Too much Weight

[Piccola]

Dave C.

I don't know what more to add other than I do my bouyancy check as I have been trained. Normal breathe at the surface-float, exhale - sink head below the water. My problem is that I don't sink much farther than a foot or so. But once I get below about 5 feet-no problem. The deeper I go, the more I sink. I then add air to remain neutrally bouyant.

My mention of kicking to the surface was I had to work at it. I did not add air to my BCD during my ascent as I was trained to ascend with an empty BCD.

I absolutely needed air in my BCD to remain floating at the surface and my tank was for all practical purposes - empty. I dive with an AL63.

 

[jviehe]

The "PADI weight check", which has been around and used by other diver certification agencies for decades, makes no sense. It certainly didn't weight me correctly.

Minimal weight obtains by being neutral with an empty BC, a near empty tank, breathing normally just below the surface. While I'm not sure what "hold a normal breath" means, floating at eye level with a full tank and adding "weight to compensate for the air in a tank that you will use" means that you'll be floating with half your head out of the water at the end of the dive. Half your head weighs about 5 pounds. I don't want to be 5 pounds light when approaching the surface after a safety hang.

In my own case, I was certified in 1978 and weighted using the "PADI weight check". In retrospect I suspect it "worked" because we wore 1/4-inch wet suits, which compress rapidly with depth, and we never even heard of a safety stop. Our diving was done on wrecks hugging the bottom and grasping an anchor line to ascend.

It wasn't until I started diving in the tropics without a thick wet suit and with the need to be neutral throughout the dive that I had to learn how to weight myself properly - being neutral with an empty BC, a near empty tank, and breathing normally just below the surface. There's no problem with an extra pound or two, but underweighted by even a few pounds can be exhausting.

I said it is a starting point, but its also been demonsrated to work on hundreds of thousands of students. Im not sure you understood what I said though. On average if you are using a standard set of gear including a wetsuit, and you wieght yourself such that with an empty BC and your lungs half full (which is a normal breath), you will float at eye level and at that point be perfectly neutral at the surface.

Now, as you dive, your tank will become lighter and more bouyant, which is why you add weight to compensate. This means that when you end the dive, you should be neutrally bouyant at the surface again. Again, this is all very general. YOU must then tweak your weighting to acheive the desired affect.

 

[TSandM]

There's periodic discussion here about what the ideal weighting is -- Not in terms of how you figure it out, but actually what the goal should be. Should you be neutral at 10 fsw with 500 psi? Or neutral at the surface with 500 psi? Or a little negative at the surface with 500 psi? Or a lower psi goal?

I think the key is to remember what you are trying to DO with the weighting. You want to be able to stay underwater at the end of the dive until YOU decide to come up. Therefore, I've found a good double-check is not only whether you can float at eye level with empty suit/BC/near empty tank, but whether you can DESCEND with an exhalation. And I also learned the hard way that, if you are going to try to keep an SMB upright during ascent, you need to be able to remain slightly negative throughout, and if you've weighted yourself precisely for that "neutral at 10 fsw", you can't put any downward tension on the SMB line or you'll cork.

Anyway, even better than the "hang at eye level" test for me was lying down in very shallow water and seeing if I could exhale and go to the bottom, and inhale and float up. THAT's neutral, and I prefer it at 3 fsw rather than at 10, and at 300 psi rather than 5.

 

[waynel]

I've read a couple comments concerning weighting and "ego." I have to admit my wife did make a comment about how it all seemed to be a competition between the male divers. We had a number of lady divers in our group and that night I asked some of them and to a person, they all said the same thing. They asked me why, if you have no problems getting down and up are we (men) so obsessed about dropping weight. Let's be honest guys, could it be a little, just a little...about competition?

 

[dave4868]

Dave C.

I don't know what more to add other than I do my bouyancy check as I have been trained. Normal breathe at the surface-float, exhale - sink head below the water. My problem is that I don't sink much farther than a foot or so. But once I get below about 5 feet-no problem. The deeper I go, the more I sink. I then add air to remain neutrally bouyant.

I hope this isn't becoming belaboring to you. I certainly don't want to sound like I'm being critical. It's just a point of trying to understand and clarify to be constructive.

Your description of adjusting your weighting sounds good, but the end result sounds like it was faulty. Help me reconcile that, because both can't be true.

If you want to continue discussing it, feel free to reply. Otherwise, I'll take the hint.

Just think about your description of the situation for a minute....

If your buoyancy check on exhale brings you "a foot or so" below the surface, why wouldn't you continue to be negative and sink, or, if the drop was more like a temporary bounce, why wouldn't you bob back to the surface?

Also, was that with a full tank or empty tank? That makes about a 4 to 5 lb difference with the al63 you're using. That difference will show up later when the tank is depleted.

My PADI manual (c. 1990, 1994) on page 115 says about proper weight adjustment, "As a final test, exhale. You should sink slowly." I assume that means one would become negative and continue to sink.

Of course, the bone of contention was that PADI recommended this testing with a full tank, and they even state that the diver will be positive at the end of the dive with a depleted tank. I prefer to use an empty tank or calculate for an empty tank, so I don't become positive at the end of the dive.

I'm guessing you don't sink "a foot or so" below the surface, but, you sink just to the point where you still have the top of your head just at or above the surface.

That slight buoyancy won't be hard to counteract. It's probably only a pound or two of positive buoyancy.

