Saildocs by Sat Phone

[AlanH]

I just found the saildocs grib request service.

http://www.saildocs.com/gribinfo

I tried it, and lo and behold within 5 minutes of sending in a request for a grib file, I had it. I requested a 24-72 hour grib file like this:

send gfs:20N,40N,120W,160W

send gfs:25N,38N,120W,140W


The first one is basically the whole race course, from Kauai to San Francisco, plus a bit extra on the sides. The Second one is smaller, from 25 deg N 140 W to 38N, 120 W. That's the area where we all make big decisions during a TransPac.

The default give wind speeds and pressure isobars every 4 mbars. File size was 2 kilobytes, which is pretty darned small.

Does anybody have any experience pulling down GRIB files like this with an Iridium phone and a POP mail account, offshore?

 

[tiger beetle]

Check in with Mark/Alchera - you are describing what Mark routinely does, though I cannot be certain if he is using a POP email account.

- rob/beetle

 

[solosailor]

Well if you use a standard email program it could cost a lot in time on the iridium. There is a pc/mac pogram called Xgate that helps to reduce time on the network.

 

[Paul Elliott]

I have been using Xgate with my Iridium satphone for several years and am quite happy with it. I understand that SailMail now also provides a similar optimized connection protocol for satphone connections, and the email tools provided with new Iridium accounts have been improved, but I've got no experience with these.

You might be interested in a write-up I did on the VALIS website, describing my comm and nav setup. I receive gribs from Saildocs, and wxfax charts from the internet, all via the satphone. It takes me about 10 minutes of connect-time to get a big grib, the current surface chart, the 24 and 48-hr surface charts, and the 24-hr wind/wave forecast chart. Here is the URL: http://www.sailvalis.com/specs/CommTech.htm There isn't a huge amount of detail there, but it might be useful.

Paul
S/V VALIS - Pacific Seacraft 44 #16 - Sausalito, California
www.sailvalis.com

 

[AlanH]

Guys, I'm going to be downloading GRIB files once, at most twice during the trip. I will be sending and downloading e-mail from a POP account that nobody but Joan and maybe one other person knows. No spam.

Here's the X-Gate website
http://www.globalmarinenet.net/email.htm

It says right there that a 3 month X-Gate subscription, plus the compression software is $139. There is no one-month X-Gate plan listed.

Let's say that it takes the unlikely length of time of fifteen minutes to download a GRIB file. It takes another five minutes to send a 1,000 word e-mail and download another 1,000 work email. I'm gonna send/pick up e-mail about every third day during the race, or about 5x, maybe 6x.

Total time for downloading GRIB files, twice, is 30 minutes.
Total time for downloading/sending e-mail, 5x is 25 minutes.

Thats' 55 minutes. I will use 55 minutes of airtime during the entire race devoted to e-mail and GRIB file download. At $1.50 a minute that's $82.50
X-Gate costs me $139. It will likely cut my airtime by 2/3rds or thereabouts. That means I'll still be spending 18 minutes of airtime, at $1.50 a minute. That's $27.

So without X-Gate, JUST FOR THE RACE it will cost me $82.50 to do what I want to do.

Using X-Gate, JUST FOR THE RACE it will cost me $156 to do what I want to do.

If I lived on the boat or was out cruising for months, X-Gate would make lots of sense. You bet. Unless I'm missing something, like maybe it's a lot more likely to drop a connection in the middle of the transmission of a 2k file if you're NOT using X-Gate, so that you may waste a lot of airtime only getting half your file....then for this short-term application, I can't see it.

 

[AlanH]

You might be interested in a write-up I did on the VALIS website, describing my comm and nav setup. I receive gribs from Saildocs, and wxfax charts from the internet, all via the satphone. It takes me about 10 minutes of connect-time to get a big grib, the current surface chart, the 24 and 48-hr surface charts, and the 24-hr wind/wave forecast chart. Here is the URL: http://www.sailvalis.com/specs/CommTech.htm There isn't a huge amount of detail there, but it might be useful.

Paul
S/V VALIS - Pacific Seacraft 44 #16 - Sausalito, California
www.sailvalis.com

I looked at your website, and that was very helpful! Here's a quote from it, which is basically a repeat of what you just wrote...

Since we have been using satphone email, we have stopped directly receiving the WFAX broadcasts, and instead receive the WFAX graphics files sent to us by email. Each file is around 30KBytes, and we typically receive four of them: the current Surface conditions, the 24 and 48-hour surface predictions, and the 24-hour wind/wave forecast. Receiving these files through SailMail would exceed our time limit, but with the Iridium email it takes about ten minutes for these plus the gribfile to be received.

