Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[bbdave]

Ok so assuming i have my wtc built and calculated the volume Pye x r2 x h etc.  assuming it is 500 cubic cm therefore displaces half a kilo.

So if all up weight of WTC including gear is 350g all i'd need is to take on 150ml of ballast to submerge 200ml to be sure?

Dave

[Subculture]

If volume is 500ml, and the weight is 350grams, then you would need to take on 150ml to go neutral, and a few grams more to go negative, should you wish your boat to dive statically.

Dependant upon the system used, people size their tank a bit bigger to account for changes in water density 10-15% is generally the ballpark figure. Some system don't lend themselves well to an oversized tank, as they need to be completely full or completely empty if the boat is to remain in trim when diving. Systems that work well with oversized tanks are those based on pistons or a sealed tank or bag with a water pump.

[bbdave]

Thanks as long as i have the theory correct i can work it out best i can.

Dave

[salmon]

May I ask some really dumb questions? How did you figure 500 cubic cm displaces half a kilo or that 350g is 150ml? it may be obvious once you explain it, but right now I am not getting it.

[bbdave]

Not at all 1 cubic cm weighs a gram therefore 500cubic cm = 500g

The 350g is just a guess of combined weight of the  WTC cylinder the end caps and all the running gear inside, so if i then pump in 150g of water the all up weight would be 500g causing it to be neutral buoyancy which would be perfect for dynamic diving (using forward speed and dive planes to dive) if i pump a little more in say 200g total the sub should static dive.

Hope that helps salmon

Dave

[Subculture]

The wonderful thing about the metric system is that it is very easy to transfer between units of measure.

1 litre (1000ml) of water weighs 1kg (1000 grams) and occupies 1cubic metre or 1000cc. See how easy it is. You can't do this with the imperial measurement system.

Cold water or salt water is denser, and weighs a little more, the difference is small, but that is why ideally you want some allowance in your ballast system, or you may have to fiddle about with pieces of lead.

[derekwarner]

  ....sorry Guys.........in OZ..."1 cubic metre" of water in the simple metric system =  one thousand kilograms or one tonne [+/- a bit for salinity] 

Subculture....not having a shot..... ...I make these simple mistakes too .......Derek 

[Subculture]

Whoops, good catch- that should have been cubic decimetre (dm). In general stick to grams and millilitres unless you're building something very big.

[salmon]

Thanks guys! I will work on this!