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Trim: the nitty gritty

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This is an expansion on request of an earlier article I wrote about trim that now includes some images to try and explain what I was talking about, and also includes some tips on how to actually improve trim in the water. Let’s start with a definition: what the hell is trim anyway?

Trim is often assumed to be our “angle in the water”. A diver that is “flat” in the water is said to have good trim, and a diver that is not flat is said to have less than perfect trim. However, this is course is silliness. Trim is more than this. It’s a combination of two elements. The first is indeed our angle in the water. The second, however, is in how we hold our body position in the water.

Visualise a line between our chest and our knees.  If we are in "good" trim, then this line is straight between the two points.  If we continue to visualise this line, and if this line is horizontal in the water, we can be said to have flat trim.

Consider the following image:

Trim flat

You can see that this diver has a straight line between the chest and the knees. This will generate the most efficient position in terms of resistance to the water. Now, in the image above, the diver has “flat trim” which is something many divers seem to obsess about. God knows I’ve been guilty of it in the past. Eventually, however, you recognise that what is important is “appropriate” trim. Whilst flat trim is the ideal for general open water swimming, for reasons will explain in this article, there are other occasions when flat trim is not appropriate. For example, when swimming up a cave at an angle, or swimming up a corridor in a wreck at an angle, then flat trim becomes inefficient, and in fact rather stupid. What is appropriate here is an awareness of appropriate trim, and the ability to swim in any trim required. Pulling yourself along a wreck with your hands if you need to go against a current is perfectly appropriate trim in my opinion. There are people who obsess about being flat in the water, but I'm far more concerned with being aware of our position in the water, and having an ability to change it at will then just getting flat.


So what is the fuss about flat trim?

Well, as I’ve just said, it’s the most efficient for open water swimming. Presenting the minimum amount of ourselves to the water means we have the minimum amount of water to move out of the way as we swim along. This results in a saving of energy.  This in itself results in a more relaxed diver and almost inevitable subsequent saving of gas.  If we are trying to swim horizontally then being in flat trim will present the smallest profile to the water.  In other words, as we swim along, there will be less water to move out of the way. This will translate to using less energy, which will translate to less stress, and lower gas use. In a word, efficiency.

Now, let’s look at it from a perspective of propulsion.  A diver that is swimming along in open water  with poor trim is directing some of the energy of their propulsion in a downwards direction.  Think about the traditional scissor kick. The fins are pushing water up and down, not back. This is incredibly inefficient, and so difficult that scuba training agencies actually build cramp removal into their courses. Call me a revolutionary, but I'd rather teach people efficient kicks that don't give them cramp in the first place!

If we can take that diver and make them flat in the water, we can direct a far greater proportion of the energy created by the diver’s kick directly backwards, which will move that diver forwards far more efficiently. This is what we are after. The energy of the diver’s kicks are now being directed backwards. This means that he or she is not wasting energy. Have a look at this video. This is me, doing a frog kick. The important thing to notice is that I am not actually continually kicking. I am saving energy with an efficient “glide” phase of the kick. This is only possible because I am in flat trim.

On a similar vein to propulsion techniques is buoyancy control. A diver swimming along at 45 degrees is almost certainly slightly negatively buoyant.  They have to be.  If they were perfectly neutrally buoyant and directed a proportion of the energy generated by a powerful kick in a downwards direction they would simply swim up.  The end result is a diver that tends to keep themselves slightly negative to compensate for this, even without realising it.  To understand this you have to think about where the energy is directed. 

Think about it. You are hovering motionless in the water at 45 degrees. You are a master of buoyancy control, perfectly neutral. Now you start to kick. What happens? If you are perfectly neutrally buoyant, and at an angle of 45 degrees you would just swim up, right? People DON'T swim up, so there can only be one explanation - they are keeping themselves negatively buoyant.

We already know that a diver swimming at an angle is directing energy downwards. When you direct energy downwards, you go upwards. It’s physics. So a diver swimming at such an angle will almost certainly be kicking themselves slightly upwards, and then drifting downwards. So here’s tip number one. Stop it. Kick, and stop. Hold. Wait. Wait. Wait. See what happens when you are not kicking. See what happens when you freeze. Of the people I have coached and taught since the last year 1 has not been slightly negatively buoyant. 1. It’s because we treat negative buoyancy as a comfort blanket. We are taught and conditioned to be more worried about going up out of control than dropping to the bottom. Hey, what’s the worst that can happen if we drop down a little bit. Well, this is the ramification of that habit. In this manner,  trim and buoyancy control cannot be viewed as separate and distinct skills, but rather two parts of the same thing.

