Trim with Steel 120s

ScubaSloan · Jun 21, 2009

I just bought my first tanks, two steel 120s, and took them for a spin at the quarry this weekend. I have about 40 dives under my belt and was finally getting my buoyancy and trim to the point that I was comfortable with AL 80s (or at least no longer embarrased to be seen in the water) so why not mix things up and start from square one? :bash:

With the 120s, I find that I have to put the tanks much higher to avoid being so foot heavy that I fall into a vertical position if I stop finning. The tank valve is rather high up on my head (and I think it still needs to go higher). Unfortuneatly, I don't need any weight with the tanks, so I don't have that to trim me out. I have moved around my miscellanious gear to help out. Has anyone else encountered this problem? Solutions? or is it just dive, dive and dive some more? Is there anything that I am not thinking about in terms of reasons why it would be bad to have the tank so high up on my back?

ivobj · Jun 21, 2009

What do you use? BC or BP? With a BP/W and STA you will have some weight in the middle of your back that might help compensate. I use that and my cylinder is just in the point I begin being able to reach the valve and manipulate it. I use same setup with AL80, just adding weight in 2 pockets I have on the STA rigs for trimming. With that I can use both types of cylinders with the valve in a similar position in relation to my head.

ScubaSloan · Jun 21, 2009

I use a Zeagle Ranger BC.

dave4868 · Jun 21, 2009

Which 120 do you have? I'm thinking it must be something other than the PST HP120 (3500psi) which is listed as only 1.3 lbs negative when empty, 10.3 lbs negative when full.

Since you've adjusted tank position already, you might try increasing the positive buoyancy of your feet.

You could wear more thermal protection on your feet and/or wear lighter fins.

Buoyancy in the feet has more leverage than in the torso.

Dave C

pickens_46929 · Jun 21, 2009

Stretch your arms out in front of you a bit more, not quite like Superman but elbows out, arms front. Bend your feet at the knees. Both of these should bring you a bit more horizontal.

Wear a bit more neoprene overall or add more air to your BCD. Finning to stay in one spot tells me you aren't neutral, you're actually too heavy. Add a couple small puffs to your BCD.

Remember fin pivots in Open Water class? Go back and do that again to figure out what it takes to get yourself neutral. Relax and have fun.

Your going to love the 120's

ivobj · Jun 21, 2009

With a BC probabbly the best solution would be as Dave (both of them...) mentioned, as I told, I have no problem with BP/W setup, but in your case I thing that increase buoyancy in your legs and bend your knees would be a good start, diving with a little more air in the BC might help as well.

Slonda828 · Jun 22, 2009

What exposure protection are you wearing?

If I dive a 3mm wetsuit, I cannot even use a HP120 as I become dangerously overweighted even if I do not use a weightbelt. If you find that you are perpetually feet down, then you may be diving a tank that is too heavy for your exposure protection and adding so much air to your BC that you are going feet down. I have to limit my HP120 use to my drysuit.

ScubaSloan · Jun 22, 2009

The tank is an XS Scuba steel 120, -2lbs when full, so -1.4 is about right at 500 PSI. With the same setup (exposure protection, gear) I was using 10lbs in salt water with an AL80 during a proper weight check. I was thinking about 4lbs with the 120. In the quarry, with no weight I sank like a rock though. I weigh 170lbs, call it 180 with my gear and a fudge factor, so about 4.5 lbs (2.5%) of extra buoyancy in salt water v fresh water. To get neutral at 15 ft with 500 PSI in the quarry with the 120, I needed 5 very short bursts of air into my BC. From my math moving from the AL80 to the ST120, I should be neutral with 2 to 4 lbs, but with the amount of air I had to put in the BC at the quarry, I am wondering...

dave4868 · Jun 22, 2009

ScubaSloan:
The tank is an XS Scuba steel 120, -2lbs when full, so -1.4 is about right at 500 PSI. With the same setup (exposure protection, gear) I was using 10lbs in salt water with an AL80 during a proper weight check. I was thinking about 4lbs with the 120. In the quarry, with no weight I sank like a rock though. I weigh 170lbs, call it 180 with my gear and a fudge factor, so about 4.5 lbs (2.5%) of extra buoyancy in salt water v fresh water. To get neutral at 15 ft with 500 PSI in the quarry with the 120, I needed 5 very short bursts of air into my BC. From my math moving from the AL80 to the ST120, I should be neutral with 2 to 4 lbs, but with the amount of air I had to put in the BC at the quarry, I am wondering...

In-water testing is so much more reliable than math.... at least for me!

Your weighting is close enough to perfect, IMO, especially if you ever want to putter around closer to the surface with a near empty tank....

So, to address your sinking feet, it looks like you still need to redistribute negative and/or positive buoyancy.

By the way, you didn't mention your height (length of the lever arm) and the buoyancy of your fins.

Your avatar pic shows somebody with long, thin legs.... If you put heavy fins on the end of that lever, you'll tip the scale on that side pretty easily, right?

IMHO, it won't take much of a change in the buoyancy at your feet to fix this. You might only need a pound of increased buoyancy at that end.

Dave C

ScubaSloan · Jun 22, 2009

Skinny legs?! Its tall dark and handsome...Thanks for the input, I dive 3mm boots, do you think 5mm boots would be enough to get the feet up?

Trim with Steel 120s

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