ADVERTISEMENT

Author Topic: Under what circumstances that a diver needs to dump weight?  (Read 4688 times)

Crash

  • Member
  • ***
  • Posts: 56
  • Liked: 17
  • Karma: +2/-0
  • Gotta Live Before You Die
    • Google
Then it will get more puzzled on why he will need to inflate BCD when diving down, only to know that BCD is faulty and he ditch the weight to go up again uncontrollably. This is dangerous boy. Keep your weight, trust me.


LOL, I think there is a grave misunderstanding here. In no way am I trying to insinuate not using a weight belt or any form of ditch-able weight system nor am I suggesting ditching weights with an inflated bcd. I use ditch-able weights myself. :)

But what I think barebear (based on my inference. but maybe i'm wrong  ???) is trying to convey and what I was trying to affirm is in the unlikely but still plausible scenario of a failed bcd (not being able to provide any positive buoyancy due to a ruptured/blown out bladder like what my friend had) during the start of the dive at depth, the diver can ditch his minimal 2-6lbs weight to make him less negatively buoyant (he is still negatively buoyant due to the weight of his full tank and equipments) to assist him in making a slow controlled ascent to the surface or make any safety/deco stop with minimal effort. Yes, some might argue that they can ascend effortlessly with all their weights intact. Good for them. But with some divers being grossly overweight with >10lbs weights like what you've seen, I highly doubt they can make a slow controlled ascent with minimal effort from the bottom with a ruptured wing/bladder. Essentially we both agree the best way to avoid all these problems is by carrying as little weight as possible; which is basically the whole idea of a balanced rig. Use minimal ditch-able weight so that in the event that one intentionally or accidentally drops weight, there won't be a sudden steep buoyancy swing to cause an uncontrolled ascent.

Now...if the diver's bcd works fine, malfunctioned (due to a faulty power inflator hose, etc) but still has air in it or is still able to provide lift, please please please for the love of God, do not ditch your weightbelt. It will definitely lead to a fast uncontrolled ascent like what some have mentioned here or seen when new divers unintentionally dropped their over-weighted belt during dives.

sorry for the wall of text. caffeine rush from my morning coffee.

dive safe!

epwing

  • Jr. Member
  • **
  • Posts: 27
  • Liked: 2
  • Karma: +0/-0
  • Singapore Scuba Diving Forum
Hey no worries. Appreciate your clear explanation.(the caffeine works).haha. Since this is an open forum, I just wanted new divers to know that ditching of weights due to BCD failure on the surface or underwater is a no no. This action may causes lives instead of saving one.

BareBear

  • Member
  • ***
  • Posts: 623
  • Liked: 39
  • Karma: +18/-6
  • Singapore Scuba Diving Forum
I think what he meant by 'start of the dive' is when one has already descend to depth with a full tank at the point the 'suit is fully compressed'. Please correct me if i am wrong barebear.

Yes Crash, that is what I meant, thanks for the clarification. At the start of the dive, tanks are full of air thus heavy, and wetsuit is fully compressed because you have already descended to depth, and they have lost their buoyancy characteristics. Sorry I wasn't clearer.

Pre-dive BCD checks are good and should always be performed, but they are not always failure proof.
If the BCD is fully inflated and if you are carrying a heavy rig and do a giant stride into the water, the OPV may not be able to dump fast enough as the BCD hits the water, and if there is a weak link, it may cause something to give way (after the pre-dive checks are done).

Also when dumping weights, it isn't a good idea to ditch the entire weight belt which may be carrying all your necessary weights. When you ditch the entire weight belt and start your ascent and your wetsuit starts to regain buoyancy, you will need those weights to maintain your stops and not float up uncontrollably.

I have been taught that the amount of ditchable weight should be equal to the weight of the gas in all your tanks. However, I was told by an experienced GUE instructor that this does not apply for all cases, and may not be so straightforward especially for technical divers who have to consider the buoyancy of their empty tanks.

As I am not very clear on the details of that part, I will leave the explanation to the experts...

BareBear

  • Member
  • ***
  • Posts: 623
  • Liked: 39
  • Karma: +18/-6
  • Singapore Scuba Diving Forum
Posted this in an old discussion on the topic of dumping weights, slight modification to 7mm wetsuit:

I think a simple illustration might help.

Let's assume 0 is neutral buoyancy. Anything positive, e.g. +2 is positively buoyant. Anything negative, e.g. -2 is negatively buoyant.

We assume all gear plus the diver make the diver neutrally buoyant. Numbers used are arbitrary but are pretty close.

