"neutral" trim

My buddy is under the impression that it's possible to set up your rig (by rig I mean the whole kit of dive gear including BC, weight belt, everything) so that your trim is completely neutral. What I mean by neutral trim is that there is no particular orientation that is predominate; in other words, whatever position you get into, it takes no effort to maintain that position - you don't have to resist flipping over.

I would love it if I could get there, but haven't been able to.

Not that I think it's impossible, just that I've never been able to attain it. I've tried several different ways of distributing my weights, including backplate weight plates, ankle weights, weights on the tank straps and around the valve, even small weights on the front of my shoulders.

It seems to me, that, with one of the most dense things (the steel cylinder) on your back, above everything else, the only way to "neutralize" your trim would be to put compensating weights equidistant from your Center of Gravity (CG), which would mean on your chest or belly.

Even then, the bubble (I wear a drysuit) is closer to your CG than your ballast is, and that can't be good.

A couple of years ago I really struggled with this; it seemed like I always had to fight to keep from flipping over on my back. I talked to people, adjusted my gear, etc. but basically ended up just resigning myself to the fact that I will have to expend a certain amount of effort (not much, but more than none) to maintain a nice, horizontal, face down trim. If I totally relax, I'll flip over onto my back.

In my previous quest for knowledge I learned that many people think their trim is neutral, but when I questioned them a bit further, most people revealed that they do, in fact, have to expend a certain amount of effort to keep from flipping over. I think it's similar to how people often don't realize they are finning; it's not much effort, and they've gotten so used to doing it they don't realize they're doing it.

We dive in cold water, with drysuits (wet hoods and dry gloves), steel backplates, weight belts, and steel cylinders. Our Force Fins are slightly negative, and I wear ankle weights.

Here's what I'd like to know from you guys:

1. Do you have neutral trim? If so, do you dive in cold water?

2. Do you wear weights that are located at the bottom when you are in your normal diving position?

3. How much effort does it take you to return to face-down, horizontal trim if you have gotten onto your back?

4. How much room to maneuver do you need to get back to face-down position? (I ask this because I only ever get discombobulated when I'm in a tight space, and have to try not to knock into everything getting back to trim)

sambolino44:

Here's what I'd like to know from you guys:

1. Do you have neutral trim? If so, do you dive in cold water?

2. Do you wear weights that are located at the bottom when you are in your normal diving position?

3. How much effort does it take you to return to face-down, horizontal trim if you have gotten onto your back?

4. How much room to maneuver do you need to get back to face-down position? (I ask this because I only ever get discombobulated when I'm in a tight space, and have to try not to knock into everything getting back to trim)

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1. I would prefer my BC system assist me to maintain horizontal trim
2. Some drysuit novices use ankle weights, but not at the expense of horizontal trim
3. How frequently are you on your back? That would not be a good tendency...

I forgot to mention this:

Most discussions of trim are about whether you tend to go head up or feet up (pitch?); that's not what I'm talking about here. I'm concerned with belly up or back up (roll?).

Subtle body positioning changes can help one attain proper/stable horizontal trim.
If you've spent a fair amount of time troubleshooting your gear, perhaps it's appropriate now to focus on body positioning. This can change several things: the position/magnitude of the bubble inside your drysuit and the effect of weight at the end of your feet, among other things.

I'd recommend reading ae3753's thoughts on the matter. He's a UTD instructor who has written a very insightful online essay on why horizontal trim is important and how to achieve it.

Hope this helps...

sambolino44:

Most discussions of trim are about whether you tend to go head up or feet up (pitch?); that's not what I'm talking about here. I'm concerned with belly up or back up (roll?).

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To clarify, you're wondering about left-right stability, right?
If so, then moving lead so that it has a "keel" effect might help. This can be achieved by moving weight slightly forward (from the perspective of the geared up diver standing vertically on the ground). You should also make sure that your ballast is left-right symmetric.

sambolino44:

.............Not that I think it's impossible, .........

