Best way to Calculate RMV?

Monkey

what is the best way to calculate RMV? or should I jsut wing it with 20 Litres bottom and 17 Litres Deco?


Thanks


BAM

Pelagian

Assuming that you mean OC diving the best thing is go diving.

Write on a slate every few minutes, your remaining pressure, depth and time.

IF you can get 3 or more consecutive readings at the same depth(or within 3m variance) the better.

When you surface, work out your avg Bar/min for a given depth. Take this back to the surface by converting the depth to pressure and and dividing that into your avg bar/min.

This give you an equivalent surface air consumption in bar/min. Work out from your tank volume how much one bar is worth 8l, 10l, 12l etc and multiply the two together to get your magic figure: RMV.

You can then try it under different workloads - current, sling tanks, one broken fin etc.

Since I'm nearly always moving at deco(when I can) I keep my deco RMV the same as my bottom. If you need to get back to the surface, deco gas is what you'll need so better to have more of that.

Hope this helps

Seb

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Monkey

Thanks... I am looking for an acurate way of calculating the amount of Bail out I will need to carry for a given depth....

Pelagian

The best way is to run the drills for real, and then do the calcs.

Coz then you'll be simulating the same equipment load, just don't blow your actual bail out during the practise.

Cheers

Seb

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Mark Chase

TDI recomend a 40RMV for calculating deep bailout. You'r own SAC dosent realy come into bailout planning much as its asumed you will be puffing like a train.


So (depth / 10) +1 X RMV = gas usage, then calculate with 5m reductions at stop depths.


40 RMV @ 50m = (50/10=5) +1 =6 6X 40 = 240lpm


Devide cylinder volume by this get gas usage and time feed back.


On 40RMV the numbers are scary.

ATB

Mark Chase

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Pelagian

Scary is the word.

Our supervisors use 35 l/min and 40 l/min for our commercial diving, where we're walking around carrying a shitload of lead and working a lot harder than I would be on a sport dive.

I can't see why TDI would recommend a fixed rate over a personal calculation. I've seen all sorts of warm water breathing rates from the mutantly low of 6 l/min in quads, to 30 l/min for some of the bigger/older/unfit divers.

I prefer to constantly retest my RMV to get the most accurate readings.

I'm pretty much binning my numbers from the Caribbean now that I'm getting into UK diving but I can't see em jumping as high as 40 l/min.

At least I bloody hope not.

Cheers

Seb

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Mark Chase

Yeah but they are asuming C02 hit induced mega breathing. Didnt Dave hit 100lpm or something daft after a C02 hit?

I personaly used to plan on 30 for the deep bailout and 15 for shalow. My SAC was arround 12-15 for the dive and 8-10 for relaxed deco. Recent revisits to 0c have shown i am loosing the nack of low SACs My avg SAC on an easy peasy single tank dive was best 12.9 and worst 16.2 (but i was towing my lazy wife)

As a result I have upped my deep bailout to 35lpm and deco to 18

Id rather have too much and laugh about it after.

ATB

Mark Chase

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Monkey

I agree....this principal should apply to both cash and bailout.

divelermentov

but hence we are diving Rebreather's it is rather difficult to apply this to the cash scenario.
But please let me kn ow whenever u have discovered the advanced cash flow improvement logarythm

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Drmike

RMV at rest or even at work isnt the concern - its RMV when under stress (like imediately after bailing deep) or with elevated breathing rates from a CO2 hit)

IIRC I hit 45LPM+ once just through stress induced elevated breathing rates


But I was soiling my pants at the time

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