Weight Swing When Going From AL80 to a Steel 119

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Bopper

Contributor
Messages
320
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114
Location
San Diego, CA
# of dives
100 - 199
So I'm going to get to try my new Steel 119 soon and I've only dove w. aluminum 80's prior to that. I'm 5'9" 198lbs and I usually wear 28lbs w. a 7MM suit here in SoCal. I usually have a hard time sinking w. the 28lbs, but eventually I do but I'm usually the last one down.

I recently bought the 119 and have never used it. I'm concerned about how much weight I should drop to compensate for the steel tank. The steel tank is a Worthington X-Series 119 and a little digging around the internet shows that the buoyancy, in pounds, is -11.7 when full and -2.0 when empty. I guess you can assume that the AL80's I've used are just run of the mill Catalina 80s considering I've rented them every time.

Obviously I don't want to be overweighted, but I also want to make sure that I'm going to sink (it will be about a 200 yard kick out shore dive). Ppl have mentioned a swing of 5lbs is pretty safe. So I'm thinking 24lbs just to make sure.

Anybody have any input into this subject? What would be the max weight you would feel comfortable bringing?

Thanks in advance.
 
Simple math.
Look at the empty buoyancy specs for each tank.
Using the Tech Diving Limited chart...
For a Catalina S80, an empty tank is +4 lbs. buoyant.
For a Worthington X8-119, an empty tank is -2.0 buoyant.
The difference is +4 - (-2) = 6 lbs.

This means that, when you move to the X119, you should be able to remove 6 lbs. of ballast so that you're carrying only 22 lbs. of lead. Of course, this assumes that you were properly weighted when using the AL80. I think it's reasonable to carry 24 lbs. of lead to ensure that you aren't under-weighted. If, for whatever reason, you cannot conduct a weight check prior to diving, it would be prudent do a conservative dive with respect to max depth, nitrogen-loading, and gas management. Then, prior to exiting the water, purge your tank down to 500 psi and conduct a weight check in the shallows.

That being said, you should make every effort to conduct a proper weight check prior to the dive. Since you know that the buoyancy swing (full vs. empty) of your X119 is 8.9 lbs. according to the Tech Diving Limited chart, you could easily do an in-water weight check with a full X8-119 and compensate for the gas in your tank. If you're diving La Jolla Shores, it's easy enough to do a weight check just beyond the surf zone. Arrange for your buddy to help you.

I can't emphasize enough the importance of being properly weighted and knowing how to conduct a proper weight check. If you have a difficult time sinking with a certain amount of weight (and you've ruled out the possibility of air in the BCD, air bubble in your wetsuit, you doing weird things with your breathing, unconsciously finning up, etc.), that might be an indication that you are under-weighted. Something to think about...
 
Here's that chart Bubble referred to.
 
Simple math.
Look at the empty buoyancy specs for each tank.
Using the Tech Diving Limited chart...
For a Catalina S80, an empty tank is +4 lbs. buoyant.
For a Worthington X8-119, an empty tank is -2.0 buoyant.
The difference is +4 - (-2) = 6 lbs.

Makes perfect sense.

This means that, when you move to the X119, you should be able to remove 6 lbs. of ballast so that you're carrying only 22 lbs. of lead. Of course, this assumes that you were properly weighted when using the AL80. I think it's reasonable to carry 24 lbs. of lead to ensure that you aren't under-weighted. If, for whatever reason, you cannot conduct a weight check prior to diving, it would be prudent do a conservative dive with respect to max depth, nitrogen-loading, and gas management. Then, prior to exiting the water, purge your tank down to 500 psi and conduct a weight check in the shallows.

The dive will be conservative - 40 ft max depth. And I will in fact do a buoyancy check prior to the dive, but I'd rather be in the ballpark when doing the check than to be way off.

That being said, you should make every effort to conduct a proper weight check prior to the dive. Since you know that the buoyancy swing (full vs. empty) of your X119 is 8.9 lbs. according to the Tech Diving Limited chart, you could easily do an in-water weight check with a full X8-119 and compensate for the gas in your tank. If you're diving La Jolla Shores, it's easy enough to do a weight check just beyond the surf zone. Arrange for your buddy to help you.

So does this mean that w. a full tank I should do the buoyancy check, get a neutral buoyancy @ eye level w. a deflated BC, record that weight, then add appx 8.9lbs to that weight?