So, thinking about that energy being directed downwards, what other effects might that have. Well, most divers will have experienced swimming behind another diver that is close to the bottom. Some divers will stir up the bottom, whilst some divers will not disturb it at all. The difference between them is where they are directing the energy of their kicks. Part of it is the type of kick selected. For example, the straight leg flutter is designed to use the large muscles of the legs for power, and to direct energy backwards, but it also directs energy downwards, whereas the frog kick is designed to put energy back and UP, thereby avoiding disturbing the environment. However, the second part of the equation is the diver’s trim. A diver in flat trim is far, far less likely to disturb the bottom than a diver swimming at an angle.

Whilst this might be seen as a nicety, some of us consider it far more important. If I am penetrating a wreck, even in shallow water, I do not want to silt out the wreck for the people behind me. For those divers that swim over delicate surfaces, be they organic or metal, an awareness of how to position their body to avoid disturbing it can be very important indeed. With proper trim there is no need to disturb the bottom.  At all.  This permits divers to get much closer to the bottom without disturbing it, which has obvious benefits whether they are examining a reef, or taking a photograph.  It also affects safety. Disturbing the silt might be irritating in a quarry as it makes it more difficult to keep everyone in sight when teaching, it can be far more problematic when inside a wreck, where a complete silt-out can dramatically increase stress levels.

Then there’s the environment. If you want to swim three inches above a reef, you need to be sure that you knees are also three inches above that reef, otherwise you are going to kick the crap out of it.  The same is true in a cave or wreck, where I personally like to know that the environment I have been diving in has changed little from my presence (apart from perhaps the odd crab wondering why they are being attached to an SMB).

Here’s another thought. With a very few exceptions (and sorry solo divers, but you are the exceptions) the vast majority of us dive in teams. It’s irrelevant what agency taught you, or whether you call them buddies or teammates, the people you are in the water with need to be considered. If they, or indeed we, have a problem, then we want to be able to get to them as quickly and efficiently as possible. 

We have already discussed the fact that combining efficient propulsion techniques with flat trim is the most efficient way to move horizontally through the water. If a team mate has a problem, we want to get to them with one kick and glide. Flat trim is a part of this. There is also a visibility element. If we view each other completely flat in the water, we can clearly see the valves of our team and have instant and unobstructed access to them in the event of a problem. This puts us in a position where we can view leaks, but also where we can easily step in and take over diagnosis and resolution of any issues with the valves.


So that’s why trim is important, but the next obvious question is, how do we achieve good trim?

Firstly, we have to understand our body. It really doesn’t want us to be in good trim. It wants to bend and move in all kinds of inconvenient places. Have a look at the image at the start of this article. Now, I like this image. It’s simple, but it tells us a lot about what we need to know about trim. I’m going to explain what I can about achieving good trim in the water, but I have to be honest and say the best way to achieve it is to go diving with people who understand what you are trying to work on and get good feedback. Either that, or get in the water with an instructor who understands trim, and can video you or give you feedback that will enable you to improve. This is stuff that makes interesting reading on the internet, but there is no substitute for in-water time and feedback.

So that’s the caveats out of the way, on with the show.

There are three elements to trim. These are buoyancy control, which as we have already discussed, is inextricably linked to trim. Then there is weighting. Finally, there is body position.  Notice I didn’t say kit, or equipment. Trim has absolutely nothing to do with what you are wearing. Sure, some configurations are more streamlined than others. But once you understand trim, and how to adjust it, you should be able to trim anything out, whether it be a wing and backplate or a BCD.

I’ve discussed buoyancy control and it’s importance at length in other articles so I’m not going to rehash them here. However, suffice to say that without good buoyancy control, efficient trim is just not going to happen. You are simply not going to be stable enough. Moreover, you will be so task loaded maintaining buoyancy control that you will not have the spare capacity to focus on trim. So let’s assume you have your buoyancy control sorted. That leaves weighting, and body position.

Weighting is an interesting one. It can be separated into the amount of weighting used, and weight distribution. Overweighting is a problem. It’s going to play havoc with your trim. Luckily, its going to play havoc with your buoyancy control as well, so you need to get this sorted. My buoyancy control lecture on fundies lasts a couple of hours, and I’m not going to try to teach GUE fundamentals online, so let’s just agree that overweighting is not your friend. It makes everything difficult, makes everything more stressful. Do a proper weight check. I do one every couple of months, and it changes. Weight yourself as neutral for nearly empty cylinders. Once you’ve got that sorted, we are ready to look at your weight distribution.

