GRIBs on PredictWind Satellite Communicator

Hi everyone,
An update on progress in obtaining GRIB files from our PredictWind Satellite Communicator.  Another geeky post!

SailDocs GRIB file received on our Satellite Communicator

At present PredictWind doesn't support the supply of GRIB files to the Satellite Communicator.  This is ostensibly because the Iridium Short Burst Data (SBD) service doesn't support email attachments.  However there is a way around this, as the above image shows!

By placing the email attachment (the GRIB file) into the body of the email the GRIB data can be communicated.  This isn't cheating in any way - you still pay for the data you transfer.  The overall email still has to fit within the 2KB Iridium SBD limit after compression.  The actual limit is about 4KB before compression.  This is about the size of GRIB file we normally downloaded via HF, and provides very useful data.

Unfortunately the GRIB files available via email from PredictWind appear to contain a minimum of 5 forecasts.  This means the area covered can only be about 5degrees*5degrees, with only a single variable (one of wind, rain, atmospheric pressure etc) in the file.  Anything bigger creates an oversize email.

SailDocs and zyGrib allow the user to define the GRIB file required with more freedom.  For example SailDocs allows a single forecast 10degree*10degree GRIB with two variables or a dual forecast 5degree*5degree with 4 variables are both well within size limits.


After researching all this we've designed and tested a system which allows us to get GRIBs on our Satellite Communicator.  At present we can get them from PredictWind, SailDocs or zyGrib.  We create request emails aboard in the format required by each service, but send them to one of our shoreside email addresses.  The email is automatically redirected to query(at)saildocs.com or grib(at)predictwind.com.  This results in the response email being sent to the ashore email address, where the GRIB attachment is reformatted to lie in the email body.  The modified response email is then sent to the Satellite Communicator.  All automatically.

The extra processing adds a only minute or two to the overall process, and as soon as the response is available it shows up in the Satellite Communicator email inbox.  No connecting twice as is the case with HF email!

Below is an example response email.  The dense block of text is the GRIB file encoded and placed in the body of the email.  It provides two wind data forecasts, each covering a 5degrees by 5degrees area. The block of text is about 700 bytes in size, yielding a GRIB file of about 500 bytes.  This is the GRIB file displayed in the image above.

Example response received aboard

Getting from the text block to the GRIB file involves running a simple script (program) to decode the text into the binary data which forms the GRIB file.

If anyone's interested in accessing our system for their Satellite Communicator let us know!

Email Systems for Blue-Water Cruisers

Hi everyone,
For some time we've been considering whether HF is the most cost-effective means of sending and receiving email from Zen Again.  We don't need to browse the internet, but we do need to be able to download weather information in the form of GRIB (or similar) files.  Apart from GRIB files we only need plain text email.

We've used HF email for many years and it has worked well for us.  But it does have some disadvantages:

• Purchase cost of Pactor-3 modem ($1500) or Pactor-4 modem ($2000+)
• Purchase cost of modem is on top of cost of the HF transceiver ($1500-$3000)
• Running cost $250 per annum using SailMail, or $0 for Licensed Amateurs using Winlink
• Limited number of coast stations in the Australasian area
• Variable propagation conditions depending on time of day and other factors
• Non-trivial learning curve to optimise HF system and its use for email
• Requires planning, effort and sometimes luck to successfully send/receive emails
• Need to actively connect to a coast station to check for emails - maybe twice a day max - with each connection taking more than 15 minutes in marginal propagation or busy conditions

We've looked at satellite phones several times over the years, but for our email needs they too have disadvantages:

• Purchase cost $1000-$1500
• Running costs (voice or data) around $1 per minute
• Data rate limited to 2400bps
• Data connections prone to drop-out
• Often requires external antenna to make data connections workable
• SMS/texting cheaper but size limit too small, and no GRIBs of course

Recently we found an alternative.  At last!  We discovered the PredictWind Satellite Communicator.

