antenna spacing on a sternrail

[pandroid]

Raymarine will sell you a GA150 GPS receiver, "Ideal for installations where the display is mounted below decks or under a hard top"

Garmin will sell you an under deck mount for their GPS receiver. "Mount your antenna under a fiberglass surface with this under deck mount"

Quote from the Raymarine eS7 MFD Installation instructions:
"Above Decks Mounting : provides optimal GPS performance.
Below Decks Mounting: GPS performance may be less effective and may require an external GPS antenna mounted above decks"

 

[prv]

Raymarine will sell you a GA150 GPS receiver, "Ideal for installations where the display is mounted below decks or under a hard top"

Um, that's exactly my point. They're saying that if you mount the plotter (with integral GPS) below decks or under a hard top, then you might need that separate GPS instead.

Pete

 

[neil1967]

The Furuno GPS will certainly work very well through a thin layer of GPS so try to put it under the deck somewhere, where it will not be damaged.

Tha NASA AIS will probably work ok on the pushpit, but the higher the better.

I think Echomax radar enhancers are the devilish work of a clever British entrepreneur who expertly marketed them to gullible British sailors who are all cultishly obsessed that they are a must-have on their boat. Oddly the rest of the world has never caught on, which is why British yachts can be recognised at great distance by their rugby ball half way up their mast. I stand by with asbestos blanket to be flamed by all the Echomax worshippers who defiantly believe that they are more useful than an AIS transmitter.

Not sure where the rugby ball comes in - an echomax active radar enhancer is a pole antenna, in my case mounted at the top of the mast. As far as I am concerned the echomax and my class B AIS are complementary..........

 

[JumbleDuck]

They're probably expecting the majority of those plotters to be mounted in cockpit binnacles or motorboat centre consoles, though. It's been quite a few years now since most boatbuilders cottoned on and stopped hiding plotters downstairs where you can't use them properly.

You do your passage planning in the cockpit?

 

[JumbleDuck]

Um, that's exactly my point. They're saying that if you mount the plotter (with integral GPS) below decks or under a hard top, then you might need that separate GPS instead.

On the OP's Victoria 800, it ought to be possible to mount the GPS antenna inside the cockpit coaming, which would put it about 2/3 of the way between sea level and aft pushpit height.

 

[lw395]

On the OP's Victoria 800, it ought to be possible to mount the GPS antenna inside the cockpit coaming, which would put it about 2/3 of the way between sea level and aft pushpit height.

And most likely to have somebody sat on it?

 

[prv]

You do your passage planning in the cockpit?

My main passage-planning tools are a paper chart (where I can usually see the whole passage at once at an appropriate level of detail, and step the dividers across it to quickly measure distance), the Imray tides app on my phone, and a suitable pilot book. Of course you can substitute the first two with a plotter, but I don't find it a very convenient way to work - not even for the two years when the plotter was at the chart table because my refit work hadn't progressed to resiting electronics yet.

Pete

 

[JumbleDuck]

And most likely to have somebody sat on it?

Why not? Read my previous posting carefully.

My main passage-planning tools are a paper chart (where I can usually see the whole passage at once at an appropriate level of detail, and step the dividers across it to quickly measure distance), the Imray tides app on my phone, and a suitable pilot book.

Old Skool! Yay!

I do wonder, though, how people without paper charts cope with a plotter on a binnacle at the wheel. Or even people who like to sit down sometimes.

 

[pandroid]

I do wonder, though, how people without paper charts cope with a plotter on a binnacle at the wheel. Or even people who like to sit down sometimes.

The latest plotters allow you to use them from an iPad, which you can do,lying on a bunk if it suits you. Also, with autorouting, you only have to put in the start and end point and the box does the rest. Paper? Pah..

 

[[70521]]

Not sure where the rugby ball comes in - an echomax active radar enhancer is a pole antenna, in my case mounted at the top of the mast. As far as I am concerned the echomax and my class B AIS are complementary..........

+1

One day u want to remove the "rugby ball" from the mast and replace it with an echomax.

I wonder if Ric has read the MAIB report that led to UK yachts adding radar reflectors?

 

[PaulRainbow]

In the same way that you can slap a TomTom on the dash of your car and it will mostly work, but the system on the Merc with an aerial on the roof works better when you drive under some trees or between lots of tall buildings.
You make a choice about going to a bit more effort for a system that has more margin for when conditions are poor.

I drive around all day with a sat nav on the screen, i drive around the countryside, under trees and in built up areas with tall buildings, i never seem to lose the sat lock.

I don't tend to sail my boat under trees or between tall buildings, i don't ever lose the sat fix with that either. Garmin seem to be confident that their GPS receiver will work under a deck, they make an under deck mounting for it. Works for me.

 

[PaulRainbow]

Um, that's exactly my point. They're saying that if you mount the plotter (with integral GPS) below decks or under a hard top, then you might need that separate GPS instead.

Pete

Tut tut Pete, selective quoting

Don't forget the other half of my post, where Garmin say the opposite.

