Proper Weighting

[bennenrkc]

I know these questions come up all the time but I am trying to work on my bouyancy as much as possible as I am a new diver. Last weekend I dove in fresh water wearing a 7mm wetsuit, hood, and 3mm gloves.
I have an oceanic islander 2 for a bcd. I dove with 22#s. I know I was a little heavy, and when I go this weekend I am going to play with the weight some more.

THe biggest problem I was having was maintaining a level trim, my feet were always low. I had the 20 lbs in my droppable around my waist and the 2 on the tank strap.

Using basic logic, I think I need to move more weight to the tank strap and maybe slide the tank up a little. I have arrived at this conclusion in that my upper body is lighter and therefor could use more weight. (I will try reducing the weight from the ditchable before moving the weight around.

Is my logic right. Is there a fraction to use as a baseline to determine how much should be where. I understand everybody is different however not having anything to go off of, it takes a lot of work and time to try and get stuff figured out by guess and by golly, and I would rather use that time for working on other skills and just having fun.

Thanks for all of the help in advance!

 

[DivemasterDennis]

I think a big part of your trim issue is being over-weighted. That means you dove with more air in the bcd than desirable, making the top half of your total underwater person more buoyant than the bottom half. I don't think changing weights location will have as much impact as dropping a couple of pounds (or more.) DO a good buoyancy check before removing weight, and remove in 1 lb increments if you can.
DivemasterDennis

 

[TSandM]

Unfortunately, it just takes a few dives of playing with weight and balance to get it right. Proper weighting you can solve in one, with a good, formal weight check, but weight distribution is highly idiosyncratic, because it depends on the interplay of lift and weight, which is different for each body type, exposure protection, and equipment configuration.

I agree that you should do a formal check and drop the weight you can before you move a lot around. Also be aware that posture has a very powerful effect on trim -- if you are bending at the hips and dropping your knees below you, it will tend to rotate you head-up, almost no matter how you have your weights arranged.

HERE is a very nice article on trim (and there are tons of good articles elsewhere on the site, too!)

 

[boulderjohn]

I still have an old BCD with shoulder-leve trim pockets that I occasionally still use for diving. If I have the same amount of weight in the shoulder trim pockets as the waist pockets, I am just about perfect.

The real question is how much weight needs to be ditchable.

Let's assume that you get your weight down to the proper amount. First remember that with a 7mm wet suit, you will always be overweighted while diving. You need a certain amount to submerge, but once you are down, the wet suit compresses so much that you don't need nearly as much weight. Next, remember how a weight check works. If you hold a normal breath without moving with an empty BCD, you should float at eye level. Whether you need to add any weight to account for the lost weight of air used during a dive is controversial, but even if you do add a few pounds for that purpose, the key fact to remember is that with an empty tank, you should not be able to submerge. That means that if you are properly weighted, the only amount of weight that needs to be ditchable is equal to the weight of the air in your scuba tank. Go a few pounds more than that to be safe.

 

[Steve_C]

the key fact to remember is that with an empty tank, you should not be able to submerge. That means that if you are properly weighted, the only amount of weight that needs to be ditchable is equal to the weight of the air in your scuba tank. Go a few pounds more than that to be safe.

Note the few extra pounds. If you are diving in the open ocean you really don't want to go light during an open water ascent if you have to make one.

 

[alewar]

I agree that you should do a formal check and drop the weight you can before you move a lot around.

How do you conduct your formal weight check?

 

[TSandM]

I do a weight check two ways -- one is to weight myself to where I float at eye level with a full tank and normal breathing, and then add the weight of the gas I intend to use. The other is better, which is to do it at the end of a dive, by free-flowing a regulator until the tank is at 500 psi, and seeing if I have any weight I can jettison without floating to the surface.

 

[spectrum]

bemmemrkc,

You don't say how much history you have in this specific gear or if this is a change in salinity. From your dive count and question I'll hazard a guess that you have not made an objective weight check. Here is a page I wrote that walks though the why and how. Your answer will be unique so just pay your dues and follow the procedure. The check I describe at the end of the dive is going to provide the best answer. Anything that will get you to the end of your next dive is good enough.

Just for prospective I find myself putting 4-8 pounds up in cam band or trim pockets. The actual varies with a host of variables.

Pete

 

[boulderjohn]

Note the few extra pounds. If you are diving in the open ocean you really don't want to go light during an open water ascent if you have to make one.

I agree with this, but I would like to point out that i was talking only about how much of your total weight needs to be ditchable. How much total weight (ditchable and not-ditchable combined) you really need is another issue.

 

[GDI]

Trim and buoyancy are two different things. Think of one as UP and Down (Buoyancy) and the other as your angle of attack (Trim), Streamlining will come into play once your trim and equipment adjustments are made and balanced out. Read this Genesis Dive Institute of Florida presents: Scuba Diving Tips maybe it will help you get to where you want to be, keeping on it, Good Luck