Trim is one of the four fundamental skills in scuba diving, yet there are many divers who don’t always have good trim. Why is that, and is it really that important? Although the concept of trim is fairly simple, it’s not always so simple to achieve it. Today we’ll take a look at what trim is exactly and why it’s important. I’ll also give you some tips to help you achieve perfect trim, and discuss common problems.

Trim is the fourth and final skill in the Scuba Fundamentals series. We’ve previously discussed finning techniques, buoyancy control, and breathing.

What is trim?

In scuba diving the terms trim and buoyancy are often used in combination with each other, but they are not the same thing. Buoyancy is the tendency of a body to float, sink or rise when submerged in a fluid. But when we talk about trim in scuba diving, we mean a diver’s body position and posture in the water. A diver has ‘good’ trim when his body is in a horizontal position, with the legs in a 90 degree angle (more on how to achieve perfect trim later). Most divers with ‘bad’ trim have their legs drop below the rest of their body, or even worse: are completely vertical when swimming!

A diver with good trim looks pretty cool, but that isn’t the main reason why trim is important – although it may be for some. Trim is all about streamlining and minimizing water resistance, and thereby reducing swimming effort. The following illustration will show you what I mean with that.

Trim and water resistance in scuba diving

You can clearly see that the second diver with ‘bad’ trim has to fight against greater water resistance to move forward. Not what we are going for!

Is trim really that important?

Having good trim may not seem as vital as for example having good buoyancy control. It’s true that being in trim is not going to save your life in an emergency. Here’s what it WILL do:

  • Make your dive smoother and more enjoyable
  • Make it easier to swim against currents
  • Prevent you from kicking and disturbing marine life
  • Improve your air consumption (because less work!) which can lead to longer dives
  • Allows for optimal gas exchange in the lungs. Read more about why you should care about that here!
  • Did I mention it looks cool?

How to achieve perfect trim

Hopefully you agree with me now that trim deserves its status as a fundamental scuba skill. Now let’s take a look at how to achieve good trim!

  • Horizontal body position
    • Your body should be parallel to the bottom.
  • Knees bent in a 90 degree angle
    • Point your feet up by bending your knees as if you were sitting on a chair.
  • Fins flat, in a horizontal line with the bottom
    • Flex your feet so that your fins are flat and parallel to the bottom.
  • Arched back and flexed glutes
    • Yes – you actually have to put in some work too!
  • Face forward
    • Don’t forget to look where you’re going 🙂
  • Arms in front of you
    • This will help you stay horizontal. It also keeps your dive computer in your visual field.
If you ever feel silly for practicing trim on land, just remember that I once posed in my scuba gear on a table for a photo.

It can sometimes be hard to estimate your body position in the water. In the beginning it may feel like you’re completely horizontal, when in reality you’re nowhere near 🙂 So the easiest thing to do is practice on land! It may feel a bit silly – but I promise you it will make all the difference. So get down on your belly on a chair, the sofa, your bed, the floor – it doesn’t matter! You can even put on your scuba gear to make it more realistic (and hilarious for bystanders).

The first thing you may notice is that keeping this position for a longer time can get a bit uncomfortable and tiring. Well yeah, why do you think so many divers are out of trim? It’s a pretty unnatural position for us humans, so your body is not used to working those muscles. The good news is, you do get used to it if you practice regularly! After you have successfully adjusted your trim, you may also need to change the way you use your fins. Click here to read more about that.

Common reasons for bad trim

So you’ve practiced on the sofa and you’re flexing those muscles like crazy, but underwater you still can’t seem to stay in the right position. It does take some practice to get it right, but there are a few easy fixes that can help you in the right direction.

Weight distribution

This is often the number one reason why divers are out of trim. Most new divers learn to dive in a jacket BCD and a weight belt. The big disadvantage of using a weight belt (besides the fact that they’re just really annoying) is that it places the additional weight below a diver’s center of gravity, dragging the hips and legs down. Depending on how much weight you carry, this effect can be quite extreme. You could try to move the weight belt up a bit, but chances are you won’t get very far because of the bulky jacket BCD.