 

[Ric]

+1

One day u want to remove the "rugby ball" from the mast and replace it with an echomax.

I wonder if Ric has read the MAIB report that led to UK yachts adding radar reflectors?

I presume that you have been on the bridge of a reasonably modern ship and have seen the clear radar reflections that come from the smallest craft, even in very rough conditions? Even my 18" Raymarine radar can pick out returns from flags on lobster pots in calm seas, and can easily see a small yacht (without even passive radar reflectors - I have tested this) at around 3 miles in very rough conditions. Active radar reflectors are dinosaur technology. If you really want to be sure that you are visible, fit an AIS transceiver which has less current draw, is easier to fit, and gives far more information to other vessels.

 

[prv]

Don't forget the other half of my post, where Garmin say the opposite.

Sure. If you'd only posted the statement that agreed with your point, instead of the one that explicitly disagreed, it wouldn't have looked so silly

Anyway, we're in agreement that modern GPS antennas work perfectly adequately under fibreglass, even if some of their manufacturers suck their teeth over the practice.

Pete

 

[noelex]

Anyway, we're in agreement that modern GPS antennas work perfectly adequately under fibreglass, even if some of their manufacturers suck their teeth over the practice.

Modern GPS units are fantastic at getting an adequate fix in poor conditions, but give the units a clear view of the sky and they do better.

The advantages of the clear sky view are noticeable in situations such as when trying to determine if the anchor has moved slightly and reducing the incidence of false anchor alarms. The other improvement is the accuracy of COG data which helps tide estimation etc. The chance of getting an SBAS fix in marginal areas is much better. The benefits are greater in adverse conditions such as when a wet deck and sails create some additional attenuation and multipath distortion.

GPS has become our primary navigation instrument. Many boats accept an "adequate" position fix when for only a little more trouble the quality of position could be significantly improved.

Most GPS have some display of quality of the position fix. At least take a good look at these numbers. Even better look at the scatter of the position fix when the boat is fixed in position, such as in a berth. When installing a chart plotter try hooking it up on a temporary basis outside and compare the quality of fix to the same unit inside. This will give you some idea if an external aerial is worthwhile.

Many people are surprised at the difference. This does not have any impact on offshore sailing, but try retracing your steps through a narrow pass, or when trying to detmine if your anchor is slowly dragging and the stable, accurate position of modern GPS unit with a clear view of the sky is nice to have.

 

[yimkin]

I assumed that the GPS antenna had to be mounted externally with the "dome" end uppermost. From various posts it would appear I can mount it below, under the deckhead.
Does it still have to be mounted "dome" upwards or can it be mounted in any attitude including "upside" down? Apologies for the non-tech terminology.

 

[noelex]

Does it still have to be mounted "dome" upwards or can it be mounted in any attitude including "upside" down? Apologies for the non-tech terminology.

The GPS still needs to mounted "dome upwards". Upside down would give poor results.

 

[[70521]]

I presume that you have been on the bridge of a reasonably modern ship and have seen the clear radar reflections that come from the smallest craft

I admit it has been some time since I have been on the bridge of any ship, but if an active reflector is no worse than a passive one why dismiss it?

While I transmit AIS how do I know that on the bridge of the big modern ship they are not filtering out Class B transmissions?

To date I've only been called once on the radio by name due to AIS and that was by the Range Safety Vessel at Lulworth to advise me that they were live firing. I view the use of AIS as a nice add on not an essential, but will be really useful should there be a MAIB investigation into an incident.

Looks like my radar needs updating as I don't have that level of detail on my kit!

 

[JumbleDuck]

Anyway, we're in agreement that modern GPS antennas work perfectly adequately under fibreglass.../QUOTE]

I don't think GRP is the issue with using GPS receivers below decks - it's using them inside a great big hole in the water which causes problems. My GPS72 acquires faster when I stand up in the cabin than if I use it sitting on my bunk, when it's below sea level and therefore inside a conducting cone.

 

[lw395]

Anyway, we're in agreement that modern GPS antennas work perfectly adequately under fibreglass.../QUOTE]

I don't think GRP is the issue with using GPS receivers below decks - it's using them inside a great big hole in the water which causes problems. My GPS72 acquires faster when I stand up in the cabin than if I use it sitting on my bunk, when it's below sea level and therefore inside a conducting cone.

As someone who's measured the performance of a few antennas, GRP can have significant influence.
GRP with lots of rain or heavy spray running over it even more so.

When electronics designers design products with GPS it, it's common to use a ceramic antenna which, in air, is tuned higher than the GPS frequency.
The presence of the plastic case lowers the tuning to the right place.
Those little magnetic gps aerials you can get on ebay are off-tune unless mounted on a big enough metal plate as intended.
By mounting them on a smaller metal plate, you can actually tune them to work really well under a GRP deck.
If your employer lets you use about £30k's worth of test equipment at lunchtime.
And so long as there's not to much water or carbon-based life forms on the deck.
Balsa core is a bit lossy too.