Blog posts from Gareth, Imogen and Neil
On a recent course I was asked what trim actually is and why GUE/DIR divers go on about it?
Trim is not just our angle in the water, but also the position in which we hold our bodies. 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. But why all the fuss?
As GUE divers, we try to become as efficient as possible. 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.
Then there’s propulsion. A diver that is swimming along at 45 degrees, is directing some of the energy of their propulsion in a downwards direction. 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.
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. Only by forcing that diver to stop, freeze their arms and legs, and hold their breath, do you discover what is really going on. GUE divers focus on buoyancy control for a variety of reasons, but trim and buoyancy control are not totally separated skills.
Protecting the Visibility
The direction of that energy also has another effect. Energy directed downwards will stir up the bottom. This means that a diver who is swimming along with poor trim who strays too near the bottom is going to stir up the environment while finning. You see this in divers everywhere.
With proper trim there is no need to disturb the bottom. At all. Divers can get much closer to the bottom without disturbing it, which has obvious benefits whether examining a reef, or taking photos. It also affects safety. Disturbing the silt is irritating in a quarry as it makes it more difficult to keep everyone in sight when teaching, but it can be disastrous 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).
Divers facing each other on an ascent in flat trim. GUE divers place a massive emphasis on team responsibility. 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.
Flat Trim or Appropriate Trim?
It is worth mentioning that flat trim is not the final story. When swimming up a cave at an angle, or swimming up a corridor in a wreck at an angle, then flat trim becomes inefficient. What is appropriate here is an awareness of appropriate trim, and the ability to swim in any trim required.
So that’s why we spend a significant amount of time on courses and in practice putting in place a solid awareness of trim and tools to tweak it where necessary. Along with buoyancy control, it provides what we call the "platform", on which we build all the other skills.