Across mass of water

martin6651

I was wondering how accurate would a land gps be to navigate across a large mass of water.

KoolKid

How accurate do you want it.
On roads at street level location can be out by 10s of meters but it snaps to the nearest road because that's where it knows your should be.

martin6651

Accurate as possible for boat cover during 13k swim.

Alun

GPS is GPS, it doesn't care if it's on land, sea or even up in the air. You'll get pretty good accuracy on open water as there will be no obstacles on the horizon to reduce the number of visible satellites, and you should also be able to use WAAS/EGNOS, so could get down to a couple of meters accuracy in the best case scenario.

Marine GPS's do have specific features such as special marine maps, anchor drift alerts and the ability to connect echo sounders for depth alerts, but in essence they're using exactly the same positioning technology as 'land' GPS's.

KoolKid

Well for that your not going to have to be within 1 or 2 meters are you?

eirman

I used my nuvi a few years ago as a passenger on the holyhead ferry. The position on the Irish sea and the speed seemed quite accurate. I even changed my nuvi vehicle to a boat, much to the amusement of fellow passengers.

There was no way to set a heading at sea and to monitor when you move off course. It would mean constant monitoring and adjusting. If you were to use a compass to keep to your heading that would help a lot.

A handheld eTrex would be easier to use at sea as you just have to follow the pointer arrow.

coylemj

eirman wrote: »

I used my nuvi a few years ago as a passenger on the holyhead ferry. The position on the Irish sea and the speed seemed quite accurate.

How could you tell that it was accurate in position and speed in the middle of the Irish Sea?

eirman

coylemj wrote: »

How could you tell that it was accurate in position and speed in the middle of the Irish Sea?

The accuracy of speed would be be universally accurate, so long as you can lock on to four satellites. I know that my satvav is much more accurate than my car's speedo. The speedo always indicates speed as being about 5kph greater than reality. This seems to be a very common and deliberate inaccuracy (veering on the safe side of inaccuracy)

I cannot prove that my position was accurate as there are no landmarks along the way! I could however see my 'boat' making steady progress through the Irish Sea. This was more evident near the harbours. At one stage I set a welsh destination and the countdown time to the destination gradually decreased.

Alun's post above is spot on

coylemj

I know all that, I have used an eTrex on the HSS. I was just amused by your statement 'The position on the Irish sea and the speed seemed quite accurate.'

It seemed quite accurate??

KoolKid

I would imagine reception would be better at sea, having a clear line of sight to the sats.

coylemj

You cannot hold a device in your hand and say that it 'seems to be accurate' when you are not comparing it to another source of information. The statement is meaningless.

I'm only commenting on the subtlety of the statement which I find amusing, I have no doubt that the GPS unit the OP was holding showed the exact speed across the water.

I'm currently on my third eTrex (original yellow model, Legend and now Legend C) and also have a Nuvi in the car plus two Bluetooth GPS receivers in case anyone thinks I don't trust the technology.