I can't emphasize enough the importance of being properly weighted and knowing how to conduct a proper weight check. If you have a difficult time sinking with a certain amount of weight (and you've ruled out the possibility of air in the BCD, air bubble in your wetsuit, you doing weird things with your breathing, unconsciously finning up, etc.), that might be an indication that you are under-weighted. Something to think about...

Yeah I've always thought about being properly weighted as being NOT overweighted, but I can see how not being underweighted can be just as important.

Thanks for all the info. :wink:
 
You need to clarify if the Catalina AL80s you have been using are standard or compact, which is a four pound difference. I've been in areas where one or the other is used as a standard. It sounds like you're talking about a compact, if you think the difference with the steel 119 is five pounds.

Bubble's advice about the weight check is good. You state that you have trouble sinking but don't say anything about difficulty holding your safety stop at the end of the dive. If you don't have any problems with buoyancy at the end of the dive, it might be a sign that you are unconsciously finning as you descend, or possibly some other issue mentioned by Bubble. Try crossing your legs before descending; you'll discover you're finning if one leg kicks the other.
 
Thanks, vladimir, for including the link to the Tech Diving Limited tank specs chart.
You need to clarify if the Catalina AL80s you have been using are standard or compact, which is a four pound difference. I've been in areas where one or the other is used as a standard. It sounds like you're talking about a compact, if you think the difference with the steel 119 is five pounds.
@Banyan: I have yet to run across a "compact" Catalina AL80 (C80) among rental tanks here in San Diego. I think it's safe to assume that the rental AL80s that Bopper has been using are the S80 tanks that are -1.8 lbs. buoyant full and +4 lbs. buoyant empty.
The dive will be conservative - 40 ft max depth. And I will in fact do a buoyancy check prior to the dive, but I'd rather be in the ballpark when doing the check than to be way off.
@Bopper: Where are you diving? La Jolla Cove or La Jolla Shores? :D
So does this mean that w. a full tank I should do the buoyancy check, get a neutral buoyancy @ eye level w. a deflated BC, record that weight, then add appx 8.9lbs to that weight?
Exactly. It helps to do this with a dive buddy because he/she can hold onto some weight while you're conducting the weight check.
Yeah I've always thought about being properly weighted as being NOT overweighted, but I can see how not being underweighted can be just as important.
It's better to be slightly over-weighted than slightly under-weighted, IMO.

On a related note, remember that the average human male can compensate for a buoyancy swing of approx. 10 lbs. with his lungs alone. This should emphasize two points: (1) it's critical to pay attention to how much air is in your lungs during the weight check and (2) you have quite a bit of inherent "buoyancy compensation" built into your body. This can help fine-tune your buoyancy at depth and during ascent. :)
 
Sounds like youre way over weighted to begin with. That being said which is just my opinion Ive always been told the difference is basically -8lbs for a steel tank from what you were using with an al. I dive with a steel 100 with full 7mm suit and carry 16lbs and I'm 270lbs. Is it possible to practice your weighting in a quarry or lake that doesnt have current and possibly help you relax more?
 
Sounds like youre way over weighted to begin with. That being said which is just my opinion Ive always been told the difference is basically -8lbs for a steel tank from what you were using with an al. I dive with a steel 100 with full 7mm suit and carry 16lbs and I'm 270lbs.
@MrPfeffer: If you were to swap out your HP100 tank for an AL80 and dive in salt water, how much total lead do you think you would need to be properly weighted?
Compare that number to Bopper's number. Bear in mind that all 7mm wetsuits and BCDs do not have the same amount of inherent positive buoyancy.
 
Granted not all gear has the same buoyancy in salt water I would go with 24# and test my weighting at that level first. Again I am much bigger than OP and therefore have more buoyant neoprene on regardless of type of gear he should probably have less weight on then I do. Again this is all speculative and just my opinion.
 
Simple math.
Look at the empty buoyancy specs for each tank.
Using the Tech Diving Limited chart...
For a Catalina S80, an empty tank is +4 lbs. buoyant.
For a Worthington X8-119, an empty tank is -2.0 buoyant.
The difference is +4 - (-2) = 6 lbs.

This means that, when you move to the X119, you should be able to remove 6 lbs. of ballast so that you're carrying only 22 lbs. of lead.

Without getting into what might have been wrong prior to getting a new tank, this post answered Bopper's question.
Why does every question on Scubaboard turn into an assumption based debate?
 

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