Caspian ‘Sea’

[Black Dog]

ROV

[Savante]

Open up an excel spread sheet and paste in the following equation.

c(D,S,t) = c(0,S,t) + (16.23 + 0.253t)D + (0.213-0.1t)D2 + [0.016 + 0.0002(S-35)](S – 35)tD

c(0,S,t) = 1449.05 + 45.7t – 5.21t2 + 0.23t3 + (1.333 – 0.126t + 0.009t2)(S – 35)

t = T/10 where T = temperature in degrees Celsius
S = salinity in parts per thousand
D = depth in kilometres

Range of validity: temperature 0 to 35 °C, salinity 0 to 45 parts per thousand, depth 0 to 4000 m

Coppens equation (1981).

Salinity of caspian seawater (S) is approx 12.8 g/litre

What depth are you going to? What is the water temp at this time of year in the caspian? say 2-3degrees C?

[Savante]

Long geeky answer
————————

north sea water salinity 35g/litre
caspian sea salinity 12.5(ish) g/Litre

Say roughly, density of caspian seawater is therefore 1012g/litre instead of say 1035g/Litre.

You need that buoyancy law – archimedes. Upthrust force is due to the "weight" of the displaced fluid.

w= m*g
w=v* g * p (mass of water = volume * density)

Say for a super spartan (example workclass)- volume of the buoyancy is roughly 2.5m*1.5m*0.6 (ok – ignoring routed-room for thruster cut outs, and also the equipment loadout ontop of that!)= 2.625m^3 – this would be equivalent to 26kN of upthrust roughly (ABSOLUTE MAXIMUM-BIT OVERESTIMATED!!).

Balanced by weight of approx 22,500N – so in seawater the rov should roughly be neutral. Hmm.

The difference in seawaters would be equivalent to a loss of upthrust of the order of (1.035-1.013)*2.625*1013*10=574N (57kg of push equivalent!)

If using syntactic foam – advantic, density= 0.35g/cm3 = 350kg/m^3, hence 1m^3 of syntactic gives aroun 6630N of upthrust.

then you need a volume of around 0.088m^3 to get the desired upthrust of 574N.

Say 2.5cm thick, 1.5m wide x 2.5m long

Short answer
—————-

Stick another slab of buoyancy on it and trim your verts to apply downwards force!!!

[Savante]

pandoras box for my approximations!!

hit me!!

I’ve probably missed a x10 in there, and it’s prob 2m thick

[Savante]

Without warrantee………..

100m 1444.006 ms-1
300m 1447.26
500m 1450.53
1000m 1458.77

[James McLauchlan]

Savante

On a real roll there!

[TheBaron]

I’m a shareholder in Trelleborg CRP Inc. and a Customs Official in Turkmenistan, and I violently disagree with Savante’s calculations! He failed to take into account that at this time of year the sturgeon are spawning, and that, in fact, raises the salinity level by 1.0E-14 gram/litre. My ball-park figure rounds that down to an extra whopping 20′ container-load of syntactic foam for the ROV. Savante, are you trying to do the ROV Support Industry a disservice?

[SpearROV]

Sewen Goatskin with extra lard on the interior will give you the extra upward thrust
Plus…………………………………………………………
It feels good on your hands

[Andy Shiers]

As long as the water is not chocker with debris , You will be able to adjust the threshold and gain to ‘See’
What Sonar are you using ?
As for bouyancy ya taking the monkey arn’t ya
The Orfice workers are obviously taking the piss if they expect you to ‘Trim test’ once on a bloody Rig when you have an air gap of 60 ft plus

[Savante]

ah, agreed baron, I shall retract the previous due to potential gross inaccuracies due to sturgeon mating season.

you should probably put in an order for 20 tonnes of syntactic just to be sure !!! (that’s about 1/2 million dollars isn’t it?? – I expect a DVD recorder in the post by xmas!).

[TEAMJBR]

Just done a TS Dip at DWG Field

*Density = 1.009*

You’re Welcome

[TheBaron]

Nice one JBR, you are most welcome to my humble Customs and Excise hut anytime!!

[Author]

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