There are blues and then, there are BLUES.  When I sailed with another woman out of Newcastle, Australia bound for New Zealand I was glad to see the chocolate colored water of the muddy harbor turn blue.  What I didn't understand on that first knarly upwind passage was that the BLUE water just beyond the intial blue had a power in it's depth that would sweep us south off our charts. During the 19 day trip, 10 of which we were hove-to in Tasman cold fronts, I learned my first lesson why knowing those colors was so important.  Being swept south didn't put us in danger, that time, but it did challenge calculations of dead reckoning and it did extend our days at sea, our exposure to the rough seas.  For 7 years, that lesson effected my choices when approaching a reef, a continental shelf, calculating positions, planning for our heading, speed and making contingency plans.  Sometimes the issues were huge, like deciding to run with the racing current off Mozambique in order to beat a nasty storm on our way to Richard's Bay South Africa.  Or holding a tight course for Madagascar, atop an underwater ridge extending from Seychelles, knowing the 20 foot waves abeam could become dangerous if they grew much more.  Eventually, a 25 foot wave did sweep our deck, ripping off the dodger and breaking handrails we'd use to lash things on deck.  Other times knowing the colors, the underwater topography issues, were for tame almost decadent reasons.  Finding the most clear sandy space in the San Blas for our anchor, or dropping the hook between century-old clams at Lizard Island, Australia. The subtle and dramatic displays of color, texture and temperature contain profound messages for navigation on a boat. For me, they also contained profound reinforcement to use all my senses in life.  Imagine. I first saw Aitutaki, Cook Islands as a mint green layer along the bottom of puffy white clouds on a horizon.  On my next trip to the Pacific, I saw islands first as green on a radar screen.  My whole body registered the first sighting - I felt the warming of the shallower water, smelled the land, felt the motion of the earliest bounce back waves, got my camera for a picture.  Only my eyes registered the green on the radar.  True, I love radar, as a tool.  But not as a replacement for the deeper knowledge we all contain.