Weight Fine Tuning

[latitude]

Newbie here trying to fine tune his weighting.

6' tall, 220 lbs, diving a 7mm wetsuit, usually dive an AL80.
Currently using 30 lbs of weight and I think it's too much. Here's why:

Doing the "hold your breath and float eye level with 500psi in the tank, empty BC", puts me slightly below eye level (means over weighted). I can hold my 15 ft safety stop with no air in the BC just fine (means enough weight).

HOWEVER, I have a hard time descending to start the dive (I have to swim down, even if I concentrate on breathing shallow), and those last 8-10 ft on the way up, I have to work not to exceed ascent rates on the computer (again, paddling arms or whatever slow myself). And it's very hard for me to stay shallow and stay down (10 ft or so).

I've tried more weight (4-6 lbs or so) and it does help the descent and the last part of the ascent. Should I add it back? Will the descents/final 10 ft of ascent get better as I feel more comfortable in the water (I'm careful to to be kicking while descending/ ascending now)? Would you add the weight for comfort now and reduce it later? Based on the "float test" I'm heavy, and I know underwater I'll have an easier time with less weight, but I'm afraid of the "runaway ascent" and hate having to work so hard to descend...

I'm sure it's a newbie thing...

 

[WVDiver]

It is a newbie thing, with time all will be clear. In the beginning a few extra pounds will not hurt anything. Just not too much. It sounds as though your reasoning is sound and I think you are on the right track. Just keep diving and soon you will figure it all out.

 

[GrierHPharmD]

From your comment on your bouyancy check, I think that you're probably still taking large breaths. There's no real secret to using your tidal volume (breath) to control bouyancy, but it does take practice, or at least it did for me.

Another problem is that heavy wetsuit, which adds lots of bouyancy, but you might not be able to do anything about that due to water temps.

A couple of other tips: Try a steel 100 tank. It'll let you drop several pounds of lead. Add a steel backplate style BC, and you can shed a few more.

It sounds like you're on the right track to figuring out a solution to this, but just know that it'll take a little time and a lot of practice to perfect your bouyancy. Keep it up and you'll master the most important skill in diving!

Safe ascents,
Grier

 

[triton94949]

First question: Do you dive in fresh water (lakes, quarries) or seawater (ocean or bays)?

2nd question: Have you tried adjusting your weighing in a swimming pool yet?

Suggestion: Go to a swimming pool with your wetsuit, boots, gloves, hood, mask, weight belt, weights, and extra weights. Set the weights by the side of the pool at the 5 ft depth level. Get into your suit, complete with boots, gloves, hood, and mask (these all affect your buoyancy), and stand in the 5 ft deep section of the pool by the side where your weights are. Then begin to fill up your weight belt. Take a breath (not really deep just average) and hold your breath and then try to sit down. If you cannot sit down, then add more weight until you can sit down and submerge.

Once you are wearing enough weight to submerge and sit, then you need to do two more things. For aluminum tanks you need to add 6 more pounds. And for saltwater diving you need to add an additional 6 pounds. That should get you close to proper weighting.

The next thing would be to see if there is any air left in your wing/BC at the end of your safety stop following scuba diving.

If you do all that, and then you are still "too light" for scuba, then it would seem that you are hyperventillating for whatever reason, too cold, too new, and what you need to do further is try to control your breathing. Breathe in, breathe out, breathe slightly deeper and slightly slower than you normally would on dry land. Make sure you breathe all the way out, rather than hyperventillate.

Aluminum tanks are not a good idea for cold water diving. That is because for cold water diving you are already wearing a ton of weight to compensate for the thermal protection (wetsuit or drysuit). The need to add 6 more pounds to compensate for the tank is that much more of a burden on you. Think about renting steel tanks instead.

 

[cmcarver]

It will come around. In my first 25 dives I have big problems with bouyancy. I would seem to want to float to the surface for no reason wearing a 7/5 full suit and 20lb of weight. I currently us 12-14lb with an AL80 and the 7/5 full. I will start diving with S100s next weekend and hope to be at 6-9lb weight in fresh water. Warm Salt Water is use about the same weight because I don't use a wetsuit.

With Practice you will be droping weight. I say use the 20lb for now knowing that you will need to be removing it shortly. Then dive and truely get comfortable in the water and you should beable to drop a lot of weight then. Main thing is realizing just how much air is in your lungs. When doing a fin pivot I can go from platform to being vertical off the bottom 3-4 feet with just my lungs and settle it back down to bottom with out help from BC when I'm relaxed.

