Posted by Rob Thomas 4 on 24/07/2020 12:46:36:
Could it be for measuring the level of the remaining liquid in the bottom of a liquid (oil) tank?
Regards,
Rob
Very likely. Ships and commercial operations take fuel by the ton and the huge quantities involved provide many opportunities for dishonesty. The remainders at the bottom of a tank are called ullage, and the cumulative value of ullage is big money. 75mm of oil left at the bottom of a small 20m diameter tank would amount to nearly 2.4 cubic metres of fuel, roughly 530 gallons, and the tank might one of dozens each emptied several times a year.
Tanks were frequently dipped at all stages of fullness, even those notionally empty. A small weight on the end of a line is a good way of dipping empty tanks. At least two types of fraud prevented, stealing left-overs or using an empty tank to collect fuel misappropriated from other tanks. One way of profiting from privated collected ullage is for a road tanker to arrive, do the paperwork at the gate, pretend to unload into a tank already full of ullage fuel, and then leave – still full – for private sale. Fuel isn't physically stolen from the big tank – instead the owner pays for fuel that stays in the road-tanker, while his trusted employees retire in comfort. (Or go to jail!)
Dave