Using a portable GPS at the chart table

[teshannon]

Does anyone have experience with using a portable GPS such as the Garmin 478 at their nav station. I'm wondering if it needs to be taken outside for a clear line of sight to the antenna. I'm looking for an economical backup for my Furuno unit that would also work at the nav station without going to the trouble and expense of mounting a second antenna. Repeaters from Furuno seem to be expensive.

[Diva27]

Originally Posted by teshannon

Does anyone have experience with using a portable GPS such as the Garmin 478 at their nav station. I'm wondering if it needs to be taken outside for a clear line of sight to the antenna. I'm looking for an economical backup for my Furuno unit that would also work at the nav station without going to the trouble and expense of mounting a second antenna. Repeaters from Furuno seem to be expensive.

GPS satellite signals require a clear line of sight, which is why handhelds can be a problem for hikers walking under a forest canopy. They are surprisingly functional if they can get some kind of clear view, even a partial one. I have a Garmin Nuvi 250 in my car, suction cupped to the windshield. It has the car roof obscuring a lot of its signal sightlines, but works fine. If I turn it on inside the house, no dice. I also once used a Garmin handheld in a powerboat pilothouse, feeding data to a laptop nav program. The windshield and side windows were enough to give the unit a look at a necessary number of satellites and I didn't need a separate aerial. Most (or enough) satellites as I recall tend to be within 30 degrees elevation of the horizon. You're not trying to grab a signal from straight overhead. But if your nav station is down below, then you do need an external aerial. Galileo, the new civilian GPS system being assembled by a European consortium, which is supposed to be operation perhaps by 2011(?) I think is supposed to have the ability to deliver signals through solid objects and will be available globally for free. Some new GPS receivers are already being sold with the capability to read the Galileo signals. Maybe the US system will get a similar capability with a new generation of satellites. Others on Sailnet may know better.
For the record, I have a Standard Horizon plotter at my helm, wired to a WAAS aerial on the stern rail. If you're going to use GPS, you'd sure like it to be accurate.

[LWinters]

I use a Garmin 76cs handheld as my backup at the Navstation. To get a good signal I built a small mount for it at the port window which provides plenty of horizon to acquire the requisite satellites. A small cable connects the hand held to my laptop and acts as a plotter while underway. I use Maptech's Chart Navigator Lite that comes with their ChartKits. This makes for a very robust, inexpensive, chart plotting system anytime I need it.

However, the internal hand held antenna is not suitable to pick up satellites through the coach roof. It will need to be able to 'see' some horizon.

[MiVelero]

I have a garmin etrex at the nav station when working with charts and found it unreliable, so I just put it up to the portlite above nav station (smoked plexi) and get good tracking. The same for the laptop antenna, when runing nav software I just secure ant to portlite above navstation and it works great.

[sailingdog]

Teshannon-

The 478 has a bayonet mount antenna, and you can get a remote mounted antenna kit for it. See here. However, you probably won't need it, since the Garmins generally work fairly well in the cabin of a fiberglass boat. I use both a Garmin 276, which is the predecessor to the 478 and a 192c at the nav station on my boat.

If you have any specific questions, let me know.

[k1vsk]

In theory, as others have said, you need an unobstructed view of the sky, however, in reality, my Garmon 492c internal antenna works fine at the chart table so theory isn't always what it appears.

[teshannon]

Thanks everyone for the input. I'll probably get the 478 and since it will be a backup I can move it to the cockpit if I really need it. It would be nice to have a unit at the nav station so if it works there that will be an added bonus. Sd, that antenna looks like it could be the answer if I need it, thanks for the link.

[sailingdog]

Teshannon-

Glad to help.. Done quite a few Garmin installs of different units for friends.

[Diva27]

Originally Posted by sailingdog

Teshannon-

The 478 has a bayonet mount antenna, and you can get a remote mounted antenna kit for it. See here. However, you probably won't need it, since the Garmins generally work fairly well in the cabin of a fiberglass boat. I use both a Garmin 276, which is the predecessor to the 478 and a 192c at the nav station on my boat.

If you have any specific questions, let me know.

I'm impressed you can get these things to work inside a hull. Wonder if cored or uncored decks make any difference. (Sounds like a science project coming on.) And given that you can see sunlight through the hull of my C&C 27, I wonder if the signals on other peoples' experience is coming through an uncored hull, as opposed to the deck. I guess the main thing is that they work.

[sailingdog]

The deck of my boat is about 3/4" thick with an endgrain-balsa core... I have two 4" circles of laminate from the cabintop sitting in the nav console, from when I installed my two solar ventilators.

On a steel boat, or with thicker laminate, the reception inside the cabin might be a problem.