An alternative to Doppler Speedlogs for your consideration is the AMI Ships Movement Information Display System (SMIDS). This product provides extremely accurate speed information using GPS and GLONASS satellite source data. High accuracy is achieved by mounting satellite antennas at the bow and stern of the vessel.
Installation therefore is all above the water line reducing cost and maintenance and avoiding conventional Doppler performance issues regardless of water depth, aeration, turbulence, temperature or salinity. SMIDS is IMO type-approved to A.824(19) MSC.96(72) (IEC 61023) for devices measuring speed and distance.
SMIDS can also function as a second GPS receiver in accordance with IMO regulations.