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  #1  
Old 10-07-2009
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XM satelite weather on SMALL chartplotters????

Anyone using XM sat. weather on 'small' chartplotters (4x5" screens)?
If so is the 'resolution' of the XM 'overlay of data' readable (good visual resolution?)

I use a Garmin 454 and am wondering if the XM service will be 'useful' on such a small screen.

Any advice or experience (with SMALL screen chartplotters) would be greatly appreciated.
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I had it for a while on a GPSmap 478 - cancelled the service. Just not worth it. Expensive and clunky compared to GRIBs on a laptop. Your concern is exactly correct - that on the small screen the animations and wind maps are just not that good (IMO), of course the 478 is even smaller than yours. Not sure what to do with the Garmin XM antenna now. It's a GXM30, not a bad paperweight.

If you carry a laptop on board, downloading GRIBs is far more useful and effective.
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I'd say the answer depends on how you use your boat and what you expect to get from the XM.

I have a Garmin 396 with XM weather which is an Aviation unit and my weather subscription is aviation specific also, but I still find it useful on the boat from time to time. Advanced warning of convective weather is of interest to me both when flying and when sailing. I don't find it very helpful for deciding if the wind will be better on one side of the Chesapeake than the other.

That said, the subscription is expensive and I don't know that I'd be willing to pay for it just for the boat, since I nearly always have the option of staying at the dock if the weather is iffy. It makes a huge difference in the airplane where I cover several states in a few hours and have the ability to navigate around isolated convection though.
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Is the 'resolution' of the XM downlinking 'good enough' to interpret the symbols clearly on a 396??

Do you find the XM (GRIB?) data 'real time' or delayed (if delayed, any idea how much delay?)? This is for open ocean usage and would (if with good visual resolution, etc.) be better than downloading WeFAX, waiting for SSB/Ham etc. forecasts (?) especially when VHF (NOAA, etc.) , etc. transmissions are impossible due to the distances.

GRIB - I guess I really dont know how to download GRIBs .... any sources you can recommend (of course I have a "Mac" so I'd need something compatible for that OS platform. - thanks.

Last edited by RichH; 10-07-2009 at 07:09 PM.
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Old 10-08-2009
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Quote:
Originally Posted by RichH View Post
Is the 'resolution' of the XM downlinking 'good enough' to interpret the symbols clearly on a 396??

Do you find the XM (GRIB?) data 'real time' or delayed (if delayed, any idea how much delay?)? This is for open ocean usage and would (if with good visual resolution, etc.) be better than downloading WeFAX, waiting for SSB/Ham etc. forecasts (?) especially when VHF (NOAA, etc.) , etc. transmissions are impossible due to the distances.

GRIB - I guess I really dont know how to download GRIBs .... any sources you can recommend (of course I have a "Mac" so I'd need something compatible for that OS platform. - thanks.
My response is based on the assumption that you are speaking of the nextrad specifically when you ask about latency and resolution of XM. There is always latency due to the time it takes to create a nextrad image. These images are created by multiple passes of the radar at different elevations and then assembled to create a top to bottom picture of the radar return. Then the automation has to assemble the data from several radars to create a mosaic of large areas. This process creates a delay of up to several minutes. Then there is the latency of the delivery system. When I get a fresh image on my 396, my assumption is that picture is 5-10 minutes old when I first see it. That makes a big difference when you are moving 165 miles an hour and the storm is moving at 30 mph, but is probably insignficant on a sailboat.

For me the resolution and animation features are plenty good enough to determine if the weather will be close, far or dead on top of me. I've twice altered my plans this year based on what XM has shown me. Once pulling anchor and motoring back the marina at night to avoid a serious line of convection (red is bad, purple is scary). We got tied up in our slip around 11:30 PM and the storm hit a little after midnight.

I can't comment on the other boating specific weather products since my subsciption provides aviation specific land based data. The symbologly used for aviation gives me a quick intuitve understanding of weather observations along my route and I can quickly zoom in to get a text report if I want more detail.

If you're going to have a Mac aboard you may want to see if there is a product to put XM on a PC based chartplotter. That way you'd get a much larger screen dispay and I don't really see the need for weather at the helm anyway. Its more about planning than tactics so having it available at the nav station seems adequate to me.

Lastly and most importantly for your offshore sailing, you'll want to check the coverage area of the XM sattelites. They cover CONUS and some distance offshore but are NOT global.

hth
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Quote:
Originally Posted by RichH View Post
GRIB - I guess I really dont know how to download GRIBs .... any sources you can recommend (of course I have a "Mac" so I'd need something compatible for that OS platform. - thanks.

Go to saildocs.com and download their Viewfax grib viewer. Also get documentation from their site. Evans Starzinger also has info at his site, I think it's BethandEvans.com

It's amazingly simple, for example, you just send an email to query@saildocs.com with something like the following:

send gfs:40N,45N,65W,72W|0.5,0.5|0,6,12,18,24,30,36,42, 48,54,60,66,72,78,84,90,96|WIND

This will request data on a 1/2 degree grid over the area covering 40-45N, 65-72W (happens to be an area I cruise, southern new england to maine and nova scotia), requesting wind predictives in 6 hour increments. There is other data, such as pressure and wave height, available, but I find wind most useful for route planning.

The GRIBs are free, are very small files, and the saildocs email robot responds very quickly, usually a minute or so. Their viewer is simple but very useful, however the GRIBs can also be used by many PC navigation programs.
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Quote:
Originally Posted by sahara View Post
Go to saildocs.com and download their Viewfax grib viewer. Also get documentation from their site. Evans Starzinger also has info at his site, I think it's BethandEvans.com

It's amazingly simple, for example, you just send an email to query@saildocs.com with something like the following:

send gfs:40N,45N,65W,72W|0.5,0.5|0,6,12,18,24,30,36,42, 48,54,60,66,72,78,84,90,96|WIND

This will request data on a 1/2 degree grid over the area covering 40-45N, 65-72W (happens to be an area I cruise, southern new england to maine and nova scotia), requesting wind predictives in 6 hour increments. There is other data, such as pressure and wave height, available, but I find wind most useful for route planning.

The GRIBs are free, are very small files, and the saildocs email robot responds very quickly, usually a minute or so. Their viewer is simple but very useful, however the GRIBs can also be used by many PC navigation programs.
How are you sending email while offshore?
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