Using GPS to show the effect of current
Around about this time last year, I paddled from Cornwallis wharf to Karaka Point and back with a GPS unit logging my path. Back at home, I uploaded the track log from the GPS to a program which shows the route on a map or chart. I was really impressed to see how the currents affected my paddling, especially across the Hikihiki Bank and the across the bank just off Cornwallis.
I left Karaka Point due West heading straight into the 15-20kn wind with the idea of getting shelter from South Head and assistance from the Waiuku Channel current (they were forecasting 25 gusting 35 by evening - I didn't really want to be in a wind against tide situation in the main channel). Progress was very slow across Hikihiki Bank and tiring. I struck a relatively calm patch and guessed that I was in a channel so thought 'stuff this!' and headed up to the main channel. The track shows I turned at the right point. I was pleased to see my speed increase even though the wind was slightly beam-on, because I was getting pretty tired.
[img_assist|nid=72|title=|desc=|link=node|align=right|width=200|height=145]It was very choppy in the main channel, but still much better than heading into the sea waves across the shallows. I lost GPS coverage from No.4 to No.2 lights on the way back. Not really sure why - guessed it was all the spray on the casing covering. Just after No.2, I propped the GPS further up the deck, adjusted the aerial more vertically, and all was sweet again.
From there, I was heading more NNW with the idea of going straight for the northern shore, across Karore Bank and letting the currents sweep me around the inside to Cornwallis Wharf. The currents kept me parallel with the direct course line. I should have surfed straight down the SW sea waves. The track shows vividly the difference in my course as I traveled over Te Tau bank just off Cornwallis.
Image data sourced from Land Information New Zealand data. Crown Copyright Reserved. NOT TO BE USED FOR NAVIGATION
For more information about GPS TrackMaker, see http://www.gpstm.com
For electronic charts, see http://www.gpstm.com
