What Weight Do You Need | Doing the Maths - Sidemounting.com

Have you ever gone diving with new equipment for the first time and wondered how much weight you will need? Well, that happened to us last week with our new Santi dry suits and thermal undergarments.

We could have dived over weighted and then taken weight off after the dive, but we wanted to see if we could better estimate what we “should” be using right from the start.

Here is a what we did and how we worked it out. We had to do some maths, but we tried to keep that simple and even use coloured pens!

This is part 1, stay tuned for part 2 where we go even more in depth :)

A big thank you to scubacourses for the cylinders and “correct” amount of lead weight we needed. Enjoy.

00:00 New Equipment? What Weight Do You Need?
00:31 We Weigh The Full Cylinders In-Water
01:58 Steel 12L Cylinders At 200 BAR Actual Weight
02:37 Air Weight We Expect To Loose During The Dive
03:48 Doing The Maths | Whiteboard
05:50 What We Expect The Tanks End Weight To Be
06:33 We Make Some Educated Surface Weight Checks
08:10 We Weigh The Near Empty Cylinders In-Water
09:15 Steel 12L Cylinders At 50 BAR Actual Weight
09:46 The Maths Worked! Who Knew!
10:32 Proof That Steel Cylinders Need Trimming
10:51 What To Do If You Use Different Tanks
12:00 The Conclusion - Why We Did This
13:06 Some Tips, Don't Freeze Your 1st Stages Like Us!

#santidiving, #drysuit, #staydry

[DiveVibe]

Watching you guys dangling these tanks in the water and I cant help but be relieved that I'm not the only one out there looking like a weirdo at the local harbor or boat ramp, lol.

[esanchezp]

That's it, I am switching fully to the metric system. A lot easier for everything. Superb video man, thx for sharing such important knowledge

[montypythonish]

I've been UK drysuit diving since 2005 with BSAC and I picked up a few things watching this. I love the simplicity of your weight check. Excellent video. Many thanks.

[hocksee]

Thank you for all the information. It's really so nice to learn from you what my PADI open and advance did not teach me. I find it so horrible that the instructors did not teach us anything about weights and buoancy during any of the courses and the dives, they just gives the weights approximative and the we struggle during every freaking dive on our own, either we are too positive or too negative, now that I understand the principle and the importance of the weight check, i will insist before every dive to check my weights every time. I freaking go on trips and pay too much to those people and they don't even bother checking any of that. Once I was diving with 7kgs, another time with 5 kgs, another time 6.2 kgs. My last 10 dives were at 6.2kgs with a jacket style BCD (cressi travellight) 1mm rashguard, I'm 6' weigh 200 lbs . Thanks again, I love your informative rich videos. Regards. Mike.

[OOZY]

Thank you again guys another awesome video

[johannmattis]

Very accurate! Always wanted to know these figures of my 12L Steels, but was too lazy to do this. Thx!

It is worth to note that the density of air is dependent on temperature and ambient atmospheric pressure. For instance, at 1 ATM and 2ºC, the density of air is 1, 2661 g/L, that is about 4.7 kg loss with your example (3708 L of air). Of course, a few 100g here and there might not impact the end result, but it's worth thinking that air weights more per volume when it's cold and there is high pressure and be a bit more conservative with the weights.

[vincentjadoul]

I am using a sidemount SCR. If I follow this process and just add the weight (measured in the water) of my SCR configuration (with backplate and harness plus accessories) in the equation, I guess it should work? However, I doubt I would ever be at 50 bars in both Nitrox tanks at the end of a dive.

[bar]

Do you factor any contingencies into your final weighting? For instance, if any complication during the dive required breathing in excess of the planned 309 bar, and we assume each tank would become 1kg lighter as a result of the extra demand, would you account for such a contingency in order to remain neutral during deco or safety stop?

[heikoa]

How about weighting the aluminum tank? They are always floating when it's in low volume

[pinnacledivingco]

Bet you ended up with somewhere between 6 and 8kg on the body. I typically have a “rule of thumb” for “minimum weighting”. Steel, you need to know the bare minimum just to slip under the water at the beginning of the dive, because steel is always heavy. And for aluminum, add 2kg to your steel weight (for similar capacity tanks) to account for the minimum weighting necessary at the end of the dive, because aluminum will be positive by the end. For me, in my drysuit, if I’m wearing my normal cheap sweat pants and sweat shirt with top and bottom moisture wicking base layer (good down to 15C temps), that’s 6kg for steel tanks, and 8kg for aluminum. If I wear my thicker undergarments (good to 10C temps), I need to add 2kg for each (8kg for steel, and 10kg for aluminum). If I wear my thickest undergarment (designed for 0C temps), I need 12kg for steel and 14kg for aluminum.

[triman]

stupid question...in salt water [- do you still need to do this kind of weight checking in salt water or is their a rough factor you can factor in from fresh water checks /calcs ?

[drakcheslav]

Isn't it easier now that yo know a constant (the rough weight of the spent air) and it this case just do a check with full tanks, and then add 4, 5kg to that weight??

[ameralmasri]

Great video.. just wandering why u multiplied 159 by 12L? We are not consuming the entire air volume.. we are consuming around 75% of it..

[johannmattis]

Fascinating! I myself took here the long way and figured these numbers out of 100s of dives, as I dive almost every week all year. (with only very minor changes after the 1st weight checks) Also fascinating to see the empty summed up neg. boyancy of the light steels with XTX50s at 3.6Kg is almost exactly the difference in weight I need between light steels an aluminiums (which are almost exactly neutral at 50bars in my case)
I do it the same, empty tanks empty suit/bcd half full lung neutral at the end. But be aware this could be a bit close match at the end when You have to perform a bit more intense skills on a tec-course, which makes You breathe harder. This is a complete other story than to hover Zen-like in the water. Thus I think it´s justified to be like 1-2 Kg overweighted from that point regarding this "practical aspect"

[fbmedic]

Is there a video on doing this using imperial system

[bloodymarvelous]

So basically, get yourself neutrally buoyant at the beginning of the dive with full cylinders, and add 0.2 kg per liter so you're neutrally buoyant at the end of the dive.

[tonypivirotto]

I take it what you just worked out is valid for either fresh or salt? Also what about a lesson for us Imperial people? If Vas could work it out for PSI/LBS then we would really know how good his maths is!

[Mrveescuba]

well done mate very nice video..capernwray is nice!! do you have eny contacts insta or fb ?? tnx