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WEATHER DEPENDENT LASHING
‘On 99% of the voyages, a reduction in lashings can be achieved using our WDL method, without compromising on the safety of crew, vessel and cargo.’
Weather Dependent Lashing (WDL) is the methodology that allows ship operators to reduce the amount of unnecessary lashings in favorable weather conditions.
The required amount of lashings that are prescribed in the Cargo Securing Manual (CSM) are sufficient for sailing in extremely adverse weather conditions.
Modern weather forecasts allow continuously monitoring of weather conditions anywhere on the globe. When it is known that weather conditions on the upcoming voyage will be favorable, there is no need to install excess lashings.
Siri Marine has developed a unique Flag-state and Class approved Weather Dependent Lashing system that assists the Master with choosing the most optimal lashing plan for each voyage.
A Siri Marine Decision Support System is installed on the vessel to record motion data. Measured accelerations are combined with actual wave heights and provide a matrix of forces versus wave heights for various weather conditions. This provides insight in the seagoing behaviour of the specific vessel. With the outcome of the verification period, three lashings schemes are defined: light, heavy and IMO CSM lashing. For each lashing scheme, the required amount of lashings for the various cargo positions are calculated.
This leads to a ‘WDL manual’, a documentation package that contains the outcome of all lashing calculations, which is approved by Class. When utilizing WDL, the forecasted wave height for the upcoming voyages determines the applicable lashing scheme. Ship specific hand-outs provide a simple to use overview of the required amount of lashings for the various cargoes.
Significant lashing reductions can be achieved by using the Siri Marine WDL method. The figure below gives an overview of a ship specific lashing arrangement for a selection of cargo types for the different lashing schemes. As can be seen, by using WDL, significant lashing reductions can be achieved compared to the standard IMO CSM lashings.
Fig. 1: Example of a ship specific lashing scheme.
On 99% of the voyages, a reduction in lashings can be achieved using the Siri Marine WDL method, without compromising on the safety of crew, vessel and cargo.
Analysis of voyages completed by ships fitted out with the Siri Marine WDL system, shows that a significant number of voyages year-round is performed by using the light lashing scheme (86%). The heavy lashing scheme is used 13% of the voyages. Lashing according the CSM is only necessary 1% of the voyages, year-round. This means that on 99% of the voyages, a reduction in lashings can be achieved using the Siri Marine WDL method, without compromising on the safety of crew, vessel and cargo.
Fig. 2: Percentages based on measurements over the year 2022.
Use of the Siri Marine method of WDL goes back to 2003. Over the last few years more than 75 RoRo vessels have been fitted with a Siri Marine WDL system. This makes Siri Marine the largest supplier of WDL systems on RoRo vessels in the world.
Ship specific WDL system; ensures highest achievable lashing reductions
WDL manual applicable for worldwide trade
Based on extensive in-service monitoring
Return on investment in 6 months or less
Reduce wear and tear of lashing equipment
Save on stevedoring costs
Reduce crew workload
Shortened turnaround times in port
Allows slow steaming, reduced fuel consumption and CO2 emissions
Increase safety by live monitoring ship motions
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