Vessel speed

Most Great Lakes vessels survey at 5-7 knots, depending on surface conditions.  As weather conditions worsen, vessel speed often will need to decrease to maintain data quality owing to increased noise, the influx of bubbles across the face of the transducer, and vessel pitch and roll effects on transducer motion.  At some surface conditions, data quality cannot be maintained and the survey should be postponed.  Suspension of the survey in rough weather may be particularly important if targets of interest are located high in the water column due to the increase in surface noise from bubbles. There is currently no set rule for at what sea state surveys need to be postponed in the Great Lakes.  Experience in Lake Superior suggests that usable data can be obtained even during 20 knot winds if transects are aligned with the prevailing wind direction.