Tank position to affect buoyancy

[mrjake]

I mad my first dives with a new 7mm semi-dry full suit/hooded sleeveless jacket combo this weekend and had difficulty with bouyancy control. I weigh 260# and carried 30# of weight in my BC, 10 lbs in the back and 20 in the integrated weight pockets. I could not descend until I was below 15 ft. I had to pull myself down a rope that was anchored to a training platfom below in the quarry where we were diving.

Once below 15 ft the suit compressed enough that I could control bouyancy, but it almost seemed as though I had too much weight at 60 or 70 feet having to nearly fully inflate my BC to stay off the bottom. On the first dive I had problems keeping my feet from rising requiring me to arch my back to keep them down. On the second dive I raised my tank in the BC thinking that its bouyancy would help keep my more in control, but the problem seemed worse. Should I have lowered the tank instead?

I definately need more weight because when ascending, once I get to 15ft I can no longer keep myself down. I thought about the posiblility of using some ankle weights as I have seen some drysuit divers do to keep my feet down. Is that a good idea? I'm new to cold water diving with thick suits so I need advise.

Thanks,
Bob Jacobs

 

[The Kraken]

Inherent problem with thick neoprene. Too little weight to get down and you're ok at the bottom - enough weight to get down and you're too heavy at the bottom.

You'll probably get a lots of posts saying to go to a dry suit.

I experience the same problem with my 6.5 farmer john/jacket. I'm just going to have to deal with it until I can get a dry suit.

If you have a down line, I suppose you could carry some detachable weight and then secure it to the down line after incurring neoprene compression.

It's just one of those boogers of diving.

I've been looking for a good solution to this for a while, myself.

 

[Charlie99]

If you have a down line, I suppose you could carry some detachable weight and then secure it to the down line after incurring neoprene compression.

IMO, this is a really, really bad idea.

A runaway ascent, even for the last 15' is a bad idea.

What happens if he, for whatever reason, makes his ascent somewhere other than the downline?

 

[Charlie99]

7mm semi-dry full suit/hooded sleeveless jacket ... I weigh 260# and carried 30# of weight in my BC, 10 lbs in the back and 20 in the integrated weight pockets. I could not descend until I was below 15 ft. ..it almost seemed as though I had too much weight at 60 or 70 feet having to nearly fully inflate my BC to stay off the bottom. On the first dive I had problems keeping my feet from rising requiring me to arch my back to keep them down.

Yes, it sounds like you need more weight. And the weight needs to be lower on your body. The easiest way is to move the weight from your back/shoulders down to a weightbelt.

Since you need to add even more weight and integrated pockets aren't really that good for huge amounts of weight, you should consider putting about 20# on a weightbelt and then the other 10-15# in your waist pockets.

Tank position affects trim (the position or attitude of your body), but NOT your overall buoyancy (whether your whole body floats or sinks).

 

[The Kraken]

Sorry, Charlie !!!!
Brain fart, what the heck was I thinking !?!?!?!?!?!?!?

Don't listen to me, Jake, I'll kill ya !!!!

 

[wedivebc]

I mad my first dives with a new 7mm semi-dry full suit/hooded sleeveless jacket combo this weekend and had difficulty with bouyancy control. I weigh 260# and carried 30# of weight in my BC, 10 lbs in the back and 20 in the integrated weight pockets. I could not descend until I was below 15 ft. I had to pull myself down a rope that was anchored to a training platfom below in the quarry where we were diving.

Once below 15 ft the suit compressed enough that I could control bouyancy, but it almost seemed as though I had too much weight at 60 or 70 feet having to nearly fully inflate my BC to stay off the bottom. On the first dive I had problems keeping my feet from rising requiring me to arch my back to keep them down. On the second dive I raised my tank in the BC thinking that its bouyancy would help keep my more in control, but the problem seemed worse. Should I have lowered the tank instead?

I definately need more weight because when ascending, once I get to 15ft I can no longer keep myself down. I thought about the posiblility of using some ankle weights as I have seen some drysuit divers do to keep my feet down. Is that a good idea? I'm new to cold water diving with thick suits so I need advise.

Thanks,
Bob Jacobs

Here is a tip from a 250lb 6'3 diver who was once a similar position . When I started diving, in cold water I had an obsene amount of weight. I was soon taught that so much wetsuit compression takes place near the surface that it is often hard to get under. Here are some thngs that may help:

- steel tank, they tend to be negatively bouyant or at least neutral when empty. Aluminum is postively bouyant when empty subtract 5 lb of lead.

- backplate/wings. A s/s backplate will put the weight right where you need it, under the wings so take 6 bl of lead off for that

- beathing is important, many new divers tend to hold some part of their lung capacity back when exhaling. It could be a trust issue but if you completely exhale when you submerge you will need less weight for the first couple of feet.

- movement, I see many new divers trying to submerge while still kicking their fins. Point the fins down and hold them still till you are under.

- above water weight will help you get down. When submerging try holding both arms over your head. That out of water weight will help start the descent.

I suspect you will eventually lose about 15 lb or so of that lead as you gain more experience.

good luck,

 

[MSilvia]

Don't listen to me, Jake, I'll kill ya !!!!

If it makes you feel any better, I've been reading an old (late 60's) PADI AOW manual for kicks, and it suggests the same thing.

 

[The Kraken]

God, I hate getting old and having moments like that.
Well, just as long as I have them above water and not below . . .

Gotta get a dry suit . . .

 

[mrjake]

The tank position issue is one of body attitude in the water. I need to keep my feet from floating up causing me to arch my back to regain level trim. I thought moving the tank upward would work, but that seemed to make it worse, but it was hard to tell due to struggling to stay down. Should I move it up or down to help keep my feet down?

I was not in a rapid ascent situation above 15 feet, but I couldn't stay down. The alarm on my computer didn't go off but I need more weight to be incontrol. On my second dive I even sucked all the air out of my BC before entering the quarry and still couldn't descend.

 

[Potapko]

I have the same wetsuit combonation that you do. I am a bit smaller weighing in at 175. I dive in fresh water with 12lbs on my waste and 6lb bp. But I also am using a steel 120 which I think is around 10lb negative when full. Perhaps a little more. I did some testing in the pool with my neoprene and found that it takes about 8 lbs just to sink the outer shorty with hood.
At depth, like 100 ft with the neoprene compressed, I still have half (or so) of my 35lb wing empty.

I also found that if I do not fully exhale to descend I won't. I will bob back up even with an empty wing. I am just suggesting you get in a pool and work on exactly how much weight you need to get negative. For me it took some practice to fully empty my lungs. That is, of course, as much as is possible.
You didn't mention what bc you are using but I would think that simply due to the size it would have plenty of boyant capacity.

just my .02