E-80 MARPA Problem

[offshorebri]

I have a 4 KW open Array, 2 E-80 MFDs 8001 Auto with Fluxgate.......

This has all been hooked up and working fine for years..... I just decided to try using MARPA the past few weeks and I am having problems. If I am stopped in the bay and acquire a moving target it takes maybe 10 seconds and then accurately shows the targets heading and speed.......However, once I start moving it gets all screwed up.....If I get my speed up to the targets speed it shows the target going zero knots with the heading going every which way. If I am going half the speed of the target then the targets speed is also equally half???

I am guising this is not how it is suppose to work??

Any ideas?

Like I said everything else works perfectly with tracking on the pilot, the overlay of the radar and chart, etc, etc.....

[gotumon]

You need some sort of a heading sensor like an AP or an electronic compass that will give you 10 hz update. That would update your heding info 10 time a second as opposed to 1 time a second. That will stabilize the picture and work like a charm.

[millennium]

When the chart presentation is set to relative motion (RM) the Marpa target tracking is as you have been seeing. If you are travelling north at 10 knots and the boat along side you is also travelling north at 10 knots, that boat relative motion to you is zero.

If the chart presentation is set to true motion(TM) the E display will take your boat's motion out of consideration and marpa targets will now show speed and direction over the water.

[marinerjoe]

And to add to what millennium said, if you set your chart plotter to True Motion, it makes it much easier when calling that other vessel because you can give their course and speed. I.e. "Vessel on my port bow at 3 miles on course 270 (or heading west) speed 15 knots, this is the vessel on your starboard bow, channel 16, over." It can reduce or eliminate confusion as to who you're trying to call.

With AIS, however, that can give you a name to call if that vessel's appropriately outfitted...

Joe

[offshorebri]

Originally Posted by millennium

When the chart presentation is set to relative motion (RM) the Marpa target tracking is as you have been seeing. If you are traveling north at 10 knots and the boat along side you is also traveling north at 10 knots, that boat relative motion to you is zero.

If the chart presentation is set to true motion(TM) the E display will take your boat's motion out of consideration and marpa targets will now show speed and direction over the water.

OK I tried this and you are in fact correct.....The only problem is I like running in Head up mode and True motion will not work in Head up only Course up? So if I want what I want, I need to have everything set in Rel Motion and Head up and then to effectively use MARPA I need to switch to Course up and True Motion............

[gotumon]

When you run in head up, relative motion, you get your relative speed to the target.As an example, iif you are running 20 knots and approaching a boat running in much the same direction, you will see a speed of say 6 knots relative. This means that he is running at 14 kts. . By subtracting your known speed and the relative speed, you get the closing speed. IMHO, the vector line is really the most useful feature of the program since it shows how targets are moving in relation to you. I usually turn off the info on the screen since the vector line shows me what I find important.

[capybob]

brian this is what I suspected when we were out the other day - you will have to run in course up true motion mode otherwise you will only get MARPA as relative to your boats motion- let's fish thursday looks like a little window