Weighty problem

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HAWK-EYE

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Okay everyone,

This is a re-visit to a buoyancy dilemma from last year that happened yesterday.
Here are the particulars.

Dive date / location: April 29, Rockport, MASS.
Me: Weight 232lbs.
Dive experience: 12 dives.

Equipment
BRAND NEW first time using Henderson gold farmer john 7mm.
Brand NEW first dive with aluminum Catalina S80.
BC – Oceanic Chute 3 with 10 lbs non-ditch able and 26 lbs in quick release pouches.

History

Last year rental wetsuit same BC and weights people thought I was nuts to be carrying so much weight, So I took a couple of pounds off and it seemed ok. Fast forward to yesterday first dive of the season.

There were six of us, swim out and were agree to descend. OK, we start and I let the air out of the BC and proceed to what I think go down, only I didn’t, I had no air but I was just floating there at eye-level wondering when my buddy is going to come up and help with. Only a short time and he comes up and luckily he has extra leg weights!! So on with the weights 1 lb’s and I’m off to the bottom. Problem one solved, start with 2 more lbs.

Towards the end of dive in about 30 feet of water and on our way back towards shore with about 1200 lbs of pressure I start to have to fight to stay on the bottom. I feel myself slightly rising up. I let air out of the BC and it seems ok but then a few minutes later the same thing happens. So I think ok I’m not going to fight this now and tell my partner I’m going up.

Back on shore and on the way home we discussed my problem and we came to the conclusion that the added 2 lbs solved the first problem being able to get down. That I probably would solve the second problem by adding 2 more lbs. So that I’d be carrying 40 lbs total. So now I have to go to the CFO to get some two-pound leg weights.

I think this will do it, any other thoughts?

Thanks,
 
HAWK-EYE:
Okay everyone,

This is a re-visit to a buoyancy dilemma from last year that happened yesterday.
Here are the particulars.

Dive date / location: April 29, Rockport, MASS.
Me: Weight 232lbs.
Dive experience: 12 dives.

Equipment
BRAND NEW first time using Henderson gold farmer john 7mm.
Brand NEW first dive with aluminum Catalina S80.
BC – Oceanic Chute 3 with 10 lbs non-ditch able and 26 lbs in quick release pouches.

History

Last year rental wetsuit same BC and weights people thought I was nuts to be carrying so much weight, So I took a couple of pounds off and it seemed OK. Fast forward to yesterday first dive of the season.

There were six of us, swim out and were agree to descend. OK, we start and I let the air out of the BC and proceed to what I think go down, only I didn’t, I had no air but I was just floating there at eye-level wondering when my buddy is going to come up and help with. Only a short time and he comes up and luckily he has extra leg weights!! So on with the weights 1 lb’s and I’m off to the bottom. Problem one solved, start with 2 more lbs.

Toward the end of dive in about 30 feet of water and on our way back toward shore with about 1200 lbs of pressure I start to have to fight to stay on the bottom. I feel myself slightly rising up. I let air out of the BC and it seems OK but then a few minutes later the same thing happens. So I think OK I’m not going to fight this now and tell my partner I’m going up.

Back on shore and on the way home we discussed my problem and we came to the conclusion that the added 2 lbs solved the first problem being able to get down. That I probably would solve the second problem by adding 2 more lbs. So that I’d be carrying 40 lbs total. So now I have to go to the CFO to get some two-pound leg weights.

I think this will do it, any other thoughts?

Thanks,
Click to expand...


It appears as though there are two factors at work here which will affect your buoyancy.

You have a brand new wet suit which will be much more buoyant than a rental wet suit used for 100 or more dives.

This dive was the first dive of the season for you.

In other words, what you experienced makes sense.

Maybe some of the really experienced members of the forum can add to my comments.
 
Also the aluminium tank will become more bouyant as it gets emptier and lighter. For diving with aluminium tanks you should do a buoyancy check with an empty tank. This isn't an issue with steelies.
 
Bubble Junky:
Also the aluminium tank will become more bouyant as it gets emptier and lighter. For diving with aluminium tanks you should do a buoyancy check with an empty tank. This isn't an issue with steelies.
Click to expand...
sure it is. You need less weight overall with steel, but any tank becomes more bouyant (or at least less negative) as it gets emptier.

