gps accuracy

my wife bought me a trex for my birthday. i used it for the first time while paddling(new yak). i paddled 1 mile, known course, time was 12 minutes and speed 5 mph. which seems dead on but it gave a max speed of 8.5 mph which surprised me, i have a sloppy forward stroke. i figured the wind was to my back at about 10+mph so that must be the reason. so i paddle back pushing myself a little harder because of the wind, with a hard kick at the end when i was sheltered from the wind. same results: 12 minutes, 5mph, but a 9.6 mph top speed this time. my question is; is the gps wrong, or am i a stronger paddler than i think? flat water, gp paddle, c-trek.

When the GPS is over water
and moving slower they automatically add 4 mph to make us kayakers feel better about ourselves. It’s a fairly new feature…


I was paddling with a beginner one day… When we got back her husband got all excited because her GPS said she hit 8.5 kts.

I told him the only way that GPS could hit 8.5kts. was if she threw it at me…

I think that happens when an …
…occasional instantaneous reading of your location is “off”. I’ve had the same thing happen once in a while. The best way to determine your maximum speed is to look and see what the GPS is saying during a time that you KNOW you are going much faster than normal. The reading you see at that moment will be a better indication of your top speed than an erroneous speed reading that might have taken place during a mere tenth of a second at some point during the trip.

By the way, if you ever hit 8 or 10 mph, you won’t need the GPS to tell you that something unusual is happening.

It’s probably right
so you must be paddling a Kestrel. Doesn’t everyone paddle at that speed?

Paddlin’ on


The reality is that a device that
is designed to measure position is not ideal for measuring instantaneous speed. It’s okay for getting average speed over a longer time period (I would guess a minute is plenty).

For instantaneous speed, a device that uses an accelerometer would be able to provide a more accurate measure of your speed.


Did you turn it on or off either before you put your boat in the water or after you took it out.

Sometimes I forget to shut mine off until I have the boat on the beach, and I’ll get a abnormally high “Max speed” reading.

I just chalk it up to the fact that I probably jerked the boat up quickly onto the beach.

Lately both my wife and I have been getting weird Max speed readings, but they are so high that we know they are in error.



Lots of things
can cause that, as have already been mentioned. One that hasn’t been mentioned is surfing. I can consistently hit a max speed between 8 and 11 knots if I’ve been surfing.

It’s probably just for a second or two that I’ve actually been going that fast, but if that time coincides with when the unit checks it’s position, it’s possible that it is accurate.

One time, I recorded an 11 Kt max, and it was probably right — I was surfing my way out of a tidal race, and the hull of the boat was humming from the speed. Considering it was an SK and not a surf boat, I was on the verge of being completely out of control — great feeling!

Got you beat --22 knots surfing

– Last Updated: Jul-06-08 12:10 PM EST –

Pitch poled when the wave closed out and threw the kayak end over end. Not sure if it was the ride or the rotational velocity of the crash.

The wrong top speeds are as pointed out above due to the instantaneous error in determining location. IF you are headed west and position at time A is off by 15 ft east and then at time B a second later by 15 ft west it adds 30 ft to the distance traveled. At high speed this error is negligible at 5 mph it makes the reading calculate as 8 mph. Take the top speed reading with a grain of salt unless you hide the GPS in your sons car and it says 95 mph after you retrieve it.

Notice you can stand still on dry land and get a reading of 0.5 mph.