Mike — have you run the “Intermediate Calibration” routine detailed on page 34 of the manual? This allows you to do two speed runs, and set up a calibration factor that is applied to the calculated speed. If you’re showing a little fast at four knots, and faster at six knots, this may help get things down where they belong.
Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- Bayfield, WI > On Aug 25, 2015, at 12:28 PM, Hoyt, Mike via CnC-List <[email protected]> > wrote: > > I have new i50 speed and depth and i60 wind installed Mid July 2014. Boat is > a Frers designed Carrol Marine built Frers 33. Phrf here is 114. > > Typically in the Fall the ST60 speedo we had on our last boat would be > reading slow and I would have to calibrate faster. At Spring launch would be > reading fast and I would calibrate slower. This was always because of growth > and slime. > > This Spring the i50 speed read optimistically high. I left it that way for a > while since it feels pretty good to see higher numbers even if you know they > are not correct. Eventually I calibrated ½ knot slower based on comparisons > with Chartplotter GPS speed in neutral tide situations. Since that time I > have noted that once again it is reading higher than GPS and now the boat is > in fresher water (Bras d’Ors Lakes) by about 3/10 to 4/10 of a knot. I > notice that it is further off at speeds 6 knots and above and somewhat close > to GPS at 4 knots. This is not usually too much of a problem since the > speedo is for relative speed anyway but surprises me that it is close at 4 > knots but off by a larger amount over 6. The bigger issue is that the TWS on > the wind instrument would also be affected as would my perception of currents > > Any comments on this? Are there varying methods of calibrations? > > It does seem nice to be making 6.7 knots to windward but a quick look on my > chartplotter brings me back to reality … typically we are 6.2 or so when the > boat is going well upwind. > > Mike > > Persistence > 1987 Frers 33 > Currently sitting in Dundee on the Bras d’Ors Lakes
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