What's up Dock!

jamesjermain

jamesjermain

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What\'s up Dock!

Yesterday, returning to Cargreen on the Tamar River I lost GPS fix and echo sounder at the exact moment I turned the corner into the long reach past Devonport dockyard. I couldn't regain fix or depth until I was moored up and restarted by chart plotter and sailing instruments.

Devonport is currently host to our friendly, neighbourhood Trident sub plus there was an advanced (Type 23?) frigate entering harbour.

Could these events be linked?

There is a quite scary military police and civilian police presence on teh river at the moment - polite but VERY firm
 
Re: What\'s up Dock!

I saw a notice some time ago about the MOD testing ways of blocking the GPS signal. These were done somewhere in south or mid Wales, I think. Maybe they were using what they had tested?
Allan
 
Re: What\'s up Dock!

[ QUOTE ]
I saw a notice some time ago about the MOD testing ways of blocking the GPS signal./quote]
I heard this mentioned during the Coastguard safety info broadcast while in the West Country.
 
Re: What\'s up Dock!

Of more concern than a general plotter failure, my GPS has twice jumped a few miles in error this season. Since those events I have done regular visual sanity checks against the plotter position.
 
Re: What\'s up Dock!

Not all that unusual, though first time I've heard of a depth sounder being affected!

Our VDO fluxgate compass used to play silly bug*ers with us when we were near the old degaussing set-up operating off Penlee.

I should keep an eye on your dangly bits for a week or two James - you never know.................... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
 
Re: What\'s up Dock!

I've had my GPS jump a few miles once but the RN was no where near. Its possible that you got some form of induced current from a warship radar or HF transmssion but extremely unlikey as you need to be verv very close - the RN call it RADHAZ (Radiation hazard). Once had half my guages on a Lynx helciopter fail just as we took off from the ship - sort of frightening but we were within 10 yds of an HF aerial at the time.
I've hear that the MOD Plods are taking a tougher line recently in the dockyard - must be a new broom in charge and watch out if a nuc ballistic sub is around as they shut the whole port - can't even dive off the foreshore.
 
Re: What\'s up Dock!

Had an e-mail from the club that the all vessel movements in the Port of Plymouth south of the confl. of the Lynher would be prohibited for 2 1/4 hours when Vigilant entered last weekend, is this usual?

I have passed a Trident sub in the Hamoaze previously, just needed to confirm to the modplod escorts that I would stay well clear of the channel. However before all this e-communication I may have been in ignorance of a dockyard order issued.
 
Re: What\'s up Dock!

As far as I know, all 'grey funnel liners' carry specialised RF equipment intended to degrade/distort the local GPS signals out to a classified range/extent, in times of need. One function is to deny an anti-ship missile/munition - being guided 'coarsely' by NAVSTAR/GPS - to get into the 'right ballpark' and close enough for precision acquisition by other, terminal guidance sensors so those final short-range sensors can acquire the ship. It used to be called 'jamming', but is today much more complex.

Don't forget that that's what the GPS system was designed and deployed to do.

Your echo sounder is, of course, a crude sonar device. The fact that it's 'fixed-head' and not directional is unknown and irrelevant to the automated and sensitive sonics suite onboard the sub. You got jammed/zapped.....

Now, the electronic 'boxes of tricks' have to be removed, tested, replaced, retested and calibrated at regular intervals - and when other stuff is being refitted around it, a sub's antennae being quite crowded with bits and pieces. They're not at all likely to advertise exactly when they're doing this, as the low-power but unavoidable RF emanations can be recorded, analysed - and useful stuff learned from the recordings.

/forums/images/graemlins/grin.gif
 
Re: What\'s up Dock!

What would you know about such technical stuff flyboy?

Stick to your compass and almanac /forums/images/graemlins/laugh.gif

/forums/images/graemlins/wink.gif
 
Re: What\'s up Dock!

I suspect it could be more likely that some one in the dockyard was operating a high powered radar, and boaty electronics being, in the grand scheme of things, even from Mr Raymarine, cheap and nasty, your stuff was upset by the radar.
 
Re: What\'s up Dock!

We sit in Mayflower on a couple of survey vessels and our GPS is logged 24/7. There have been no outages or problems with GPS in the last couple of months on any of our six GPS sets that we run.

I would tend to agree that you may have got blatted by a Radar transmission which caused 'things to go a bit wobbly'. Having served in the RN as a weapons tiff I'd say that they are very unlikely to be testing any of this GPS jamming equipment in port, and in any case when and if they do then it would be promulgated due to the fact that it's not only us boaty types in the world who use GPS.
 
Re: What\'s up Dock!

James
Could this be the cause. Taken from Ofcom site.

Dates: 13 to 24 October 2008.
Times: between 09:00 and 17:00 hrs.
Location: Sennybridge Training Area - within 5 km of N52° 01.181’ W003° 36.684’
Contact (during jamming exercise only) - 07766 134520

Peter.
 
Re: What\'s up Dock!

[ QUOTE ]
Had an e-mail from the club that the all vessel movements in the Port of Plymouth south of the confl. of the Lynher would be prohibited for 2 1/4 hours when Vigilant entered last weekend, is this usual?

[/ QUOTE ]

There was a vhf announcement to this effect last Saturday. It sounded like they were closing the whole port of Plymouth for 3 hours or so, but maybe I misheard them.
 
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