Don’t get me wrong I wouldn’t venture out to sea these days without a GPS. However I also really like my paper charts and low-tech navigation tools. My favourite and, I would claim, indispensable navigation tool is the Portland speed-time-distance calculator. It’s just a simple, cheap, plastic slide rule with no batteries or buttons. It’s also impervious to saltwater, tea, coffee or rum for that matter.
This is how it works:
It has 3 scales representing speed time and distance. Say you have 31 miles to go to your destination and you need to be there in 4.75 hours to catch the tide. Simply line up the 4.75 mark on the time scale with the 31 miles mark on the distance scale by sliding the centre rule. On the adjacent time scale the marks will line up at the appropriate speed of 6.5 knots which is your minimum speed required to get there on time.
It’s not exactly necessary when the GPS plotter can tell you at a glance I know. It’s nice to have a back up though.
Does anyone else have favourite gadgets or applications?
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