When surveying a reef, getting towed can be a more effective way of covering a large area and conserving diver energy. The boater must pay special attention to currents and make sure to go slow enough for comprehensive data collection. If divers are towed at over 3 knots, they could have trouble holding onto equipment and their face masks or mouthpieces might fall off. (To get an idea of how fast 3 knots is, currents of 1 knot are considered the limit that a normal diver can successfully swim against.)