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Garmin 76CS – Pros & Cons

I was lucky enough to get a RC400 and a Garmin 76CS as wedding presents in August 2005.

There seems to be a number of discussions on various forums about the pros and cons of these units so I thought I would give my experiences of using both while sailing in the English Channel for the past 2 years.

Garmin 76CS – the Pros:
Garmin 76CS 11. Although I have the Raymarine RC400 mounted at the helm – the Garmin can go anywhere with me – to the Marina office, to the cafe, to another yacht etc.. its truly portable because the batteries last. Unlike the RC400 the batteries last for at least 24 hours of use.

2. It has its own GPS so it is another backup for position data separate from my main GPS / C120 setup.

3. The BlueChart software is loaded from the laptop – you dont need another copy like you do for the RC400. The software auto loads all relevant charts for the route you have planned. Interfacing to the Garmin BlueChart software on my laptop is easy and always works perfectly.

4. You can use it in the car too – there are comprehensive charts for Europe including detailed maps of all major cities.

5. Garmin continue to manufacture and support this unit. There is a tremendous amount of software and add-ons for it on the Net. The latest 76Csx uses the latest SiRFstarIII chip set

Garmin 76CS – the Cons:

1. The screen is hard to see in poor light, it is quite dim and you need to press a power button to turn the brightness up – quite awkward when you are wearing gloves or have stubby fingers like me.

2. The buttons are above the screen – why ? They are small and hard to press accurately.


Portable device – Charging batteries

If you are anything like me you have a tendency to hoard useful electronic gadgets – as a result I have a garage that has many battery chargers from many different eras. I refer to the task of charging so called rechargeable batteries for torches, PDA’s, GPS units and so on…

Well the latest and fastest (?) charger that I have acquired is the Uniross X-Press 700 Charger RC104311 – cost £18.94 including delivery from Battery Logic in the UK.The impetus for this was the fact that the Raymarine RC400 that is mounted at the helm will now only run on the mains power that I have installed there and the batteries are refusing to hold a charge any more. The batteries supplied with this unit are the AA 2300mAh NiMH type.

Uniross x-press-700The Uniross X-Press 700 Charger looks like a good unit and comes with 4 new batteries – which are 2500mAh (ultra high capacity) so I hope they will perform even better in constant use on passage than the previous set.

Charger features:

• Includes 4 x AA 2500mAh Ni-MH rechargeable batteries.
• The Xpress 700 will charge AAA & AA size batteries.
• This charger will charge 2 or 4 Ni-Cd / Ni-MH batteries.
•Due to an intelligent charge control inside, the charger will switch to trickle charge after charging.
• V-MAX technology protects against damage from using with non-rechargeable technologies.

Charge time for batteries:

Type Capacity Charge time
AA- Ni CD 800mAh 1h 15m
AA-NiMH 1300mAh 2h
AA-NiMH 2100mAh 3h 30m
AA-NiMH 2300mAh 4h
AA-NiMH 2500mAh 4h 15m **
AAA-Ni CD 250mAh 45m
AAA-NiMH 700mAh 2h 15m
AAA-NiMH 900mAh 3h


Garmin MapSource & Google Earth

Having upgraded my Garmin MapSource chart plotting software I thought I would just check out a few of my previously saved routes and fell over a menu option that I had never seen below which simply said “View in Google Earth” – ok, I am losing my sight, but I had honestly not noticed this before – so I clicked – and to my amazement, Google Earth loaded and zoomed right in on the exact lat/long for my route, and superimposed the route on a map of the English coastline with waypoints all labled and shown in the correct place !

Route - Mapoint

Route - Google

Garmin Mapsource route from Newhaven to Brighton…. …and Google earth with same route shown – just click to see a larger image.

Just click on the images to see a larger screen shot…


Marine Charts for Google Earth !

Fantastic aerial views of marine charts on to Google Earth!

Check out EartNC limited to North America at the moment:-(


EarthNC for Google Earth is the first ever integration of NOAA ENCs, marine weather and real-time positioning data directly into the Google Earth platform. EarthNC Marine charts feature full-integrated Google Earth renderings of over 600 official NOAA and 70 U.S. Army Corps of Engineering ENC charts.


Sailors now see satellite images of sailing areas with links to :

  • bathymetric data
  • AIS data
  • Weather data
  • Navigation aids
  • Tide data
  • National radar

They even claim that with a laptop running Google Earth and a low-cost GPS receiver, you can use EarthNC as a real-time chart plotter.!!

What a shame they havent got the UK and Europe covered – lets hope the do a deal with the authorities here too.


AIS Class A – What is SOTDMA?

The operation of AIS depends on the Self Organizing Time Division Multiple Access (SOTDMA) data communication technology, which was developed in the 1980’s.

It allows for large numbers of transmitters to share one single narrow band radio channel, by synchronizing their data transmission to an exact timing standard. Under SOTDMA each minute of time is divided into 2250 time slots or 26.67 ms each time slot. With a transmission speed of 9.6 kbps this translates into 256 Bits/time-slot, sufficient for one AIS report.

The exact timing signal of the GPS receiver is essential to synchronize the time slots of communicating AIS ships, as well as providing the position data for each ship. When a ship first “talks” to another ship, it takes up an unoccupied time slot, and it reserves a time slot for its next contact, depending on the status of the vessel according to the standards

For example a ship sailing at 23 knots updates its information every two seconds and therefore “reserves” a time slot 75 slots on from the first contact (2250/30=75) and so on).

The range of the system is the VHF horizon for each AIS-ship, with the ship in the centre of its own communication “cell”. The size of this cell will adjust to the traffic density, if slot capacity starts to run out, the system will automatically discard targets at a greater distance and assign those time slots to targets of greater importance.