Honing in on a waypoint

[Tone357]

Why is that when I point my heading sensor at a waypoint, the closer I get, the more it seems to move? As I get closer, I have to make major adjustments in steering to try to run straight over it. Is this the normal?

[Jig_Man]

I think it is a speed thing and how a gps functions.

[bobcoy]

If you have a working HS(no magnetic interference and installed and calibrated properly) and you display the heading sensor projection(Orange on Solix or Purple on Helix) not Green because that is not accurate on slow speed(COG) is computed by the GPS. The heading sensor gives you the actual bearing the boat is headed and if you line the waypoint up it will not seem like the waypoint is moving around. Unlike the results you get using the COG projection.(Green) Bob

[Tone357]

If you have a working HS(no magnetic interference and installed and calibrated properly) and you display the heading sensor projection(Orange on Solix or Purple on Helix) not Green because that is not accurate on slow speed(COG) is computed by the GPS. The heading sensor gives you the actual bearing the boat is headed and if you line the waypoint up it will not seem like the waypoint is moving around. Unlike the results you get using the COG projection.(Green) Bob

I have verified that I do not have any magnetic interference Bob, but after looking for info on calibrating the HS. I can find nothing on it. Can you point me in the right direction?

[G48]

I have verified that I do not have any magnetic interference Bob, but after looking for info on calibrating the HS. I can find nothing on it. Can you point me in the right direction?

Calibration, at least the way I did it, was to turn on the green line (COG) along with the heading line at the same time. Find a calm area otw, no wind , waves or current and idle at 4.5 mph. I turn the cog and heading data boxes on my chart screen and if the conditions are right and both degrees match then your heading sensor will be calibrated. I don't know of any way to mechanically calibrate an AS GPS HS puck. If there is I would be interested. Depending on how far off the degrees are from matching should indicate an issue with magnetic interference or the puck alignment with the keel of the boat is off. The solixes do have a heading offset to help line up the HS line. Downside is it resets every time u power down and restart.

[bobcoy]

Tone, I will look later for a page #, basically you drive in a straight line on a calm day at over 4.5 MPH and match your Heading to the COG using the heading offset to make them the same. Bob.

[Wayne P.]

I have verified that I do not have any magnetic interference Bob, but after looking for info on calibrating the HS. I can find nothing on it. Can you point me in the right direction?

Manual page 22------GPS Receiver and Heading Sensor Installation Guide (johnsonoutdoors.com)

[bobcoy]

Thanks Wayne. The Solix specific pages are 24 & 25

[SLYDoggie]

There are some really good suggestions above but, be aware that your Waypoint will actually be off by the distance between your GPS source and the transducer you are using at the time. The closer the GPS source to the transducer, the more accurate Waypoints will be. Also, be aware that the amount of error will depend on which direction you are approaching the waypoint from compared to the direction you were going when the waypoint was created. If you are approaching from the exact opposite direction in which the Waypoint was created, then the error will be double the distance from the GPS source to the transducer. All that is in addition to the normal GPS error factor.

[bobcoy]

The key is it seems to move around. With an inaccurate waypoint you can go directly to the inaccurate waypoint. Your target just won’t be where its marked. Without the HS each steering correction will be a little late and wrong. Seems like a moving target.

[Tone357]

The key is it seems to move around. With an inaccurate waypoint you can go directly to the inaccurate waypoint. Your target just won’t be where its marked. Without the HS each steering correction will be a little late and wrong. Seems like a moving target.

That's the issue I'm having right now with the HS installed. I seem be trying to hit a moving target! Thanks for the help guys!

[picollen]

I understand the normal error factor but what you are saying doesn't make sense to me. I've marked fish cribs many times and have approached from all different directions and when I hit the waypoint on my map sure enough, the brush pile is on my sonar... GPS coordinates are what they are so why would the direction of the approach affect the accuracy of the coordinates? If you think about military applications (I get that they have better technology) using this theory wouldn't the direction of the missle have to be the same each time???

[Wayne P.]

I understand the normal error factor but what you are saying doesn't make sense to me. I've marked fish cribs many times and have approached from all different directions and when I hit the waypoint on my map sure enough, the brush pile is on my sonar... GPS coordinates are what they are so why would the direction of the approach affect the accuracy of the coordinates? If you think about military applications (I get that they have better technology) using this theory wouldn't the direction of the missle have to be the same each time???

The GPS antenna's location in relation to the sonar transducer's location affects the Waypoint that is created. For a sonar waypoint to be accurate, the GPS antenna has to be where the sonar transducer is. ANY error you create with a location difference between the two is doubled when approaching from the opposite direction than when created. Sonar doesn't not locate a waypoint, GPS does.

[SLYDoggie]

I understand the normal error factor but what you are saying doesn't make sense to me. I've marked fish cribs many times and have approached from all different directions and when I hit the waypoint on my map sure enough, the brush pile is on my sonar... GPS coordinates are what they are so why would the direction of the approach affect the accuracy of the coordinates? If you think about military applications (I get that they have better technology) using this theory wouldn't the direction of the missle have to be the same each time???

Yeah, commercial GPS is a different animal from military GPS.

I don't know if I can explain it well in words but will try. For this example, I will assume that the GPS is 100% accrurate and that there is no random error...

