What's this blue arrow on my plotter screen?

[Deleted User YDKXO]

This blue arrow has appeared on my Raymarine E120 plotter screen this year for no apparent reason (I haven't updated it or anything). It only appears when following a route and always points in the same direction ie to starboard relative to the direction of travel. Anybody know what it means?

 

[PeterBoater]

Should be the current but I don't know why it always points on the same side. It works by comparing the heading from the fluxgate compass with the GPS track over the ground; if one or both of these sensors is missing or faulty, I think the arrow can be removed somewhere in the setup menu. However, in your picture it seems to be showing the correct thing; the red heading vector being pushed to starboard by the current to give the green track over the ground (not an elegant description but I hope you get my drift, boom boom).

 

[Whitelighter]

Is not a tidal vector of some sort?

I've seen that when sailing to indicate actual direction with a tidal push vs heading which is derived from the compass

 

[longjohnsilver]

On mine it's direction of tide, but it always points in the direction I'm travelling. Assume it's a software glitch. Do you get much tide over there?

 

[Deleted User YDKXO]

Do you get much tide over there?

Not enough to spill my G & T

How does the unit know tidal data?

 

[longjohnsilver]

Not enough to spill my G & T

How does the unit know tidal data?

I thought you only drink shandy?

If you go into menu it's one of the options, although you will need to search for it.

 

[jimmy_the_builder]

If it's related to the fluxgate compass, and if you haven't recently made any config or software changes ... have you perhaps stowed something metallic somewhere proximate to the fluxgate compass?

 

[MapisM]

Considering your position on the screen, the route you were following is the green(ish) line, I suppose? You would have soon run aground by following the red one...!
And the red line must be the vector showing where the vessel is heading at any given moment (which is consistent with the orientation of the vessel icon on the screen), right?
If my assumptions are correct, since the arrow appears only while following a route, it would make perfect sense in those conditions as an indicator of the steering direction required to stay on your route.
Otoh, looking also at the track behind you, it seems that you were actually following the route nicely, in spite of the fact that the boat seems to be heading 20+ degrees to port. And obviously, current/tide could NEVER justify that, in this area.
The only possible reason for having the boat (momentarily) heading off course are waves, particularly with a stern sea.
Then again, you said that the arrow is always pointing to stbd, while waves would obviously push the boat (hence the red line) randomly on both sides.
Bottom line, here's my guess: your electronic compass is not calibrated and sends to the plotter a wrong heading.
As a result, the vessel heading (red line) on the plotter is constantly pointing to port of your real heading.
And when you set the plotter to follow a route, it keeps telling you that you must steer to stbd for the very same reason.

It might sound complicated, but I already saw this happening.
And if my guess is correct, a compass calibration is all you need - unless as JTB said you placed something magnetic near the sensor.
Calibration is easy peasy anyhow, just requires going out in calm seas, set calibration mode, and keep turning in slow, large circles - a couple of them usually is enough.
Do you already know when you will be back onboard next time?

 

[Deleted User YDKXO]

Considering your position on the screen, the route you were following is the green(ish) line, I suppose? You would have soon run aground by following the red one...!
And the red line must be the vector showing where the vessel is heading at any given moment (which is consistent with the orientation of the vessel icon on the screen), right?
If my assumptions are correct, since the arrow appears only while following a route, it would make perfect sense in those conditions as an indicator of the steering direction required to stay on your route.
Otoh, looking also at the track behind you, it seems that you were actually following the route nicely, in spite of the fact that the boat seems to be heading 20+ degrees to port. And obviously, current/tide could NEVER justify that, in this area.
The only possible reason for having the boat (momentarily) heading off course are waves, particularly with a stern sea.
Then again, you said that the arrow is always pointing to stbd, while waves would obviously push the boat (hence the red line) randomly on both sides.
Bottom line, here's my guess: your electronic compass is not calibrated and sends to the plotter a wrong heading.
As a result, the vessel heading (red line) on the plotter is constantly pointing to port of your real heading.
And when you set the plotter to follow a route, it keeps telling you that you must steer to stbd for the very same reason.

It might sound complicated, but I already saw this happening.
And if my guess is correct, a compass calibration is all you need - unless as JTB said you placed something magnetic near the sensor.
Calibration is easy peasy anyhow, just requires going out in calm seas, set calibration mode, and keep turning in slow, large circles - a couple of them usually is enough.
Do you already know when you will be back onboard next time?

