Stus-List i50/i60 question for Fred

Hoyt, Mike Mike.Hoyt at
Tue Aug 25 13:28:30 EDT 2015

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.


1987 Frers 33
Currently sitting in Dundee on the Bras d'Ors Lakes
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the CnC-List mailing list