Weighting & Buoyancy

[Nay]

I am fairly new to diving and have a question about weighting.
I know that it's optimal to dive with as little weight as possible but I'm not seeing it happen. During my OW class, the instructor intentionally had us a little heavy so we could sit on the bottom while doing out skills. I've heard a lot of people who like to talk tell me that I shouldn't be diving with much weight at all but after having to swim down a little to descend today my instructor/LDS mngr said that maybe I need more weight.
I'm 5'6", 152lb, wearing a 7mm full suit, boots, gloves, hood and I'm diving with an aluminum 63. (Unlike the standard 80, it's negative full and neutral empty.) I was wearing 24lbs on my belt today and that seems like a whole lot. Once I got past 5-8' I typically descended with no problems but I just couldn't get those first few feet today.
I don't have any of my own gear yet (except the wetsuit) but it really seems to me like I should be able to dive with less weight and still not have to fight to get down. Does everyone have issues with the first few feet of a descent?
I know that I'm opening a huge can of worms because everyone has their own opinion on weighting and buoyancy but any advice on people who've had similar problems starting out would be greatly appreciated.
Thanks!

 

[Warren_L]

Proper weighting can be a difficult thing to work out. In general, yes it is better dive with as little weight as required. If you have too much, you tend to be inefficient and you might be burning through more air than you need to.

However, you do need weight if you cannot get down. It can actually be dangerous to have to swim down to get down if you are too buoyant. The problem is not so much the swimming down, but rather the ensuing ascent. If you are positive to begin with, you may have a hard time controlling your ascent (i.e. no way to get neutral). As well, as you dive, you become more and more positively buoyant since you draw down the weight of the gas in your tank. This just exacerbates the problem. You want to be weighted such that you are neutrally buoyant at the surface at the end of your dive (typically with 500 psi in your tank).

Don't despair though, as you improve your diving, you will find that you will begin to drop weight (i.e. the amount of weight you require should decrease). This can be due to a number of factors including better buoyancy control, increased comfort with your gear, better dive techniques, etc. But these can all be improved over time.

People that tell you you shouldn't be diving with much weight are not telling you the full story. Unless you are diving warm water with little or no exposure protection, chances are you will need some weight. With a 7mm wetsuit, it is very likely you will need weight. To hazard a guess, with your current setup, I would think at least 20-22 lbs would be a ballpark guess, but to be certain, you need to do your own buoyancy check. The key after a while is to ditch as much extra weight as possible and have only what you really need.

 

[DA Aquamaster]

I wore around 24 lbs with an XL sized 7mm suit and a steel 72 that is similar to your AL 63 in terms of bouyancy. So you are not too far over the mark weight wise.

The big thing I notice with many new divers is that on the surface they often unitentionally kick their feet while on the surface and also while trying to descend. For a new diver not moving either their hands or their feet can be very difficult particularly if they are not real comfortbale in the water. Learnign to relax in the water and practicing not moving at all in the water can be very valuable in an effort to reduce weight requirements.

Many instructors have a bad habit of overweighting students to get them quickly though check dives rather than address the underlying bad habits and far too many divers continue to overweight themselves well into their diving careers.

 

[crpntr133]

I do have to agree with everybody. I dive a 5mm L suit with pretty much the same set up as you and I wear 18. My instructor wanted me to wear 24 because he had me wearing 8 in the pool with nothing but swim trunks; I am now down to 4 in the pool.
A buddy of mine wears, are you sitting down, 32 lbs. He is a rather large man, probably a XXL, and wears a 5/7 Henderson Gold suit. I personally think that he is over weighted but he has been diving for years with that weight. He is also the one in his DM class that just lays back and floats around the pool while everybody else is treading water. Some people float, other sink.

 

[fins]

Nay...

Don't know if this will help or not but....

When I purchased my gear and was deciding on size of ditchable weight pockets the LDS manager told me that it takes about 20lbs just to sink an XL 7mm fullsuit.

 

[HammerNoMore]

You want to carry as little weight as possible because if you are overweighted at depth when your suit compresses, you will have to compensate with more air in your BC. All that air in the BC will expand and contract as your depth changes so the more air you have in there the bigger the compensation will need to be, thus you bouyancy will be harder to control. Unfortunatly many instructors overweight their students as you mentioned and for the very reason you mentioned...they want to be able to keep them planted on the bottom to perform skills.

However, "as little weight as possible" doesn't always translate to a low number. A thick wetsuit or a drysuit usually requires a fair amount of weight to sink. Once they compress at depth they don't need as much so you wind up being a little overweighted but that is necissary because when you ascend (and are lighter from the air usage) you want to be in control.

Needing 24+ pounds in a new 7mm is not odd at all. The number will go down slightly with use but not that much.

Here is how I recomend you calculate your weight, it's a two step process. If you have an empty cylinder (200lbs or so) you can skip to ahead step two.

1. Get geared up with a full cylinder and hop in. Keeping your lungs inflated with a normal size breath, dump all the air from your BC. The water should be around eye level. If not add or remove weight until it is. Exhale and you should sink. Once you get that weight add 5 lbs to it to account for the weight your AL63 will lose as you breath off of it. (Use 6 for an AL80.)

2. At the end of your dive with a close to empty cylinder, perform a similar test, except this time you will be adding/removing weight until you can remain neutral (no finning, no arms, no vertical movement) a couple of feet below the surface. If you are neutral here you don't have to worry about being too light during your safety stop or going too fast the last few feet.

You can do either test or both. Number 2 is a little better but you have to have a nearly empty cylinder to do it.

James

 

[donacheson]

I am fairly new to diving and have a question about weighting.
I know that it's optimal to dive with as little weight as possible but I'm not seeing it happen. During my OW class, the instructor intentionally had us a little heavy so we could sit on the bottom while doing out skills. I've heard a lot of people who like to talk tell me that I shouldn't be diving with much weight at all but after having to swim down a little to descend today my instructor/LDS mngr said that maybe I need more weight.
I'm 5'6", 152lb, wearing a 7mm full suit, boots, gloves, hood and I'm diving with an aluminum 63. (Unlike the standard 80, it's negative full and neutral empty.) I was wearing 24lbs on my belt today and that seems like a whole lot. Once I got past 5-8' I typically descended with no problems but I just couldn't get those first few feet today.
I don't have any of my own gear yet (except the wetsuit) but it really seems to me like I should be able to dive with less weight and still not have to fight to get down. Does everyone have issues with the first few feet of a descent?
I know that I'm opening a huge can of worms because everyone has their own opinion on weighting and buoyancy but any advice on people who've had similar problems starting out would be greatly appreciated.
Thanks!

The minimum weight you need to carry is just enough for you to be neutral with an empty BC and a near-empty tank just below the surface. If you determine how much weight you need to be neutral with an empty BC just below the surface but with a tank with plenty of air in it, add 1 pound for each 13 cubic feet left in the tank. If you determine the minimal weight in fresh water, you must add 3% of your total weight (you plus all your equipment) for salt water.

As for troubles getting down initially, that's often the result of air bubbles trapped inside of dry and/or just-donned gear. They usually work themselves out quickly once underwater.