Why ditchable weight?

[Wijbrandus]

Here's a question that I don't really understand the stock answer for.

Why does a diver need ditchable weights? If your gear configuration makes you neutral on your weight test?

If I'm slightly heavy at depth, and have enough enough neg in my gear to keep neutral at my safety stop with 500 psi, why would I want to reconfigure to make me need a weightbelt?

 

[H2Andy]

you're right.. you don't really need ditchable weights if you are weighted optimally. i have been able to kick my way up from 100 feet without ditching my weights. it does take a bit of effort. (i am a strictly warm-water diver, no dry suit).

but they are ditchable in case of an emergency, so that you are not "married" to having 10 lbs of lead around your waist. i just like knowing that i can ditch them, should i have to (like what if i get a cramp on the surface and can't inflate my bc? ditching weights is a nice way to gain bouyancy).

 

[pt40fathoms]

If you are in the tropics and diving without much if any exposure protection, and have no need for lead because your gear and other items are sufficient. Then your gear becomes your ditchable weights at surface in the event of an emergency where you need to establish positive bouyancy.

Easy to say, but in reality, people do not think rationally in an emergency, and will not even dump lead because "it cost me money"! Sad but true, the accident reports are filled with divers who failed to establish positive bouyancy in an emergency, sunk and drowned, while still carrying all their gear and weights.

 

[Warren_L]

If you've got any sort of exposure protection on, you're going to lose buoyancy as you go deeper. If something happens at depth, it may be advantageous to ditch some weight to help you ascend. Also, at the beginning of your dive, you would typically be negative to compensate for the buoyancy change as you draw down your air, so having ditchable weight during this time can be a benefit in an emergency.

 

[IslandHopper]

In an extreme emergency (say you become unconsious), making you bouyant (by ditching some of your weight) is the easiest and most fool-proof way for a "buddy" to get you to the surface. .... I'd take DCS over drowning most days.

 

[MikeC]

This is a good question, but shouldn't this have been explained during OW class time? No slam meant to Wijbrandus. Robert, when did you get certified? I'm curious.

 

[IndigoBlue]

Here's a question that I don't really understand the stock answer for.

Why does a diver need ditchable weights? If your gear configuration makes you neutral on your weight test?

If I'm slightly heavy at depth, and have enough enough neg in my gear to keep neutral at my safety stop with 500 psi, why would I want to reconfigure to make me need a weightbelt?

In an ideal situation, you would be neutrally buoyant at all times during your scuba dive. The only situation which approaches that in the real world is with a drysuit and a closed circuit rebreather. In that case, you would not NEED any ditchable weight to be safe underwater. But even so, most CCR divers in drysuits still opt for some ditchable weight, although they would rarely ditch it.

In the real world of recreational scuba diving, there are two reasons why ditchable weight is a very good idea.

First, the air in your open circuit scuba tank is constantly decreasing. Since it weighs 0.08 lbs per cu ft, it weighs in total about 6.4 lbs at the beginning of your dive. It weighs less than 1 lbs near the end of your dive. This suggests that if you are diving with a drysuit, then your ditchable weight should at least equal this 5 lbs difference.

Second, if you are diving with a wetsuit, the buoyancy of the suit will approach zero as you dive deeper. At 100 ft it is 1/4 of what it is near the surface. At 130 ft it is 1/5. This suggests that if you are diving with a wetsuit, then in addition to the 5 lbs of ditchable weight you should have to compensate for the weight of your compressed air at the beginning of the dive, you should also have additional ditchable weight of 4/5ths times the weight it takes to neutralize the buoyancy of your suit at the surface.

That way, if you dive to 130 ft in a wetsuit at the beginning of your dive, and your B/C wing fails, you can ditch your ditchable weight and swim up. You will have to flair, as the wetsuit becomes more buoyant near the surface, but at least you will not be trapped at depth overcome by your nonditchable weight, if you had no ditchable weight.

With a drysuit, you would need less ditchable weight.

Without ditchable weight, you would be taking a risk that you may not be able to swim yourself back up, under all circumstances, like severe cramps, a strong down-current, etc. in conjunction with a wing failure.

 

[Wijbrandus]

This is a good question, but shouldn't this have been explained during OW class time? No slam meant to Wijbrandus. Robert, when did you get certified? I'm curious.

No slam taken. That's why I mentioned I had heard the "stock answer" when I was certified last summer. The theory was explained to me then, but I'm not sure I agree with it entirely. This is why I was asking for some more details from the board.

The reason I'm asking is my current rig makes me negatively bouyant in fresh water without a wetsuit, or even with a 3mm shorty. Not dramatically, but by about a pound or two. Since I normally dive salt, and haven't done any dives in the cold water here in Colorado, I figure I'll need about 2-4 pounds of lead in the ocean with a 3mm full suit, and that's ok with me. That'll be my "normal" scenario until I get into drysuits.

I'm taking my advanced open water next weekend, though, in Homestead Crater. The conditions are a hot spring that runs 95F year round, and no exposure protection is allowed. Rather than rent the LDS crappy jacket, it is my intention to simply use my gear, and be aware of the risks involved.

At most, I'm only about 4 pounds overweighted without a wetsuit, and that's a piece of cake to swim up.

 

[DA Aquamaster]

That way, if you dive to 130 ft in a wetsuit at the beginning of your dive, and your B/C wing fails, you can ditch your ditchable weight and swim up. You will have to flair, as the wetsuit becomes more buoyant near the surface, but at least you will not be trapped at depth overcome by your nonditchable weight, if you had no ditchable weight.......

....Without ditchable weight, you would be taking a risk that you may not be able to swim yourself back up, under all circumstances, like severe cramps, a strong down-current, etc. in conjunction with a wing failure.

This is a good argument for having ditchable weight but with the caution that dumping it will most likely result in you going all the way to the surface with no deco or saftey stops.

I have helped buddies off the bottom on deep dives when they had insufficient bouyancy and a buddy assist is much more preferable to dumping weight as it allows a fully controlled ascent and saftey stop.

Personally, given that I frequently solo dive, I prefer a liftbag and a reel that allows deployment of an ascent line that I can "climb" if required in the event of a wing failure and severe leg cramps, etc.

Ditchable weight in my opinion is most useful for quickly establishing positive bouyancy for a tired/panicky/unconsious diver on the surface. Dumping weight under water is very much an option of last resort where all the other options have either failed or been missed through poor planning but where being bent is obviuosly preferable to being dead.

So in my opinion the importance of ditchable weight is best viewed from a systems perspective where you assess your abilities, your gear configuration, your normal dive profiles and a healthy dose of conservatisim to determine how much ditchable weight should be used.

 

[Warren_L]

Is it possible to adjust your rig? If you are using a stainless steel backplate for example, you can switch to an aluminum for example, or if you are using steel tanks, go AL. Being unneccesarily overweighted is generally not good. But 4 pounds overweight at the start of the dive might be appropriate given you will draw down your air during your dive and become more positive.

As well, you might want to consider carrying some redundancy like a lift bag.