Problem with trim using doubles

[Denver]

I recently switched to doubled PST HP 100s and cannot maintain trim at all. Here is the setup.

Drysuit
AUL SS Heavy BP and wings
Double HP 100s
No weightbelt

The problem:

My center of gravity is to far forward (high on my body). When trying to maintain horizontal the air in my DS goes to my feet and I end up inverted. I remain fairly neutral when this happens. I have tried using 2 sets of ankle weights which helped but did not totally correct the trim problem, but the use of ankle weights is not acceptable.

Would gaiters fix the problem? I have tried using the DS as my primary BC and just putting in enough air to take the squeeze off. Pretty much the same results either way.

I have the doubles bolted to the top hole in the BP. Would moving it down (about 2") help?

BTW I have no problems with a single AL80.

Thanks
Paul

[WreckWriter]

Do you have your doubles slid as far down in the bands as possible? I keep mine just past the tank shoulder, on the first available pieces of straight tank.

Since you're diving dry gaitors might help. Do you feel that it's an air movement issue or just tank balance? Ankle weights are bad for sure.

On my aluminum doubles I took a v-weight, cut it in half and just use half of it on the bottom bolt. That helps me stay trim and provides the tiny bit of weight that I need. With steels I don't know that you'd want to add weight.

I'd try adjusting tank position first. Just be sure you can still reach your valves.

Tom

[trheeltek]

Originally posted by Denver

My center of gravity is to far forward (high on my body). When trying to maintain horizontal the air in my DS goes to my feet and I end up inverted. I remain fairly neutral when this happens.

If you're neutral, you could always just dive inverted : ). Ok, maybe not.

I helped a friend with this problem, diving dry with double LP104s. Gaiters and an AL. backplate to reduce weight helped a lot in his case; the bands were already just below the tank shoulder. We also played with weights on the tanks to move the center of balance, but that didn't work well.

FYI, I've heard that the HP100s are a bear to get right since they're so short and therefore put the weight too far forward. Good luck with it, hope you find the sweet spot.

[WYDT]

Originally posted by Denver
When trying to maintain horizontal the air in my DS goes to my feet and I end up inverted.

It sounds like you've got too much air in the suit. You should have as little air as possible in it. Use the BC for buoyancy and just a small squirt of air every 30ft or so in the suit to soften the squeeze (note: not eliminate it). If you can feel air in your feet you've got too much air in the suit.

DSAO!!

[Bottomfeeder]

The heavy backplate is a problem. Do you have a wing with more than one set of holes? If you do, try using the bottom holes. As others have suggested, move the tank bands as high as you can.

[CincyDiver]

Originally posted by Bottomfeeder
The heavy backplate is a problem.

I am in the market to get a backplate and I have been trying to figure out if I want to get an Al or SS backplate. I was under the assumption that a heavier SS backplate was a good thing when diving with a dry suit. Are the doubles adding too much weight then? Sorry to get off topic here.

[Denver]

Finally able to get out and try the suggestions offered. I put less air in the DS and was able to take one ankle weight off. But I was somewhat chilly in 48F water.

When I tried to change the BP/Tank setting I discovered that I had put the lower band in the lowest hole on the BP with the top band in the top hole. I'll have to try that suggestion next time.

Thanks again.
Paul

[Denver]

Double post. Sorry.

[detroit diver]

Originally posted by CincyDiver


I am in the market to get a backplate and I have been trying to figure out if I want to get an Al or SS backplate. I was under the assumption that a heavier SS backplate was a good thing when diving with a dry suit. Are the doubles adding too much weight then? Sorry to get off topic here.

Hi Chris,

I dove with a SS backplate and double LP104's until a couple of months ago. I couldn't get my feet to stay down after purging my drysuit. I tried a weight belt to bring my hips down, but that was just overweighting. What was happening was that there was too much weight too high up on my body, and the fulcrum just forced my feet to compensate.

I switched out my backplate to an AL plate from FredT and have been very happy since. First of all, I didn't need the extra 5 or so lbs to carry around. And I didn't need the 5 or so lbs of bouyancy to offset it. My balance and trim improved greatly.

If you've got an AL plate to borrow, do yourself a favor and try it. I think you'll like it.

Jack

[DPS2]

I, too, am having a problem maintaining my trim... except that for me, my feet always want to sink. I am a big guy (6'1"/225#) with a fairly athletic build - broad shoulders, etc. I am assuming that my upper torso is displacing more more water than my lower torso and is therefore throwing my buouancy off. I moved my tank bands lower on my tanks (double PST104's) which helped, but I don't want to get them too low.... Are there any other "big" divers out there that have the same problem? How did you fix it? By the way, it doesn't matter if I dive wet or dry (although I can control it better when I am dry). My fins are Scubapro Jet Fins which are quite negative, but I refuse to give them up! Any ideas are greatly appreciated!

[ckharlan66]

DPS2,

We would need more information to make any recommendations.

What type of gear are you using?

If it is a BP is it AL or SS?

How much weight do you wear and where is it positioned?

Chad

[Uncle Pug]

DPS2 once bubbled...
I, too, am having a problem maintaining my trim... except that for me, my feet always want to sink.
What I am going to suggest is paradoxical and not intuitive... but bear with me.

