End of dive trim issue

[atlas750]

At the end of my dive I am having a difficult time staying in a horizontal position. I am getting into a head down trim. This happens with less that 1000 PSI in my tank. Otherwise my trim in pretty good (working on it). I dive a SS backplate, al 80 tank, single wing and a drysuit. I have 10 lbs on a weight belt and 6lbs in pockets on the upper cam band. I have about 5 dives in my drysuit and still practicing. My next thought is to get the weights out of the cam band pockets and try my tank in a different position. Thanks for the help.

 

[Bubbletrubble]

AL80s have a tendency to get butt-light as they empty. Weird, huh. At least this might explain why your horizontal trim is good at the beginning of the dive and head-down/feet-up at the end of the dive. Foot-leg-body positioning can affect your trim as well. Subtle changes can help compensate for this change in tank buoyancy during the course of a dive. Tank re-positioning could work, too.

You might try moving one of the trim weight pockets to the lower tank camband. I position one weight pocket on one side of the upper camband (cinched up close to the STA) and another weight pocket on the other side of the lower camband (once again, cinched up close to the STA). This maintains good left-right symmetry while shifting a little weight down your head-toe axis. I recommend putting 3 lbs. in each camband weight pocket. You'll be surprised how much it helps. Experiment with shifting weight around on your rig. Be patient. It will take some trial and error to get it right.

Since you are a new drysuit diver, another thing to consider is that you're allowing too much air to pool in your lower legs. This can occur due to a combination of baggy legs and your inexperience. You can avoid this during your ascent by momentarily breaking trim to achieve a vertical position...just enough so that the squeeze forces the air out of your lower legs. Sometimes it only takes doing this once during an ascent to stave off floaty-feet.

Good luck.

 

[PfcAJ]

More practice will help a tonne.

If you stretch your legs out and pull your arms in a bit, it will rock your center of gravity and stop that head down problem. If that doesn't work, try repositioning the cam band weight and lowering your tank a little (still make sure you can reach your valve).

 

[kanonfodr]

Question: Are you checking this when trying to hold the same position in the water column, or ascending? The difference could be air expanding in the legs of your drysuit as you ascend, which could be hard for you to vent. That happens to me a lot, I'm a new drysuit diver.

Other than that, lots of AL tanks like to ride really butt-light in the water at lower pressures so that could be adding to the issue as well. In that case it could be possible for you to adjust with body position alone: extending or flexing the legs, putting your arms out in front ala Superman vs folding them across your chest, even head position makes a difference.

If none of those work, it could very well be a matter of weight positioning. If you have thigh pockets on your drysuit it could be worthwhile to move some ballast to your pockets. Fins can make a difference as well. Scubapro Jets are fairly negative compared to many other fins and could provide the needed weight on your legs to keep you from going head down.

Some more specific information on how your rig is setup could probably help other troubleshoot the problem much better than I am able to.

Peace,
Greg

 

[rongoodman]

Switching to a steel tank would not only help with the head-down issue, but take a few pounds off your required weighting too.

 

[atlas750]

Thanks for all the input. The problem was at its worst during my safety stop at 15 feet. I could not remain stationary at all and had to move around to keep my depth steady. I tried moving around to get the air out of the legs of my drysuit so I think it was more of a tank issue. I will try the different body positions and moving my tank up/down and or the weights on the upper and lower cam bands. Learning the drysuit has been more work than I thought! Still have a good time though.

 

[rjack321]

6lbs on the upper cam band and a SS plate is alot of weight up high. Its working ok when the tank is full because you have gas in your wing compensating for the weight of the gas in the tank. As you dump that wing gas you are getting increaingly butt light in the tank and proportionally head heavier. Solution: move lead south (towards your feet).

Easiest thing to do is flip over your STA or move the 6lbs to the lower cam band. If that doesn't solve it, try moving it to your waist.

 

[PR_SMITH]

Brand of tank can make a difference to trim as well. Luxfer's tend to be more nose heavy than Catalinas.

 

[LiteHedded]

Thanks for all the input. The problem was at its worst during my safety stop at 15 feet. I could not remain stationary at all and had to move around to keep my depth steady. I tried moving around to get the air out of the legs of my drysuit so I think it was more of a tank issue. I will try the different body positions and moving my tank up/down and or the weights on the upper and lower cam bands. Learning the drysuit has been more work than I thought! Still have a good time though.

that sounds more like a buoyancy issue. I'd work on getting that squared away. i bet once your stop moving you'll be able to better maintain that horizontal position

 

[elan]

that sounds more like a buoyancy issue. I'd work on getting that squared away. i bet once your stop moving you'll be able to better maintain that horizontal position

It is usually the other way around, once you stop moving you start falling head down By moving he offsets that tendency.


To the OP. like others said you have air in your wing that supports the tanks in the beginning. Do your weight trimming when you wing is empty at the tank is at 500 psi att end of the dive. Get some 2lb weights and put them on snaps, then ask your buddy to move them around until you are able to maintain horizontal position stationary then make permanent weights.