A set of scales, perfectly balanced. This is what, as divers, you are trying to achieve. You are trying to find a mid point where everything is balanced. How you achieve that is down to the individual diver, but certain things should seem obvious. If you place all the weight at one end, in the form of a huge weight belt, that is going to drag the lower half of your body down. The weight needs to be distributed along your body. The precise distribution is unique for every diver, and the only way to find it is to fine tune it with experience. A word of caution here though. I think you need 20 dives after trying something new before you really understand the effect it has had on your diving. A diver and instructor whose knowledge I hugely admire thinks you need fifty. The number is irrelevant, but the reality is that you cannot move a weight, do a dive, move a weight. Distribute the weight along your body in the form of a backplate, or trim weights, or v weights or p weights, and then go do a bunch of diving. So here’s tip number 2. Don’t get trapped into changing things every dive. You learn nothing. Make a conscious change, and then dive it thoroughly until you understand it.

So let’s talk about body position. If we want to be flat in the water, that causes us a problem in terms of looking where we are going. Look at the picture above. The natural position for this diver’s head would have him looking straight down. This is not exactly sensible when one wishes to avoid swimming into something head first. It’s also not sensible from a buddy perspective – you need to be looking around to see a problem if one occurs. There is also a problem from a perspective of trim. Your head weighs between 8 and 12 lbs. That’s quite a weight. Lower that weight, by looking down, and it will pull you into a head down position. So, for a variety of good reasons, it makes sense to keep your head up. Look at the following video.  I’m putting up an SMB. That’s actually not the important bit. The important bit is that I’m keeping everything up so that I can keep my head up and still see my buddy.

Keeping your head back Is all important. If you drop your head, you will tilt your body so that you can still see forward. So keep your head back.

So that’s your head. Now if you stand up and try to look straight up in the air you will find that you can only look up so far by putting your head back. In order to look straight up you need to do something extra. You need to lean back. The same is true when we are flat in the water.  Now, this is where a lot of people go wrong. They read on the internet that you have to arch your back. Then they find it all uncomfortable, and end up with a bad back. It’s not supposed to be uncomfortable. It’s supposed to be fun. The trick is not to arch your back. The trick is to raise your arms by rotating your shoulders. Bring your elbows up to shoulder height and that will put enough of an arch in your back without having to be a contortionist.

OK, let’s move further down the body. No we come to the hips, and this is where the vast, vast majority of people have a problem. Your legs weigh a lot, and they naturally want to drag beneath you. Thus your natural position is to bend at the hips. This drags you out of trip, creates drag, and basically wrecks what you are trying to achieve. There is only one way to stop this. You need to clench the muscles of your arse. This tightens the muscles in your things, and brings your knees up. This is what creates the straight line between your chest and your knees, and in many ways is both the most difficult and most important piece. It’s difficult because firstly its very difficult to tell if your own knees are dropping and secondly because until you  get used to it, keeping them up is an unnatural position. My tip on keeping your knees up is to try settling slowly down into a flat position on a platform – and see what hits first. For many people, it will be the knees. You are not necessarily out of trim, you are probably just dropping your knees.

Further down your body, and you find your knees, which need to be bent. The degree to which you kept them bent depends on your individual trim needs. Your calves and feet and fins are a significant weight at the end of your body. Think back to the scales. You need to play with how far you extend the legs, because changing that length will definitely change your trim. The right degree takes a while to find, and its something that you will just know when you find it.

Finally, the feet. You need to keep these parallel to the bottom. If your fins are vertical in the water, then they will provide no resistance to your body from rocking up and down like a see saw. Keeping the blades of the fins flat in the water provides a huge amount of resistance, which helps to stabilise you in the water.

So that’s head, shoulders, arse, knees and ankles. Think your way down your body when you get in the water. At first, it will take quite a bit of your capacity to remember everything – which is why you will almost certainly drop your knees. However, after a while, it will all come together.

So, how do you put it all together. Easy. Practice, practice, practice. You don’t need to get in a quarry to practice this, you can practice it on every sea dive. Practice it, and then get some feedback. If you can get a friend to point a camera or video at your then this is incredible feedback, and a very powerful educational tool when used correctly. When you do get a chance to practice somewhere, find a flat location and drop slowly onto it. Literally lie on the platform. Get a feel for what being flat feels like. Get your head up and look straight ahead. If you need further advice or would like a helping hand we offer great one-to-one or group coaching sessions that specialise in trim and buoyancy, I’m always happy to help.

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Gareth Burrows is a GUE Instructor trainer, and a personal diving coach for recreational and technical divers of all levels, specialising in improving buoyancy control, trim and stability, in-water confidence, and ascent management. He has trained with PADI, TDI, IANTD and GUE as well as serving as a DO in a BSAC branch. He has been diving cold water wrecks in Europe and around the UK for over a decade, and can usually be found diving out of Brighton, Portland or Plymouth. He is qualifying later this year as a cave diver and looking to become a GUE tech1 instructor in the 18 months. He has trained or coached hundreds of divers from newly qualified open water divers, to course directors and technical instructors.