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Estimating dive weight


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#1 Itsa

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Posted 06 March 2012 - 01:05 PM

I've been curious about estimating my dive weight. Up to this point a DM has pretty much just sized me up and given me 10lbs. I did a quick search here and when I didn't find a formula quickly I googled it. I've been in the same scenario each time I've dived: 126-155 body weight, 3mm suit, salt water, AL80 cylinder. According to the article I should be at 16lbs, which I absolutely do not think is correct. I'm wondering if others using this formula will find that it's over-weighting them too. I'm just trying to find reliable information. Here is the link:

http://knows-dive.co...hts-estimation/

Also, during my refresher class in the pool I had 2lbs on (no wetsuit), which worked quite well. Given my body weight it looks like this formula recommends at least 5lbs. Just curious to hear what everyone thinks!

Take care,
Itsa

#2 Jerrymxz

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Posted 06 March 2012 - 02:30 PM

Great question!! I've seen a couple formulas for estimating weight needed but I consider them a starting point. I go to my log book and read what Iíve used in other situations where my gear is configured the same and start from there. But this only works when you take good notes. If you get to the end of a dive take 2 lbs off your kit and try to submerge. If you can, there's two lbs you can leave behind the next time. At the end of that dive try it again. Do this until you can't leave every bit of air out of your BC, exhale and submerge. At the start of a dive trip you may need a pound or two more than this until your gear is wet and you're back in the groove. But it all boils down to taking notes.
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Posted 06 March 2012 - 03:42 PM

I think most experienced divers find the equations a curiosity at best since most have experienced what you described.
Those equations are really only starting points that assume you fit the body mass index tables that you see online. I don't know anybody that meets those tables. They say I am borderline obese and I don't think anyone that has ever seen me would agree with that assessment. A few would say I am barely overweight at worst and most would not even say that.

Jerry in on the mark as usual. It is mostly an experimental process and each person does it differently. I usually take what I dove last time as a starting point. If I have to struggle holding a safety stop then I take out a few pounds or add a few lbs per dive until I don't struggle anymore. I personally consider the safety stop to be the critical point to optimize on. Your suit is wet and your tanks are partially empty so it is easier to do a judgement at that point. In fact at some locations I have asked for a nearly empty tank just to do a weight check on in shallow water. Sure makes life easier if that is a safe option. In a lot of locations (Bonaire for instance) it is.

Each location, even freshwater, is different also so you will have to fine tune at each location you go to.

#4 peterbj7

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Posted 06 March 2012 - 09:01 PM

I've never seen a formula that I feel worth spending the time reading, let alone following. Dowhat others have said - guess based on previous dives, then at the end of the dive experiment with taking weight off. Never attempt to check weighting at the start of a dive, other than ensuring that you can in fact get down.

As to where someone is relative the the height/weight tables, don't get me started on that. Those tables are utter nonsense, or at least the way they're used is.

#5 Sharklover

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Posted 07 March 2012 - 01:50 PM

Hi Itsa,

For what it is worth, I don't find the formulas helpful at all. There are so many factors they do not consider. Things like lung volumes, gender, body composition as opposed to weight, diver comfort, etc. They are built for someone who is average, and I don't know anyone who is average. They do not come close to what I actually require and in my case grossly overestimate what I need. I am tall and umm, floaty, I take no weight with a HP 100/3mm, and 12 pounds with an AL 80/3mm. I will be redoing my weight checks soon as I have leaned up a bit over the winter and have a new 5mm suit which will probably be my primary suit here at home.

Nothing can replace doing weight checks. I'd recommend doing them in freshwater when it is convenient, and then adding 4 or 5 pounds when you hit the ocean, then verifying that you are weighted correctly at your safety stop. Or if you are at an ocean location where it is easy to do them in salt, even better.

I do mine at my safety stop and if I need to be able to hand off weight to my buddy when I am doing so, we plan for that up front. If I have an empty BC, low tank, am not finning, and can move myself with my breathing, I'm golden. I'll be taking a guess when I take my new 5mm out for it's first dive as the local quarry will be too cold. But I'll stop at the hangline (a NC thing) and make sure that I am in the ballpark before descending.

I took a diver out last summer who had never been in the ocean. He had a HP steel 100, was about 5'10", thin and lean, and was carrying 24 pounds. That is what his OW instructor had put on him in training. He was hesitant about giving any of it up. So I sent my other buddy in first, she waited at 15 feet, and sent him in with a full wing because we were worried that he was going to sink like a rock. He had a tad of trouble with buoyancy control as we guessed he would and we had to turn out dive on his air supply. We had talked about doing a weight check at the safety stop. He handed me 2 pounds at a time, stopped finning, and let some air out of his BC. He was pretty negative each time. I got 12 pounds off of him that first dive. Next dive we did the same thing. I got 12 more pounds off of him that second dive. The third dive his bouyancy control was much better, his air consumption improved, and we actually turned that dive based on NDL instead of his air supply.
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#6 Itsa

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Posted 07 March 2012 - 03:31 PM

Thanks for all of these tips! I've had trouble staying down during my safety stops, but I haven't been sure if it's been due to finning or not carrying enough weight (my guess is some of both). I was curious about how the formulas worked and it seems like they estimate on the high end. I'll be sure to keep good notes and make adjustments as needed.