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Might be. As long as you have a bubble in your suit or BC that can move, I don't see how you can attain this state.

Lynne's response in this thread is very helpful, but it still seems that, besides somehow attaching weights to your shoulder straps (very inconvenient and uncomfortable), the only option for putting weight forward of your centerline is down low on your weight belt.
http://www.scubaboard.com/forums/basic-scuba-discussions/305049-trim-how-distribute-weight.html

Neutral trim, as you are defining it, is not possible: "whatever position you get into, it takes no effort to maintain that position"

Unless every aspect of yourself and your gear is the same density, there will always be a tendency for the more dense portion to be lower than the less dense portion. Moreover, as your dive goes on, the buoyancy of various parts of your gear change. Your tanks get lighter. Your wetsuit compresses. Your drysuit's air compresses. The water temp, salinity, etc change. What is perfect one moment is not perfect the next.

Having said that, we teach people to be neutrally buoyant in a face-down horizontal position. Yes, gear can be set up so that you can be neutral in that pose. You can even set your gear up so that you can be neutral in other poses with minimal changes in your setup. (something that can be done on the fly)

1. My trim is not perfect. I can achieve neutral buoyancy. Since my weight is distributed, based on my setup and environment, I can move from position to position with only a little effort. Some positions (upside down) are not positions I am counting as I tend to avoid them. And, yes, I dive Monterey if you call that cold.

2. Yes, I have weights on the back of my shoulders, under my back inflation BC and on the front (and back) of my waist. Depending on my choice of fins, I might also have ankle weights.

3. For me, it is simply a couple flicks of my SD-1 force fins to spin like a cork screw.

4. I can pretty much remain in place when I spin.

My guess is you are looking for a better way to distribute your weight. My first question to you is are you properly weighted in terms of amount of weight. How much air is in your BC and Drysuit? I have very little air in my drysuit and use my BC for buoyancy as needed. I start my dive with a couple puffs and dump most of it by the end of the dive. I suspect you have too much air in your drysuit and it is moving around too much as you change positions.

Bubbletrubble:

I'd recommend reading ae3753's thoughts on the matter. He's a UTD instructor who has written a very insightful online essay on why horizontal trim is important and how to achieve it.

Click to expand...

Thanks for the kind words, glad people are reading and finding it helpful!

sambolino44:

Lynne's response in this thread is very helpful, but it still seems that, besides somehow attaching weights to your shoulder straps (very inconvenient and uncomfortable), the only option for putting weight forward of your centerline is down low on your weight belt.
http://www.scubaboard.com/forums/basic-scuba-discussions/305049-trim-how-distribute-weight.html

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A very helpful post indeed. I like Lynne's (TSandM) explanations and writing style.

As for roll, if you totally relax, you should not be flipping over. There is an imbalance in the system, either in weight placement or air management.

First check that your weights are equidistant and your tank is actually centered. This fixes most problems.

In water, if your still roll, recheck your weight belt and see if there is shifting. Also take the time to rebalance your wing and insure that distribution is equal.

For the larger wings, it's not uncommon that you have more air on one side than the other. Anytime I dove a wider wing, I would have to actively manage the gas between the sides to insure balance.

In addition to the above, proper body position plays a significant role in roll stability. Also, consider the drysuit and strategic placement of gas to increase stability. It's a very useful tool.

Good luck!

Bubbletrubble:

To clarify, you're wondering about left-right stability, right?
If so, then moving lead so that it has a "keel" effect might help. This can be achieved by moving weight slightly forward (from the perspective of the geared up diver standing vertically on the ground). You should also make sure that your ballast is left-right symmetric.

Click to expand...

Right, but what everybody seems to keep missing is that I'm not concerned with fine-tuning my trim for when I'm in a good face-down horizontal position. What I'm talking about is being completely trim-neutral, with no forces trying to pull you into any position; if you completely relax, you will remain in whatever last position you were in.

Now, what about answering my questions above?

Is YOUR trim neutral?

Thanks