GPS Issue

Hello Fellow Boaters,

I am having an issue with my GPS System where the icon of my boat on the GPS Screen wanders and points to a different direction than my heading....

Could this be the receiving unit that is loose??

first time owner and first post. thank you for any help....

Genecag

Re: GPS Issue

The icon on your GPS screen normally points in the direction that the vessel is traveling in. Which is not necessarily the same direction that the vessel is headed. If you are sailing or motoring slowly the wind and/or tide can push your vessel in a very different direction from which you are headed.

This difference in course (sometimes referred to as leeway) is usually negligible when travelling at high speeds.

So if this is happening to you while travelling a slow speeds I would guess that leeway may be the cause.

Re: GPS Issue

Welcome to the board. Lots of good people here to help and hope to learn from you also.
I supect your problem may the way you have the unit set.
Most GPS units you can set 3 ways.
Your boat icon Should allways point to the direction the boat is moving.
Yes you can get some side drift from wind or current.

First way to set is North up so the North on the chart will always be up even if your heading East, West, or South. This can be confusing for many.

Second way is to set for Track up or heading up so your vessel will always be pointed at the top of the screen.
Many like this mode better. In this mode what you see out to the right will be to the right on the sceen.
What you see out the window to the left will be to the left on the screen.
Also if you see the wayoint your headed to at the top center of the screen then your headed right at it.

The third mode is course up. So the waypoint your headed to will be at the top center of the screen.
The vessel shown will point to where your headed so if your off course to port the vessel icon will point to the left.
If off course to Starboard then the vessel icon will point to the right.

Myself I usuall run in heading up mode on the boat but I also turn on some data fields.
Usually Range or distance and Bearing or compass heading. Also usually turn on a speed data field. When running a long route will usually turn on ETA also.

I hope this makes some since.

When useing in the car I run a lot is course up mode.
This is because in heading up mode it will try and keep the direction your going at the top of the screen.
The reason for this is if you are running on a winding road and have a slow to redraw GPS like a Garmin then most of the time the screen will be blank. In heading up mode it will try and keep the direction your running in at the top of the screen.
This is because after each turn it trying to redraw the map but before it get done you have made another turn and it is starting over.

In course up mode then it will keep your next waypoint at the top of the screen and
even thou you are constantly turning it will not have to redraw the entier map so will have a map most of the time.

Re: GPS Issue

geencag said:

Hello Fellow Boaters,

I am having an issue with my GPS System where the icon of my boat on the GPS Screen wanders and points to a different direction than my heading....

Could this be the receiving unit that is loose??

first time owner and first post. thank you for any help....

Genecag

Click to expand...

If you have a compass also in the boat...mounting the GPS too close to that may be causing some of your issue as well.

Re: GPS Issue

I am having an issue with my GPS System where the icon of my boat on the GPS Screen wanders and points to a different direction than my heading....

Click to expand...

Depends on whether you're moving or not.

If you're moving, the icon should point in the direction you are heading or there's something wrong with your GPS.

If you are NOT moving, then the GPS knows your location but has no way to tell which way your boat is pointing. In that case, the inherent inaccuracy in the GPS system (several feet minimum) can lead to the icon heading "wandering" as the GPS computes your location moving around inside that several foot inaccuracy circle, although in reality you are not moving.

Re: GPS Issue

Look through your menu and see if it's set to track north, or track up (or direction). Track north the map is orientated north and the icon points the cardinal direction of travel. Track up the map is orientated to direction of travel and the icon follows.

edit: guess if I'd read that's what Boatist said. What brand is it?

Re: GPS Issue

gps != compass. At least in the marine environment, they are pretty slow about using a backup compass in the gps for when you are not moving. (most automotive/handheld/phone gps systems are now using a magnetometer for direction if not moving)

Re: GPS Issue

Thank you to all for responding....

The setup was from the time of boat purchase and one day the icon on the plotter starting pointing in a different direction then the direction of the boat. As I am moving, the icon will being pointing some considerable degrees off of my heading....

genecag

Re: GPS Issue

Genecag said:

Thank you to all for responding....

The setup was from the time of boat purchase and one day the icon on the plotter starting pointing in a different direction then the direction of the boat. As I am moving, the icon will being pointing some considerable degrees off of my heading....

genecag

Click to expand...

The GPS unit does not know what direction your vessel is pointed unless you have a commercial unit that is getting information from your compass. The GPS only indicates what direction the vessel is travelling in. Which can be two different directions in a slower moving vessel.

You don't mention what you're using to find your heading so I will assume it is a magnetic compass.

Magnetic compasses have two inherent errors.

The first is called variation, the difference between the direction of true north and magnetic north. Which varies by your geographical location and can be found on a marine chart of your locale and probably on your GPS.

The second is called deviation, the difference between the direction of magnetic north
and compass north. Which is caused by the magnetic fields on you vessel and has to be measured for different heading and conditions. (Usually done by a professional compass adjuster)

If your GPS is set to display headings in true then you will have a total difference of variation and deviation between your compass and GPS. If your GPS is set to display magentic courses then you will only have deviation to contend with.

Perhaps you could give us some more information about the type of vessel you have and the brand/model of your GPS unit.

Re: GPS Issue

In San diego you are probably at 12-13 degrees East declination. Your compass will point to magnetic north. If you GPS is set to true north you will be that many degrees off. Also you don't mention the type of boat and how much metal is surrounding you in the boat. An lastly there is always the possibilty (though I have never seen it happen on water) that the area you are in is surrounded by high walls of rock containing a lot of iron. I used to survey for timber sales and have found areas that you will not get an accurate compass reading in no matter waht you do.