MARINE ELECTRONICS - Electronic Navigation 101
As we threaded our way through the myriad reefs of the northern Great Barrier Reef in pitch darkness under autopilot, I reflected on the reliance we have on electronic navigation.
Just imagine the pickle we’d be in if the Americans switched their satellites off or something like an asteroid shower destroyed them? Of course, diligent sailors should plot a course every hour on their paper chart so that based on boat-speed, current and leeway, an estimated position (EP) can be found should all the electronics be fried by a lightning strike or other total power failure. On top of that, we all used to take transits with hand-bearing compasses in the days before GPS was fully switched on in 1995.
However, the reality is that we usually have several backup GPS systems aboard and this delivery trip from Airlie Beach to Darwin was no exception. In my bag on the Seawind 1250 sat my trusty Garmin 78S at the ready and on the chart table on top of paper charts the iPad was fully charged with Navionics Australia software; while in my bunk I lay back to monitor our course with my smartphone — the excellent Samsung Galaxy S2 with Navionics. By the way there’s an upgrade (Navionics V2.5.9) recently been released with improved tracking and passage planning.
What the chart showed caused me to pause, as I lay snugly in my warm bunk because over to starboard it showed Pandora Passage near the Murray Islands. As some readers may recall, HMS Pandora was wrecked there and I realised it was during this very same week (August 26) in 1791. The wreck lies just south of Flinders Entrance and Bligh Entrance, which tell similarly dramatic stories of mariners making for the Torres Strait, off Cape York.
Onboard our new catamaran, we didn’t’ need to rely on star sights and ‘shooting the sun’ at noon to establish position. For the early navigators longitude was the challenge due to lack of accurate timepieces — Cook had a copy of John Harrison’s No.4 clock to accurately solve longitude.
STAR WALKING
In stark contrast my own very rusty celestial navigation skills were given a refresh with the Star Walk iPad app. This app is a great way to settle any arguments about the location of the Southern Cross or the controversy about Pluto by simply pointing the iPad in the air for the screen to instantly display and track the heavenly bodies.
Star Walk uses the iPad’s GPS to determine your location, along with its compass and accelerometers to track as you move and tilt your screen, allowing it to display the night sky in real time.
James Cook would have loved this during the transit of Venus, I bet! Other useful features include the Time Machine, which shows the night sky over a multiple year period while Sky Live gives you a view of the moon’s phases and elevation, as well as rising data for the Sun, Mercury, Saturn, Jupiter and Venus.
Top photo: Approaching Lizard Island to visit the lookout of famed navigator Captain James Cook. From here he was dismayed to see a maze of reefs stretching north beyond the horizon.
Electronic navigation is fantastic, but good seamanship dictates that paper charts should be used for recording position as well.
Never lose sight of the Southern Cross again — use the Star Walk app on your iPad.
Navionics has just upgraded its smartphone charting to improve routing and also includes a tab on marine articles.
[GEAR TEST]
› Raymarine TH32 Thermal Camera
As our Seawind 1250 didn’t have radar my Raymarine thermal camera proved a very useful device for night approaches to tricky anchorages. It picked out trailing ropes, mooring buoys and low-lying reefs (with some turning out to be crocodiles!). When on-watch I also used it to check the halyards and sails, without losing my night vision.
There are two versions, the basic TH24 and the higher resolution TH32 (which sells for $3495) with 2X zoom. I found the effective range to be about a kilometre.
It’s very user friendly with only a couple of colour modes and zoom button to choose, while the battery life is excellent — I only recharged it once during our two-week trip. It was particularly useful the night we weaved our way through dozens of craft at Gove in Arnhem Land on our way west.
The Raymarine night-sight is simple to use and has long battery life.
The Raymarine thermal camera is also a good safety aid for MOB.
From Bright Sparks column, Trade-a-Boat Issue 432, Oct-Nov 2012. Story: Kevin Green. Photos: Kevin Green; Raymarine.