CURRENT METER MOORINGS

COMPARING SPHERICAL FLOTATION WITH SUBS FLOTATION

Spherical Floatation

You will note that each mooring holds three RCM8 and one S-4 current meter.

The oscillation of the mooring on the left is caused by vortex shedding from the spherical flotation, while the mooring on the right has eliminated vortex shedding by using streamlined SUBS flotation.

The mooring at left will oscillate at approximately .2 Hz, with an amplitude of .5 meters. This means that a current meter in the center of the mooring line will travel (from side to side) a distance of about 1 meter and back every 5 seconds.

The mooring line oscillation depicted at left has been shown to cause significant current meter under-reporting. When the mooring on the right is stabilized by using SUBS streamlined flotation, the data correlates very well with ADCP data recorded over the same time period.

The data set improvement is very similar for both RCM-8 and S4 current meters.

Both moorings have the same amount of flotation, but the SUBS mooring has less inclination, because the frontal area of the buoyancy has been reduced.

Different mooring designs will have different amplitudes and oscillation rates, but the dynamics will remain the same as long as spherical flotation is used.

SUBS Floatation

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