My mention of kicking to the surface was I had to work at it. I did not add air to my BCD during my ascent as I was trained to ascend with an empty BCD.

Sorry, I was thinking a little differently. What you say makes sense for an out-of-air situation. I can understand your rationale. I assumed the free-flow meant you had enough air to use the bcd, too.

I absolutely needed air in my BCD to remain floating at the surface and my tank was for all practical purposes - empty. I dive with an AL63.

How can this be?

Think about what you've described.

Your empty tank is lighter, yet you're negative at the surface, whereas you described not being negative when you did your weight adjustment.

I'm baffled. Help me understand it.

Dave C

 

[dave4868]

The "PADI weight check", which has been around and used by other diver certification agencies for decades, makes no sense. It certainly didn't weight me correctly.

Minimal weight obtains by being neutral with an empty BC, a near empty tank, breathing normally just below the surface. While I'm not sure what "hold a normal breath" means, floating at eye level with a full tank and adding "weight to compensate for the air in a tank that you will use" means that you'll be floating with half your head out of the water at the end of the dive. Half your head weighs about 5 pounds. I don't want to be 5 pounds light when approaching the surface after a safety hang.

In my own case, I was certified in 1978 and weighted using the "PADI weight check". In retrospect I suspect it "worked" because we wore 1/4-inch wet suits, which compress rapidly with depth, and we never even heard of a safety stop. Our diving was done on wrecks hugging the bottom and grasping an anchor line to ascend.

PADI's "weight check" makes sense if you realize they were trying to achieve a margin of safety by having the diver become positively buoyant by the end of the dive at the surface with a cold-water wet suit.

They mention that positive buoyancy in the OW manual.

On page 115 of the PADI Open Water Diver Manual (c. 1990, 1994) with my embolden:

"With all your equipment on and with your BCD deflated, you want to wear just enough weight so you float at eye level while holding a normal breath. This is considered optimal weighting for several reasons:

1. You can begin a slow, feet first descent by merely exhaling.
2. When you return to the surface, you'll have slight positive buoyancy.
3. It will minimize the necessary buoyancy adjustments while diving."

Of course, "holding a normal breath" means holding an inhalation. For most people that's about a half liter of air. That's about 2 cups' worth. Not much. About 1 lb of buoyancy.

Floating at eye level is a rough approximation, probably not "half your head", since most people's eyes are higher than the midpoint. YMMV.

Also, most people could exhale a little over a liter (4 cups) of air after the normal exhale of half a liter, so it's very conceivable that such a decrease in buoyancy could initiate the descent, which could continue with the aid of compression of the neoprene. One liter would have about 2 lbs of positive buoyancy.

By the way, PADI's manual talks about this weight adjustment in the context of "typical cold-water wet suits", which they mention immediately prior to this exerpt in their discussion of "a good approximation for cold-water wet suits is approximately 10% of your body weight".....

In fairness to PADI, their guidelines are sensible, conservative and easy for a newbie to follow.

Of course, experience quickly leads one to tweak those guidelines, as you and I and many others have.

I'm sure PADI expects their instruction to be a starting point to be augmented greatly by experience.

Dave C

 

[ScubaBeez]

Just speaking to the 10% rule, I would guess that does not apply to each individual. Everyone has a different body composition so weight alone can not determine how much lead you'll need. I use 16% of my body weight and that has worked pretty well. I would guess you need to play around with adding and removing weight until it feels right.

 

[jviehe]

Dave, well said.

 

[dave4868]

Just speaking to the 10% rule, I would guess that does not apply to each individual. Everyone has a different body composition so weight alone can not determine how much lead you'll need. I use 16% of my body weight and that has worked pretty well. I would guess you need to play around with adding and removing weight until it feels right.

Exactly. That's really what is intended. It's a starting point that needs to be tweaked in-water.

I can only speak to the "10%" "approximation" that PADI refers to in my OW manual (c. 1990, 1994) on page 115.

"With an exposure suit, the amount of weight you need can vary, but a good approximation for typical cold-water wet suits is approximately 10% of your body weight (slightly more for dry suits)."

Perhaps it was quite a few years ago that they wrote about the "10%" approximation, and at that time, typical cold-water wet suits may have been one-piece 1/4" (6mm) neoprene, not the 7mm, highly buoyant neoprene two-piece Farmer Johns we often see today.

Anyone know when it originated?

Being sensible, PADI probably chose a percentage that would be likely to be a little light for everybody.

No doubt, they would hate to lose divers by recommending too much weight to start with!

Dave C

 

[donacheson]

I said it is a starting point, but its also been demonsrated to work on hundreds of thousands of students. Im not sure you understood what I said though. On average if you are using a standard set of gear including a wetsuit, and you wieght yourself such that with an empty BC and your lungs half full (which is a normal breath), you will float at eye level and at that point be perfectly neutral at the surface.

Now, as you dive, your tank will become lighter and more bouyant, which is why you add weight to compensate. This means that when you end the dive, you should be neutrally bouyant at the surface again. Again, this is all very general. YOU must then tweak your weighting to acheive the desired affect.

You're NOT perfectly neutral at the surface - you're floating.

My gripe with the "PADI weight check" is that's all that's taught. It appears that proper weighting isn't, yet being neutral throughout a dive can make scuba such a pleasure.