22-11-2017, 04:16 PM
3600
Re: Leisurely Scribbles (part 5)
Originally Posted by
Robert Jnr.
->
I have 2 questions for our Pug
ONE
SHIPS TONNAGE (ie WEIGHT OF SHIP)
Thus, Oasis of the Seas at 220,000 gross tons is considered a bigger cruise ship than Navigator of the Seas at 137,000 gross tons. Because the word “tons” is used in connection with this measurement, people often think that the gross tonnage is the weight of the ship.
WTF are they talking about, surely the weight is the weight.
TWO
I have forgotten the 2nd question, I'll post it later
I thought the mass quoted is the mass of water displaced by the boat, not its actual mass.
So, you take a lump of steel weighing 1 tonne, and drop it in water. It will sink.
If you take the same lump of steel and roll it and beat it until it is boat shaped and drop it in water, it should float, displacing a mass of water.
If you change the shape of the lump of the steel, it still weighs 1 tonne, will still float, but will sit higher or lower in the water depending on it's shape.
The mass of water displaced will therefore be different, even though the "weight" of the ship is still 1 tonne.
I'm guessing there is a standard density of water when quoting tonnage since the amount displaced will vary with temperature and mineral (salt) content.
This is also why there is more than one Plimsoll Line on a ship. Loading a ship in cold dense sea water could cause it to sink in less dense warm tropical fresh water because the vessel becomes less buoyant.
Measuring the displacement of a ship could be done using the same goldfish bowl method already explained.
Put the boat in a dock full of water, and measure the volume of how much spills out. Knowing the water density then allows the volume to be converted to mass.
As a retired aerospace enginerd, I can conform that everything I have said is pure guesswork.