Weight is measured in Metric tons at some places and in long tons at other places and barrels at 60 deg F at other places.Volumes are measured in cubic meters at some places and barrels (like in the US) in other.If that was not enough, humans on this planet earth have managed to confuse it further. We need the density of the cargo to convert the volume of cargo to the weight.Īnd as the density also changes with the temperature, we would need the density of the cargo at the cargo temperature to convert the observed volume to weight. We need to convert the volumes to the weight of the cargo in each tank. Let us say we got the volumes from the ullage tables and the volumes for each tank are as per below.Īs the volume changes with the temperature, this cannot be the measure of how much cargo we have loaded or discharged. Remember volume changes with temperature. This will be the volume at the observed temperature. Now we get the volumes for each of these tanks for the corrected ullage that we have got. We also measure the temperature of the cargo preferably at three levels and take the mean of these three temperatures to get the temperature of the cargo. We first measure ullage (or Sounding) of the tanks by UTI tape (or radar gauge in CCR). Ok, now let us get back to basics of cargo calculations on tankers. The first page of the ASTM table 56 provides the factor for converting weight in vacuum to weight in air and vice versa. How to convert weight in Vacuum to weight in Air? Ok, so now here is the first thing that we can learn. Converting weight in Vacuum to Weight in Air and vice-versa In the vacuum, there is no buoyancy and hence the weight is more than the same weight when measured in air. This is because, like with water, air (and any other medium in which the weight is present) would offer some kind of buoyancy which reduces the weight. Well, the weight is Vacuum is always more than the weight in Air. No problems, make a wild guess even if you don’t know. Remember, for stability and draft calculation we still would need to use the weight in air.Ĭoming back to the topic, can you guess for the same amount of cargo which weight would be more? Weight in air or weight in Vacuum? Unit of weightĪpart from the units, weight is measured in air or in Vacuum.Įven though on ships it is more common to measure the cargo weights in the air, sometimes you may find that the charterers would give the requirements for measuring weight in Vacuum. Volume changes with temperature but the weight remains the same.Įven when we hear some weight of cargo, let us say 30000 Tons of cargo, there are two things that we need to be aware of. Basics about Volume and weightīefore we proceed to the complex things, it is better to start with the basics. Sometimes it is difficult to understand which one to use and why.īut don’t worry!!! This article would aim to simplify the cargo calculations on tankers. There are so many tables to use and so many terms that float. It is sometimes difficult to get a hang of these calculations. This is something a chief officer cannot afford to do it wrong.īut here is the thing. We make sure that there are least constants on the ship, the ballast is pumped out to the last drop and many other things like these.Īll this to make sure that we have the capacity to load maximum cargo and ship owner has a chance to earn maximum from it.īut while we do all this, sometimes we just fail to do the simpler things right. We do so many things to make sure that ship owners get the maximum out of their investments on buying and running a ship.
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