GPS wipeout by ferry!

[al40]

Just spent 2 glorious weeks cruising the west coast of scotland. One thing I noticed (it happened 3 times) was that when I passed close in front of a ferry or other large ship, the GPS stopped working!

It's a lowrance 3500C Plotter with the remote LCG-2000 antenna (which is the actual GPS receiver). When I got near the front of said ship, I got a position lost message followed by a "cannot communicate with antenna"

I can only assume that the radar on the ferry caused the antenna to lock up! I know they have powerful radar sets but never thought they could cause sufficient disturbance to cause latch-up of a GPS antenna!

Anyone else seen this problem?

[geoffs]

Normally when you get too close to something big you start loosing satellites and might lose lock if you get too close. Radar and GPS operate on widely differing frequencies, so interference should not occur, although mounting a gps antenna directly in the beam of a radar is not good, but this is then more down to massive RF power beiing forced in!

Never seen a unit say it cannot communicate with antenna as you are seeing unless there was a fault and then it tends to be permanent.

If you get the opportunity to try this again, get the satellite page up prior to getting close and see if the unit is just giving a duff message and should really be telling you that it cannot see where it is. You should see the same thing if you get up under a cliff or sea wall, but without the possibility for interference, if you do not the I suggest you speak to Lowrance and ask their opinion.

[al40]

I don't think I was close enough for the superstructure of the boat to cause any sat visibility issues and each time (it happened 3 or 4 times), the unit stopped working when I passed in front of the boat / ferry.

If it was the boat blocking the sats this would indeed cause a loss of position but would not cause the communication problem between the Antenna and GPS. Doing a power off / on solved the issue which is why I think it was the radar effectively causing the antenna to lock up. I believe that ferries introduced some form of low looking radar as well as longer range so they could see boats close to the bow and assume this must be the culprit (ie radar zapping the antenna).

Interesting!

[codprawn]

I remember there being a case in one marina where nobody could get sat lock - turned out to be an active tv aerial............

[MarkM]

Is the LCG-2000 getting the voltage directly from the 3500c or from the battery? You can see that by the wiring.

I have the 7000c with the same problem. Questions asked at several forums in the USA and Lowrance. Answer was: the new areals have the voltage directly from the battery. The older ones (my areal is the LGC-12W) from de Lowrance unit itself. Sometimes the voltage for the areal drops to 11 volts which is not enough.
New areals don't fit the older units.

So I cleaned out all the connections, sprayed contact spray (not WD40!) and made a direct connection from battery to 7000c.
The voltage in the 7000c is now 13,9 and on the connection to the areal 11,87. And that works fine.
When the voltage on the screen of the 7000c drops to 11,6 the connection is gone. The areal gets even less at that moment.

[SeaSkills]

Originally Posted by al40

when I passed close in front of a ferry or other large ship,

Nothing to do with GPS, but can't help commenting that this is not generally recommended - it's just not a good place to be

[al40]

Originally Posted by MarkM

Is the LCG-2000 getting the voltage directly from the 3500c or from the battery? You can see that by the wiring.

I have the 7000c with the same problem. Questions asked at several forums in the USA and Lowrance. Answer was: the new areals have the voltage directly from the battery. The older ones (my areal is the LGC-12W) from de Lowrance unit itself. Sometimes the voltage for the areal drops to 11 volts which is not enough.
New areals don't fit the older units.

So I cleaned out all the connections, sprayed contact spray (not WD40!) and made a direct connection from battery to 7000c.
The voltage in the 7000c is now 13,9 and on the connection to the areal 11,87. And that works fine.
When the voltage on the screen of the 7000c drops to 11,6 the connection is gone. The areal gets even less at that moment.

That's a very good point! The voltage drop on the instrument itself (through it's own wires) is significant - 0.4v between bright and dim on the display so I guess the antenna will also suffer. Mine is connected directly to the instrument. I'll maybe have a quick chat with Lowrance UK before doing this but it's a good suggestion

[al40]

Originally Posted by SeaSkills

Nothing to do with GPS, but can't help commenting that this is not generally recommended - it's just not a good place to be

It's all relative! Ferries are big so anything seems close. I agree that being directly in front of a ferry is not a good place to be but it's always been what I would deem to be "safe" proximities. When entering or leaving busy harbours or ports (like Oban for instance), the chance of meeting a ferry in the relatively narrow channel is high and even if off to port or starboard, you can still end up "ahead" of the ferry in terms of it's low level radar (without crossing in front of it's bow)! As mentioned, this happened 3 or 4 times. One of them I was on a morring eating fish&ships when the ferry passed in front of me!

[jyasaki]

Radar sets, especially larger units, have been been known to scramble (and in some cases, kill) GPS antennas. The older Lowrance units (early LGC-2000's especially) were prone to this (later ones were hardened a bit, I think; then they went to LGC-3000's.)

