New tank throwing off my trim

[halocline]

I used to dive with AL 80's and 10lbs of weight. I had very good trim and was very comfortable with that set up. I recently upgraded to some LP 108's from XS scuba. I have only dove with them once now but it felt very awkward in the water. I ditched all of my weight because of the buoyancy characteristics. I was able to sink just fine but I had my BC fairly full to keep myself neutral. I also had to fit from flipping over like a turtle on my back because the distribution of weight was much different than what I am used to. Do you guys have any advice or tips on how to counteract these symptoms?

Thanks for your advice.
Chris

The difference in buoyancy between an AL80 and a LP108 is about 7lbs, so if you use 10 lbs with a AL80 and no lead with a LP108, you 'should' be a little underweighted, not overweighted. You should try a weight check with the tank near empty just to make sure you're dialed in. If you need a couple of pounds you could put those in front pockets, that might help with the rolling.

You might feel a little heavy with a full tank because the tank holds more air and so you'll have a couple of extra pounds at the beginning of the dive, but I'm sure you understand that you choose weight for an empty tank.

You can practice and get much better at handling the new tank (everyone who tries doubles goes through this) but the bottom line is that some people will simply prefer some tanks for trim. You can adjust, but don't expect a LP108 to feel like an AL80, it won't.

 

[Storker]

Unfortunately 108s are about as heavy and negative as you can get.

They are?

I'm not familiar with US tank sizes, so I had to do some googling. According to this table, an LP108 weighs about 40lb (18kg) empty without valve, is 1lb (0.5kg) negative when empty and about 8lb (3.5kg) negative when full, with valve. Corresponding numbers for an HP120 is 26-28lb (11-12kg), 1lb and 10lb (4.5kg).

My steel 10Lx300bar weighs 15.4kg (34lb), my steel 15Lx200bar weighs 16.3kg (36lb) and my 15Lx300bar weighs 24.5kg (54lb), all without valve. When empty they are 4kg (9lb), 0kg and 7kg (15lb) negative, respectively, and when full they are 7.5kg (16.5), 3.5kg (8lb) and 12kg (26lb) negative, respectively.

Also...if you went through a GUE Fundamentals class, you would see it is essentially impossible to hover properly with the very heavy steels....

The only divers i have known that struggled with steel tanks where wearing jacket style BCDs and the only solution was to go to a wing style back inflation configuration.

I've dived with a poodle jacket and all the above mentioned metric tank sizes, and the only problem I had was that when I used a lot of air in my DS (due to the cold water), I got a bit tired in the small of my back when using the 15Lx300bar tank since the rig was pretty darned negative while I and my suit were noticeably positive. Yes, I did feel a little unbalanced with the 15Lx300bar and felt the tendency to turn turtle, but not more than I could handle quite easily.

From the specific to the general: around here, a steel 10Lx300bar (~35lb topside, ~9lb negative when empty and 16-17lb negative when full) and a jacket-style BCD is the normal configuration for rec divers, and I haven't heard much bitching about turning turtle from my diving buddies.


Bottom line: Based on my experience I don't believe that it's as difficult to keep trim as some of the posters claim. Yes, a back-inflate BC or a BP/W will make it easier to keep right side up with a heavy, negative steel tank, but it's quite doable also in a jacket style BCD.

 

[Tickler]

I dive with a Hollis HD 100 BC (back inflate) and do a lot of cavern diving and will be taking intro to cave fairly soon which is why I wanted larger volume tanks and why I will certainly not be using free diving fins. I will play around with the position of it on my back and try adding 2lbs to my weight pouches to see if any of that helps.

Thanks for your responses and advice.

 

[SWAMPY459]

I dive with a Hollis HD 100 BC (back inflate) and do a lot of cavern diving and will be taking intro to cave fairly soon which is why I wanted larger volume tanks and why I will certainly not be using free diving fins. I will play around with the position of it on my back and try adding 2lbs to my weight pouches to see if any of that helps.

Thanks for your responses and advice.

Since you've only dove it once and the hollis uses a horseshoe wing, double check and make sure there's not more air getting trapped in one side of the wing. If it is, go vertical for a split second to let the air equalize in both sides of the wing, then go back horizontal and see if that helps.

Also, to do a proper weight check and make sure your rig is truly balanced, you have to do it at 500 psi at 15-20 ft, at the END of your dive so all the trapped air is out of your suit then Let ALL the air out of your bc, every bubble, and then see if you are neutral at mid breath. if you have to fin up to keep your stop under those conditions, you are too heavy. If you have to grab a log to keep from going butt up, add a couple pounds

try both of these before just adding weight to see if it helps. adding weight will only make you have to add more air to your wing and increase your drag and screw with your buoyancy.

