Wednesday, 15 April 2015

CM93 Charts and GoogleEarth Imagery on iPad

Hi everyone,

!!! NOTE !!!
From SEAiq version 4.0 (released December 2015) CM93 charts are no longer supported.

On Zen Again we have been using CM93 vector charts and KAP raster "charts" (produced from GoogleEarth imagery using GE2KAP) in OpenCPN as an aid to navigation.  See our blog from 2012 on the latter.  Ever since then we have been under the impression there was no software to present this information on our iPads.  During our cruise through SE Asia we found no-one who knew of such software.

Today we discovered we were all wrong!  Thanks Carolyn for pointing us in the right direction.  There _is_ an app which can display CM93 and KAP charts on iPad.  SEAiq is the answer and it is brilliant.

Within minutes of downloading and installing the app I had installed our CM93 charts.  A few minutes later I had a few KAP files installed too.  Once aboard Zen Again it took only a few minutes to configure SEAiq to accept AIS, GPS and instrument data from our Vesper XB-8000 AIS over WiFi.

The two screenshots below show example KAP and CM93 views, both of Direction Island in the Cocos-Keeling Islands.  Changing between the two involves switching one setting (Raster Charts On/Off).

KAP file GE image of Direction Island (Cocos-Keeling)
CM93 chart of Direction Island (Cocos-Keeling)
The two screenshots show the presentation of CM93 charts in Fremantle with WiFi data enabled.  The Status Bar the top of the screen is now populated, Zen Again is the black ball and AIS targets are shown.
Success and Fishing Boat Harbours close up
Here's another view with CM93 chart detail set to "Basic".  This reduces clutter to make AIS targets clearer.
Simplified CM93 View of Fremantle and Gage Roads
SEAiq has a good table view of AIS targets.  The information page for each target is very detailed.

AIS Targets Page
Individual AIS Target Page
SEAiq also supports email requests for and display of GRIB files.  It will generate an email request to send to SailDocs.  It would be nice to see the range of GRIB providers expanded.

Weather Page
SailDocs GRIB Request Email
I later loaded a set of several hundred KAP files.  This wasn't as straight-forward as I had hoped but I eventually got them all installed and working.  I used iTunes to transfer both CM93 and KAP files.

The two issues I have found so far are:
  • Some zip files containing kap files are not accepted by SEAiq, despite successfully loading the same set of files individually
  • Unsurprisingly SEAiq gets a little slow if a large set of KAP files is loaded
Update (20 April):  The zip issue has been identified by SEAiq as the presence of Mac OS X hidden files in zip files.  These files have names like __MACOSX and .DS_Store and can be searched for in zip files using the command [unzip -l <filename>] (without the square brackets).  If such files are found use the command [zip -d "__MACOSX*" "*.DS_Store*”] to remove them from the zip file.  The next release of SEAiq will ignore these files.

It is surprising that SEAiq is not listed when one searches for "marine navigation" in the App Store.  I think that explains why we've never heard of it before.  I have mentioned this to the SEAiq folks.

Update (20 April):  SEAiq will be listed under "marine navigation" from its next release in the App Store.

One thing's for sure - SEAiq is a very useful iPad app for sailors who need their charts supplemented by GoogleEarth imagery.  It is a very nice chartplotter generally, but the support for both CM93 and KAP charts sets it apart.  Very cool.


  1. Hi Yacht Zen, I found your blog to be very helpful and am downloading GE2KAP as we speak. Thanks for making it easy. Regarding the Ipad, how do I install open cpn and the CM93 chart on my Ipad Air?
    On a sail from Phulet to Fiji, currently in Palau and will find the kap files very helpful!!
    Thanks again from Barry on S.V. TWOCAN

  2. Hi Barry,
    Thanks for your comment. OpenCPN doesn't run on iOS so you can't use it on the iPad. I recommend SEAiq which costs $50 but is worth every cent. SEAiq Open supports both CM93 charts and KAP files.

  3. Hi Mike, enjoying your current voyage informative blog and wish you and Nik all success. Please keep it up. Very envious of speeds you're achieving. A very basic question I know but how do you transfer files to the iPad. Cheers, Rob (Jolie Brise)

  4. I am running version and it says "CM93 charts are no longer supported" with the file in the charts tab. Tell me there's some way around this!!! Downgrade?

  5. Hi Flemming, I have asked the SEAiq folks about this but received no reply. I suspect downgrading to 3.x is our only option. I suspect chartplotters supporting CM93 will gradually disappear entirely.