Descending Vertically Vs Horizontally

[Xanthro]

I think your right on about being relaxed. I need to work on that. I get so excited about diving its hard to just chill out sometimes. About having to add air with the wet suit. I dont. I dont know why but I just always seem to level out were I want too. I thought I was under weighted so we practiced hovering at 15 ft our last dive and no probs. I also think I move my fins while desending without thinking about it. This weekend I will not move a muscle and let you know if it works better. Ty for your help

At first boat dives were hard for me to relax, because of all the commotion on the boat. Gearing up, waiting to get into the water, anticipation of the dive. It was hard to relax before starting a descent. Once I recoginzed this, it was much easier. Now I just take a second or two to control my breathing on the surface, and descents are much easier.

It's great you never have to add air and can get neutral, I have to add a little air in a 7mil or at depth.

Another trick I've found is controlling depth by relaxing. If I'm neutral and completely relax, I'll sink, if I flex, I'll raise. With practice I can ever roll and turn by relaxing one side and flexing another.

One of my favorite parts of diving now is simply underwater flying. The weightless and near effortless movement through the water.

BTW, I'm jealous, I've had bronchitis of more than a month now and that means no diving.

 

[Jim Lapenta]

I did not mean any thing personally to you. my problem is with the instructor. It is his job to address all the issues that I mentioned. It was just your post that got me on this tirade because a few weeks ago at our local training site an instructor was rushing through several students and I saw one young lady in tears because she could not descend and the instructor had no patience with the situation. And basically faulted her for not knowing she was too light. This was her first time in open water and we were told later by her father who also took the class that the weighting issue was only briefly covered in her class.I also observed another student's second stage fall apart when he breathe tested it while using gear provided by this same outfit. We pay our instructors to teach us proper ,safe, and yes fun diving. My point is that while we have to learn and be willing to be taught we should get what we pay for.BTW we picked up a couple new students for further training that day.

wow. I dont think you read my post at all. But if I my ignorance can help you advance to pro status and be a better diver, well then your welcome

 

[markfm]

... I use the pst steel 80's which are 1&1/2 lbs neg empty so I usually don't add any more. ...

That doesn't make sense to me, I must be missing something. What you are compensating for is net buoyancy change due to the gas you burn (exhaust) during the dive, not the weight of the tank per-se.

Air weighs about 0.077 pounds per cubic foot.

An AL80 is actually on the order of 77 cubic feet. If you start with a standard 3000psi fill, want your safety stop with you being at the surface again at 500 psi, you have to accomodate a buoyancy change (air that's been used) of (3000 - 500)/3000 x 77 = 64 cubic feet.

64 cubic feet x 0.077 = 4.94 pounds.

That is where the "add 5 pounds" comes from -- not a bad thing, based on physics. If you are neutrally buoyant with your full 80 at the surface, you will be 5 pounds lighter at dive's end, so want to make yourself -5 at the start by adding that bit of weight.

The basic math holds no matter what you are diving, just need to run the numbers for how much air you will use. Say you have a steel 120, where the 120 is a nominal 3000 psi fill (I don't know steel psi, but the "120", "119", whatever is defined for a standard fill pressure for a given tank). Say you wish to end the dive, at the surface at 400 psi.

(3000 - 400)/3000 x 120 = 104 cubic feet of air has been used.

104 x 0.077 = 8 pounds.

So, if you have yourself at the baseline surface buoyancy (no air in BC, float at eye level, exhale sinks you, inhale raises you), you would want to add 8 pounds of weight so that you would have a clean state at the end (controlled ascent).

The only variance comes if the combination of your gearing (you + wetsuit + BC + tank +...) is such that you can never get to the above baseline, you are always negative when the tank is full, need air in your BCD at the surface to keep from sinking with zero weight. In that case you really need to burn your tank down to the desired end state (400 psi, 500 psi, whatever), add weight until you are neutral when the tank has that many psi in it.

If it turns out that you are negative with zero weight, tank down to as many psi as you desire to be your ending point, then you of course need no weight.

(There may be a small errata, due to the base atmospheric pressure of 14.7 psi, but when dealing with 100s and 1000s of PSI it's insignificant)

 

[ScubaTwo]

At first boat dives were hard for me to relax, because of all the commotion on the boat. Gearing up, waiting to get into the water, anticipation of the dive. It was hard to relax before starting a descent. Once I recoginzed this, it was much easier. Now I just take a second or two to control my breathing on the surface, and descents are much easier.

It's great you never have to add air and can get neutral, I have to add a little air in a 7mil or at depth.

Another trick I've found is controlling depth by relaxing. If I'm neutral and completely relax, I'll sink, if I flex, I'll raise. With practice I can ever roll and turn by relaxing one side and flexing another.

One of my favorite parts of diving now is simply underwater flying. The weightless and near effortless movement through the water.

BTW, I'm jealous, I've had bronchitis of more than a month now and that means no diving.

