based transport over the same route. A ship also has a better chance of
avoiding stormy areas and has the ability to control its wave heading in adverse conditions. A barge can be over a kilometre behind its tug, allowing for little, if any, heading control.
Seafastening In order to ensure the safe transportation of a container crane, it needs to be secured to the deck and internally reinforced. The crane structure by itself is typically not strong enough to accommodate the worst- case inertia forces it may be subject to during the voyage. Additional bracings may be required to stiffen the large open portals. Crane manufacturers have developed in-
house systems for use on their new cranes to be delivered. Often the components are sized so that they can be shipped back to the yard in standard containers and re-used on the next shipment. For older cranes, bracings are often custom-designed. After loading, the container crane is
supported under its wheels by rails or flat bars. Stoppers welded on either side of the outer bogie wheels prevent rolling. Before the voyage can commence, the crane has to be secured to the deck of the carrier. The crane corners are rigidly connected to the vessel deck using pipe seafastenings. During the transport, the barge and ship hulls will flex in the waves. The spacing between the crane legs is typically small enough not to be significantly affected by this deflection of the carrier. However, if the boom tip of a longitudinal stowed crane is supported, this support
98 January/February 2017
After loading, the container crane is supported under its wheels and secured with heavy seafastening
pipes, welded to the crane corners and the vessel deck.
must allow for some relative motion. All seafastenings are to be designed so
that there is a clear load path and high stress areas are avoided. Brackets need to be supported by strong points inside the crane structure and under the barge/ship deck. In case of high local point loads, adequate load spreading has to be provided. Full welding of the seafastenings should not commence until the barge or ship has been ballasted to its final departure condition. Unless used for securing of small items
and packages, stretchable lashings such as wire ropes can only be used on manned ships, where the crew can check the wire tension on a daily basis and adjust where necessary. All nuts and bolts must be secured to ensure they do not come loose during the voyage. Any shackles and turnbuckles also need to be secured so that they cannot become unscrewed.
Internal seafastenings During the transport, the crane will move back and forth tens of thousands of times. Any play will allow for a small movement that may become larger over time, thus increasing the mass inertia, until a critical point is reached resulting in failure. Internal seafastenings are applied in order to limit any movement and prevent (heavy) items
All seafastenings are to be designed so that there is a clear load path and high stress areas are avoided.
from gaining momentum and breaking or causing damage. When the cranes are transported by
towed barge, the inspections are limited to frequent remote checks of the overall condition through binoculars. With the barge trailing the tug at a large distance, no details will be visible. Barge roll motions can only be estimated.
Inspections During a ship-based transport, the cranes can be inspected daily from top to bottom, weather permitting and provided that safe access is available. The seafastenings between the cranes and the deck are inspected for cracks or other signs of high stress. Minor repairs and fixes (re-inserting of shim plates for instance) can be made before it is too late. The ship motions are monitored and recorded. In adverse weather conditions, the speed and heading of the ship can be optimised to minimise the accelerations on the crane and avoid exceeding the design values. Cargo safety is of primary concern and
areas with severe weather are avoided if at all possible. Once under way, daily weather forecasts will assist the master to plot his course and make changes where needed. In case of very restrictive design criteria, active weather routing by a specialised weather routing service will further help the master in plotting the best possible route. Proper engineering, crane preparation
and reinforcements, seafastening, warranty survey and prudent seamanship will ensure the safe arrival of the cranes at their final destination, whether transported by towed barge or by self-propelled ship. HLPFI
www.heavyliftpfi.com
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