When you create a waypoint, the transducer is over the "thing" but the waypoint is created where the GPS Source is located. Let's assume you are using the GPS Source from your unit at the helm but the transducer is on the Transom and it is 8 foot away from the helm unit. Let's assume you are approaching the "thing" from the south. When you create the waypoint, it will actually be located 8' to the north of the "thing" because you already passed over it with the GPS source.

Now let's assume you want to revisit the waypoint but you are approaching it from the north. When your unit says you are over the "thing" it will be 16 feet until the transducer is once again over the "thing" and you see it on your screen... the original 8' error as well as an additional 8' error because the transducer still hasn't arrived at the "thing".

This is the reason many people have a GPS/Heading Puck on Both the front and back of the boat. The front one is used when you are using a Trolling Motor Transducer and the rear one is used when you are using the transom transducer. Getting the GPS Source as close to the Transducer as possible will greatly reduce or eliminarte this error.

Hope this makes sense.

[picollen]

Yes it does. Thx for the explanation…

[JFB]

The GPS antenna's location in relation to the sonar transducer's location affects the Waypoint that is created. For a sonar waypoint to be accurate, the GPS antenna has to be where the sonar transducer is. ANY error you create with a location difference between the two is doubled when approaching from the opposite direction than when created. Sonar doesn't not locate a waypoint, GPS does.

Wayne, here’s a question relative to your statement about “the gps antenna has to be where the sonar transducer is”… I have a Helix on the bow of my boat but I use it only for a chart screen view and do not have the Minn Kota us2 universal transducer connected nor do I have an external transducer. So I don’t have a transducer up front but I do have a heading sensor pick up front and connected to the bow unit. I have a Si transducer at the rear of the boat connected to my console helix. Does this mean when I press mark at the bow (because I don’t have a front transducer connected) that the gps is reading the rear SI transducer?

[CatCanDoo]

Not to answer for Wayne, but I think he is saying the transducer and GPS antenna need to be close because you are typically marking something that you are looking at on the sonar return as you mark it. For example, I see a tall stump on my bow graph and want my GPS antenna as close as possible to the transducer where I see the stump when I mark it.

[Wayne P.]

Wayne, here’s a question relative to your statement about “the gps antenna has to be where the sonar transducer is”… I have a Helix on the bow of my boat but I use it only for a chart screen view and do not have the Minn Kota us2 universal transducer connected nor do I have an external transducer. So I don’t have a transducer up front but I do have a heading sensor pick up front and connected to the bow unit. I have a Si transducer at the rear of the boat connected to my console helix. Does this mean when I press mark at the bow (because I don’t have a front transducer connected) that the gps is reading the rear SI transducer?

GPS has nothing to do with any sonar, so it does not "read" any transducer.
When you push the MARK button, the unit creates a Waypoint where the GPS antenna is or where you move the position curser from the GPS antenna position to a location, but is in relation to the GPS antenna's physical location.

To create an accurate sonar based waypoint on the SI view of the bow unit, the bow unit's GPS source should be the console unit's added external GPS antenna at the transom. GPS and Sonar should be at the same place.

Once the waypoint is created, THEN you can use the bow unit's GPS antenna to locate it, BUT probably won't be displayed on the SI view of the bow unit since the bow's GPS antenna is boat length away from the SI transducer. Basically you can mark a brush pile and use the CHART view to cast to a waypoint's location, but won't see the brush pile on sonar with your setup.

[JFB]

GPS has nothing to do with any sonar, so it does not "read" any transducer.
When you push the MARK button, the unit creates a Waypoint where the GPS antenna is or where you move the position curser from the GPS antenna position to a location, but is in relation to the GPS antenna's physical location.

To create an accurate sonar based waypoint on the SI view of the bow unit, the bow unit's GPS source should be the console unit's added external GPS antenna at the transom. GPS and Sonar should be at the same place.

Once the waypoint is created, THEN you can use the bow unit's GPS antenna to locate it, BUT probably won't be displayed on the SI view of the bow unit since the bow's GPS antenna is boat length away from the SI transducer. Basically you can mark a brush pile and use the CHART view to cast to a waypoint's location, but won't see the brush pile on sonar with your setup.

Would hooking up the us2 built in transducer at my bow help my set up for when I’m standing at the bow and hit mark? (I have an external heading sensor at the bow but currently the closest connected transducer is in the rear).

I plan to eventually get two heading sensors but for when I’m standing at the bow and hit mark, sounds like I still want both a transducer and heading sensor right together.?

[Wayne P.]

Would hooking up the us2 built in transducer at my bow help my set up for when I’m standing at the bow and hit mark? (I have an external heading sensor at the bow but currently the closest connected transducer is in the rear).

I plan to eventually get two heading sensors but for when I’m standing at the bow and hit mark, sounds like I still want both a transducer and heading sensor right together.?

GPS and sonar should be at the same place. The GPS can be a display's internal GPS antenna, an External GPS (AS GRP or AS GPS HS), or iPilot LINK.

Marking a subject viewed on sonar, the GPS antenna needs to be where the transducer is. You can't get an accurate waypoint with a bow unit's GPS antenna (internal or external) viewing SI from another unit that has the SI transducer at the transom.