Diver trim

The trim of a diver is the orientation of the body in the water, determined by posture and the distribution of weight and volume along the body and equipment, as well as by any other forces acting on the diver. Both static trim and its stability affect the convenience and safety of the diver while under water and at the surface. Midwater trim is usually considered at approximately neutral buoyancy for a swimming scuba diver, and neutral buoyancy is necessary for efficient maneuvering at constant depth, but surface trim may be at significant positive buoyancy to keep the head above water.

In midwater, a swimming diver is propelled with least exertion when the body is aligned with the direction of travel, as this minimises drag, Finning effort required to maintain depth is additional to the effort to move in the desired direction. Stable level trim is efficient when swimming at constant depth. Competent recreational scuba divers will usually spend most of a dive at near neutral buoyancy and level trim, clear of the bottom and other solid surfaces.

When working on the bottom it is usually safer and more comfortable to be trimmed more upright, particularly in a dry suit, and negative buoyancy can help stability while working. This is common practice for Surface supplied divers, but they may also find level trim useful if they operate in midwater at neutral buoyancy.