Problems with trim, feet sinking

[oddible]

Just finished a great dive vacation in Maui but had problems maintaining trim on most of my dives. When I mounted the tank very high on the BCD I was fine but this was occasionally a bit awkward when I looked forward and my head was resting on the valve. I ended up having to do a lot of little finning to keep my trim - I'm sure this affected my air consumption.

How could I have resolved this? I asked the LDS we rented our gear from but they had zero suggestions (probably just the uninspired dude working the counter that day). The only thing I could come up with was putting a weight at the top of my tank. I was using an AquaLung weight integrated BC. I didn't have this problem at all in a prior dive trip also using weight integrated. I'm 6', 185lbs, so pretty normal body size. I'm looking at making a BC purchase soon and if there are things I should be considering to help this I want to be aware of them. Any suggestions would be helpful.

 

[Scott L]

Not to beat a dead horse, but a BP/Wing with give you much more flexibility to distribute weight accordingly. A stainless steel plate would place 6lbs right where you need it most (over lungs)...

 

[Indian Valley Scuba]

There could be a number of factors that affect that trim position (head up, feet down) in the water, so here's a short list to consider:

1. You may be overweighted. Every extra bit of excess negative buoyancy requires additional gas in your BCD to compensate for that, and that tends to make the upper part of the body rise with the positive buoyancy, while the lower part, your hip area, sinks with the negative buoyancy. Of course your feet are below your hips so if they are down, so go the feet.

2. Once you are certain you are not overweighted, and can dive with essentially no or little air in the BCD to maintain your position in the water column, then you can consider moving some of the weight you are using up further on your back, as in trim pockets, or even by using an ankle weight around the tank valve. Remember, this is not additional weight, this is weight subtracted from your hips. If you are considering the purchase of a new BCD make sure it has trim pockets on the upper back.

3. Your fins may be substantially negative - toss one in the water and see if it sinks rapidly. (Best to do this in a shallow area!!) If they are negative, you might consider changing brands.

4. Finally, use your gut muscles to pull your head and chest down. Be pro-active with regards to your trim and position in the water, not passive. If you allow it, without moving, the odds are that you will in fact end up with in a heads up / feet down position, so you just need a minor correction via your abdominal muscles to help achieve this. Remember, where the head goes, the body will follow, so keep your head pointed down or forward in the water as you swim, not up.

I hope this information helps!

 

[Brendon]

I agree, You might try a set of fins like the scubapro twin jet fins, The blue, gray, and yellow fins are slightly positively buoyant. Not sure if that will be the cure though... Try before you buy. You may find the issue to be something else... No need to waste money if it doesnt help.

 

[oddible]

Thanks, I probably should have played with my weighting a bit more - I've been using 12lbs consistently since I started diving but have no issues on descent/ascent and use very little air in my BC at depth. Would have been a good idea to shave a couple pounds off and see how it went. I was using AquaLung Slingshot fins - not sure what their buoyancy is but with the mechanics involved it is likely this was a contributing factor.

@Scott L, yeah I'm likely going the route of BP/W, but it seems a considerably more complex purchase than just buying a BC off the shelf - I see several package options of course but the complexity is due to the flexibility of the modular system.

 

[1_T_Submariner]

Get weighted correctly (not under or over) Weighted so you sink fairly easily at the beginning of a dive and it is easy to maintain you safety stop or even accent in 3-5ft of water. Then Dive Dive and Dive experience and being aware of your position in the water will help. Your own gear will also help since you will learn the particulars of your own where rental gear you probably won't.

 

[Brendon]

Get weighted correctly (not under or over) Weighted so you sink fairly easily at the beginning of a dive and it is easy to maintain you safety stop or even accent in 3-5ft of water. Then Dive Dive and Dive experience and being aware of your position in the water will help. Your own gear will also help since you will learn the particulars of your own where rental gear you probably won't.

Most last recreational safety stops are practiced at 3-5m 15-20ft, this is were you should be able to maintain neutral bouyancy.

 

[ScubaWulf]

I have a similar issue. Inherited chicken legs from my Dad which have no fat on them and don't float worth a darn. After a couple hours in the pool trying to stretch out and keep my arms in front of me and still sinking I finally bought a set of tank band weight pockets. My Oceanic Vipers seem slightly negatively buoyant but not by much. I lost one once during my cert dives and it was just slightly below me kind of just hovering around. In salt water with my new 3 mil suit I am running fourteen pounds. 8 in the tank bands and 6 in the side pockets which keeps me trim. Took me a few dives in salt water to get to this config and am really happy. It feels great to be able to come up to your safety stop and just level off and float under control looking around and not having to hang on for life to the anchor line to keep your depth or trim. Can't wait to get back in the water. What a stupidly addicting hobby this is!!

Just to add, on my final dive (shore dive) with this weight setup, when we started getting in shallow water I was having difficulties staying down which I didn't feel I should be having. Did a couple of twists in the water pulling on my dump valves until a litle group of bubbles came out and I settled right back into trim. Amazing how little air it takes to mess up your buoyancy and trim.

 

[oddible]

I'm not having any buoyancy issues, I can park at my safety stop and hover there with no problems at all. My issue is with trim, and my center of gravity in the water allowing easy positioning horizontal or vertical rather than always tipping vertical.

 

[g1138]

Other than correcting your total weighting, one thing I haven't seen anyone mention is your positioning. A diver laying full plank will have an easier time sinking feet down. I speak from first hand experience. I personally think body position is more important than adding or moving weight around. As long as the majority of your weight is at your hips or on your back (Bp/W), you shouldn't have a problem with trim due to weight placement.
Additionally you may want to put on a weight belt if your BC doesn't fit you like a glove. It'll put the center of mass more on you rather than on your BC which presses onto you. (if that made any sense). I personally split it up between the BC and weight belt.

Onto body positioning:
Try holding your hands in front of you and keep your knees bent with the soles of your feet parallel with the surface of the water. If you continue to sink feet first, try extending or retracting your legs, play around with it. The point is to distribute your body weight close together to get an even center of mass.

You'll want to look like the guy in this video more or less.
Trim video
Some people have their legs at a 90 angle other have it at 45 or less. YMMV

In terms or kicking in this position, you can either frog kick or flutter kick normally. The thing to remember is if you need to go stationary and hover, you're going to have to revert back to this position. It comes naturally with practice.

Edit:
Forgot to mention. Don't try to hold your position rigid. Be fluid with it.