Actually we had just stopped to view some dolphins when the photo was taken so that is probably why the boat appears to be heading off track. Ordinarily the boat follows the autopilot very well and the electronic compass is always consistent with the magnetic compass on board and the course to waypoint given by the plotter so I don't believe there is any intereference with the fluxgate compass and I don't believe that it needs calibrating. The fluxgate compass is very well situated out of the way of any other components so I'm pretty confident that there are no nearby sources of interference

No the blue arrow cannot be an indication that the boat is off track because it always points to starboard even if the boat is to the starboard side of the track; I checked that. The other puzzling thing is that it has appeared this season; I certainly didn't notice it last season

 

[benjenbav]

I believe it may be the Daily Mail App if it is telling you always to turn right.

 

[BartW]

How does the unit know tidal data?

the Navionics data card , (is that what you have ?) also has tidal info (the card on my Karnic does)
but I have no clue if this has anything todo with your blue arrow

 

[Deleted User YDKXO]

I believe it may be the Daily Mail App if it is telling you always to turn right.

I think you might have got it there, bjb. I have noticed that the blue (it would have to be blue wouldn't it!) arrow has got appreciably larger since JC was elected

 

[Lightning]

I have an E80 (on a sailing boat ) but don't imagine there is no difference between the 80 and 120 (apart from screen size)

The red line is the ships heading (from the heading sensor)
The green line the the course over ground (derived from GPS input)
the blue arrow is a tidal vector
and if you switch it on (and have wind input) there is a yellow arrow showing wind direction.

If you press the round "data" button (top right) then press the "chart vectors" one of the soft keys at the bottom. You will then get the options to switch the various vectors on and off.

Maybe it has been switched on by accident.

If the course over ground and heading vectors are vastly different when you are travelling then I would suggest the you need to re-calibrate the heading sensor. However, if, as you indicate you had stopped and were drifting, then I would imagine that would result in the difference shown on your screen.

 

[MapisM]

it always points to starboard even if the boat is to the starboard side of the track; I checked that.

Fairenuff, there goes my theory. Daily Mail App it is, then!

As an aside, less than a couple of weeks ago, while cruising together Pinnacle and his wife, a trio of flippers welcomed us in the very same area, came to play with our bow for a while, and one of them even greeted us with a full jump out of the water, before leaving!
Nice to hear that you spotted some around there, because we never saw them before in that spot, or anywhere else in the shallow waters of Sant'Antioco Channel, for that matter.

 

[MapisM]

the blue arrow is a tidal vector

If that's what it is, I'm not sure I would trust it a lot.....
Aside from the fact that tides are close to nothing where Deleted User is now cruising, the fact that the arrow always points to stbd makes it pretty much useless regardless of what it's supposed to mean.
I could as well attach a sticker with an arrow on the screen of my older plotter, and pretend to have upgraded it to an E120.....

 

[Croftie]

I believe the thickness of the line indicates the tidal strength. The thicker the line the stronger. As yours always points to starboard and is thick I suspect tidal info is not available and its just showing a default value.

 

[Deleted User YDKXO]

As an aside, less than a couple of weeks ago, while cruising together Pinnacle and his wife, a trio of flippers welcomed us in the very same area, came to play with our bow for a while, and one of them even greeted us with a full jump out of the water, before leaving!
Nice to hear that you spotted some around there, because we never saw them before in that spot, or anywhere else in the shallow waters of Sant'Antioco Channel, for that matter.

In fact we saw them twice this weekend on separate trips in that same location and like you say, we haven't seen them in that area before this year. I was wondering if the recent mistrals had caused currents which had blown some tasty fish into that area? We saw some agitated sea conditions there where it seemed that the south east going currents going around the west side and east side of the island met up

Probably thats rubbish of course and actually the dolphins just got lost

 

[nickd]

As i understand it the blue tidal vector is worked out by the plotter by looking at bearing, actual heading, wind speed and direction, COG and SOG and adding that lot up the tidal vector is then the diffrence between them all.
The reason I assume this is becuase my speed log is barnacled up and so my speed through the water was always 0 as far as the instruments were concerned, so then when sailing as 5 knots SOG it would give me a tidal arrow pointing dead a head of 5 knots, as it new i was moving at 5 knots but also though I was not moving through the water so it has to assume that the water is moving in my direction at 5 lnots as well.

 

[Deleted User YDKXO]

If you press the round "data" button (top right) then press the "chart vectors" one of the soft keys at the bottom. You will then get the options to switch the various vectors on and off.

Maybe it has been switched on by accident.

Ah now that is a possibility! It could be that I or somebody else has been playing with the plotter and inadvertently pressed a button. Thanks I'll take a look at that the next time I'm out there

 

[MapisM]

Probably thats rubbish of course and actually the dolphins just got lost

Haha, yeah, possibly.
Time will tell, I suppose. I will keep an eye around when scubaman will come in Oct, I'm sure his kids would love to spot those creatures!