Water Speed on Garmin

[shantycrew]

We have a Garmin 700 series chartplotter and I am puzzled by the 'Waterspeed' readings I get. Forgive my ignorance but I learnt to sail with charts in the UK and wonder if this is actual 'speed over the water'. To confuse further waterspeed often reads as zero but sometimes springs into action and can read, say 4knots when we are doing GPS speed of 4.1knots. Does this mean that we are actually only doing .1 of a knot? If anyone can enlighten me I would be most grateful.
Cheers

[StuM]

Sounds like you have a water speed transducer hooked up to your Garmin and the wheel in it is sticking (zero reading) periodically and then spinning.

4 Knots water speed v 4.1 knots per GPS means that there is a difference of 0.1 knot between your measured speed through the water and speed over the ground, assuming that the readings are accurate that would mean that you have a slight current assisting you.

[MarkSF]

"4knots when we are doing GPS speed of 4.1knots. Does this mean that we are actually only doing .1 of a knot?"

You're going to have to explain this bit to me. I'm a bit slow. Surely, if there is no current, you would expect the waterspeed (aka speed through the water) to be the same as the GPS speed?