 

[The Kraken]

Latitude,
I think the crux of your problem, if it is really a problem at all, is the fact that you're a big fellow and you're wearing a lot of neoprene.

All thick wetsuits will generate the same type of issue you're having. Because of the large amount of positive buoyancy created by the wetsuit at the surface, you need a lot of weight to descend. Once you hit the neoprene compression depths, about 13 feet or so, you lose a great deal of the inherent buoyancy that your wetsuit gave you at the surface and now you feel like you're overweighted.

A basic law of physics . . .

It's just one of those things that one has to solve individually.

Unfortunately there appears that there is nothing that can be done to overcome the loss of buoyancy due to the compression of neoprene.

Some will say, get a dry suit . . . good solution if they'll ante up the funds !!!!

 

[Marek K]

Once you hit the neoprene compression depths, about 13 feet or so,

Hey Kraken--

What do mean, "neoprene compression depths?"

Edit: Never mind. For some reason I thought you were saying that neoprene stops compressing at some depth. I suppose neoprene would compress less-linearly as depth gets greater, because of the volume of solid neoprene separating the closed-cell bubbles...

But surely the biggest percent compression -- and therefore effect on buoyancy -- starts happening as soon as you start descending?

--Marek

 

[Rookie_J]

I have the same problem wearing my 2 piece 6.5 mil.

 

[The Kraken]

"But surely the biggest percent compression -- and therefore effect on buoyancy -- starts happening as soon as you start descending?"

You're exactly right, but with farmer johns and jackets, especially in the thicker materials, there is quite a noticeable compression loss somewhere around 13 feet or so.
It can be quite unnerving to a new diver. The student does the confined water work, is used to the characteristics of the exposure suit in that environment and then goes out for the open water dives. S/he starts a normal descent and then at about 13', ZOOM !!!, down they go!!!
Seen it more than once.
It's like the greatest area of bubble build up in your blood stream will occur between 20' and the surface.
Needless to say, this has even more of a reverse effect when surfacing with a nearly empty aluminum 80!!! Yeeeeeee haaaawwwww - - - UP WE GO!!!!!!

 

[latitude]

Latitude,
I think the crux of your problem, if it is really a problem at all, is the fact that you're a big fellow and you're wearing a lot of neoprene.

All thick wetsuits will generate the same type of issue you're having. Because of the large amount of positive buoyancy created by the wetsuit at the surface, you need a lot of weight to descend. Once you hit the neoprene compression depths, about 13 feet or so, you lose a great deal of the inherent buoyancy that your wetsuit gave you at the surface and now you feel like you're overweighted.

A basic law of physics . . .

It's just one of those things that one has to solve individually.

Unfortunately there appears that there is nothing that can be done to overcome the loss of buoyancy due to the compression of neoprene.

Some will say, get a dry suit . . . good solution if they'll ante up the funds !!!!

That's kind of what my thinking was also... I've tried more than the 30 I'm diving with now and it does make the shallow depths more manageable... I think I've also got some of that "taking big gulps of air" going on. On descent, I'm midful of shallow breathing and it helps, but I probably have the newbie deep breathing thing going on (I'm right at 30 dives now - so things are getting better).

Once I'm down to 10-15 ft or deeper, I'm fine, and I have plenty of lift to stay neutral down at 100 ft (the depest I've gone so far-AOW course). Below that, I'm pretty good staying exactly where I want to be - the other day my buddy and I lost the ascent line and wound up doing a free-water safety stop at 15 ft - no problems. "Runaway descents" are not really a problem either, because I have no problem anticipating the loss of buoyancy in the 10-15 ft range and add air to compensate.

So my question is: Would you add the extra weight to compensate for the first and last 20 seconds of your dive and tote around the extra 4-5 lbs for the rest of your dive? Or would you just deal with the "hard to descend" and "having to flare fins and wave arms" to slow the ascent? Ideally, I'd like to be able to get neutral anywhere in the water column (including just below the surface if needed), but those 4-5 extra pounds make me have to fiddle with the inflator a bit more as I move around the bottom (plus it makes the walk to the water, and the surface swim less enjoyable).

I guess it's kind of a catch-22...