What's in your drop pocket

[dumpsterDiver]

Let's assume that you have done a very careful weight check and are diving with the correct amount of lead. Let's also say that you are diving with an AL 80 tank.

If you recall how a weight check is done, you are supposed to dump all the air from your BCD while holding a normal breath. If you are properly weighted, you will float at eye level without kicking your feet.

Now, if your tank is full when you do this, there is some controversy about how much weight (if any) you need to add to compensate for the weight of the air in the tank, which will be lost as you go through the dive. So to be safe, let's go with the more extreme argument that you need to add weight equal to the total amount of the weight of the air in your tank. Let's estimate that at 6 pounds for an AL 80.

That means that if you have a completely full tank, if you drop 6 pounds of weight, you should be able to float at the surface with no air in your BCD and without making any physical effort. If you are halfway through the dive and drop that weight, you should float to the surface

For that reason, a lot of people argue that a properly weighted diver only needs to have the equivalent to the weight of the air in the tank in ditchable weight.

The above analysis does not calculate in wet suit compression.

The diver is very large wearing a 7 mm suit and 40 lbs of lead. Suit compression IS the issue, not a few lbs of air in a tank?

Your comment about dropping 6 lbs of lead is irrelevant, at best, to the situation at hand..

---------- Post added December 20th, 2013 at 07:54 PM ----------

ssi does teach buoyant ascents. at least my instructor did as i just did the OW class with them last month.

How do they do that, I am very curios about the procedure used? How much lead did you drop and what exposure suit were you wearing?

 

[boulderjohn]

The diver is very large wearing a 7 mm suit and 40 lbs of lead. Suit compression IS the issue, not a few lbs of air in a tank?

Your comment about dropping 6 lbs of lead is irrelevant, at best, to the situation at hand..

So if the diver is wearing a 7mm suit, then he needs to add some weight to that equation. It isn't that hard, and I bet a lot of the people reading this thread have enough intelligence to figure that out.

 

[dumpsterDiver]

So if the diver is wearing a 7mm suit, then he needs to add some weight to that equation. It isn't that hard, and I bet a lot of the people reading this thread have enough intelligence to figure that out.

Yeah I can ride my bicycle 50 miles an hour on a flat road... if we leave out wind drag in "my analysis".

A huge guy wearing a thick wetsuit is the issue, it is not "some weight" it is 3 or 4 times as much as is required for the swing in weight in an 80 cuft tank.

 

[flots am]

So I just got around to transfering my log notes from the weekend onto my computer ( were i can log in better detail ) and i was looking at my weighting as i had some problems i wrote about already and i noticed that on this dive I had most of my weight in my ditch system on the bcd. (Almost 75%)

I keep all mine in a DUI weight harness.

While it's possible to ditch the whole thing, it's very easy to pull up a velcro flap and start dropping 2's, 3's or 5's until you're happy with your buoyancy.

With a drysuit in the winter, I could easily have 30 pounds of lead.

 

[TSandM]

maderadiver, to answer your question, no, there is no formula for how much to have ditchable.

The goal is to be able to get back to the surface and stay there. If you are at maximal depth, 70 feet, and the corrugated hose pulls off your BC, so it won't hold air and you can't put any in it, you have got either to be able to swim back to the surface, or to jettison enough weight to be able to do so. Most people can swim up 10 pounds or so, so if you are carrying 30, you might want to have 20 ditchable (this is assuming maximal compression of the wetsuit at your maximum depth, and near total loss of wetsuit lift). I was told, during my Fundies class, that a new 7 mil wetsuit, taken to 100 feet, can lose as much as 23 pounds of lift, which goes along with those numbers.

If your exposure protection is lighter, you will lose less lift at depth. If most of the lead you are carrying is to sink YOU, which I suspect, given the data earlier in this thread, you will need less ditchable weight, because your body won't lose any buoyancy no matter how deep you go.

As already pointed out, if you have integrated weights in your BC, you have half of your weight on each side. You can dump just one side -- it will make you a bit unstable in your roll axis, but if you are dumping weight at depth, the last thing you care about is whether you can elegantly swim in perfect trim.

Going back to the initial issue, though . . . run through your mind the scenario where you lose ALL buoyancy, cannot add any air to your BC at all, and you don't have a buddy nearby to assist. That's a LOT of mistakes to have made in one dive.

 

[redneck23ms]

The diver is very large wearing a 7 mm suit and 40 lbs of lead. Suit compression IS the issue, not a few lbs of air in a tank?

Your comment about dropping 6 lbs of lead is irrelevant, at best, to the situation at hand..

