Trimming dive posture/weight position

[scubadiver888]

Mikemath,

Your build sounds a lot like mine. I'm 240 lbs. and 6' tall. I don't have a lot of fat on the extremities but a bit of a tire around the middle.

When I tried diving just my 7mm (no 7mm tunic) I was using 26 lbs. in the pool. This was with an AL80. Wearing 32 lbs and a steel cylinder seems like a lot more weight for someone who sounds a lot like my build.

It could be trapped air. I make sure I squeeze out any air pockets in the crotch and armpits when putting on my wetsuit. Additionally, I've learned where air flows in my BCD and developed a technique for rolling and dumping to get rid of ALL the air in the BCD. I found for my style BCD, it was easiest to go head down for a few seconds, rolled away from the side with my bottom dump valve then pull my bottom dump valve.

If you have an air bubble rolling around in you BCD this could explain why you are okay with hovering but will occasionally get into a head up or head down position (bubble rolls to bottom of BCD and you'll go head down but still neutrally buoyant).

I figured out I had an air bubble in the BCD by pulling the dump valves (each one) with it in the highest position. I heard the bubble come out the bottom dump valve and saw it when I turned around.

I'm now realizing that a good BCD will not trap as much air or it is easier to clear. This is one reason I'm considering switching to a wing.

 

[DevonDiver]

- Dive mostly cold saltwater in a 7mm wetsuit with hood
- Carry 32lbs of shot weight distributed with 5lbs each in two trim pockets between my back and tank, and the remainder in integrated pockets in my Aeris Atmos LX.
- When using ankle weights, I remove the offsetting weight from the integrated pockets
- I dive a steel HP80 that is about 2lbs negative
- Fins are very slightly negative Oceanic V-16
- Overweight (working on that), but with virtually all fat in the midsection. Legs are lean from training for 10k runs the past 6 months and the rest is slowly following.

Get your weighting sorted.

Being over-weighted means you have more lead below your Centre of Gravity (CoG) pulling your legs down...and, consequently, more air above your CoG raising your upper torso.

Less weight means less air needed in your wing/bcd...and that is often what throws your trim out (not the distribution of lead).

At the moment, I dive an ali cylinder...ali backplate...and 3mm wetsuit. I need NO extra weight.

When diving cold water...in a trilam drysuit and thick undergarments, I use 4kg of lead.

My weighting has benefitted from a lot of experience and being relaxed in the water, BUT I can usually get my open-water students down to 4-5lbs of weight, plus SS backplate...in a 3mm suit.

The buoyancy difference between a 3mm and 7mm suit is, what, perhaps another 5lbs max?

 

[scubadiver888]

The buoyancy difference between a 3mm and 7mm suit is, what, perhaps another 5lbs max?

I dive 12 lbs in a 3mm in salt water. I dive 26 lbs in a 7mm in fresh water. That is a difference of 14 lbs.

How much buoyancy in the wetsuit depends on how big it is (XS versus XXL is a huge difference) and how good the neoprene is. My Caribbean wetsuit (3mm) is stretch and compresses a lot more than my cold water wetsuit (7mm). My 3mm is just inherently less buoyant.

 

[DevonDiver]

The easiest way to confirm buoyancy of a suit is to put it into a mesh bag and see how much weight you need to submerge it (neutral buoyant).

The human body is virtually neutrally buoyant to begin with...as we are mostly made of water. The only thing that drastically changes your 'naked' buoyancy is your breathing. Relaxed slow breathing, rather than rapid breathing will decrease your bouyancy generally.

What are the bouyancy characteristics of your tank? Ali or steel? Volume? etc

Finally, you need to consider the bouyancy characteristics of your equipment.

Are your fins positive or negatively bouyant?
What volume is your mask (large volume = more air space = more bouyancy)
How floaty is your bcd (some bcds have lots of foam padding etc...adding bouyancy).
How much extra metal (d-rings, knife, clips etc) are your carrying?

Nonetheless.... I haven't yet found a student that required more than 10lbs of weight in a 3mm full suit...even in size xxxl.

 

[mikemath]

Thanks to everyone for all the feedback--I haven't done a salt-water buoyancy check since I took the class and really started paying attention to buoyancy, so I'll definitely take a look at it. Could be I'm overweighted, but I'll be stunned if it's by more than 2-4 lbs.

