Too much Weight

[Twiddles]

I have questions regarding the weight issues I have read on the forum. I have heard weight talked about almost as much as bouyancy. My concern is in its actual relevance to your skill as a diver and your safety while diving. The 10% rule would indicate that I should be diving with 24.5 lbs max ( I am currently wearing 30lbs shore dive, 37.5 boat) and that as my skills increase I would see that number drop. Here is my issue with that number, is it with or without 7MM wetsuit? With or without AL80? Salt or Fresh water? Booties, hood and gloves add extra bouyancy? Diffrent BCD's have varying degrees of bouyancy some neutral some not. Fins? Body type three major types come to mind bones, medium build, heavy build, how does the 10% apply to these body types? When you add it all up how much extra is acceptable before you start getting into the overweight department?

I have heard several people say they need x amount of weight to get down, but below surface they are overweighted? I feel much the same way as (I am aware of the affects of depth and breathing on trim and bouyancy) I feel heavy at depth of say 45' and yet at 15-20' my bcd is usually dam near empty. I normally swim up as I prefer to be negative and risk sinking before blowing by my safety stop. I do notice difficulting descending in the first 10' of the dive more so on a boat dive then a swim out shore dive (swim out reduces air trapped in equipment, wetsuit??), after 10' no problem descending although, I can still surface from the safety stop with an empty bcd with a full breath.

I am curious how much of the weight issue is actually about skill and safety and how much of it is really about ego.

 

[TSandM]

The goal of most diving is to stay in a state of neutral buoyancy most of the time, except during ascents and descents, of course. To achieve neutral buoyancy, you have to balance the things which want to sink (anything with a density higher than that of water) against the things that want to rise (anything trapping air, which includes neoprene and air bladders and lungs, and anything with a density less than that of water, which incudes fat).

If you take into the water with you more weights, which are dense and negative, than you need to counterbalance the positive buoyancy of your exposure protection, your body and your gear, then you have to add air to your BC to counterbalance that weight in order to be neutral. The more excess weight you have, the more air in the bladder. Excess air does two big things: It increases your drag, because a big puffy bladder has to be dragged through the water, and it increases your instability in the water column, because this big bubble of gas is expanding and contracting as you rise or fall.

In addition, excess weight has MASS, and that mass needs to be accelerated in order for you to move around in the water. More mass means more work, and more work means more gas consumption, which means shorter bottom times.

Obviously, one can learn to manage all of these things. Technical divers who enter the water with large, full double tanks and stages, can start their dives massively negative. They learn to cope with the resulting air in their BC, but there's nothing they can do about the work increase. It just is.

New divers can have a terrible time managing the big buoyancy changes from an overfilled BC, especially in the upper thirty feet, where the proportional changes are the greatest.

Proper weighting is important for stability, safety and comfort underwater, as well as for efficiency. Spending time trying to fine tune that last pound may be more of an ego thing, but getting your weighting generally correct is important for technique and is well worth the very small effort required to do it.

The "10%" rule does not take into consideration any of the things you list. Nobody can tell you out of hand how much weight YOU need (and in most threads where people ask about it, that's something they get told). But you need some kind of a place to start, and the rules of thumb give you that.

Remember that, if you are wearing thick neoprene, it compresses with depth. Therefore, as you descend, you will have to add air to your BC to make up for the positive buoyancy you have lost with suit compression. So it would be quite normal to require a significant amount of air at depth, and have the BC near empty at the end of a dive (tanks near 500 psi) and close to the surface (with maximum lift from the neoprene).

 

[MXGratefulDiver]

I am currently wearing 30lbs shore dive, 37.5 boat

I'm curious about the difference ... do you wear different gear, depending on whether it's a shore or boat dive?

... Bob (Grateful Diver)

 

[Warren_L]

I think there tends to be a lot of confusion over weighting, and especially when people talk about being over-weighted. I tend to prefer the term "properly weighted" to avoid any confusion.

Being properly weighted means having sufficient weight to counteract any net positive buoyancy you might encounter from the beginning of your dive at the surface through to the end of your dive. This is so that you can control your buoyancy and avoid an uncontrolled ascent at any time during the dive. Really, the laws of physics do not change as your skills increase, and thusly, for you and your particular configuration and where you are diving, there is a specific amount of weight that is proper.

