TRIM -

Trim

Article by Rodrigo Jorge Silva

Have you ever been diving and noticed some divers who seemed elegant, with slow, controlled movements? You probably immediately associated them with technical or highly experienced divers. But what if I told you that this way of diving isn’t exclusive to technical diving? That this graceful posture can actually be learned right from your entry-level course?

That elegant way of being in the water is called TRIM. Trim is not the same as buoyancy. Buoyancy refers to your ability to move along the vertical axis and stay neutrally buoyant at any point on that axis. Trim, on the other hand, is your posture in the water.

To understand trim, let’s look at the origin of the word. “Trim” comes from English and means “to cut,” as in cutting through the water to move efficiently. But it also means to be or to stay balanced. It’s a nautical and aeronautical term used to describe the balance of vessels by adjusting the position of their load.

In diving, we can say that trim is the correct position a diver should maintain in the water. Ideally, this means a completely horizontal position, where your shoulders and knees are aligned on the same plane. Your knees should remain bent, and your arms can be used to adjust your center of gravity by extending or retracting them.

The Diving Position

Your shoulders, hips, and knees should remain level at all times. This requires holding your head with your chin slightly up and lifting your shoulders and knees to form a very slight arch in the back (a slight lordosis). The biggest mistake is dropping your hips, which causes your knees to drop and positions your feet downward.

Knees should be bent at a comfortable angle between 45° and 90°, which shortens the lever arm of your legs. As mentioned, experiment with different arm positions to find balance. Practicing this posture should first be done on land, and later—whenever possible—underwater while filming yourself. Watching the footage makes it much easier to self-correct your diving position.

Maintaining correct trim optimizes your hydrodynamics, which brings several key benefits:

✅ Enhances Nitrogen Elimination

If we consider off-gassing during ascent, being in an isobaric (even pressure) horizontal position makes nitrogen elimination more efficient. The depth—and thus the pressure—across the body is even, which is critical in deep dives to maximize off-gassing effectiveness.

✅ Maintains Visibility

When your trim is off and your fins are near the bottom, the water displaced downward stirs up sediment, creating a cloud that can drop visibility to zero. Propulsion techniques that move water to the sides can prevent this sediment disturbance, improving safety by preserving visibility.

Good trim also helps photographers—professional or hobbyist—frame shots more effectively by giving them a clear view of the scene they want to capture.

✅ Protects Marine Life

As divers, we are only spectators of marine flora and fauna. Seeing other divers with poor trim kicking downwards and damaging sea snails, urchins, and other creatures is disheartening. Even worse, it deprives future divers of the chance to see those animals.

It’s common to see divers who forget how long their fins are—those are the ones who strike or damage coral due to poor trim. With good trim, fins are positioned near your head and well above the seafloor or coral, preventing contact and avoiding harm.

✅ Reduces Air Consumption

Proper trim means less resistance moving through water, so you displace less water and use less energy. This directly reduces your air consumption. Horizontal alignment also makes your kicks more effective, increasing propulsion and reducing effort—and gas usage.

✅ Proper Weight Distribution Is Key

Your weighting system plays a major role in achieving good trim. Overweighted belts tend to push the diver’s legs down and raise the torso. This causes the air in your BCD to migrate to the top, leading to poor trim.

A weight belt can also hinder deep breathing by restricting the lower diaphragm area—but that’s a topic for another article on the Hogarthian configuration and its benefits.

❌ Poor Training Habits

Another key factor is training that conditions divers to kneel on the bottom. This is common in courses where instructors teach skills from that position. Students then default to it whenever upright. Over time, this ingrains bad habits—and poor trim.

This is a moment of self-reflection we must have as diving educators.

🔧 It’s Not About the Equipment

Trim is not achieved by specific gear. Trim is a posture—it can be achieved with a wing system or a standard BCD. While it’s true that wings make this posture easier (because they allow for better weight distribution, a lower tank center of gravity, and back inflation only), you can achieve good trim with a jacket-style BCD too.

It just takes training, training, and more training—correcting and learning. Learn how your fins float (some are positively buoyant, some negatively), where to place your tank, how to distribute weight, and you’ll achieve a natural, graceful trim.

And when another diver sees you in the water, they’ll say, “What an elegant posture!”

Start your SDI Advanced Buoyancy training now!

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