Switching to BP/W - Trim Help

[gextyr]

I have spent a lot of time reading old threads on the topic of trim on SB, and have found many useful tips, but I was hoping some more experienced divers here could chime in with ideas specific to my situation. I apologize in advance for the length...

Back story: I live in Florida, and my diving has mostly been (and will continue to be) in the Gulf/Atlantic or nearby springs. I have only been diving for a little over a year now (not counting the discovery dive I did 12 years ago) but I dive every chance I get (I love living in FL!) I have PADI AOW and Nitrox, and I have started Rescue Diver. I don't ever intend to get into cave diving - I like pretty fish and coral and wrecks. I don't really care about any certs above and beyond what I have - but I will take any training that I think will make me a better/safer diver.

Until recently, I was diving with a Zeagle Escape, which served me well, but I was not able to tweak much about it to get better trim. With my Zeagle, and its loosey goosey weight pockets, my trim was always FEET-DOWN. It was "good enough" for looking at pretty fish on a drift dive, but I'm trying to move past "good enough".

I have decided to switch to a BP/W configuration, for two reasons:
1) After setting one up and trying it out, it was infinitely more stable/comfortable/adjustable (my initial reaction was: OMG why does anyone still dive with a jacket?!#%)
2) I plan on starting Tec courses next year, so I figure I'd get a head start on using/understanding the required gear configuration

Here's my new rig:
-Oceanic FDX Din 1st stage + 2x Delta 4.1 2nd stages
-Hollis aluminum backplate
-Hollis backplate pad
-OxyCheq harness (may switch this out for a plain webbing harness... the extra D-rings are not removable and tend to get in the way)
-OxyCheq 18lb wing (I'm not an OxyCheq fanboy, I just got a killer deal on it at my LDS)
-No STA (the wing has the stabilizing rods sewn in, and tank stability isn't a problem)
-HP steel 120 cylinder (I will also eventually try my rig out with an AL80 since I like taking dive trips)
-ScubaPro Delta 5mm boots
-Waterproof W3 (3.5mm) wetsuit
-2 OxyCheq weight pockets (wherever they need to go, although I wouldn't mind ditching them altogether)
-barely negatively buoyant fins
-me (5'10", 235lbs, software engineer physique)

I've tried my new rig out in my pool (max 7ft) and was negative with 4lbs, an empty wing, and a 1/3 full tank. I need to get some 1lb weights, since it looks like I'll be perfect at right around 2lbs in freshwater (still need to do a weight check in saltwater.)

Problem: With my new rig, my trim is VERY HEAD-DOWN (i.e. - within a second of not finning, my feet are flying up.)
Troubleshooting: My upper cam band is right at the crown of the tank, so I can't move the tank any lower. The wing is as high on the backplate as it can go. I tried putting my weight on the lower cam band first, then on my hips (weight pockets on the harness.) The latter was better, but still not great. I borrowed some 1lb ankle weighs and they were just a bit too much (plus, I hate the idea of ankle weights.) I tried making the shoulder portion of my harness tighter/looser, but it didn't seem to change much. Same with the crotch strap. I can add significantly more weight to my hips and be in trim, but then I am over-weighted.

So, after trying everything I could think of, given then gear I have, my thought is "I need heavier/less buoyant fins". I've been wanting stiffer fins anyway, so I ordered some (traditional vented jet style rubber fins.) They should arrive this week... If that isn't enough to balance my rig, are there good options for adding weight lower on my rig (bolt-on tail weights, weight belt, additional weight on the bottom of my tank, etc.)? Is there something else I should be considering here?

I also want to verify that I am not crazy for trying to perfect my trim in <7ft of water.

Thanks!

 

[Lorenzoid]

Yes, try the heavier fins and see how that goes before you start adding weight to your rig.

 

[CptTightPants21]

Seems like you have a good understanding of what needs to be done.

Try it with heavier fins (although from the sounds of it, they won't be able to work on it alone).

Have someone film you body position--are your arms out stretched straight in front of you, head up, knees bent, fins flat? Some people think they have good position and don't realize how off they are or how little things are throwing them off.... Where are your fins when you try to stay still, are they right at 90 degrees near your butt?.....put them out more so that your legs are closer to 135 degrees, this will move weight back and help shift your center of gravity.

Also look into adding a tail weight.

I would try the heavier fins, throw those 2lbs in a tail weight, and then make sure your fins are all the way back at 135 degrees and see where you are. (Make sure someone watches you, because it can be hard for a person to judge just how far back (or not) a person's legs are....they get this muscle memory that needs to retrained. Depending on how head heavy you are, I would add 1 or 2 more lbs in the tail weight before I started looking at other options.

 

[decompression]

You've shown you are thoughtful and methodical, excellent. Great qualities in a tech diver.

