Speed on GPS vs Speed on Yamaha guages

[evetsmd]

There is a reason these two speeds are different, I was told once before but don't remember......must be my getting old....

Can anyone help with an answer?

Thanks

 

[tara11]

One may be knots and one mph ?

 

[Bryan 2530]

One is "speed over ground" the other is "speed through the water."
Depending on current they can be very different.

The GPS is speed in relation to your actual progress and the Yammi guage is speed in relation to the surrounding water.

 

[evetsmd]

Here is an example that I found that tries to explain it.....

If you're swimming upstream your "groundspeed" will be your swimming speed minus the speed of the water current. Say you're a strong swimmer and can make 4 mph. If you swim into a 3 mph current you will only make 1 mph along the riverbank. If you turn around and swim with the current your speed along the bank will be your swimming speed of 4 mph plus the speed of the current (3 mph) for a total speed of 7 mph. The speed at which you can swim has not changed, the speed along the riverbank has.

I think it makes it easy to understand.....even for an old guy like me!