GPS antenna under deck?

[mogmog2]

I need to move the GPS antenna from its current perch on the radar pole (scanner incoming, we bought the boat with a pole clearly designed to take more than a small antenna).
And will be adding an AIS transceiver ere long, so two GPS antennae to place.

If it's not a bad idea, and noting that Garmin state you can put the GPS antenna under a fibreglass deck, I was wondering about doing that and preventing clutter from the pushpit.
It must attenuate the signal a bit, but is it viable in practice? Or is it better to put up with the blighters being at eye height, photobombing a lovely anchorage view?
Function overrides form here, but if it doesn't matter, I'll take form!

I have two possible locations in mind - under the aft side deck beside the (quite high) coaming, or for more effort, in the hanging locker.

Anyone got any experience with any of this?
Many thanks.

 

[FairweatherDave]

My AIS transponder is about a foot above the chart table with built in GPS, and I have another for the DSC radio about 3ft further aft on a shelf along the quarter berth. Both seem fine to me.It is the VHF and AIS antenna that are above decks, mounted mast and pushpit rail respectively .

 

[ProDave]

I now have three GPS receivers under a GRP deck. One built into the nav tablet, one to provide position to the VHF and once for a boat speedometer.

All work well and get a quick position fix.

 

[oldmanofthehills]

My gps is built into chart plotter on control desk thus under cabin roof, and similar one in vhf nearby. Possibly slightly slower to get position than original push pit mounted external gps, but more reliable due to being out of the weather and not connected by long data cable and connections

 

[lustyd]

The main drawback is the time you’ll waste troubleshooting loss of GPS alarms when people sit above them. They do work but if possible it’s better to place them above deck where nothing will get in the way. Humans are full of water so great at stopping radio signals.

 

[FairweatherDave]

The main drawback is the time you’ll waste troubleshooting loss of GPS alarms when people sit above them. They do work but if possible it’s better to place them above deck where nothing will get in the way. Humans are full of water so great at stopping radio signals.

I have never found that an issue time -wise, literally once in a blue moon the radio loses position very briefly. Maydays and radio checks outnumber that issue 100:1. Compared to the cost of a weatherproof external GPS and installation I wouldn't worry about it.

 

[Roberto]

Like others, I have 3 or 4 gps antennas under the deck and they all work without problems. I have to replace one antenna which is on the stern gantry but I'll put that as well under the deck, saves dismantling half a boat to pass the cable.

 

[oldmanofthehills]

The main drawback is the time you’ll waste troubleshooting loss of GPS alarms when people sit above them. They do work but if possible it’s better to place them above deck where nothing will get in the way. Humans are full of water so great at stopping radio signals.

The atmosphere is full of water. I think the gps signals frequencies pierce clouds and thus might not be that obstructed by humans even to satellites directly above

 

[mogmog2]

The main drawback is the time you’ll waste troubleshooting loss of GPS alarms when people sit above them. They do work but if possible it’s better to place them above deck where nothing will get in the way. Humans are full of water so great at stopping radio signals.

That was a key concern - the water issue, in people particularly, but also wet side decks washed by seas possibly or even just rain. Which is why I mentioned the hanging locker, as no-one would sit over there as there's also a vent in it. Although outboard of the coaming is no-mans land & no body part would remain there for any length of time, although people's backs could be close, thus forming a partial shield...

 

[Shaz77]

I need to move the GPS antenna from its current perch on the radar pole (scanner incoming, we bought the boat with a pole clearly designed to take more than a small antenna).
And will be adding an AIS transceiver ere long, so two GPS antennae to place.

If it's not a bad idea, and noting that Garmin state you can put the GPS antenna under a fibreglass deck, I was wondering about doing that and preventing clutter from the pushpit.
It must attenuate the signal a bit, but is it viable in practice? Or is it better to put up with the blighters being at eye height, photobombing a lovely anchorage view?
Function overrides form here, but if it doesn't matter, I'll take form!

I have two possible locations in mind - under the aft side deck beside the (quite high) coaming, or for more effort, in the hanging locker.

Anyone got any experience with any of this?
Many thanks.

Do you actually mean GPS or does it receive additional signals. GPS seems to work fine on all phones, car
sat naves etc without an ariel. After all there are no trees or buildings to block the signal out at sea. and for ever kilo you put on the mast you should put 2kilos below the waterline.

 

[Refueler]

My GPS antennas are under deck ...... only when I am alongside a high wall or other obstruction does it ever give any problem.

 

[mogmog2]

Do you actually mean GPS or does it receive additional signals. GPS seems to work fine on all phones, car
sat naves etc without an ariel. After all there are no trees or buildings to block the signal out at sea. and for ever kilo you put on the mast you should put 2kilos below the waterline.

Yes, GPS. I'd not considered that phones' GPS etc works inside these days . I was fixating back to my days in countryside management, when the GPS units struggled if there were more than about two leaves above you

 

[MontyMariner]

When you have got the antenna off the pole, reconnect it and temporarily wedge it in the various favoured locations then look at the satellite signal strengths and make your choice.
I'm assuming that your receiver has the facility to show signal strengths. If not, a phone app such as saildroid has.

 

[oldgit]

Many GPS devices have a page somewhere that will display the satellites within range it can "see" and their signal strengths.
Easy to check if you have "lost" any in a new location.

 

[lustyd]

I have never found that an issue time -wise, literally once in a blue moon the radio loses position very briefly. Maydays and radio checks outnumber that issue 100:1. Compared to the cost of a weatherproof external GPS and installation I wouldn't worry about it.

We chartered a boat once and it happened every 20 minutes took ages to work out

 

[mogmog2]

When you have got the antenna off the pole, reconnect it and temporarily wedge it in the various favoured locations then look at the satellite signal strengths and make your choice.
I'm assuming that your receiver has the facility to show signal strengths. If not, a phone app such as saildroid has.

Good tip, thanks. I'll have a look - not familiar with the kit yet.

 

[samfieldhouse]

My AIS is inside the cockpit coaming and the aerial for the monitoring system is under a bunk cushion. even that works fine. Impressive really.

 

[mogmog2]

Many GPS devices have a page somewhere that will display the satellites within range it can "see" and their signal strengths.
Easy to check if you have "lost" any in a new location.

Thanks, that's a good point. I've seen that on this plotter - one of those pages you flick past on a system that's working ok, as there's nothing you can really do about the number it can see (assuming the antenna is outside). Obviously showing none is helpful, from a diagnostic perspective and our old GPS152 went through a phase of doing that till I replaced the coax connector.

 

[FairweatherDave]

We chartered a boat once and it happened every 20 minutes took ages to work out

I guess I was aware there could be a potential issue when I placed the gps on a 5ft cable from the radio in case I needed to experiment. But it is probably pretty much under where I sit when helming (a little aft of the genoa winch).

 

[dunedin]

Whilst the GPS antenna did seem to generally work below decks, it may depend on precise location and what is above it.
Ours tended to lose signal regularly when we first got the boat. The engineer who investigated recommended moving the antenna to above deck and 10 years later the problem has never recurred.
Must have been something in the structure around the chart table area that impacted the signal.