The reason why it is often said that you drop weight as your skills improve is because typically new divers carry more weight than is required for their dive. Rightfully or wrongfully so, this tends to be the case. Presumably because newer divers do not generally have a good a feel for their buoyancy control than more experienced divers, and having more weight than is needed makes it easier not to experience an uncontrolled ascent. Sometimes with newer divers, it may be as simple as not being able to fully vent their BCs or wings, resulting in trapped air, which can unnecessarily contribute to positive buoyancy. As you become more experienced, this, amongst other things, becomes less of an issue.

When people say they need "x" amount of weight to get down, and below the surface they are overweighted, that is true to a degree. Again, I really hate the term "overweighted" as it can be misleading. Exposure protection, be it wetsuit or drysuit, typically compresses to a degree and becomes less buoyant once you reach depth. So as you descend, you become more negative, which is normal. You then need to compensate by adding air to your BC or wing to counteract that negative buoyancy once you reach your desired depth (actually, you compensate all the way down for various reasons, but primarily to achieve a controlled descent so that you are not adding all the air you need once you reach depth - this avoids slamming into the bottom and excess draw on your regulator's first stage).

Please note that though you may be negative if you have no air in your BC or wing at depth, it does not necessarily mean you are overweighted. Overweighted to me means having more weight than is required to do the dive. Being properly weighted will still mean that you are negative at depth (neutral by compensating with air in your BC or wing) by just enough to compensate for the buoyancy shift of your exposure protection and the amount of air you plan to use on the dive. Any more weight than this will mean you're over-compensating for the buoyancy shift by adding additional air to your BC or wing. While this achieves neutral buoyancy, it is a waste of gas and can result in unnecessarily increasingly rapid changes in your buoyancy as you ascend or descend, thus making buoyancy control more difficult (than it has to be).

 

[Garrobo]

What Warren L said. I couldn't have said it better if I was explaining my own conception of weighting. At least, that's how it works for me. And I'm no 'expert' by any stretch of the imagination.

 

[Scubakevdm]

I have questions regarding the weight issues I have read on the forum. I have heard weight talked about almost as much as buoyancy. My concern is in its actual relevance to your skill as a diver and your safety while diving. The 10% rule would indicate that I should be diving with 24.5 lbs max ( I am currently wearing 30lbs shore dive, 37.5 boat) and that as my skills increase I would see that number drop. Here is my issue with that number, is it with or without 7MM wetsuit? With or without AL80? Salt or Fresh water? Booties, hood and gloves add extra buoyancy? Different BCD's have varying degrees of buoyancy some neutral some not. Fins? Body type three major types come to mind bones, medium build, heavy build, how does the 10% apply to these body types? When you add it all up how much extra is acceptable before you start getting into the overweight department?

I have heard several people say they need x amount of weight to get down, but below surface they are overweighted? I feel much the same way as (I am aware of the affects of depth and breathing on trim and bouyancy) I feel heavy at depth of say 45' and yet at 15-20' my bcd is usually dam near empty. I normally swim up as I prefer to be negative and risk sinking before blowing by my safety stop. I do notice difficulting descending in the first 10' of the dive more so on a boat dive then a swim out shore dive (swim out reduces air trapped in equipment, wetsuit??), after 10' no problem descending although, I can still surface from the safety stop with an empty bcd with a full breath.

I am curious how much of the weight issue is actually about skill and safety and how much of it is really about ego.

If your BCD is empty at the end of the dive, and you have trouble not floating to the top, then you have taken all of the weight off that you can afford to, perhaps even a bit more. As far as using the extra 7 lbs on a boat dive, I'm not sure what could explain that. You might try diving your shore dive weight from the boat along with the following: (and by the way you are right that sometimes it takes a little while for all of the air in your wetsuit to be replaced with water, especially if it's thick and high quality.) When you jump in with your shore weight:
1.When you're ready to descend, exhale COMPLETELY and stretch out the last part of the exhalation for as long as you can stand it.
2. Swim down the first 5 or 10 feet to help compress your wetsuit and fill it with water.

