Trim – The Good, The Bad and The really Ugly by Vikki Batten

There is a general misconception that good trim means being flat in the water with your feet raised in the “sky diving” position. While this is certainly one part of it, a dogmatic belief that it is the only good position to be in while diving is not beneficial for anyone. Being in the best position for the environment and yourself, by choice rather than by luck is the aim and is GOOD.

Practising cylinder removal and replacement

While trim usually refers to the diver’s body position and streamlining to their equipment, the two go together. One without the other, undoes much of the good work.

To understand the ideal trim we need to remember its purpose.

Good trim and streamlining help us to:

Move through the water with the least resistance. Swimming is much easier when you are flat, because there is less resistance. So, why do tec divers sometimes ascend in a flat position? There is a hypothesis that this helps off gassing, because our bodies are at the same pressure throughout. While I agree that it is well worth being flat during a deco stop, there are times when I think ascending flat causes more complications than it has potential benefits. Communication with buddies can be more difficult and it can be harder to exhaust gas from drysuits. While I don’t think there is any need to be completely vertical, tilting your “sky diver position” a few degrees to vent gas or signal your buddy is better than a rapid ascent or lack of communication.

Red Sea Silence 2013 3

Avoid disturbance or damage to the environment. In a cave environment this can mean distorting your body into various positions to keep your feet away from silt (which can be on walls and ceilings as well as the floor) and twisty turn passages needs lots of changes to body position to keep good trim. More commonly we respond to the marine or lake landscape, which is less extreme. Descending down a slope in a horizontal position can result in trailing fins, if we do not adjust our body position. The diver’s body needs to be at a similar angle to the slope (or a greater distance from it) to avoid problems. By the same token, if you are hovering over a drop off hundreds of metres deep and fancy tipping your body up to take a photo – no probs – you’re not going to kick anything.

Be in control. This is the key for me, the diver should choose their position based on where they are and what they are doing. Returning to the default flat position,  where it easiest to swim horizontally, in between. Trim should not be compromised by lack of buoyancy control, but new equipment may require a period of adjustment to regain your normal trim, streamlining and control.

Of course, if you or your students are swimming around kicking up the vis and/or damaging the environment that is BAD – ‘nough said.

So what is the really UGLY? I have recently started to see and hear divers talking who feel so pressurized into being flat in the water that they prioritise it to the detriment of everything else. Just one example, was a newish diver on a workshop recently. She had yet to really master buoyancy control in her new drysuit, but unfortunately, she had been led to believe that being flat in the water was the most important thing. This caused massive physical struggles and significant frustration for her, because she couldn’t control her buoyancy well yet, so everytime she tried to get flat in her drysuit and ascend the air went to her feet and she lost control. We discussed it afterwards. her weighting was good and her equipment well streamlined and balanced, so I suggested practising hovering and ascending without worrying about body position, then progressing to controlling body position. Unfortunately, she had been so indoctrinated by a more experienced tec diving partner that she believed good trim was more important than good buoyancy control….

luke hovering

I’m not saying new divers can’t learn buoyancy control and body position at the same time, that is certainly the ideal, but if that isn’t working, like any skill, it may need to be split into smaller sections to achieve mastery and some divers may take longer than others to put it all together.

Personally, I think buoyancy control is always the most important skill and the foundation for others. Not only does this example underline that importance, but it also highlights the need to build confidence and to allow newer divers to progress at their own pace, not push our tec diving expectations onto them. I firmly believe this diver would have done better if she had been told to aim for good trim, but not worry if it took a while to get it right. Instead she was convinced that being anything other than horizontal was a mortal sin.

Sidemount02

Good buoyancy control, equipment streamlining and weighting allow you to change positions underwater at will, not be pinned in a particular attitude by your kit or lack of buoyancy control. The freedom to choose the best position for the situation you are in is my definition of good trim.

Vikki

Categories: News

3 replies »

  1. Thank you Vikki! You’re so right – How often have I heard divers who’s gone through initial tec training, especially it’s of it the hardlining DIR-oriented sort, be completely obsessed about trim. Then later I see the same divers have sore necks, because they want to deco in the more rigorous parachute position possible, and have strained their necks to see their buddy team. I sometimes joke that the second most important rule in scuba diving is looking cool, being in a nice trim is cool. Being a trim fanatic when it’s not nescessary, is a bit like wearing sunglasses at night. You think it looks cool if you do it, but others who’ve been there, just smile.

  2. Dear ‘Marine Conservation Philippines’, I’d like to add some facts to your comment. The “hardlining DIR-oriented sort” have been teaching adaptive trim for years. We have also been teaching neutral buoyancy from day 1 of all our student courses. These techniques come from experience gained in the most extreme diving environments and are used on all our courses from “newbies” through to trimix cave rebreather.

    The reason for the “heads up” position is two-fold and neither of them are to do with looking cool. First, situational awareness is critical to survival in a dangerous environment. Ask any airline pilot, soldier or racing driver. How can you have situational awareness if you are constantly looking down? How can you keep contact with your buddy or team if you are not looking at them? Secondly, the trim position is affected by the position of your head. Try it underwater while getting someone to film you and you will quickly understand the relationship between position of the head and position of the body.

    Vikki’s view on buoyancy vs trim is spot on and something we have been teaching for many years. Buoyancy is always first and of primary importance. Trim is for economy of effort and also to assist with good buoyancy. Think of a bottle filled 1/3 with enough liquid so that is is very slightly negatively buoyant. Now put it into the water vertically – it will probably sink. If you put it into the water horizontally it will either not move and stay neutrally buoyant or else sink very slowly. Why? because we are giving our old friend Archimedes more surface area to work with to help support it. This is also true when performing deco. On a dive that requires long deco stops, frankly we appreciate any help we can get to remain at each stop with minimal deviance from the required depth and staying relatively flat helps. Should you adjust trim to deal with an emergency buoyancy situation such as venting a wing or a drysuit? Absolutely.

    Does the trim position help with decompression itself? I haven’t read anything conclusive on that topic from the medical community, so I guess it becomes a personal call as to which position delivers the best post dive feeling after a deco dive.

    At the end of the day, a good diver is a thinking diver. Blindly following diving doctrine can be dangerous, especially on technical dives. All the skills we teach are put into your personal “toolbox”. We also provide guidelines as to what can be considered best practice for your safety and wellbeing. After that, it’s up to you and your team mates to decide the best way to use these tools to ensure you have fun and get home safe and well.

    By the way, if your friends really do have sore necks, I can point them towards some good stretching exercises that will help… 😉

    Safe diving

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