Satellite Communicator (at home)

The Satellite Communicator uses the Iridium Short Burst Data network and integrates a GPS and ZigBee wireless link to a PC or Mac running PredictWind's email software.  The advantages of the unit from our perspective are:

• Cost-effective (similar or cheaper purchase and running costs to the alternatives)
• Always on
• Low power (0.05Amps in standby, 0.2A transmitting)
• Very simple to install
• Very simple to use
• Tracker function transmits position hourly to PredictWind regardless of PC/Mac connection
• Plain text email transmit & receive
• Any plain text (weather, news & more) such as from SailDocs is retrievable
• Weather routing service from PredictWind (requires Professional package)

The Satellite Communicator needs further development to maximise its cost-effectiveness.  The most important is provision of GRIB files (subject to Iridium SBD size limits).  Here are the features we'd like to see:

• Provision of GRIB forecast and GPX route files instead of current text-based routing
• Email client very basic (eg can only add/delete contacts but not modify, can't create folders etc)
• Iridium and GPS signal strengths not available on PC/Mac
• GPS data not available on the PC/Mac
• Tracker messages not copied to PC/Mac (would confirm they're really happening)

PredictWind costs may seem a little high at first glance, but it's worth noting you can move between the Basic, Standard and Professional packages as often as desired.  This should make the running costs similar to SailMail for many cruisers since one only needs Professional when on passage.  Normal email works regardless of whether you have a PredictWind subscription or not.

So far we've only been testing the unit at home here in Perth but are very pleased with what we see so far.  The unit is far easier to use than HF email.  In our opinion it's worth a look if you want email aboard your blue-water cruiser.

As soon as GRIB and GPX files can be retrieved the Satellite Communicator will be a far better solution than HF email.  In the mean time I have a workaround which delivers PredictWind GRIBs and GPXs to our unit after a little intermediate processing!

ps - We have no association with PredictWind save being a satisfied customer!

Relaunch and Refit Week 15

Hi everyone,
She floats!  On Tuesday morning Zen Again returned to her natural element.  Since then Precision has just about completed all refit work items.  A new forestay base fitting was made and fitted, a boom sheaves pin modified to allow fitting of new (dual) mainsheet blocks, and the new mainsheet arch fitted.  The only items still to be fitted are two pushpit-mounted gas bottle holders.

Prior to launch the propellor and shaft were painted with PropGold.  'Twill be interesting to see how it performs.  We also fitted Kleenhull anodes which are very small and should last many years.  Kleenhull is a Western Australian product and it will be very interesting to see how they perform.  These anodes are intended to work well with Coppercoat antifoul.

Propellor and shaft painted with PropGold

New Kleenhull anode - tiny isn't it!

Ready to go!

Launching

Floating!

Forestay fitted

Anchor roller is a big improvement and the stemhead much simpler 

Fully rigged, but with messengers replacing second main & jib halyards

Double-decker organisers to handle added reef tack lines and mainsheets

Below decks we have a new cabin sole.  The oiled teak with sikaflex stripes is much better non-slip than varnished teak and holly, and the new boards latch, rather than screw, down.

New cabin sole - nice but highlights the poor varnish!

Today the new mainsheet arch was fitted.  It has a large base plate with dual backing plates port & starboard, and feels very strong.  It needs to be!  We now have dual mainsheets which lead forward along the boom, down to the deck and aft to clutches.  Exactly what we had on Degrees of Freedom and the system worked very well for us.  Best of all there's no traveller or mainsheet in the cockpit which is a big safety improvement.

Mainsheet arch - note large base plate on coaming

Mainsheet arch - note one sheet each side

Zen Again is now at home in a pen in Boat Lagoon Marina, where she'll stay for at least a month.  We hope to return in late July for sea trials and perhaps to move to Krabi or Rebak.

Zen Again at rest

The refit carried out by Precision Shipwright Services has exceeded our expectations.  We recommend Scott and his team without reservation.  We had expected to need to stay in Phuket to oversee the work but the first couple of weeks showed that simply wasn't necessary.  The work has been carried out to a very high standard.  We're now confident our yacht is better than ever structurally, and looks good as new!

Blogs will be less frequent now our refit is complete, until we go sailing of course!