Misc. Links 1
For racing, dragen boats are always rigged with decorative dragen heads and tails and carry a large drum aboard.
The caller issues commands to the crew through hand signals and voice calls, and also exhorts the crew to perform.
If paddlers are't synchronized, the result is a centipede effect whereby each pair of blades hits the water a fraction of a second behind, with the stroke of the boat falling out of synch.