Buoyancy Basics – Seven Ideas for Adjusting Trim Without Adding Weight


Before making any adjustments to his gear, a diver must first check his trim. He should enter the water with all of his diver gear and attempt to hover in a horizontal position without moving his fins or arms. He can then note whether he has a tendency to hover head or feet up, or to roll to one side.

1. Move Weights Around

Changing the position of a diver’s weights may help to adjust his trim. Many buoyancy compensators (BCs) have trim weight pockets just below the diver’s shoulders. A diver who tends to float head-up may use the pockets to redistribute his weights, placing a few pounds in each pocket. For example, a diver who uses ten pounds of weight may want to carry six pounds on his weight belt and four pounds (two on each shoulder) in his trim weight pockets. If a diver’s BC does not have trim weight pockets, some divers will place a weight on the BC’s tank band for a similar effect.

Redistributing weights is not always possible, as in the case of a diver who uses very little or no weight, or a diver who uses a BC without trim weight pockets. Some divers simply find that redistributing weight does not correct their trim. Fortunately, it is possible to manipulate other pieces of dive gear to perfect a diver’s trim.

2. Tank Position

A diver’s tank position affects his trim. A tank can be lowered or raised in relation to a diver’s BC by changing the position of the BC strap on the tank. A diver who attaches his BC strap near the top of his tank will find that the tank sits low on his body. This may help to correct for a foot-up position by shifting the weight of the tank towards the diver’s feet. Attaching the BC to a lower part to the tank will have the opposite effect.

3. Reposition the Buoyancy Cell

Some equipment configurations, such as a backplate/ wing system, allow a diver to move his buoyancy cell (the part that inflates and deflates) upwards or downwards in relation to his harness. A diver can move the buoyancy cell towards his head to compensate for a foot-up position, or towards his lower body to correct a head-up position.

4. Change Your Neoprene

The thickness and distribution of a diver’s neoprene garments can have a huge effect on his trim. Thick, full-length wetsuits, especially wetsuits that have 5 mm or 7 mm legs, have a tendency to cause a diver to float feet-up. Switching to a wetsuit that has a 7 mm torso and thinner legs can remedy this situation. Similarly, thick wetsuit booties can cause a diver’s feet to float. Simply switching to thinner booties may solve a foot-up position. Finally, warm-water divers who find themselves floating foot-up may consider switching to a short wetsuit, as long as the suit still provides adequate thermal protection.

Adding neoprene layers to the torso may also have a slight effect on a diver’s trim. Thick vests and hoods add buoyancy to a diver’s upper body, and may be useful in compensating for a foot-up position.

5. Change Your Fins

Changing your fins may sound like a drastic step, but switching your fins can often be a helpful method of correcting trim. Different brands and styles of fins have astonishingly different buoyancy characteristics. For instance, SCUBAPRO Jet Fins are some on of the most negatively buoyant fins on the market. Other fins may be neutral or even positively buoyant. Heavier fins can compensate for a foot-up position, while lighter fins can compensate for a head-up position.

6. Change Your Regulator First Stages

Regulator first stages can be very heavy or relatively light. A heavy regulator first stage can help to fix a head-up position, and a lighter regulator first stage can help to compensate for a foot up-position. Of course, regulators should be selected first and foremost for their breathing characteristics, but given the choice between several similar first stages, a diver may want to make his final decision based on weight. The weight of the first stages is of particular interest to technical divers, who use at least two first stages on every dive.

7. Consider Your Accessories

Finally, a diver may want to take a look at his accessories and consider their effect on his trim. A diver who carries a heavy dive light may have a tendency to list to one side — in this case he may want to place other accessories (or counterweight in a worst-case scenario) on the side opposite side of his light. Divers who carry huge, heavy reels on their rear d-rings may notice that they float head-up. Switching to a lighter reel may fix this problem without any other adjustments.

In most cases, a diver’s trim can be adjusted without adding weight. Before making any adjustments, a diver should attempt to hover in horizontal trim with all of his dive gear in place (even accessories) to diagnose any trim problems. He can then begin repositioning or changing dive gear to improve his trim. It is advisable to change or reposition only one piece of gear at a time, and to get into the water after each adjustment to evaluate its effect. It is difficult to determine the result of an individual alteration when several adjustments are made at once.

 Take your time and make methodical adjustments to your equipment, one change at a time, until you are happy with your trim.