Luckily there’s an alternative: use a BCD with an integrated weight system. These often place the weight higher on a diver’s torso. If that’s not an option or if it still doesn’t work; you can buy special weight pockets to attach to your tank. Alternatively you could also add a weight to the tank strap, but those can usually only hold a smaller weight.

Not enough weight

Although bad trim is usually associated with a diver’s legs dragging down, the opposite may also be true. When your legs float up above the rest of your body, this usually means that you don’t carry enough weight. It often happens to divers towards the end of the dive, when they have consumed the majority of their air and their tank gets more buoyant. Download my free E-book to learn more about proper weighting.

Air distribution

Just as weight distribution may affect your trim, so does the air distribution in your BCD. Remember that air always travels up to the highest point, so if you find yourself in a (slightly) upright position and can’t get horizontal, chances are there is some air trapped around the shoulders. Throw your bum up like a wild horse to allow air to travel to the lower part of the BCD!

Equipment

The equipment you have probably learned to dive with (jacket BCD and weight belt) are unfortunately not always the best to achieve good trim. 

  • Backplate and wing BCD: In a backplate and wing BCD, the entire bladder is located on your back, which will help tremendously to get into a horizontal position. These types of BCD also offer integrated weight systems, so you can kill two birds with one stone and ditch the weight belt.
  • Fins: how heavy are your fins? If your legs have the tendency to sink, it may be worth it to switch to neutrally buoyant (or even positively buoyant) fins.
  • Booties: another opportunity to play around with buoyancy. Thicker and higher booties will be more buoyant than low and thin ones. So if you have heavy fins that you don’t want to say goodbye to, you could compensate by using positively buoyant booties.

There are other equipment items that may help you achieve good trim, but all the best dive gear in the world can’t help you if you don’t put in the work yourself. It’s too easy to simply blame bad trim on bad equipment. As mentioned, it can feel awkward and tiring in the beginning to stay in perfect trim. The only real solution is to practice and train your muscles. But while you do that, fine tuning your equipment will help to bring you closer to your goal.

Should you always be in perfect trim?

I’ve mentioned before that many people dive out of trim. Does this mean they’re all amateurs that have no idea what they’re doing? Could be, but not necessarily. I don’t dive in perfect trim all the time. But I know how to do it, and can switch to good trim in a second. Generally speaking, it’s ok to be out of trim if it’s by choice. Even so, I must admit that when I’m out of trim, it’s mostly because of laziness. 

Acceptable trim

Different types of trim in scuba diving

In my opinion there’s a difference between perfect, acceptable or bad trim. We’ve already established what perfect trim looks (and feels) like. Acceptable trim is – in my humble opinion –  when a diver’s torso is (more or less) horizontal. The legs are bent in a 90 degree angle but may drop a bit below the body. The arms don’t have to be stretched out in front as long as you keep them still. Although far from perfect, diving like this will be enjoyable and effective for most people in calm water. As long as you don’t disturb marine life with your fins by keeping your feet up, there’s no reason why diving like this shouldn’t be ok.

So although perfection doesn’t always have to be the goal, there is such a thing as unacceptable trim. For example when the legs are not bent and dragging down, causing a diver to kick and disturb the bottom. Or – and yes this really happens – when a diver is completely upright and moves around by doing a bicycle kick. Diving like this is usually caused by lack of skills, and not by choice.

Common trim problems in scuba diving

Ultimately, when you’re diving for your own enjoyment, you should do whatever feels good for you – as long as it doesn’t compromise your safety. But understanding the concept of trim and being able to master it is essential to being a prudent scuba diver. So practice it often, then decide for yourself if this is something you want to do at all times. If yes, power to you. If no, just make sure that you’re still within acceptable limits and enjoy your dives 🙂

Enjoyed this article? Click here to learn more about the other fundamental scuba skills!

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