First pool dives in doubles - advice please

[RiverRat]

OK did a search but didn't find anything. I'm stepping it up to TDI Adv. Nitrox and Deco with Bernie Chowdhury and I'm getting ready to jump in the pool in my double HP100's. I've got the rig fairly squared away, new Apeks WTX4 wing etc. I decided to bolt up my AL plate versus my 9# steel as that might be a bit heavy now that I'm going to a tech config. So I plan on hitting the pool in drysuit etc. to closely match my OW dives for the class. I've been getting great info from Bernie but I'd like to hear from others that have "been there, done that" to hopefully pickup some tips to help me get squared away for my initial dives.

 

[Grounded]

What perfect timing....

I tried out a set of faber fx100s in a pool this past weekend with a thremo 200 bar manifold, highland bands, Zeagle Flathead VI regs, an aluminum backplate, and a Dive rite 44# Trek wing. I found that I was pushed into a pretty strong head down position from horizontal (that, if left alone, resulted in me ending up on my back). I was wearing a 3mm wetsuit.

I, too was wondering if anyone had any tip for balancing things out.

 

[RiverRat]

I, too was wondering if anyone had any tip for balancing things out.

Well stay tuned No pun intended, but your handle "grounded" seems to fit at the moment

 

[battles2a5]

There is no magic bullet for trimming out doubles. It depends on your body's center of gravity, the Cg of the tanks, your BP/W, the lift profile of your wing, and your exposure protection. So the best thing to do is invest some time in the quarry and the pool and do some trial and error testing. So here are some things to try...

For head's down trim:
- move the bands up on the tank. They should be right at or just below the neck of the tank
- Mount the wing on the lower sets of holes. This will keep more of the air up near your shoulders. This doesn't help much towards the end of the dive when there isn't a lot of air in the wing
- loosen your shoulder straps and shorten your croth strap. This will move the tanks further down your back
- Add a tail weight to your rig.
- Use trim weights
- Use better technique (e.g. hard arch in back, back of head to the isolator, use legs in/out to effect trim)
- You can use a heavier fin, like Jets or Turtles

I would try any of these or a combination of these before looking at different gear. In some cases, the gear just isn't right and needs to be changed. In most others, you can fix it with the suggestions above. Your instructor should know this and should help you get sorted.

 

[TSandM]

I would suspect doubled steels might be difficult to trim out in a 3 mil wetsuit, because you probably don't need any additional weight at all, so you're really limited in how you can manipulate the center of gravity of the diver/gear system.

BUT -- I will also say, from personal experience, that where trim really gets critical is in doubles. By trim, I mean the diver's posture -- You really need to put your head back until it jams into the isolator, and keep your torso FLAT and your knees bent. Letting your head fall will really increase your tendency to play lawn dart.

In addition, the shape of the wing has an influence. Wings which are wider across the bottom (delta shaped) will tend to accentuate the head-down tendency. Wings which have a broad upper arc can be used to balance some of the weight high on the body.

The tanks can be moved down by the two methods cited, but must always remain high enough so that the diver can reach the valves.

I went to an Al plate with my 85s, so that I could move weight into a belt and thus further down my body. It's frowned upon in cave, but it was what it took to trim me out. Interestingly, I dive the same tanks, with the same plate and less exposure protection in Florida, WITHOUT any belt at all, and trim out fine. So a lot of it is posture and technique.

 

[RiverRat]

Thanks.....all good stuff. For me, looking at my rig now, there does not seem to be a whole lot of wiggle room as far as moving the wing etc. Most likely due to mating up the particular wing I have, Apeks WTX4, with my HP100s. It's a fairly uniformly U shaped wing so I think it will balance well as far as air in the cell goes. I think adjusting the harness and crotch strap might be crucial right off the bat and something to address before moving anything else around. Thanks for the pointers!

 

[battles2a5]

Just exercise some patience and invest the time in trial and error. I wouldn't go radical in one direction. You may need a combination of things to get it right. Most wings have a few sets of mounting holes that you can choose from. Just make sure that if it is mounted up high that you can fully inflate it without kinking your hoses too badly. It will take some tinkering. Let us know how it works out for you.

 

[RiverRat]

Will do. Yep I've got the wing inflated now with just enough hose room and the bottom just about even with the bottom of the tanks. I've got options moving the bands, spacing, holes etc. but I'm gonna dive it this way and see how it feels. Like you said, move one thing at a time. I've been there before when you change too many things at once and start spinning in circles, not good. I'll report after my first pool dives. BFN....

 

[Grounded]

I'll also give thanks for the pointers.

I think I have enough space to move the bands up maybe a half or 3/4 inches. Is it OK to loosen the bands (maybe one at a time?) with gas in the cylinder?

 

[RiverRat]

You're not supposed to in case you stress the manifold........
Be carefull. Better to be safe and drain them.
Yeah move one at a time if you have to.

I just did the same thing last night I laid them nice and flat on the rug in my living room and did one band at a time. Take note that when you loosen up the bands you have to re-check that they're squared up, you can throw the set out of alignment fairly easy. You don't want to stress the manifold when you tighten the bands. But in my case I re-threaded the isolator so I had to measure everything.