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I'm reading a thread where someone asks: "If you add 500 thousand pounds of crabs to a crab boat; is it 500 thousand pounds heavier?"
There's some genuinely funny responses, but it's the people trying to be serious that are hurting my brain.
People don't have any understanding of weight, mass, displacement, ballast, stability...
People who are answering authoritatively, but are not accounting for things you'd know if you'd watched a couple of episodes of The Deadliest Catch.
But since I have to figure it out, because I'm me...
The average density of crabs is 1.27. So crabs are 1.27kg/l.
500,000 lb. of crab is 226,796.2kg of crab.
226,796.2kg of crab is 178,579.7l of crab.
178,579.7 l of water is displaced by the crabs and that weighs 393,700.85 lb.
So the boat is 106,299.15 lb. heavier.
Update:
178,579.7 l of seawater, being denser and thus heavier than regular water weighs 403.543.44 lb.
So our boat gets 96,456.56 lb. heavier when we toss all that crab into the holding tanks and the boat settles a little deeper in the water.
Commenters: One of the givens is "crab boat" confine your rebuttals and criticisms to that.
Clearly it's an obscure fact that the holding tanks are full of seawater on a crab boat and that as crab is added, it displaces water overboard. That's why adding 500,000 lb. of crab to a crab boat doesn't add 500,000 lb. of weight to the total assembly.
Crab boats do not sink when they stuff those holding tanks with crabs which are heavier than the water they used to carry. No more than a canoe sinks when you put the cooler in the middle and it displaces the much less dense air that previously occupied the space inside.
Crab boats do not operate anywhere but Earth, so quibbling about 1g is just being... put in what will insult you the most here.
I CALL INVALID ANSWER!! Based on the question as stated, "If you add 500 thousand pounds of crabs to a crab boat; is it 500 thousand pounds heavier?"
ReplyDeleteYes it is. You didn't state the boat was floating in water. If the boat is sitting in dry dock, it does indeed weigh 500,000 pounds more.
I'm kinda nit-picky like that. Pissed off many teachers in my youth.
You forgot to mention the treadmill.
DeleteYou're not being nit-picky. You're making different assumptions JUST to be an ass for humorous effect.
DeleteAs a fellow ass, I welcome you to the tribe!
Ummm ... no.
ReplyDeleteI'm not saying that your numbers are wrong, but the application seems dubious.
Yes, 500,000 pounds of crab at a density of 1.27 kg/l WOULD displace 178,579.7 litres of water - but they aren't IN water, and if they were they would sink.
Boats float because their average density is less than that of the water that they displace, so for the boat to continue to float, it must now displace 500,000 pounds more salt water. That's why heavily-laden boats ride lower in the water, after all.
Is the boat 500,000 pounds heavier? Of course it is. In a uniform 1g gravity field, it doesn't matter whether it's beached, floating, or flying.
No, the boat does not have to displace 500,000 more pounds of seawater to remain afloat.
DeleteWe're replacing seawater in the tanks with crabs. Net increase in weight is just under 100k lb.
Just like filling those holding tanks with diesel would be a net decrease in weight because it's less dense than seawater.
I recall mentioning something about watching an episode or two of Dangerous Catch...
Boats float because the water is not getting in the boat.
ReplyDeleteAny vessel afloat will displace an amount of water equal to the weight of the vessel. No more, no less. The cargo is a minor consideration, as long as the cargo doesn't move the righting arm to negative.
Now you're just changing the rules. :)
ReplyDeleteI read the question, and didn't see any mention of "replacing" anything - it plainly says "add".
Not having watched the show that you mention, I was most certainly not au fait with the storage methods vis a vis crabs on crab boats.
You live and learn.