Monday, November 5, 2007

Gamefishing with a laptop

A couple of winters ago myself and a good friend, Dead Ant, thought we would try and develop a system that would put realtime GPS, depth and temperature readings on to bathymetric charts as we were fishing. We also wanted to put realtime GPS information into georeferenced Sea Surface Temperature (SST) charts. This was the 'Cunning Plan'.

Some of you may be interested to see how all this Cunning Plan stuff works in practice (and then again you may not). I was very aware during the winter when Dead Ant and I were beavering away that this might just be a techo wheeze that didn't in the end do anything. Far from it - this works. This is just the chart plotting bit - there is the SST bit as well. Maybe later.


This is what we generated last week at Houhora. It is taken off a scungy old laptop that was lying around at home and DA breathed over it to give it a new lease of life before it became 'El Boat Computer'. It is running a fairly old version of Maxsea as the machine doesn't have enough grunt to support the graphics of the newest versions. In all these screen shots the 'Nav Data' window shows loads of noughts as there is no GPS connected in my office. All the fields are filled on the boat via NMEA output from the Raymarine C120.




This an overall summary of the weeks trolling. The track changes colour as the temperature changes (blue cooler, green to yellow warmer) and is set on a rasterised bathy chart. I only connect the guessing machine up after the lures are set and pack it up before we steam home so that is why we appear to have been teleported into the area off Cape Karikari. It is obvious that we were a bit obsessive about one area with a wander off to Berghans on Day 4 - more of that later. Also notice the one short track going North out of the mess. This was going off for another bit of topography but we only went on the proviso that the water didn't go tits up on us. The SSTs predicted it would and the track colour changes true to form so we came back. Right, let's zoom in on the place that held our attention for so long.



With the eye of faith you can see that the depth contours come together a bit here but it is not really striking. Turn on Maxsea's 2D feature with range set to 70-250 metres and the contours set at 2 metre intervals and it all becomes a little clearer.



This depth info comes from a built in database that is in Maxsea and is taken from C-Map charts. Over this is superimposed actual depth readings taken off 'Surprise Surprise' as it traverses the territory (these are the bright red crosses). If you now turn on the 3D function it becomes even more obvious why this, with all other things (bottom composition, bait, bird signs, hook-ups etc) might be worth giving a right royal thrashing.



We had the structure (the fishfinder shows that this is all foul ground and a rocky drop off with sand on either plateau - it was also covered in bait all week) and we had all the other ingredients - except temperature. This was not the warmest water around at all. On Day 3 we downloaded a new SST and it showed a good temperature break heading out off the Berghans/Cone area. Maxsea would have us believe that this bottom structure was also there:





How can we go wrong? Day 4 sees us toodle down to Berghans (see track on first screen) and the water was warmer as we had predicted. It was also a great colour. It also had no bait or fish in it. However once we had taken some real soundings off the bottom the predicted structure looks nothing like we were led to believe:





Creating this picture was terribly amusing. Drive over a mythical Maxsea hill and it just vanishes in front of your eyes. It's a good feeling moving bits of the planet around. The last two pictures represent what is really there.

However all this techo nonsense is a guide only. There were no fish (for us anyway) at the sure fire spot off Berghans. We caught our last fish by looking at the sea and seeing some abnormal dolphin behaviour and thinking we saw some non dolphin fins in amongst the mammals. But at least the new toys put us in the right place to be able to see that.

It works for me and it is huge fun.

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