Things I will do on Sunday (open water in Monterey):

Overall Weighting:
- Buoyancy check on surface: float at eye level holding a normal breath
- Buoyancy check on bottom (30-40 ft): fin pivot with little or no air in BC
- Buoyancy check at end of dive: remove weight at 10ft and <500psi until i can no longer maintain depth without finning

Trimming Hover Position:
- Putting current integrated weights in a belt to move center of gravity down
- Adjusting tank position for fine-tuning
- Using head/arm/leg position to tweak hover orientation
- Practice, practice, practice

I'll get my buddy to take video and pictures for further analysis on Monday. Looking forward to more comments then. Thanks!

 

[mikemath]

Are your fins positive or negatively bouyant?

Very slightly negative--they've slowly dropped to the bottom when I've accidentally let go during entry.

What volume is your mask (large volume = more air space = more bouyancy)

It's a cheap mask, don't know the brand/model name off-hand. It wasn't advertised as ultra-low volume, so it could be contributing somewhat. It's on my list of things to upgrade soon.

How floaty is your bcd (some bcds have lots of foam padding etc...adding bouyancy).

Definitely some padding on the BCD. I haven't let it float in the water without a tank/weights, so I don't know how buoyant it naturally is. I'll try it this weekend.

How much extra metal (d-rings, knife, clips etc) are your carrying?

The rest of my gear is pretty minimalist. BCD has 2 d-rings, no knife/spare air/metal clips.

 

[DevonDiver]

Could be I'm overweighted, but I'll be stunned if it's by more than 2-4 lbs.

It is simply stunning what you 'can' get down to. When I remember back to my early days of diving, I would never have believed that I could now be diving with the weight I use currently.

What I do with students over the space of an open water course is...

1. Start a little heavy for the confined water training. Over each session, I pay close attention to how much air the student is adding to attain neutral bouyancy. This is especially evident when they are practicing fin pivot and hover. 2-3 short squirts of air is acceptable - anything more tends to show they are just compensating for excess weight. If this is the case, I remove weight there and then. I tend to do the bouyancy skills towards the end of each confined session, as this has the benefit of them being 'settled down' and also closer to 500psi.

2. As the students move onto their OW dives, I am keeping a close eye on the air they are adding on descent. Again, too much air added tends to highlight overweighting. Towards the end of the dive, I am watching to make sure they neither scull nor fin downwards due to under-weighting. If they are struggling to stay down, I first check they have emptied their bcds properly (easier for them on my classes, because I teach them to dive in wings...and they dont tend to trap air as readily).

3. I keep analyizing them for common mistakes that lead to the illusion they need more weight. Such as, subtle instinctive finning when trying to descend, not emptying their lungs fully to begin descent, poor breathing habits, trapped air in the bcd (not dumping fully) etc. Also, I work on their trim...because if they are 'head up', then the act of finning forwards will also have the impact of driving them upwards in the water...another illusion of being underweighted (caused by over-weighting).

I teach the 'standard' surface bouyancy check, as this is a moderately accurate way of pre-dive checking your weight requirements - however, it is not as accurate as other methods. My primary analysis comes from assessing how much air the student has to add into their bcd to attain neutral bouyancy.

The AOW PPB theory session contains a set of 'weighting guidlines' but, again, these are pretty inaccurate and tend to lead to over-weighting also. Good to give a general idea - or starting point - when diving in drastically different kit or when moving between salt-fresh water.... but they do always bring you out over-weighted.

 

[ae3753]

Mikemath: You got some very good advice, and it looks like you have a good game plan for the weekend. Make sure you're explicit with your instructor what you want to achieve from the class and what you want him focus on. Ideally, this is not necessary, but it doesn't hurt to set his/her expectations.

In your plan for the weekend, no need for "Buoyancy check on bottom (30-40 ft): fin pivot with little or no air in BC." At 30-40', you'll need enough gas to compensate for unused gas in your tanks and the wetsuit compression. This will be more than a little or no air in the BC.

With regards to trim hover position, definitely take TSandM and nemrod's advice. Do the body position adjustment first, then determine any weight adjustments.

If you want additional in water advice after this weekend, drop me a PM. I'm in Santa Clara, so coordinating schedules and times should be quite easy. Hopefully you'll get what you want from the PPB course.

Best of luck and have fun!

