Compression weighing means weighbridges, portable weighing mats or load cells on the chassis or trailer. Ideally, containers should be weighed at or near the shipper's or consolidator's premises. This means both that the weight is verified for shipping purposes [probably not twin 20s for weighbridges and mats] and the legality of the load for road transport in terms of gross mass and axle loads can be determined.

Compression weighing is the total supply chain solution. Unfortunately, as was made clear during the final ICHCA pre-DSC/18 workshop in London last week, the supply chain is outwith IMO's competence, as its remit is shipping and port terminal to port terminal. For a total supply chain solution to the problems caused by misdelcared container weights, other intergovernmental organisations, ILO and UN-ECE, would have to be involved with IMO.

All the same, clearly there is a commercial opportunity here for enterprising container road haulage companies to provide a weighing service to the shipping line, shipper or forwarder, whichever is his contracting party for the road haul to the port. It is worth noting that some 3PL providers are now fitting axle weight readers to the side of their road trailers.

There is one total supply chain solution within IMO's competence and that is weighing-by-calculation (as proposed by Germany at DSC/17). This will likely be acceptable to shipping lines and national maritime administrations for homogenous cargoes shipped in regular trades, but the calculation methodology will probably need to be accredited to the relevant international standard and/or quality assurance audit. Clearly there is an opportunity for suppliers of FLTs used for stuffing containers to fit weight readers.

Nobody knows what percentage of the world's container traffic will be covered by weighing-by-calculation - 10%? 50%? However, individual shipping lines will have a fair idea for their own trades based on their customer profiles.

Tension weighing means hoisting equipment with a suspended container load using calibrated and certified equipment - and this generally means ports (seaports, inland ports, container barge or rail terminals) where the vast majorty of the world's container lifting equipment is located and where the container is transferred from the road truck.

This is the port solution. It is not as comprehensive as the total supply chain solution, but it will probably be the most common way of verifying container weights. Clause 14 of the draft Revised Annex 2 of SOLAS VI/2 states that "all port terminal facilities handling containers should have a means of verifying the gross mass of packed containers."

Port operators will not be obliged to provide this service - the responsibility for ensuring that the "verified gross mass is stated in the shipping document" remains with the shipper. However, many port operators will see a commercial opportunity here to enter into a container weight verification (CWV) contract with the shipping lines. Annex I of the draft Amendment to SOLAS VI/2 states: "If the shipping document with regard to a packed container does not provide the verified gross mass and the master or his representative and the terminal representative have not obtained the verified gross mass of the packed container, it shall not be loaded on to the ship."

The Port Equipment Manufacturers' Association (PEMA) will shortly issue guidelines to port operators on CWV equipment. These are believed to include the following information:

• STS gantry cranes - load cells accurate to +/- 5% of full scale (FS); subject to dynamic loads (4-5 secs to "fix" weight; twin 20 problem
• RTGs/RMGs - load cells accurate to 3-5% of FS; subject to dynamic loads (2 secs to fix weight); twin 20 problem
• MHCs - load cells or hydraulic pressure measuring, accurate to 3-5% of FS; twin 20 problem
• Straddle carriers - load cells or hoist motor current measuring, accurate to +/- 5% of FS; twin 20 problem
• Reach stackers - load cells (in rotator mounting pins) or cylinder hydraulic pressure measuring accurate to +/- 5% of FS; twin 20 problem(although reach stackers are not generally fitted with Twin 20 spreaders)
• FLTs - load cells (in the chain anchors) or cylinder hydraulic pressure measuring, accurate to +/- 5% of FS; twin 20 problem (although container handling FLTs are not generally fitted with Twin 20 spreaders)
• Spreader twistlocks - diaphragm around the twistlock or strain gauge inside it, accurate to 0.5-1% of FS; no twin 20 problem as sensors are fitted to all twistlocks

Unofficially PEMA estimates that the world population of container spreaders is around 35,000, of which those "eligible" for fitting with CWV equipment (usually the main handling equipment for stacking in the yard) is around 12,000.

Retrofitting on such a scale is highly unlikely. However, port operators willing to supply a CWV service to their shipping line customers have started to specify CVW-equipped spreaders on new handling equipment in increasing numbers. CWV equipment already in service is already being used to collect data on load ex-centricity. This can be fed back via shipping lines to shippers and encourage them to load containers more evenly, which would greatly enhance road transport safety.