You can do a bouyancy check at the beginning with a full tank which is a little more useful for getting it right on the first dive instead of suffering through it - just look up what the bouyancy change will be for your particular tank and add that much. There's plenty of charts with this info.
 
Seems like a lot of weight. Assuming you have done a bouyancy check. Are you sure you BCD is empty? Does it have a shoulder dump? If so raise that shoulder and try to dump all the air. The next thing is to make sure you are exhaling completely at the same time. Once you get a few feet down, compression of you wetsuit will allow you to breathe normally.

If you haven't tried this try do it before you add more weight. It is not uncommon to drop additional weight after your first few dives. Some it takes longer.
 
Hawk-Eye,

Another issue that is confronting you is the lack of compression of the neoprene above ~ 15' or so. A 7mm farmer john/jacket is a LOT OF NEOPRENE and requires an inordinate amount of weight to get it down on your first dive, and also on your subseqent dives, but not to such an extent.

You've probably noticed that around fifteen feet or so you started to descend rather quickly - that's due to the "neoprene compression zone". It seems like the neoprene bubbles like to give up their buoyancy at this depth.

Another down side to what I just mentioned is that, diving an AL80, you will require yet another 4 pounds of weight to offset the buoyancy swing of the tank once it's breathed down.

Once properly weighted in your FJ/J to descend and to maintain neutral buoyancy at a safety stop, you'll be somewhat "overweighted" at depth.

The reason I put overweighted in quotes is that you're really not "overweighted" because that's the weight required for you to effect a proper dive plan.

There will probably be a lot of people jumping in here to tell you to buy a dry suit. If so, ask them for donations.

the K
 
Damselfish:
sure it is. You need less weight overall with steel, but any tank becomes more bouyant (or at least less negative) as it gets emptier.
Click to expand...

The effect is minimal with steelies, therefore it isn't an issue. I didn't say it doesn't change.
 
HAWK-EYE:
Last year rental wetsuit same BC and weights ,
Click to expand...

Same weights with rental and new wetsuit ? A new wetsuit will need more weight. New neoprene is thicker than it will be a few years down the line.
 
Bubble Junky:
The effect is minimal with steelies, therefore it isn't an issue. I didn't say it doesn't change.
Click to expand...
well, 80cf of air weighs the same no matter what kind of tank it is in.

The swing varies because of what the tanks displace, sure. Like 4.5#for a HP steel 80 and near 6 for a AL80 or LP steel. I'd have a hard time saying 6# matters and 4.5# is minimal - if I was 4.5# light I'd have a problem. (Especially since I dive w/ 6# so that may give me a different viewpoint. :) )
 
You read my mind on the drysuit....

I dive a 3mm neoprene drysuit, practically new, that I got on ebay for $300. I will never wear a 7 mm wetsuit again after diving dry. It is either a 3mm wetsuit or dry from now on.

Also-I wear 16 pounds of weight with my drysuit, an aluminum 80 and a BP/W. The BP/W is negatively buoyant when empty, which helps me take weight off the belt. I am not hijacking this to a BP/W thread. I am just pointing out one way to take weight off the belt.

The Kraken:
Hawk-Eye,

Another issue that is confronting you is the lack of compression of the neoprene above ~ 15' or so. A 7mm farmer john/jacket is a LOT OF NEOPRENE and requires an inordinate amount of weight to get it down on your first dive, and also on your subseqent dives, but not to such an extent.

You've probably noticed that around fifteen feet or so you started to descend rather quickly - that's due to the "neoprene compression zone". It seems like the neoprene bubbles like to give up their buoyancy at this depth.

Another down side to what I just mentioned is that, diving an AL80, you will require yet another 4 pounds of weight to offset the buoyancy swing of the tank once it's breathed down.

Once properly weighted in your FJ/J to descend and to maintain neutral buoyancy at a safety stop, you'll be somewhat "overweighted" at depth.

The reason I put overweighted in quotes is that you're really not "overweighted" because that's the weight required for you to effect a proper dive plan.

There will probably be a lot of people jumping in here to tell you to buy a dry suit. If so, ask them for donations.

the K
Click to expand...
 
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