Tools · Trim & kicks

Glide like an airplane, not a rocket

Underwater you are not trying to get anywhere fast — you're there to enjoy the dive. So the goal isn't speed; it's to move as cheaply and cleanly as you can: the least air, the least effort, and the least mess left behind for the divers following you. Two things decide that — how you're angled, and how you kick — and both come straight out of the way water moves.

That little equation is the whole story. Drag rises with your frontal area A — how much of you faces the way you're going — and with the square of your speed v. The effort to push through it, and so the air you burn, rises with the cube of speed — and a current stacks straight onto that speed, while deeper water makes the gas itself thicker to breathe. Flatten out and slow down and the cost falls away faster than you'd guess. Tilt the diver, change the kick, and watch.

Start with the kick, because it's the one most divers get backwards. The flutter kick — the alternating up-and-down scissor you learned swimming laps — is built for the surface, where you want speed and there's no bottom to disturb. Its power stroke drives water downward as well as back, and underwater that downwash is exactly what lifts silt off the bottom and hangs it in the water for everyone behind you. The frog kick — a slow out-and-sweep, like a breaststroke with your legs — sends its water straight back and slightly up, away from the bottom entirely. Same propulsion, but given the direction the water actually goes, the frog kick stirs the bottom the least. That's not a matter of being gentle; it's a matter of where the wash is pointed.

Then there's how you're angled. Trimmed flat — horizontal, streamlined, gliding like an airplane — you present almost nothing to the water you're moving through. Angled head-up and feet-down, you're "walking" underwater, dragging your whole front through it and aiming whatever your fins throw straight down at the bottom. We don't walk down there and we don't porpoise up and down like a rocket; we glide, flat and level. Tilt the diver above and the frontal area climbs, the drag with it, and the silt with it too.

Put the two together and the equation pays you back twice over. A slow frog kick keeps speed low, so the cube-of-speed term stays small; flat trim keeps the frontal area small, so the drag term stays small; and the frog kick's glide — kick, then coast, then kick — means you're not even working most of the time. Flat, slow, and frog-kicked is quietly the most efficient thing you can do underwater: the least air out of your tank, and the least silt into the water. The diver who looks like they're barely moving is usually the one who has understood this.

And keep your hands still. New divers reach and scull with their arms as if they were swimming a pool, but a hand has almost no area to push against the water — beside a fin it moves nothing, makes no useful thrust, and mostly just slews you off course. All it does is spend, and the spending runs in a chain: the more your muscles work, the more oxygen they need; the more oxygen they need, the harder you breathe; and the harder you breathe, the faster the tank empties and the sooner the dive is over. Every motion you didn't need — an extra kick, a hand waving at nothing — is air traded for nothing. The most useful thing your hands can do underwater is fold, and rest.

Which is the real point, underneath all the angles and kick cycles: down there, the goal was never to be somewhere else. I tell my students — look around you. You are swimming hard to be where someone else is, while they swim hard to be where you are, and all either of you has managed is to empty a tank getting nowhere. Have you actually seen all there is to see? The art of seeing is in becoming one with the ocean — slowing until you are part of the water instead of a thing fighting through it, taking it in as an observer. The diver who moves the least sees the most.