 

[danvolker]

I dive with a Hollis HD 100 BC (back inflate) and do a lot of cavern diving and will be taking intro to cave fairly soon which is why I wanted larger volume tanks and why I will certainly not be using free diving fins. I will play around with the position of it on my back and try adding 2lbs to my weight pouches to see if any of that helps.

Thanks for your responses and advice.

And if I was doing cave, I would be using my Extra Force Fins ( way better than Jets or Hollis), and in fresh water for cave, the Al 80 is no longer the preferred tank....but in your original post, I was not aware of the freshwater and cave oriented intentions.

For cave though, you will end up in doubles...whether double 80's or something larger....and the doubles sit closer to your back( less lever effect to roll you), and the wings run up the side of the tanks far enough to left and right sides, to act like catamaran hulls to stabilize you....with a set of doubles on, it is amazing how you can get neutral 6 inches off the bottom...and just hang there motionless, that double system acting like a gyro stabilizer so you have no effort to do a motionless hover.

 

[Instructor_Tom]

Tickler;

I know some training agencies/ shops will start you cave training in a single tank with an H valve, but honestly you should be looking at moving to a doubles configuration. You need to invest in a backplate with continuous 2" webbing fitted to you ( my opinion ) and a wing for the tanks you will be using. You can always rent the tanks while training until you find the setup you like best. Some shops might rent you everything you need.

Everyone has there own preference on what tanks work for them based on there body size, weight, and repository volume. For me at 6' 1" and 220lb with a high RMV, it was a set of dbl108's with a 65lb lift wing. as stated before you will immediately notice that because of the weight and the lateral stability that you can hover with less effort, but also know that if you train in cave country you will be dealing with flow and if you are not in a horizontal position that flow will get up under those tanks and send you tumbling on exiting.

Part of the training is learning how to deal with the flow so that it is second nature.

cave training is a very humbling experience, but it will make you a much better diver.

T.


Sent from my iPad using Tapatalk HD

 

[teknitroxdiver]

They are?

I'm not familiar with US tank sizes, so I had to do some googling. According to this table, an LP108 weighs about 40lb (18kg) empty without valve, is 1lb (0.5kg) negative when empty and about 8lb (3.5kg) negative when full, with valve. Corresponding numbers for an HP120 is 26-28lb (11-12kg), 1lb and 10lb (4.5kg).

My steel 10Lx300bar weighs 15.4kg (34lb), my steel 15Lx200bar weighs 16.3kg (36lb) and my 15Lx300bar weighs 24.5kg (54lb), all without valve. When empty they are 4kg (9lb), 0kg and 7kg (15lb) negative, respectively, and when full they are 7.5kg (16.5), 3.5kg (8lb) and 12kg (26lb) negative, respectively.

I'm not familiar with the tanks you mention, but compared to the common steel tanks in the states, a 108 is within 3 or 4 pounds of both heaviest weight and most negative when full.

 

[kelemvor]

I made that exact same transition last year (al80 to worthington/xs lp108) and had the same problem. I solved it by moving the tank as low as possible on the BC. My bc has two straps, and the top strap ends up being exactly at the top of the bottle right before it tapers toward the valve.

It took a few dives to get used to still, but having the rig balanced made all the difference in the world.

It does make the valve harder to reach behind your head, but for me this solved the exact problem you are describing.

After that change I was diving the lp108 with no lead very comfortably. Hope this helps.

 

[Instructor_Tom]

I made that exact same transition last year (al80 to worthington/xs lp108) and had the same problem. I solved it by moving the tank as low as possible on the BC. My bc has two straps, and the top strap ends up being exactly at the top of the bottle right before it tapers toward the valve.

It took a few dives to get used to still, but having the rig balanced made all the difference in the world.

It does make the valve harder to reach behind your head, but for me this solved the exact problem you are describing.

After that change I was diving the lp108 with no lead very comfortably. Hope this helps.

I have to ask, with the tank that low, can you actually get horizontal? On me the 1st stage actually touches the back of my head when i look up and i have to use my light fins (dive rite exp) to get neutrally horizontal.




Sent from my iPad using Tapatalk HD

 

[DogDiver]

Xs scuba usually sells Worthington steel cylinders. The 108's are ball busters and are known for being very negative buoyancy. Great for salt water diving with a dry suit. You would have been better off with 108 Faber's. Much better buoyancy characteristics.


Sent from my iPhone using Tapatalk