The fact that you feel that you seem to be heavy at depth is probably aggravated by the compression of a thick wetsuit, and one way to get around that is to dive a drysuit.

What I would recommend is that you dive alot, and if you begin to notice that you do have excess air in your BCD at you safety stop, (with an empty-ish tank) then you can begin pairing off some of the weight, but if you're BCD is empty on the safety stop, you really can't afford to lose the weight.

I'm not sure what to say about the ego thing. I mean, I feel pretty strongly that diving shouldn't be a contest, but I know that a fair amount of ego seems to creep in somehow. I guess you've gotta say, "Hey, this is the weight that works for me, I'm here to go diving and have fun, so gimme the lead so I can get down there."

Once more possibility is that you may have air trapped in your BCD that you are not aware of, or your BCD may have been manufactured with materials that have some inherent buoyancy. You may want to have a buddy carefully check your BCD for air on your next safety stop, and do the following with your BCD:
1. Suck every bit of air out of the derned thing.
2. Put it in water. (not too deep!)
3. Add weight until it sinks.
4. If it requires alot of lead to sink the totally empty BCD take it to your LDS and tell them they suck. (unless you bought it online)

 

[Blackwood]

I have heard weight talked about almost as much as bouyancy.

As it should be. Weight is an inherent part of the buoyancy equation. It makes little sense to discuss one without including the other.

My concern is in its actual relevance to your skill as a diver and your safety while diving. The 10% rule would indicate that I should be diving with 24.5 lbs max ( I am currently wearing 30lbs shore dive, 37.5 boat)

As TSM pointed out, the 10% "rule" is nothing more than a starting point. Since most people have no idea what the volume of their body is (+ whatever gear divers strap on), you just have to start somewhere. Someone offered up "ehhh... 10% of what you weigh" and called it a day. But you have to dive and you have to fine tune it.

There is no should about the 10% rule, and it indicates nothing.

and that as my skills increase I would see that number drop.

Possibly, but not necessarily. Many new divers fidget quite a bit, and that moving around often creates upwards thrust. As we become more comfortable and aware of ourselves in the water, these tendencies diminish. Then we can take weight off because we're no longer inadvertently pushing ourselves up.

When you add it all up how much extra is acceptable before you start getting into the overweight department?

Ask ten divers to define overweight next time you hit the beach and you'll likely get eight different answers.

I like to define absolutes (such as OVER or UNDER) as they relate to safety. From a safety standpoint, overweighted is too much to get to the surface. Say you lose the use of your BCD. Can you swim up? If not, you're overweighted. Of course, some of your weight is likely ditch-able, etc..

A different viewpoint: if you have so much weight that it's no longer doing anything but sinking air in your BC, you are overweighted.

 

[MSilvia]

The 10% "rule" is worthless as anything but a starting point IMHO. You need the amount of weight you need, and it'll be different with different gear. There is no magic formula that will tell you how much weight you need without taking gear into account.

I'm curious why you use different weight for boat and shore dives though.

 

[doghouse]

I am about 200, and dove with 18# the other weekend. I realized that I was underweighted when @ 10' I suddenly hitched a ride on the express train to the surface.

On the next shore dive, take some time at the end of the dive to find where you can just barely float with full lungs and an empty bc.

JMHO - take it for what it cost.

 

[dave4868]

I am curious how much of the weight issue is actually about skill and safety and how much of it is really about ego.

It's certainly not about skill. It's very easy to get one's weighting adjusted in just a few minutes.

Safety might be an issue if one is underweighted and unable to hold an important safety stop. Gross overweighting might create buoyancy control issues which could cause a rapid ascent.

Ego would be an unlikely reason for beating one's breast over such a simple skill. The posturing would be entertaining to watch, though.

You mentioned being able to ascend at the end of the dive with an empty bcd by taking a full breath.

If that means you would sink when you exhaled, then it sounds like you've got your weighting just about right. I'm assuming a near-empty tank, of course.

I can't explain your perceptions of difficulty getting down at the beginning of the dive, especially boat dives. The beginning of the dive is when you're most negative (full tank).

Maybe you've got air still trapped in the bcd.... I doubt much is trapped under the neoprene, though.

Dave C