At start of dive at surface:
7mm wetsuit  = +6
Air in tank = -2
Weights = -6
Air in BCD = +2
Result = 0

At start of dive at 30m:
7mm wetsuit = 0
Air in tank = -2
Weights = -6
Air in BCD = +8
Result = 0

At end of dive at 30m
7mm wetsuit = 0
Air in tank = 0
Weights = -6
Air in BCD = +6
Result = 0

At end of dive at 5m for 3min stop:
7mm wetsuit = +6
Air in tank = 0
Weights = -6
Air in BCD = 0
Result = 0

If your BCD fails to inflate at the start of the dive at 30m, you will be 6lbs negative. With no ditchable weight, you may not be able to swim up. If you ditch 2lbs of weights (which is the weight of gas in your tank), you will be able to fin up and make a somewhat controlled ascent, though still slightly positive at 5m (which can be compensated by your breathing if needed).

poh6702

  • Member
  • ***
  • Posts: 585
  • Liked: 74
  • Karma: +40/-9
  • Singapore Scuba Diving Forum
It brought up one question in my mind: what is the underwater weight difference between a 200Bar and 50Bar tank?

BareBear

  • Member
  • ***
  • Posts: 623
  • Liked: 39
  • Karma: +18/-6
  • Singapore Scuba Diving Forum
It brought up one question in my mind: what is the underwater weight difference between a 200Bar and 50Bar tank?

I believe it's about 2lbs.

siaokao

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 2343
  • Liked: 153
  • Karma: +57/-55
  • 2xKS diver..
So they call it a 'FACT' coz someone made some statements on a 'FACT SHEET'? hummm...

trekdive

  • Member
  • ***
  • Posts: 91
  • Liked: 13
  • Karma: +2/-0
  • Singapore Scuba Diving Forum
Just to add in some though, maybe case study. I had an experience of diving with a broken BCD.

This happen when I was wearing a 7mm long john wetsuit in ~20oC water plus quite inexperience and only mange to sink with ~12kg weight(I think). First dive was ok and on the 2nd dive, did a giant stride from a jetty (~3m high) into the water and start to heard bubble. Buddy say ok, did not see bubble so we went down. Only at the bottom I start to realise where the bubble sound and leak is from the elbow tubing of inflator. But manage to complete the dive at real bottom(some air can still be trap in BCD but its like half handstand).
The problem or question of dumping weight situation was after the dive at the surface. On surface, have about ~100m to swim and air cannot be trap by BCD since I am in a upright position. So question to me was to dump or not the weights at surface, with buddies all way ahead. Weight are too expensive for me to dump then, so I used quite some energy to swim back to the ladder(0.5m above water). And took another 10mins to get up the ladder after burning all muscle.
This might be a near situation of dumping weights on surface- If you have no one around, sinking due to too negative, personal energy/fitness level going down.

limk

  • Sr. Member
  • ****
  • Posts: 1735
  • Liked: 27
  • Karma: +99/-36
Only at the bottom I start to realise where the bubble sound and leak is from the elbow tubing of inflator. But manage to complete the dive at real bottom(some air can still be trap in BCD but its like half handstand).

And took another 10mins to get up the ladder after burning all muscle.

hence it's now a view of some to use only rear pull dump with valves that are inward towards bcd as should that leak/get damaged - (outward valves leak air faster)

sounds like a tough experience with 12kg! sounds like a bit heavy.
i agree with other posts about not using over-heavy weight belts as these are rather hard to manage/handle/hand-off and should it for some reason get dropped it's going to cause serious trouble.
i used around about 7kg before (spongy drysuit that was v buoyant) and put 4kg as non-dumpable on the tank strap. if a kind DM on the surface can help u out and take your weight belt that would be awesome..

i think in general my eyebrows will be raised if someone is saying a normal 3mm wetsuit dive in this region needs more than 5kg weights...it'll prob be some buoyancy control issue there.

for SEAsia tanks can get real floaty at the end of the dive...just keep in mind since they are aluminium. other countries may use steel..
« Last Edit: 08 Jul 14, 18:33 by limk »

trekdive

  • Member
  • ***
  • Posts: 91
  • Liked: 13
  • Karma: +2/-0
  • Singapore Scuba Diving Forum
Ops- went to check my log, its 10kg(5x big weight) in ~16degC water. It is still very heavy, that's why I like SEA diving, I now use 1 small weight.
The leak happen at the corrugated hose, not valve. And I not sure if there is a valve at the elbow in that bcd.
It was a great work out in the cold weather then and there is no DM, only buddy who is already up on the land(ready to load the car) by the time I got to the ladder. ::)
I believe in the drysuit or semi-dry case more weight is needed.