 

[Nemrod]

Interesting--those numbers sound strange to me compared to what I learned in the buoyancy class but I'm new to this so bear with me and correct me where I'm going wrong. From the PADI literature, here's the recommended differences in approximate weighting when going from fresh to salt water:

| Body Weight | Weight to Add |
| 100-125lbs | +8lbs |
| 126-155lbs | +10lbs |
| 156-186lbs | +12lbs |
| 187-217lbs | +14lbs |

Your 2lb difference sounds odd on this scale. I'm not going to list my weight, but I dive 32lbs in salt water and 14lbs in fresh--as I said, I'm a big guy. I've done normal breath-hold bouyancy checks on the surface and can do fin pivots with no air in my BC at 15 feet (need to add a tiny squeeze from my inflator when deeper due to compression). I'm pretty sure I'm not significantly overweighted, but please let me know what else I can do to check.

The only thing I hate more than a heavy, hot, sweaty, stinky wetsuit is a weight belt so large I cannot pick it up. Truth be known, I don't follow all the rules of thumb like your chart. I often weight for -15 feet. Yeah, I may be a little positive at the end of the dive but not so much I am out of control and can still hold my safety stop. When you first submerge, there is air trapped in the suit, the suit has not yet compressed. Over the course of the dive the suit will compress (and become less buoyant) as you descend and as well may compress further during the duration of the dive and additionally most of the trapped air will find it's way out, this often leads to folks being over weighted. Upon return to the surface or ascent yes the suit will un-compress but not all the way. A suit tends to be more negative after the first dive, especially new suits, older suits that are already flat may not vary as much. So, you are right, my addition of only two to four pounds (fw to sw) seems light but as usual I am breaking all the rules so as to eliminate as much weight as possible. You will probably find you need a bit more differential. Weighting per a chart will probably just not work for anything more than a starting point. If I used all those charts I would have 32 pounds also and I ain't a big guy. If in fact you need 32 pounds then so it is but I still think you are over a bit.

Oh, and Teamcasa is THE Man. Sorry Team, I was just grouchy the other night. Off my meds again :kiss2:

N

 

[mikemath]

Thanks to everyone's suggestions, I had an extremely productive couple dives on Sunday, and really tightened up a few things. Some findings:

Overall Weighting
I was indeed overweighted by more than I would have expected. I was stunned to be able to drop from 32lbs to 24lbs (and really happy that I won't be lugging that much weight around in the future). I may even be able to drop 2 more, but I didn't have a weight configuration that would let me try it. It was really surprising to me, and I see a few potential factors to my earlier overweighting:

• I think I was not holding a "normal breath" for my surface check previously, but rather a "full breath". I may also have been unconsciously finning.
• I underestimated my lung capacity before--the fact that I could fin pivot with no air in BC while being overweighted by 10 pounds misled me that I was weighted correctly. Now that I'm normally weighted, I found that in 20 feet of water, I can completely ascend to the surface and descend to the bottom based solely on breathing--no finning. I can fin pivot using maybe a quarter of my lung capacity.
• I've lost some significant weight since my last ocean dive (20lbs in the last 3 weeks).

The "hold a 10 foot stop with a 500psi tank" test was by far the most useful. I wish I had tried this at the end of earlier dives. It's mentioned a few times in PADI literature, but wasn't actively practiced in any of the classes I took. It might be good for instructors to actually do this in AOW classes or in the Peak Performance Buoyancy class.

Trim and Body Position
I was not able to find time to get a weight belt during the week, so I resolved to find a way to make my current equipment work. I started by positioning my tank about 1.5 inches lower. Since the trim pockets on my BCD are around my shoulder blades, I thought they might be one reason I was going feet-up. After finding from my weight check that I could drop significant weight, I removed all weight from my trim pockets, so my only lead was in my integrated BCD weights (12lbs per side, with most of it towards the front).

I found on the surface that my feet still felt "floaty", but based on another suggestion on the board, I reached down and broke the seal of each boot, letting in a shockingly cold (52 degree) bit of water, and releasing a medium size bubble with a "blorp!" It turns out that my boots were so well-sealed they were effectively acting as dry boots, and keeping a bubble of air inside. Wiggling in my wetsuit, I was able to move a few more bubbles from my legs up through my wetsuit and out the neck seal. After this, no more floaty feet!

I descended and was able to hover indefinitely in the skydiver position using my arms and legs to adjust my orientation (by modifying position of limbs, not by paddling or finning). What a great feeling to be stable in the water! I'll take some different weight configurations with me next time and see if I can purge a couple more pounds--I'm on a mission now to get my weight to a minimum.

I can't thank all of you enough for helping me correct these issues, and I'm sorry I was so skeptical of being generally over-weighted. :blush: I'm amazed at how much progress I feel like I was able to make by following all of the suggestions from this thread. It felt like I was test driving a new sports car down there!