An 'Archim Tank"; a good idea?

[Finless]

I was watching a program about ancient Greece and the supposed birth of science and ............ Archimedes.

Given that buoyancy is such a critical thing to get right with regards to a comfortable dive and not getting a DCI and ........ Well, why isn't there a tank full of water that us divers can get into and weigh the displaced water and .............

Surely this would be a bit of a draw at Stoney or some other inland site?

Hmmmm, maybe I'll build one ........... scaffolding, bathroom scales, two old baths ......... how hard can it be?

[nigelH]

I admit my toolbox has two cheap fisherman's scales to do a quick dangle check to see what things like stages weigh in and out of the water. A lot of my dive kit has been in the rainwater butt at times so I can best guess what weight I need for a hard boat dive where a buoyancy check just isn't going to happen.

The thing that always shocks me is that freediving in the club pool in just my skinny 3mm shortie I need 4.5Kgs to go neutral. Given that I only weigh 80Kgs I'm surprised.

[Finless]

Originally Posted by nigelH

I admit my toolbox has two cheap fisherman's scales to do a quick dangle check to see what things like stages weigh in and out of the water. A lot of my dive kit has been in the rainwater butt at times so I can best guess what weight I need for a hard boat dive where a buoyancy check just isn't going to happen.

The thing that always shocks me is that freediving in the club pool in just my skinny 3mm shortie I need 4.5Kgs to go neutral. Given that I only weigh 80Kgs I'm surprised.

I only got an O level pass in A level physics and my memory is poor and I never really knew to begin with .................... and .............. er ................. the weight of the displaced water doesn't really prove much beyond what your "float point" is?

Now I've got broadband at home and web pages load in seconds rather than minutes I will have a troll round to see if I can learn this stuff again ie dif between mass and weight.

Were it not for parking restrictions and having to pay to park everywhere nearby I would go to my local library and get out the relevant books.

[nigelH]

Originally Posted by Finless

I only got an O level pass in A level physics and my memory is poor and I never really knew to begin with .................... and .............. er ................. the weight of the displaced water doesn't really prove much beyond what your "float point" is?

Archemedes, him say: the upthrust is equal to the weight of the water displaced.

So dangle something in water and the weight you read reduces by exactly the weight of the water displaced. So you know the volume exactly. However all we divers are intersted in is how much a thing weighs in water so we know if strapping it on or taking it off means we need to adjust the lead on our belt.

Now I've got broadband at home and web pages load in seconds rather than minutes I will have a troll round to see if I can learn this stuff again ie dif between mass and weight.

Mass is how much stuff there is there, weight is how strongly gravity pulls on it. Mass is best measured in Kilogrammes and force in Newtons but we talk about Kg-force and confuse ourselves. The real problem is that converting Kgs to Newtons depends where you are. 9.81N for a Kg in England, 8.73N in the Red Sea, 1.6N for a Kg on the Moon.

Yes, that's right, I'm bored at work. How could you tell?