Body positioning has a major effect on trim. Often we compensate for incorrect balance in the rig by unconsciously altering our body position.

For instance... a diver who is weight too heavy toward the head and has a tendency to go head first into the sand will compensate by dropping the knees and leaning back... this makes their feet sink and they think that they are foot heavy.

It is possible that you need to move weight back... ie. you are too heavy toward the head! The easiest way to find out is to experiment.

Move your tanks in the bands until they are as high as they can go... (as wreckwriter described.) With your height and weight I am sure that this is correct placement for you.

Then to test your balance... get suited up and head for the water... depth isn't important here but don't be in the surge as it will mask what we are trying to discern.

Get horizontal in the water and have your buddy check you to make sure you really are horizontal... that is thighs in a perfect plane with the torso... not dropping the knees... back slightly arched... and knees bent so that your lower leg is pointed straight up... you should be able to assume this position even if unbalanced.

Now tip your head down and look directly behind you. If you can't do this you are not horizontal... tip further over until you can look behind you. Now stop all finning and hand waggling (cross your ankles and hold your hands if you need to) .

What happens?

My guess is that before you even get to the point of being able to see under your belly and behind yourself you will start to topple over onto your head. If that is the case then you are too heavy at the head and the drooping foot syndrome is really a compensation mechanism.

IF this does indeed turn out to be the case then the solution will be to add a small amount of weight lower on the torso (not the ankles!)

However I think that with the tanks as low as they can go in the bands you should be close to right on.

You don't say... but are you diving cold water and wearing a weight belt ?

[ckharlan66]

Uncle Pug once bubbled...
Now tip your head down and look directly behind you. If you can't do this you are not horizontal...

If I did this the only thing I would see is my gut.

Chad

[Uncle Pug]

ckharlan66 once bubbled...
If I did this the only thing I would see is my gut.

How far does that thing hand down there anyway?
Or could you possibly turn your head to the side a little and look around it? :D

[ckharlan66]

Alot less that it use to. Thank goodness.

Chad

[Rick Murchison]

There seems to be a great deal of resistance to using ankle weights here. Especially when the problem is trim, ankle weights have the greatest moment arm available and therefore require the least weight to effect a change in trim if the problem is too much weight too far forward after moving the tanks as far down as possible in the bands and on the backplate.
Rick

[jbd]

and when Chad turns sideways and sticks out his tongue he'll look like a zipper :eek:

Actually he's almost DIR from a dietary perspective. Eating healthy and excercising.

[DPS2]

UP,

Thanks for that great info! I will certainly try that ... either at the lake or in the pool at my LDS and let you know how it goes!

By the way ckharlan66, my gear is a Dive Rite SS BP, Classic Wing, double PST 104's. No additional weight.

Thanks again for all the help!

[ckharlan66]

Try what Pug suggested and let us know how it goes.

Good luck.

Chad

[Uncle Pug]

Rick Murchison once bubbled...
ankle weights have the greatest moment arm
And resistance is a keyword as well.

Ankle weights add an unnecessary amount of resistance to movement by being out there on the ankles... and even if one only uses the frog kick... that moment arm still exacts a toll... but more so for the flutter kicker.

The weight movement necessary to effect a balanced rig can be as simple as moving the tank down... or wearing a weight belt that rides a little lower on the hips (as I do) or using that little half or quarter V weight that Tom referred to... none of which extract an energy penalty like ankle weights do.

[Uncle Pug]

Weight belt is applicable to diving the single only imo.

[Rick Murchison]

Uncle Pug once bubbled...

And resistance is a keyword as well.
Ankle weights add an unnecessary amount of resistance to movement by being out there on the ankles... and even if one only uses the frog kick... that moment arm still exacts a toll... but more so for the flutter kicker.
The weight movement necessary to effect a balanced rig can be as simple as moving the tank down... or wearing a weight belt that rides a little lower on the hips (as I do) or using that little half or quarter V weight that Tom referred to... none of which extract an energy penalty like ankle weights do.
I think the "unnecessary amount of resistance" is overstated. Especially with 95's (yes the bands are at the shoulder, yes the bolts are in the lower holes) - (104's are longer and eliminate the problem - know where I can get a good deal?), I have to move some weight aft, and I'm more comfortable with small ankle weights than with even more dead weight at the waist. Frankly I don't even notice they're there as far as any affect on kicks.
Rick

[Uncle Pug]

Rick Murchison once bubbled...
Frankly I don't even notice they're there as far as any affect on kicks.
But I'll bet the DIRF video would show what is really happening :D

I'll bet it would show that your knees are dropping and that your body is not in a plane... and that adds up to resistance.

Anyway... that is one of the principle complaints about the 95s and 98s... a little too short... unless we are talking about a fairly short diver.

That is also a problem with the HP100.

So why not a small V weight for the doubles or a small channel weight for the singles? Shoot... if you still have boots on your tanks you could hide some wheel weights in there.

Cheap 104s??? Sure... I hear you can buy stretched out ones cheap down there in cave country :D

[Rick Murchison]

Uncle Pug once bubbled...
Cheap 104s??? Sure... I hear you can buy stretched out ones cheap down there in cave country :D
Naw, I gave up on the stretch models .... ain't gonna say it... tempted though...
Rick