Submerging, weight, buoyancy

[rsdancey]

You're probably underweight.

An Aluminum 80 tank will become 6 pounds postively bouyant when empty, so figure about 5 pounds positive at 500psi. If you're barely able to submerge with a full tank, you won't be able to hold a safety stop at 5 meters with an empty tank.

You should test your bouyancy with a tank with 750-500psi of gas remaining. Enter the water, and with your BC totally deflated, you should be able to descend by completely exhaling - down to the last gasp of air in your lungs. Be absolutely still during this process - even tiny movements of your fins or hands can affect this test.

Prior to the test, in a wetsuit, I'd recommend diving upsidedown, swimming down a few feet, and trying to hang vertical (but upended) to get bubbles of air out of the suit. I found (when diving wet) that this had a very significant effect on my boyancy. It may also help to have a friend "feel" the BC looking for trapped air pockets.

Other factors that will affect how much weight you carry is the temperature of the water, how much air is trapped in various pockets and folds of your BC, the positive boyancy from your BC and other gear, your body mass, and how old your wetsuit is (as wetsuits age, they can become compressed and fail to return to their original volume, which has effects on thermal protection as well as bouyancy).

There is no "standard amount of weight" - so many factors affect each individual that you need to get the right amount for you and that amount will change over time. As you gain experience, you'll probably find that you're able to take weight off - or you'll redestribute it to backplates, steel tanks, etc. Working out in the gym and changing your diet can have a big effect too.

Good luck!

Ryan

 

[TSandM]

One piece of advice . . . find somebody who dives a BP/W to help you get everything set up and adjusted correctly. HERE's why.

 

[ScubyDoo]

Hopefully I'll be able to get some help setting up the BP/W and weight before I go. But, just in case, could you guys make sure you're down there when I go?

Sure! Your picking up the tab right?

 

[Atticus]

You're probably underweight.

An Aluminum 80 tank will become 6 pounds postively bouyant when empty, so figure about 5 pounds positive at 500psi. <snip>

psi cf diam length weight empty full
Tank full full eter empty buoy buoy
Luxfer 80 3000 77.4 7.25 26.06 31.38 4.4 -1.4

I'm guessing you're not counting the valve in the buoyancy figure when you say 6lbs? We generally refer to these tanks as above: -1.4 to 4.4 swing in buoyancy.

The backplate will be 6lbs-8lbs negative depending on the thickness. That should help significantly in your weighting issues. Do get some qualifed help in setting it up (as you mentioned).

 

[miketsp]

..snip..
That a HUGE amount of weight for a 5mm suit.
..snip..
Id say 12lb or so max for that sort of suit is needed.
..snip..

26 pounds sounds like an awful lot of weight.
..snip..

wow 26lbs and only a 5mm thats a lot of weight. are you in fresh water or salt? I hope thats salt water.
..snip..

I just love these threads where you have to conform to the norm or you're doing something wrong.
When I dive a full 5mm I need 12kg which is 26lbs and that's after hundreds of dives, some years diving & dozens of weight checks to establish neutrality at 3m at 40bar. I'm totally relaxed and I don't fin without realising it.
The 12lb quoted by String won't even get me down when diving in just a T-shirt, without any neoprene.

You're probably underweight.

An Aluminum 80 tank will become 6 pounds postively bouyant when empty, so figure about 5 pounds positive at 500psi. If you're barely able to submerge with a full tank, you won't be able to hold a safety stop at 5 meters with an empty tank.
..snip..
Other factors that will affect how much weight you carry is the temperature of the water, how much air is trapped in various pockets and folds of your BC, the positive boyancy from your BC and other gear, your body mass, and how old your wetsuit is (as wetsuits age, they can become compressed and fail to return to their original volume, which has effects on thermal protection as well as bouyancy).

There is no "standard amount of weight" - so many factors affect each individual that you need to get the right amount for you and that amount will change over time. As you gain experience, you'll probably find that you're able to take weight off - or you'll redestribute it to backplates, steel tanks, etc. Working out in the gym and changing your diet can have a big effect too.
Good luck!
Ryan

This was the only decent answer I saw...

 

[AlanDeep]

I am 6' and 240lbs and I float like a cork in a bathing suit in sea water, so (and don't be scared) I use 30-32 lbs with a tight 5mm suit, boots, gloves, and hood.
My camera/strobe floats 1lb, Light Cannon sinks about the same. Reel sinks, C4 light sinks. Sausage probably floats. If I had a backplate instead of a BC I would add less lead.

I took a Peak Performance Bouyancy course and used a 500psi Steel 80 in fresh water and optimised to 20Lbs with 5mm and 6lbs with polypropylene (skin).
I would add 5lbs for AL80. Salt water AL80 makes it 30Lbs for 5mm and 16Lbs for skin.

Crossing ankles to prevent finning (thanks TSandM) is an excellent idea.

I prefer to not swim down to hold at my safety stop!

 

[String]

Its a decent ball park to start. You get the usual bell curve where most people fit in a certain range and the numbers decreasing the further from it.

That sort of figure is a decent start. New divers are often grossly overweighted as well so i see no hard in suggesting the rough figure and going from there.

 

[micknewton]

There is no "standard amount of weight" - so many factors affect each individual that you need to get the right amount for you and that amount will change over time. As you gain experience, you'll probably find that you're able to take weight off - or you'll redestribute it to backplates, steel tanks, etc. Working out in the gym and changing your diet can have a big effect too.

Thanks Ryan!

And, many thanks to the rest of you too! You people are great! :bang:

 

[Charlie99]

Salt water in Banderas Bay, Mexico. The big mouthfull that I swallowed later that day didn't taste very fresh at all.

In addition to the other possibilities mentioned (unconsciously finning, having full lungs rather than exhaling hard, brand new wetsuit, etc.), there is also the possibility that you didn't really have 26 pounds. This is particularly true in locations where they cast their own "lead" weights from various sources of scrap lead, such as old lead acid car batteries.

Two other possibilities:

1. You still had air trapped either inside the bladder of the BCD. With some BCDs and wings it takes some contortions to work all of the air up to the highest point so you can dump it.

2. At the beginning of a dive, your 5mm wetsuit has a lot more buoyancy than later during the dive after it is saturated with water. (Think of the difference in weight between your suit when dry and when fully soaked).
This is one reason that when doing weight checks it is best to have been in the water for a while first.

 

[duckster3d]

weighting issues vary from diver to diver, most have given great tips, and or advice. It takes time and lots of dives. to really get the right amount of lead. I also tend to over-weight my students for their first openwater dives. Reason, I want them to be able to sink and stay down. once skills are out of the way and they start to just dive, I explain about feeling their weight in the water and start to pull off a few pounds each time they start to feel that they are negative in the water. Again this takes time and lots of diving. I dive without a weight belt when diving dry with double tanks, and a ss bp, in salt water, in fresh i switch to an alum bp. if i'm diving students then I'm in a wet suit, single tank with a bcd. i use 6 to 10 lbs on a weight belt, but only have the weight belt because i have to wear one when i teach. I really don't need it. for the most part if diving a single, and bcd i'll keep 2, 2lb weights in the pockets and no problem popping up at the end of the dive with a couple of hundred left.