So, yes the jet fins will help. Other options; SS cam buckles, a cam band with a weight placed at the bottom of the tank. Thinner booties.

You didn't say if this was with your steel 120 or an Al 80. I assume an 80 as a 120 would tend to make you feet heavy.

Also, ensure your in a proper trim position.

It's a work in progress, keep us posted.


Sent from my iPhone using Tapatalk

 

[gextyr]

Thanks for the replies!
The scenario is with an HP 120 (I figure this is the biggest reason I was always feet-down with my Zeagle.) I don't use AL80s that often - I am not a complete air hog, but my wife (primary dive buddy) uses much less air than me. And she hates it when I thumb a dive and she still has half a tank left.

I _believe_ I am at least close to the correct position. Horizontal body, shoulders/knees in line, legs bent at ~90 (+/-10) degrees, arms straight out in front of me. I guess I need to get my instructor to work with me on that next time we dive together. Maybe I'll have my wife film me as well.

I have a pair of slightly less buoyant booties I can try. I have currently plastic cams - I might look at SS. I wonder if the weight/buoyancy difference is significant? If the fins don't solve the problem, I will pick up another cam band to try putting some weight at the bottom of my tank.

As a geek and engineer, I always try to approach this type of problem in a methodical way... but eventually, I am sure I'll get sick of gearing up just to jump in my pool At least the weather in FL is perfect this time of year!

 

[Patoux01]

I _believe_ I am at least close to the correct position. Horizontal body, shoulders/knees in line, legs bent at ~90 (+/-10) degrees, arms straight out in front of me. I guess I need to get my instructor to work with me on that next time we dive together. Maybe I'll have my wife film me as well.

Head up, shoulders wide, can't believe you'd be able to get yourself so top heavy that you'd flip instantly...

 

[gextyr]

Patoux01 - Could be that I have a really dense skull

You do make a great point though - I don't always keep my head up enough. I spend a lot of time looking down for some reason. I try to be conscious of my head position, and I'm sure it contributes to my problem, but looking down for a moment shouldn't cause my feet to fly up! I know there's some fine-tuning of technique I need to do once I get my rig balanced, and that will just take time and practice.

 

[Insta-Gator]

Think of your cam bands as a pivot point. Now think of your tank as a movable balance weight that you can slide up or down on that pivot point you can use to adjust where the weight is (above or below) the pivot point.

I know it took me a while with a BP/W and AL 80 to figure out tank position so the positive buoyancy was lifting straight up on the pivot point rather than lifting my feet up. At 1/3 full, your 120 should be about 3.3 pounds negative. So try moving the tank down on your harness, toward you feet.

Anyway, that's my 2cents. Good luck.

 

[CptTightPants21]

Thanks for the replies!
The scenario is with an HP 120 (I figure this is the biggest reason I was always feet-down with my Zeagle.) I don't use AL80s that often - I am not a complete air hog, but my wife (primary dive buddy) uses much less air than me. And she hates it when I thumb a dive and she still has half a tank left.

I _believe_ I am at least close to the correct position. Horizontal body, shoulders/knees in line, legs bent at ~90 (+/-10) degrees, arms straight out in front of me. I guess I need to get my instructor to work with me on that next time we dive together. Maybe I'll have my wife film me as well.

I have a pair of slightly less buoyant booties I can try. I have currently plastic cams - I might look at SS. I wonder if the weight/buoyancy difference is significant? If the fins don't solve the problem, I will pick up another cam band to try putting some weight at the bottom of my tank.

As a geek and engineer, I always try to approach this type of problem in a methodical way... but eventually, I am sure I'll get sick of gearing up just to jump in my pool At least the weather in FL is perfect this time of year!

That +/-10 degrees is what I was talking about, depending on body position, weight distribution it can/should be as high as 45 degrees from 90, at around 135. Nothing happens in a vacuum, if you reach out with your arms you are changing the weight distribution, you should be adjusting your leg position to compensate for the slight shift---you are not permanently locked in at 90.

Arms out provides more lift, arms in provides less (head heavy). Feet forward (near the butt) put more weight towards your front making you head heavy, feet further back (around 135) shifts the weight back and makes you less head heavy.

 

[gextyr]

Just to be clear, when we are talking about leg degrees, let me wow you with my ascii art skills.

legs - body - head - arms
/__o_ ==> less than 90
|__o_ ==> exactly 90 (legs straight up)
\__o_ ==> greater than 90
___o_ ==> exactly 180 (legs straight out)

So yes, moving from 90 degrees to 135 degrees makes sense to balance me out. When I get my new fins, I will definitely try a few different positions. If I need my legs extended past 90 degrees, I expect it will take me a while to get them to "remember" that position.