OK, check my math here.

You are getting four, 30 kbyte files plus a grib file of....well, you don't say but I'll guess 4 kbytes. That takes you about ten minutes, using X-Gate over your Iridum phone.

So that's 124 kilobytes in ten minutes....roughly. WITH X-Gate.

I'm just planning on downloading a single 2-4 kbyte GRIB file, grabbed from NOAA by saildocs. I got e-mailed two of them on Wednesday evening, and they were 2k and 4k respectively. Let's call it 4 kbytes, that's the worst case. So I'll be downloading approximately 1/30 of the amount of data you download. That should in theory take 1/30th of the amount of time, right?

OK, one thirtieth (1/30) of ten minutes (600 seconds) is 20 seconds. Wow, that's fast.

So with X-Gate, the download of the single GRIB files that I will want will take me something like 20 seconds, certainly under a minute. I have to send saildocs the e-mail request for the file, and THAT e-mail will take a minute to send out, too. Anyway, the total time will likely be well under 4 minutes, and will cost me at most $6.00.

OK, now let's figure out how long it will take WITHOUT X-Gate.

I hear that X-Gate will cut your airtime to about a third of what it is, without X-Gate. Let's be really generous and actually say that it cuts it to a fourth of what it is without X-Gate. OK, another way to say that is that if a file takes one minute to download with X-Gate, it will take four minutes to download, without it.

Let's apply that ratio to the 20 seconds it will take to download the GRIB file, that we calculated, above.

Um....that means that it will take 80 seconds to download my single 4 Kbyte GRIB file. It will cost me $3.00 since the minimum airtime charge on the Iridium phone is for one minute. OK, OK...whoops, it was slow today and it took me 122 seconds! DARN. $4.50. I have to request it, and that takes another e-mail, or another $1.50. Let's pretend that sending the request e-mail is slow and it takes two minutes, and costs $3.00. Whatever the case it could easily cost me around $7.50 to request and download that GRIB file on my Iridium phone, from Saildocs.

So the difference in price between using X-Gate to download a single 4 Kbyte GRIB file and NOT using X-Gate is $1.50. I'm going to do this probably twice, so call it three bucks during the race.

I'm not gonna spend $139 to save three bucks. Even if the "without-X-Gate" download failed twice and I had to re-do it for a total of three times, it doesn't make $$ sense.

OK, I bet there's a flaw in this logic. Well, the LOGIC is fine but I bet there's a flaw in the reality of it! Anybody want to pipe up?

 

[Paul Elliott]

Too true about the cost. I have to warn you about using a non-satellite-aware connection to a POP account, though.

*** My experience without Xgate was several years ago, and there may have been improvements ***

I tried connection to my regular email POP account using the raw internet gateway provided by the satphone. It was practically useless. The latency seemed to screw up the session, and if the satphone connection dropped in the middle of a transfer all data was lost and I had to start over from scratch. Iridium connections do drop out fairly often, even with a well-placed antenna. Xgate, and I believe other systems, have tweaked the connection protocol to provide good performance on a high-latency path, and provide mid-stream resumption of dropped transfers.

Without Xgate it would take several minutes for the simplest email download. The same download with Xgate can be just a few seconds. The improvement was staggering.

Since I started using Xgate, I believe that the "native" data service available through Iridium has improved, perhaps significantly. I hope so, because the original system was useless.

 

[AlanH]

Too true about the cost. I have to warn you about using a non-satellite-aware connection to a POP account, though.

*** My experience without Xgate was several years ago, and there may have been improvements ***

I tried connection to my regular email POP account using the raw internet gateway provided by the satphone. It was practically useless. The latency seemed to screw up the session, and if the satphone connection dropped in the middle of a transfer all data was lost and I had to start over from scratch. Iridium connections do drop out fairly often, even with a well-placed antenna. Xgate, and I believe other systems, have tweaked the connection protocol to provide good performance on a high-latency path, and provide mid-stream resumption of dropped transfers.

Without Xgate it would take several minutes for the simplest email download. The same download with Xgate can be just a few seconds. The improvement was staggering.

Since I started using Xgate, I believe that the "native" data service available through Iridium has improved, perhaps significantly. I hope so, because the original system was useless.

OK, now THAT makes sense and is a powerful incentive to either use X-Gate or....because I'm budget-conscious.... ask around and see if in fact the native data service through Iridium has improved. If X-Gate is the difference, basically, between being able to send mail and get files...and NOT send mail and get files, well....there ya go.

Thanks!