Thursday, May 17, 2018

The Delight of Range Marks

A pair of range lights with white and red screens.
Credit: Google images
You are going to start out thinking this doesn’t apply to you, because I’ll begin talking about ships and tugs.  That is just the easiest way to explain the concept, so stick with me.  This is for you also.  
I was watching a video done by a friend about his trip in the Boundary Waters Canoe Area.  He was paddling across a rough bay to get in the lee of the land.  He held the wind on his starboard bow, and guessed that even as he paddled into the wind, having it on the side of the bow would push him into the bay.  All of that was true, of course, but he appeared to be working intuitively, and couldn’t tell for sure what was happening or how fast.  That brings us delightfully to the wonderful world of range marks.  Using them takes a little thought at first, but they eventually become as second-natured as walking, and add a whole new dimension to getting your boat to do what you want and take you where you want to go. 
The two operative words here are set and drift, and we’ll add a few other terms in the narrative.  Any time you are on the water, unless aground or made fast to the shore, your boat is being pushed about by wind, waves, and current.  Set is the direction you are being pushed, and drift is the speed at which you are moving off course.  Set and drift take on great importance in any navigational solution, but the beauty of range marks is they enable you to solve for set and drift by eye, and continuously, without throwing the protector on the chart and drawing and measuring vectors and triangles.  They are one of the greatest gifts and blessings a boater has at his disposal regardless whether skippering a 15-ft. pack canoe or a 1000-ft. ore carrier. 
To begin with, range marks are any two objects viewed in line, one behind the other.  They will change relative position to each other based on how we are set.  Range marks are used extensively by the Coast Guard and Corps of Engineers to help ship captains remain in a river channel.  Then when the skipper reaches a port, they enable him to get through the inlet and into the port without running aground.  At night they are called RANGE LIGHTS, because lights will be set on two poles or towers so they can be seen in the darkness.  The front range light will be shorter than the rear one so both can always be seen.  Their color and flashing sequence varies to help distinguish one from the other, or one pair of ranges from another pair, but also to make them stand out from any other background lights in the area.  The poles or towers also have large placards and screens attached to their faces to make them stand out from the background and visible from a distance of a couple miles during the day, and the screens create RANGE MARKS.  Each mark sends a message.  The front mark is the reference mark.  The relative movement of the rear mark behind the front mark tells us how nature is working on our vessel.  So here’s how they work. 
As long as the two marks remain in line, one behind the other, your boat is tracking dead down the middle of the channel, and all of the surrounding scenery (buildings, trees, points of land, etc.) will remain stationary relative to the front mark.  They will move relative to the front mark too, if we really get off course, but we use the range marks for immediate feedback and instant correction.  We want to correct set right away before things get out of hand.  If we see the rear mark pop out of line and start to drift to the left of the front mark, our boat is also being set to the left, and we are moving out of the channel.  A new helmsman will always be told to steer the rear mark to keep it in line, as if it were a video game.  If the rear mark needs to go right to get back in line with the reference mark, he steers right.  If it needs to go left, he steers left.  As he nears alignment, he begins to center the helm so he doesn’t overshoot the channel centerline.  Something that is hard for people to accept initially is that this is all without regard for where the bow is pointing.  The natural tendency is wanting to point the bow right at the marks, but keeping the marks aligned is done by steering the rear mark regardless of whether the bow is any angle to the right or left of the apparent line down the center of the channel. 
Explaining how they work for tugs and ships seems to be the easiest way to explain the basic idea, but all kinds of vessels use range marks for any number of situations.  Sailors couldn’t live without them.  Racing sailors using them win races.  Those that don’t, lose.  Sailors live with the constant reality of leeway, and its resulting set and drift.  The direction the wind pushes a sailboat sideways, producing leeway, is the set, and how much and how fast the boat is set off course is the drift.  This all tells the skipper how much ground he is gaining or losing to the wind and/or current.  He wants the solution to this question resolved in seconds, and range marks will tell him that.  The longer it takes to really understand what is happening on the water, the more out of control he is, and the harder he has to work to get back on track.  However, we can see the same problem arising whether sailboat, canoe, or kayak.  Since the Coast Guard doesn’t create range marks for every immediate situation, we create our own.  We can pick any two objects, some distance apart, with one behind the other, to create our range marks.

Wanting to reach the end of an island with the wind
pushing us off course, we line up the flag in the foreground
with the house in the background.  As long as they remain
in line, we will reach our destination even though the canoe
is pointed way off course.
Let’s say you are headed toward the tip of an island.  The wind is from port (or the left) and will try to blow us away from the island.  You want to arrive right at the tip so you don’t get set way downwind and have to fight back against the wind and waves.  You find something on the point of the island, like an isolated tree, boulder, house --- anything.  In the background you look for another mark on the mainland in the background that is close to being in line with your front or reference mark.  If it is some greater distance off, we may not see individual objects, but you can still see dips in the tree line, major construction, smokestacks, grain elevators, etc.  If the sun is starting to approach the horizon, you might use a light or a star as a second mark.  We line the two marks up, hold our heading, and watch the rear mark.  If the rear mark drifts off to the right, or downwind, we are losing ground.  You begin to come closer to the wind until the two marks line up and stay stationary.  Paddling at that angle to the wind will take you right to the tip of the island without the loss of any ground you would have to make up.  If the waves are big enough, you may be wanting to hold the bow at a safe angle into the waves.  The range marks will tell how high you can point into the waves, or allow yourself to fall off the wind, without losing ground to leeway. 
Range marks can also be used for safety purposes.  You are being met by a powerboat heading toward you at a converging angle.  Will he pass you at a safe distance, or is there a risk of collision?  Line the boat up with a mark behind him, and see how the background moves.  If the background move to the left of the boat, we will be to his left when he passes.  The opposite will be true if the background progresses to the right of the boat.  If the background does not move, you are on a collision course and at risk of being run down even though he may be some distance away.  You have created three points on a line: you, the boat, and a mark in the background.  Unless someone alters course, the boat will travel that line right to you. 
By the same token, let’s say you see a canoe you know, and you’d like to join up with him.  Regardless of which direction he is going, if you are on a converging course, line him up with an object behind him.  Alter your course so the background remains stationary, and you will meet him unerringly without regard for normal set and drift. 
If the surroundings don’t offer the best marks you would like, then create your own marks.  A fish trap or a buoy can be used for one point.  Even a cloud can be used, and the further away the better, but clouds move.  It will give you immediate feedback on your current situation and enable you to set an appropriate heading that corrects for set and drift.  Minutes later, you will have to find another cloud to confirm that conditions haven’t changed.  Even with a compass heading, the heading can remain fixed as you slide off a considerable distance off the desired track.  With a compass capable of offering bearings, range marks will enable you to paddle on in greater comfort by watching distant marks rather than little lines on a dancing card.  If you start with a compass heading from your map, as soon as you get underway, pick a set of range marks for that heading.  Following the range will not only be easier on the eyes and nerves than trying to watch the compass card, but they will also factor in any leeway you may be experiencing.  If you haven’t been accustomed to using range marks, start practicing with them.  You will acquire a skill that will serve you well for the rest of your life. 

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