Don't know if any other manufacturers were subject to problems from this.


jky

[codprawn]

Originally Posted by jyasaki

Radar sets, especially larger units, have been been known to scramble (and in some cases, kill) GPS antennas. The older Lowrance units (early LGC-2000's especially) were prone to this (later ones were hardened a bit, I think; then they went to LGC-3000's.)

Don't know if any other manufacturers were subject to problems from this.


jky

I wouldn't be suprised - it can be a pretty powerful signal - look at the way TV broadcasts are often distorted when the reporter is near a warship or whatever.

[Jon.esp]

I know it’s not about being wiped out by a ferry but where did you go during your 2 weeks? I’ve put a thread up http://rib.net/forum/showthread.php?t=25754 and I guess you have just been to the part of the coast I am looking about. Any pictures, details on moorings, fuel, B&Bs, Pubs, camping etc would be great. I’m driving up there in a week to spend a couple of days looking around.

[al40]

Originally Posted by jyasaki

Radar sets, especially larger units, have been been known to scramble (and in some cases, kill) GPS antennas. The older Lowrance units (early LGC-2000's especially) were prone to this (later ones were hardened a bit, I think; then they went to LGC-3000's.)

Don't know if any other manufacturers were subject to problems from this.


jky

I still need to talk to lowrance about this when I get a mo. Will post any response I get!

Thanks.

[al40]

Originally Posted by Jon.esp

I know it’s not about being wiped out by a ferry but where did you go during your 2 weeks? I’ve put a thread up http://rib.net/forum/showthread.php?t=25754 and I guess you have just been to the part of the coast I am looking about. Any pictures, details on moorings, fuel, B&Bs, Pubs, camping etc would be great. I’m driving up there in a week to spend a couple of days looking around.

We were based just outside benderloch. Loads of campsites round there as well as pleanty around oban.

Places visited were (in no particular order):
- Tobermory (kids wanted to go to Balamory)
- Lismore and then craignure (mull)
- Connel bridge and loch etive (awesome playing in the falls of Lora)
- Easdale and Oban

plus general playing about.

Easdale has a great pub / restaurant on the water with good food.
Oban - pleanty options
Mull - Craignure again has pub that dores reasonable food
Tobermory - Lots of choice (some better than others) and the infamous mishnish!

For fuel - Pleanty garages about, although fuel on mainland is significantly cheaper than on mull. Oban being the cheapest.

Launching - puffin dive near oban I believe is a good places. Many of the campsites have slipways.

Haven't yet got any real photo's off the camera yet but it's a really nice cruising ground.

[Tony Hill]

We have also come across this as a problem. message GPS module not responding. On some occasions a full reboot will start the unit functioning. Other times one must resort to disconnecting the GPS module then reconnecting it with screen power off.
We are using Globalmap 7500, Lowrance 110C and Lowrance 112C. Problem is across these units.
I would be interested in what Lowrance have to say and how to prevent it

We are fortunate to live and work at Easdale mentioned above. The Puffer Bar/Restaurant/Tearooms have just been refurbished and are now under new ownership. The harbour at Easdale Island is an ideal stop off/somewhere to visit. It is very sheltered with plenty of space to tie up alongside. Clyde Cruising Club replaced the channel markers last winter. There is new B&B available at Garragh Mhor tel 01852 300513
You can launch at Ellenabeich (Easdale mainland side) across the stones but you do need a 4 x 4 and it is not really suitable for large heavy RIBs. There is plenty of trailer parking space in the back car park but it is worth noting that the ferry ramps are in constant use so one needs to tie the RIB up on the end wall and just avoid the ferry ramp.
Tony Hill

[al40]

Originally Posted by Tony Hill

We have also come across this as a problem. message GPS module not responding. On some occasions a full reboot will start the unit functioning. Other times one must resort to disconnecting the GPS module then reconnecting it with screen power off.
We are using Globalmap 7500, Lowrance 110C and Lowrance 112C. Problem is across these units.
I would be interested in what Lowrance have to say and how to prevent it

We are fortunate to live and work at Easdale mentioned above. The Puffer Bar/Restaurant/Tearooms have just been refurbished and are now under new ownership. The harbour at Easdale Island is an ideal stop off/somewhere to visit. It is very sheltered with plenty of space to tie up alongside. Clyde Cruising Club replaced the channel markers last winter. There is new B&B available at Garragh Mhor tel 01852 300513
You can launch at Ellenabeich (Easdale mainland side) across the stones but you do need a 4 x 4 and it is not really suitable for large heavy RIBs. There is plenty of trailer parking space in the back car park but it is worth noting that the ferry ramps are in constant use so one needs to tie the RIB up on the end wall and just avoid the ferry ramp.
Tony Hill

This will be one of your vessels I guess :-)

I'd mirror the comments above re Easdale - we visitied the island by boat and mainland by car. Island has great sheltered harbour with pleanty space to tie up!

Still haven't contacted Lowrance yet.. busy week.. but will post reply when I do