---------- Post added December 20th, 2013 at 07:54 PM ----------



How do they do that, I am very curios about the procedure used? How much lead did you drop and what exposure suit were you wearing?

it was just in a pool at 9ft or so. and the instructor explained how it was done and how we should do it. basically lay on you back near the bottom of the pool. drop your weights and spread eagle to slow the ascent. he was right there to assist as well. i had on a shorty suit and 8lbs of weight. granted it was just me(33) and 2 younger teenagers in the class.

 

[dumpsterDiver]

it was just in a pool at 9ft or so. and the instructor explained how it was done and how we should do it. basically lay on you back near the bottom of the pool. drop your weights and spread eagle to slow the ascent. he was right there to assist as well. i had on a shorty suit and 8lbs of weight. granted it was just me(33) and 2 younger teenagers in the class.

That is pretty much how I would practice it, I didn't know it was "allowed"..

 

[NAM001]

Dont confuse the need to to off load an amount of weight to make you positive bouyant. you only need enough to be able to drive your self up. so at depth say 90 ft and your suit is a +10 and you have a full tank. you would be probably be carrying 16-20 lead depending how much of a lean diving machine you are. So if you loose the wing or bcd lift and you can drive with fins to the surface with -10 than you need to dump that amount over the minus 10. By the time you get to 50 ft and then 30 your suit will give more lift and you wont have to kick much. if you dimped say 6# then you can push your self to 50 and your suit will give you 5 more. now you are only pushing <5. somewhre around 20-30 you should be near neutral and it will be elementary from there with minimal consequence for errors. you will probably want to see just what you can drive upward with propulsion only. another thing to consider is that you do not have to domp the weight in one package. Make say 2 dompable pouches cause loosing it with a 1/2 filled tank will be a different situation. requireing less of a weight drop.

 

[maderadiver]

I had not thought about a half dump and I can "swim up" 15 pounds if by swim up you mean no wetsuit and fins retrive a weight from the bottom of a pool .

My weight woes stem from being a big guy with a barrel chest 54 inch chest puts me at xxxxl 38 hip puts m at xxl bottom i am renting a wetsuit now and always get there farmer jon style in 7 mm so its 14 mm in the chest it takes tons to get me down and i always feel overwieghted when it finaly all crushes. Dont get me wrong its a warm suit and that is its job but i think a custom one piece would let me shed considerable lead

I would love to dive with less lead but honestly most of it is for me I'm 290-300 diving is part of my attempt to be more wctive and healthier

 

[NAM001]

For you 15# is the number then but doing it with fins. It is always a hard amount to figure because of the amount of compressed lift on the wet suit. Hopefully you suit compression is the only w eight you have to swim up. For you if your suit compression is 12# you are ok but if your suit compression is 20# then you need to dump 5-6 and power up. the trip will be come easirer as the suit expands. If you have a lot of suit then perhaps you need to carry a sausage or lift bag that you can vent on the way up. i actualy prefer the bag idea so long as i have a hard bottom to initiate it. with no bottom you have to power up. Your weight woes can be reduced. i was 260 and am now 235. a few #'s makes a lot of difference in your volumn and hence your bouyancy and required weight ato keep you down. If you neeed to power up in the middle of the tank then it will be easier. You could always wear a horse collar. Its an old piece of equipment but functional. Something else to consider,,,,, If you can figure where your leak is, say the bottom, then you can inflate while you are virtical. air on top and hole in bottom. If on one side roll to your side (leak down) ect. a 30# wing or bc can easily still hold 10-15 of lift like that. it onlyhas to get you up half way till the suit can take over. Other than that you need t look into a dry suit if you have to use a lot of weight and it is not dumpable. One last thing you say most of the weight needed is for you and not your suit. If so you ahve no problem cause you dont compress. Your body lift and the lead cancel out. The only compressable thing you should be comsidering is the suit. You will loose perhaps 90% of your suit lift at 100 ft. so if you have a suit that is 30 lbs then youare probably right at 90% of suit lift +5# for the tank (-32#). now with fins if you can swim up 15-20 and get to 50 ft then you will regain probably 10# of suit lift. now you only have 5-10 to lift to 20ft. do you know how much lift your suit has??

I had not thought about a half dump and I can "swim up" 15 pounds if by swim up you mean no wetsuit and fins retrive a weight from the bottom of a pool .

My weight woes stem from being a big guy with a barrel chest 54 inch chest puts me at xxxxl 38 hip puts m at xxl bottom i am renting a wetsuit now and always get there farmer jon style in 7 mm so its 14 mm in the chest it takes tons to get me down and i always feel overwieghted when it finaly all crushes. Dont get me wrong its a warm suit and that is its job but i think a custom one piece would let me shed considerable lead

I would love to dive with less lead but honestly most of it is for me I'm 290-300 diving is part of my attempt to be more wctive and healthier