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Author Topic:   GPS Receiver Mounts
1985supersport15 posted 05-13-2008 12:00 PM ET (US)   Profile for 1985supersport15   Send Email to 1985supersport15  
I have a 1985 Boston Whaler SUPER SPORT 15. [I want to mount the] GPS receiver directly on top of the dashbord. [Do I] need a stem to raise [the GPS receiver] above steering wheel and siderail to prevent interference?
Chuck Tribolet posted 05-13-2008 06:22 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
It will probably work OK. I used to run my old Garmin 175
that way. It worked fine. I later acquired an external
antenna for it, and got stronger signal bars with the


jimh posted 05-13-2008 08:04 PM ET (US)     Profile for jimh  Send Email to jimh     
The GPS receiver needs to have a clear view of the sky. Metal objects such as cockpit railings are opaque to radio signals. It is unlikely that you will have much trouble receiving signals using the mounting you describe. Most satellite signals are at elevations above 15-degrees.
1985supersport15 posted 05-13-2008 11:06 PM ET (US)     Profile for 1985supersport15  Send Email to 1985supersport15     
I see, I appoligize if I did not make clear that it is an external GPS reciever. If most satellites are above 15 degrees I should be ok without a stem mount to elevate the receiver a few inches?

The railings and steering wheel will not effect the device only "ovehead" obstructions would?

davej14 posted 05-15-2008 07:58 AM ET (US)     Profile for davej14  Send Email to davej14     
There is no way to definitively answer your question. The best solution for you is to try various locations before you drill the mounting holes. In my case, using an external antenna from Lorance, there was a very significant difference between mounting it to the dash of my Dauntless vs the rail above the windshield. In fact, WAAS reception was not possible with the antenna mounted directly to my dash.
jimh posted 05-15-2008 04:07 PM ET (US)     Profile for jimh  Send Email to jimh     
The look angle to the geo-stationary satellites which transmit the WAAS signals are much lower than most of the GPS satellites. The position of the geo-stationary satellites for WAAS is quite far west, so in the eastern United States, and particularly as you go north, the look angle to the WAAS satellites becomes quite low.

WAAS Satellites
ANIK F1 107.3°W
GALAXY 15 133°W

You can calculate your look angle to them using

For example, if you are located near Bar Harbor, Maine, your look angle to GALAXY 15 is

Latitude: 44.388°
Longitude: -68.204°
Look angle
Azimuth: 251.8°

An elevation of only 9-degrees could be a problem for an antenna mounted down on the helm console surface.

On the other hand, if you are in San Diego, the elevation is 48-degrees. That is much less likely to be blocked at the helm console level.

The GPS satellites pass over at much higher angles.

davej14 posted 05-16-2008 12:02 AM ET (US)     Profile for davej14  Send Email to davej14     
Thank you Jimh, this is a good explanation of why we are seeing differing results from people with the same or similar equipment. I did not realize that the geographical location was such a large factor.

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