I have never dove in a 7mil just 3,5 and dry so when I do that might change everything. Im so sorry to hear you have been ill. Hope you get well soon and get back in the water. Take care of yourself!

 

[ScubaTwo]

I did not mean any thing personally to you. my problem is with the instructor. It is his job to address all the issues that I mentioned. It was just your post that got me on this tirade because a few weeks ago at our local training site an instructor was rushing through several students and I saw one young lady in tears because she could not descend and the instructor had no patience with the situation. And basically faulted her for not knowing she was too light. This was her first time in open water and we were told later by her father who also took the class that the weighting issue was only briefly covered in her class.I also observed another student's second stage fall apart when he breathe tested it while using gear provided by this same outfit. We pay our instructors to teach us proper ,safe, and yes fun diving. My point is that while we have to learn and be willing to be taught we should get what we pay for.BTW we picked up a couple new students for further training that day

I feel I got more then my moneys worth. I have very good bouyancey control and I can thank my instructor for that. He gave me the intiative by watching him. To this day I can call him with any questions I may have and hes there for me. My problems with descending have not to do with weighting or with his instruction and he has worked with me tirelessly on it . Gladly I have gotton lots of good advice on this thread that will actually help

 

[Firefyter]

You are overweighted if you have to descend in that manner.

I dive AL80s on most boat dives, being weighted for the end of the dive you still should not have any air in your BCD when you start your descent.

I disagree with this part. I check my weighting using a near empty (less than 500 psi) tank, and I float at eye level with a full breath and a totally empty BC. By doing it this way, you have no problems holding a safety stop at 15 feet with a bouyant tank. For that matter, I can hold it at 10 foot, 5 foot, any depth I want. I do it every weekend. If you can't hold it at 10 foot, maybe you're underweighted.

A properly weighted descend isn't as easy as simply releasing some air and sinking. You have to release all the air in your BCD, and your lungs.You need to exhale and when you think you have no air left, exhale some more, completely relax, and then you'll get down. You'll still be properly weighted at the end of the dive.

Again, I disagree with the BC part, but I do exhale everything in my lungs. I believe that if you're experienced, and have to work that hard to get down, you're underweighted.

While you gain some bouyancy from the tank, remember, you are doing your safety stop at 15 feet, not the surface. You need to be weighted for a depth of 15 feet with a bouyant tank.

As you descend, you should only ever have to add a short burst to control your speed, depending on the wetsuit, I sometimes don't add air till I'm at 50 feet. I can simply change descent speed by breath control.

I agree with all of this, with the added step of being able to control your ascent and being able to stop at any depth necessary with a near empty tank, not just 15 feet.

It really does sound like you are just a couple of pounds overweighted.

Again, I'm sure I'm not, but you're entitled to your opinion, even if it's wrong

 

[Xanthro]

I disagree with this part. I check my weighting using a near empty (less than 500 psi) tank, and I float at eye level with a full breath and a totally empty BC. By doing it this way, you have no problems holding a safety stop at 15 feet with a bouyant tank. For that matter, I can hold it at 10 foot, 5 foot, any depth I want. I do it every weekend. If you can't hold it at 10 foot, maybe you're underweighted.

My tank is never under 500 psi, and yes I can hold a safety stop at any depth including 5' or 3'.

I'll admit my tank is rarely actually bouyant because it's exceedingly rare that it is below 1000 psi. However, when I practice with empty tanks, I never feel underweighted.

Again, I disagree with the BC part, but I do exhale everything in my lungs. I believe that if you're experienced, and have to work that hard to get down, you're underweighted.

I didn't say it's hard for me to descend. While I admit to some issues that others may not have, such as a tendency to tip over backward while descending feet first, I don't fight to get down.

I do feel that a proper descent will require the diver to concentrate on breathing and relaxing. This is not at all easy for many people, and while you may have mastered it, it is still work.

It's like driving a car, a task that is very complicated, but once you get it down it doesn't seem all that difficult. When explaining to someone who is experiencing a difficulty in a task in a dive, it's important to remember what you learned when you were at that stage. Most people when first properly weighted have trouble descending. With practice this becomes easier.

I'd daresay that there are far more overweighted than underweighted divers.

I agree with all of this, with the added step of being able to control your ascent and being able to stop at any depth necessary with a near empty tank, not just 15 feet.

Much of the difference comes with practice. If a newer diver can hold a saftey stop at 15', with practice that same diver can hold a stop at 10' with the same weight, and with more practice at 5'.

 

[ScubaTwo]

My tank is never under 500 psi, and yes I can hold a safety stop at any depth including 5' or 3'.

I'll admit my tank is rarely actually bouyant because it's exceedingly rare that it is below 1000 psi. However, when I practice with empty tanks, I never feel underweighted.



I didn't say it's hard for me to descend. While I admit to some issues that others may not have, such as a tendency to tip over backward while descending feet first, I don't fight to get down.

