I bet you the Proff is gonna chime in here . Oh,and I ain’t talking about those big things in a brewery either ! . Tanker - Builder
Well isn’t it like a partial hogshead?
Google TUN. The word has had several definitions over the centuries.
<in olden days an English ship’s capacity was measured by the number of tuns of wine it could hold>
I think arnie60 nailed it
The tunne (or tun, tonne) was a specific cask/barrel/cooperage size. It was commonly used to carry vine, although vinegar or oil were carried by the tunne as well).
What’s most important is that the approximate volume of a tunne is 100 cubic feet, and is the reason that merchant vessel sizes are expressed in “deadweight tons” of 100 cubic feet each. Which have nothing to do with the displacement weight (volume) of the vessel.
Which causes no end of confusion. Displacement is a measure of the underwater body of a ship. It’s DWT is a measurement of its entier hold capacity, from bilges to main deck. Modern containers shops really confuse the isse.
And, all that is before getting into the confusion cause by short (2000#) and long (2240#) tons. That latter being an even multiple of British Stone, and thus, hundredweight. Neither of which is a metric tonne of 1000 Kg.
Boy !
Youse guys is good ! I tried to explain this to a friend and still can’t seem to get him to accept it’s not a 2000LB. Type .Plus in shipping jargon for steel you had that dratted long and short TON too !
And, 3/4 pf the world means 1000 Kg (which is in the neighborhood of 2200#, or 5-6kg of a long ton.
Convincing people who have no idea is complicated. Try convincing people that cooperage comes in sizes, like Pony, Butte, Keg, Cask, Barrel, and the like, with Tunne being just one of those. The scuttlebutt being a water cooperage with a hole, the scuttle, poked into it. Further, that sailors were forbidden to speak on deck, except when getting water.
(it’s probably a term Tankerbuilder coined during his AB cruise with the Phoenician Navy 
)
Tanks is an original plank owner on the Ark, I hear.
Try convincing people that bottles come in sizes, not quantities.
It all gets back to the loadmaster watching the boat settle dockside.
Frankly I am a student of the upside down rules of shipping. I grew up, was around drydocks and then aircraft.
Dad was hired at United Airlines as a math whiz who wrote their book on runway loading, take off weights and eventually take off performance.
I had all my first jobs out of high school down on the docks in San Francisco Piers 60-70 as a gopherr in a open truck.
Dockmaster had cribbing, braces and other tricks up their sleeve to drydock really big ships.
Hey , Have you ever seen a ship full of anymils ? Yuck !
Been on a couple ambibs full of Marines . . .
Funny, that “Tun” showed up in the crossword puzzle today.
Was not me–been more than a decade since I diagrammed any crosswords. Promise. Five letter word for oath.
LOL.