#7 Sharklover

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Posted 07 March 2012 - 05:49 PM

Thanks for all of these tips! I've had trouble staying down during my safety stops, but I haven't been sure if it's been due to finning or not carrying enough weight (my guess is some of both). I was curious about how the formulas worked and it seems like they estimate on the high end. I'll be sure to keep good notes and make adjustments as needed.


Is your BC empty on your safety stop? Better to back off of a little too much weight than to not have enough to maintain your safety stop. Also remember your lungs. I was in Little Cayman recently. When I was at my safety stop, I saw a newer diver fins up, head down, trying to stay at his safety stop. Guy was a triathlete, probably goodly lung volume. I caught his eye and pantomimed a full exhalation. He did one and came right back down to where he wanted to be.
For whatever we lose (like a you or a me), it's always ourselves we find in the sea....ee cummings

#8 uwfan

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Posted 07 March 2012 - 08:13 PM

Over time it may be that you will need to adjust your weight too because you get better at diving - more comfort means needing less weight.

I will note what suit I'm wearing, and how much weight I have on for my diving and estimate like others are saying. It really is a guessing game and if I haven't been in the water because it's my first dive after a winter of not diving - I always add 2 or more lbs just until I get more comfortable again in the water.

Happy diving!

#9 Sharklover

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Posted 07 March 2012 - 08:44 PM

What adjustment do others make when going from a 3mm to a 5mm? It took me ages to find one, this is my first. I will be doing my first dive offshore in it and won't have the luxury of a pre dive weight check.
For whatever we lose (like a you or a me), it's always ourselves we find in the sea....ee cummings

#10 lv2dive70

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Posted 07 March 2012 - 09:37 PM

What adjustment do others make when going from a 3mm to a 5mm? It took me ages to find one, this is my first. I will be doing my first dive offshore in it and won't have the luxury of a pre dive weight check.


MY EXPERIENCE: At the aquarium, with a SS BP/W, I use no weights with a 3 MM and 12 lbs with a 7 MM... I think I may be a little heavy with the 7 MM but I'm "working" and don't want to be light.
MY THOUGHTS: if I had to guess, with a NEW 5MM, I would start out with an extra four - eight lbs. I can't imagine you'd need ten extra lbs to sink 2 extra mm's. But that's just my guess. :-) Curious to hear other's thoughts.
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#11 Sharklover

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Posted 07 March 2012 - 10:21 PM

What adjustment do others make when going from a 3mm to a 5mm? It took me ages to find one, this is my first. I will be doing my first dive offshore in it and won't have the luxury of a pre dive weight check.


MY EXPERIENCE: At the aquarium, with a SS BP/W, I use no weights with a 3 MM and 12 lbs with a 7 MM... I think I may be a little heavy with the 7 MM but I'm "working" and don't want to be light.
MY THOUGHTS: if I had to guess, with a NEW 5MM, I would start out with an extra four - eight lbs. I can't imagine you'd need ten extra lbs to sink 2 extra mm's. But that's just my guess. :-) Curious to hear other's thoughts.


Thanks Kate. With my steel 100 and a 3mm, I carry nothing. So depending on the conditions, I will pick a number in your range. Probably on the heavy end to start. Though I can always pop back up from the hang line if I can't sink :)
For whatever we lose (like a you or a me), it's always ourselves we find in the sea....ee cummings

#12 Racer184

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Posted 08 March 2012 - 07:28 AM

Using the LOGBOOK is the most important thing for me & weighting because seasonally we go from wearing nothing to 5mm full wetsuit & hood. Also, some places I am 'forced' to use 80 aluminum, sometimes I use 100 aluminum, and usually 123 steel.

Getting a 'new' wetsuit? Fill your bathtub (or pool) and find out what it takes to sink your present wetsuit (make sure you get all the air out of the arms / legs). Then find out what it takes to sink your new wetsuit. Now you know how much more or less to use with the new wetsuit, look in your logbook for whatever tank you are using, and you should be close.

When working as a dive guide or assisting an instructor, I may have 30 pounds extra (not on me, but in the car or on the boat.)

#13 Jerrymxz

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Posted 08 March 2012 - 06:30 PM

Here is something to try, put 6lbs in your pockets or weight belt. with another 3lbs put a short length of para-cord thru it and clip it off to a D-ring out of the way. Once you're in the water make the decision whether you need it or not. if you don't need it clip it off on the hang line or on the anchor where you can pick it up on the way back.

You could also put an equipment line in yourself (with permission from the capt) to put a selection of weights on it to do a good bouyancy check at the conclusion of the dive. a 2lbs and a 3lbs would probably do it. that would give you from 6 to 11lbs to play with.

When you get back let us know what you did and how much weight you ended up with.

Each wreck has a tale to tell about its life and its demise. 

If you are observant while diving in dark places listen to the account each has to tell, You cannot come away unaffected.   
Changes in Latitude, Changes in Attitude


#14 Itsa

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Posted 09 March 2012 - 01:46 PM

Here is something to try, put 6lbs in your pockets or weight belt. with another 3lbs put a short length of para-cord thru it and clip it off to a D-ring out of the way. Once you're in the water make the decision whether you need it or not. if you don't need it clip it off on the hang line or on the anchor where you can pick it up on the way back.

You could also put an equipment line in yourself (with permission from the capt) to put a selection of weights on it to do a good bouyancy check at the conclusion of the dive. a 2lbs and a 3lbs would probably do it. that would give you from 6 to 11lbs to play with.

When you get back let us know what you did and how much weight you ended up with.


That's a great idea. I'll definitely try that!
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