DSMB (Delayed Surface Marker Buoy)

An inflatable tube a diver sends to the surface from depth on a line to mark their position for boats before ascending.

A DSMB is the bright inflatable tube divers shoot to the surface from depth, attached to a line on a reel or spool. Delayed means you deploy it during the dive, typically at the start of the ascent, rather than towing it the whole time. On the surface it tells the boat exactly where you are, which is essential on drift dives and anywhere you will surface away from a fixed line in open water.

Deployment is a genuine skill: hold position, partially fill the tube with exhaled gas or a small burst from an alternate, keep the spool free running, and let it go. A snagged line or a hand clamped on the reel can drag a diver upward, so the skill is practiced under supervision until it is smooth. Once the DSMB stands up, you ascend the line at a controlled rate and hold your 3 minute safety stop at 5 m beneath it.

Orange or red is the common all-purpose color, and in some regions a yellow DSMB signals a problem to the surface team. Carry one on every boat and drift dive, and agree on color meanings in the dive briefing.