What Weight Do You Need | Doing the Maths - Sidemounting.com
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- เผยแพร่เมื่อ 5 ก.ค. 2024
- 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!
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#santidiving, #drysuit, #staydry - กีฬา
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
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.
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.
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.
Thank you again guys another awesome video
Very accurate! Always wanted to know these figures of my 12L Steels, but was too lazy to do this. Thx!
Mised this one, very useful lesson!
Interesting video 👍👍👍
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?
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.
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.
How about weighting the aluminum tank? They are always floating when it's in low volume
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.
Hi,
I actually took 9kg in the end.
That test of how easy to slip under the surface does work once you have done it enough times to know the speed you should fall at.
There are then lots of personal adjustments based on what you know suits you - but they are personal as your body composition will not be the same as every other diver.
We are not suggesting NOT to do the end of dive weight check - just that we wanted to show how to better estimate the initial weight and how the start and end are connected.
Cheers
Seems pretty accurate. I have 8kg for steel 12L tanks with thick undergarment and trilam drysuit
Wow. I had no idea undergarments would add so much positive buoyancy.
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 ?
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??
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..
The calculations were based on starting at 209 and 200 bar, allowing for an end of dive of 50 bar, the difference being 159 and 150 litres consumed.
Is there a video on doing this using imperial system
Eh! Why on earth does the US use the Imperial system, just complicate matters 🤷🏻♂️
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"
It's an interesting point and I do understand what you are saying about needing that extra 1 or 2kg in case you breathe a lot.
However, that misses the other side of the implication - which is that you will therefore have 1 or 2 litres more gas in your wing/bcd/suit the ENTIRE dive. This will be harder to manage, mean you are deliberately over weighted and making life harder and also means you are less safe on a dive.
I would then ask what tec dives you are making that throw your breathing off that much.
I'm not saying I don't see your point or that humans don't get excited and stressed, but I would be looking to close this gap before adding that much weight as my first choice.
Agree you plan for when tings goes wrong, life is not allways not perfect, 1-2 kg overweight gives you a margin of error, and some extra insulation in your suit
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.
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!
Hi Tony,
We would do the same for Salt - we have to weigh them first in salt. They would be "lighter" in Salt as the tanks would have more lift applied to them, but the loss of weight would still be the same.
For the Imperial version of the maths, then we would need one more item of data from the tanks - the "working pressure". This is because, for example, 3000psi of pressure does not mean the same thing to two tanks of the same CuFt. We have to do a middle step to calculate the actual volume of gas the 3000psi represents.
The difference is that the internal volume of a 12L tank (in metric) is constant. The internal volume of an LP100 (imperial) can vary depending on their Working Pressure that the vendor has stated - e.g. there is only 100cft of gas at a specific pressure, wheres in Europe, it is always 12L no matter the pressure.
If you can say what the Working Pressure is for a set of tank you have weighted, then I can do a working.
It is "complicated" and harder to explain that's for sure and I fully expect to be corrected now by the Imperial Forces 🙂
It could not be any simpler the entire global population gets it, only the exceptional 4% raised in Merika still struggle with basic mod 10 math.
PS: Air content does not get any heavier or lighter in SW - Seriously dude... do you ppl still measure in cubits as well?
Why calculator???😮
well done mate very nice video..capernwray is nice!! do you have eny contacts insta or fb ?? tnx
Thank you, our Facebook pages are facebook.com/diverbydesign and facebook.com/sidemounting
@@sidemountscubadiving you are in the uk??or malta?? where i can i ihave some info about training?
cheers
I will be in Gozo, Malta offering training quite a bit this year. All courses are listed on this page www.sidemounting.com/in-water-training/ have a look and drop me an email on info@sidemounting.com Cheers, Steve