Speed Differences P/S Tack

[Merrill Mant]

Bill,Welcome to Hunter Owners.In July I replaced the original 1992 TriData unit for a new ST60 Tridata. I was required to haul the boat to replace both the speed/temp and depth transducers as the originals would not work with the new instrument. The new unit works well however I have noticed a substantial difference in the speed indication between a port and starboard tack of 1.5 knots. I have validated this with my GPS. I calibrated the unit with the GPS while motoring. The speed difference appears to be almost entirely skewed to one tack. The only thing that I suspect is that despite the best efforts at aligning the paddlewheel throughhull parallel to the boats centerline, it is not aligned correctly. Would you concurr?The location of the transducers is correct as far as the recommended positions supplied, ahead of the keel, flat section of the hull slightly to port of the centerline.The boat is a 1992 Hunter 335Thanks in advance for your assistance.Merrill

 

[Bill Boudreau]

Speed discrepancy

The instrument is calibrated for a single rotation rate as the paddle travels through the water. This motion generates a pulse rate that the instrument translates into a boat speed. The paddle must be turning at a different rate on one tack. Could the transducer housing be angled to one side? Is the transducer perhaps coming out of the water (or close to it) when the boat is heeled?

 

[Don Alexander]

My Log Does it Too

Though my installetion had the impeller straight ahead I still suffered the same errors in log readings. In the end, and in desperation, I filed off the small pip on the plastic impeller housing so I can now angle the transducer midway between the two extremes for port and starboard tack. Problem now is to get it right each time I need to clean the transducer. ie. every two weeks.Similar installation of previous to ST 50 model on my last boat did not seem to suffer from this defect.Is this impeller unduly sensitive to minor cross flows and would it be a benefit to fit two flow straightening vanes on the hull?Regards,