I do feel that a proper descent will require the diver to concentrate on breathing and relaxing. This is not at all easy for many people, and while you may have mastered it, it is still work.

It's like driving a car, a task that is very complicated, but once you get it down it doesn't seem all that difficult. When explaining to someone who is experiencing a difficulty in a task in a dive, it's important to remember what you learned when you were at that stage. Most people when first properly weighted have trouble descending. With practice this becomes easier.

I'd daresay that there are far more overweighted than underweighted divers.




Much of the difference comes with practice. If a newer diver can hold a saftey stop at 15', with practice that same diver can hold a stop at 10' with the same weight, and with more practice at 5'.

Well put. Now Im going to watch Shark Week on my new cable whoo hoooooo.
Get rest and get well soon.

P.S. I used to tip over backwards too. I dont know why but it stopped happening.

 

[Jim Lapenta]

As taken from the encyclopedia of recreational diving section 3-49 a standard aluminum 80 has the following buoyancy characteristics full-negative1.80 lbs empty-positive 4.00lbs. my e series pst 80's are engineered to have the following buoyancy properties full- approximately negative 8lbs, empty- approximately negative 1.5 lbs. this is why in a swim suit only I don't need to carry any extra weight at all. that's just me and in the pool it's perfect. with my 3/2 shorty or my polartech full suit I can get by with 4-6 lbs in open water,fresh water that is, depending on what other gear I'm carrying and what I'm doing.this negative property at the end of the dive based on 500psi is why I don't need to add extra weight to compensate for the air used. again that's me.some one who has more natural positive buoyancy may still need to add the extra weight. I don't with the steel if I use an aluminum then yes I add the extra weight. different tanks have different buoyancy characteristics. the high pressure steel 95's are 6lbs neg when empty. while a low pressure steel 105 is 3.5 lbs positive.I don't know all the factors that determine this such as exact construction and engineering but hopefully by the time I have my gas blender certification I will.

That doesn't make sense to me, I must be missing something. What you are compensating for is net buoyancy change due to the gas you burn (exhaust) during the dive, not the weight of the tank per-se.

Air weighs about 0.077 pounds per cubic foot.

An AL80 is actually on the order of 77 cubic feet. If you start with a standard 3000psi fill, want your safety stop with you being at the surface again at 500 psi, you have to accomodate a buoyancy change (air that's been used) of (3000 - 500)/3000 x 77 = 64 cubic feet.

64 cubic feet x 0.077 = 4.94 pounds.

That is where the "add 5 pounds" comes from -- not a bad thing, based on physics. If you are neutrally buoyant with your full 80 at the surface, you will be 5 pounds lighter at dive's end, so want to make yourself -5 at the start by adding that bit of weight.

The basic math holds no matter what you are diving, just need to run the numbers for how much air you will use. Say you have a steel 120, where the 120 is a nominal 3000 psi fill (I don't know steel psi, but the "120", "119", whatever is defined for a standard fill pressure for a given tank). Say you wish to end the dive, at the surface at 400 psi.

(3000 - 400)/3000 x 120 = 104 cubic feet of air has been used.

104 x 0.077 = 8 pounds.

So, if you have yourself at the baseline surface buoyancy (no air in BC, float at eye level, exhale sinks you, inhale raises you), you would want to add 8 pounds of weight so that you would have a clean state at the end (controlled ascent).

The only variance comes if the combination of your gearing (you + wetsuit + BC + tank +...) is such that you can never get to the above baseline, you are always negative when the tank is full, need air in your BCD at the surface to keep from sinking with zero weight. In that case you really need to burn your tank down to the desired end state (400 psi, 500 psi, whatever), add weight until you are neutral when the tank has that many psi in it.

If it turns out that you are negative with zero weight, tank down to as many psi as you desire to be your ending point, then you of course need no weight.

(There may be a small errata, due to the base atmospheric pressure of 14.7 psi, but when dealing with 100s and 1000s of PSI it's insignificant)

 

[scubafool]

I'm a bit confused as to your question. You should have all the air out of your BCD at the surface, so there is no need to release more to descend, no matter what orientation you use.

Start feet down, dump all your air, exhale completely, exhale some more, when you get to about 10 feet, roll to horizontal, then add air to your BCD to slow your descent. You shouldn't be taking any breaths in until your are a few feet down, otherwise you'll require too much weight to descend.

If you need to let ALL of the air out of your BC to start your descent, then you need more weight.

Generally I start my descent horizontal and dump from the inflator hose when in doubles or the rear dump when in singles, as my single wing is O-shaped, the doubles wing is an upside down U shape, so dumping from the inflator hose along with rolling slightly head up keeps the air equali in both sides of the doubles wing.

Anyhow, just about the only time I dump ALL of the air out is the last 3 or 4 feet of my ascent when I am diving single tank & I have spent a lot of time shallow breathing the tank down to 300-400 PSI.