Quick Way to Know if you are in the Traffic Lanes

Sailing in Puget Sound or other areas with much ship traffic, a primary ongoing navigation concern is where we are relative to the VTS shipping lanes. It is a matter of safety, and a matter of the Navigation Rules. On smaller powerboats and when sailing, we have no rights in the lanes:

Rule 10 (j). A vessel of less than 20 meters in length or a sailing vessel shall not impede the safe passage of a power-driven vessel following a traffic lane.

In fact, it is worse than "no rights."  Normal obligations of the give way vessel start out with "When two power-driven vessels are crossing so as to involve risk of collision..." Other obligations are worded as "stay clear of..."  But "do not impede" is much stronger. This is partly explained in

Rule 8 (f) (i) A vessel which, by any of these Rules, is required not to impede the passage or safe passage of another vessel shall, when required by the circumstances of the case, take early action to allow sufficient sea room for the safe passage of the other vessel.

The Admiralty Court has clarified this even further to explain that it means not just preventing risk of collision but preventing the development of risk of collision.  (The sometimes heard interpretation of this rule to mean I can do whatever I want so long as the ship does not have to alter course, is in a sense doubly wrong as it is even more lax than staying clear.)

Thus if you choose to cross the path of a ship in the traffic lanes you have to consider not just whether you have plenty of time to get by, but you have to consider what could happen that might make this go wrong. I can't find the reference for the moment, but in recent news a collision did occur with a ship and a powerboat whose engine stalled right in front of path of the ship. Considering the speed of a ship and their inability to stop, this crossing did not avoid development of risk. The stalled engine is thus no defense at all.

I have one vivid recollection from racing in the very region to be discussed in the video below. The situation was such that the wind in the area of the lanes, toward the middle of the Sound, was much favored over winds more inshore. So there was a big advantage to be gained the farther we could sail out toward the middle. We were on a tack headed out to the lanes as a ship came down the inbound lane from some distance off. The skipper's tactic was to tack out till right in line with the ship's path and then tack back, which would provide plenty of increasing separation as we sailed away from the path of the approaching ship. It was considered a safe tactic as we did not cross the path of the ship.

Unfortunately, as happens sometimes, during the hurried tack, the sheet got a knot in it on the tack, and when you tack and do not throw off, you heave to!  Thus we were dead in the water in direct line of the ship. The sheet had to be cut, which was in retrospect a small price for making a maneuver that was indeed indefensible.  We did not avoid a circumstance within the shipping lanes that could develop into the risk of collision.

Knowing where you are relative to the lanes is crucial in these waters, as is knowing the Rules about interacting with the lanes.

With a full nav station running an echart program with the lanes marked, you could in principle see where are you are relative to the lanes at all times. But with such systems you have to zoom in and out to see what you want, and you can in fact over zoom with a slipped mouse click and lose the picture at just the wrong time. Also to be precise about it, you would have to call up a tool to actually measure the distance from the lanes etc.  Nevertheless, when you have full navigation underway and working well, this is usually not an issue to know where you are relative to the lanes.

But short handed you might not have continuous view of the echart, or in a small boat with no built in electronics you need another tool, which is the subject at hand, and electronics is the best solution.  And I would venture that if you race routinely in the area of the shipping lanes, it could well pay to set up your phone or a tablet to supplement your routine nav info with this trick that keeps you instantly aware of where you are relative to the lanes. It is an easy double check on important information.

There is no practical piloting methods that will tell us this to the level of accuracy needed in the time frame needed. We might, and often do, try to get away with just knowing there are lanes present, and then guessing where they are when we do see a ship approaching and then try to maneuver based on that.  But that can be dangerous, as we do not really know where the ship is within the lanes,  and this approach is at least very inefficient. You could be going out of your way to avoid the traffic and not need to.  (Though off topic a bit, I should add that if your echarting included a good AIS display from your own receiver—not some Internet relay, which is dangerous—that would tell you if the ships are in the right place.)

Thus we have this easy trick to solve the problem of knowing precisely where we are relative to the lanes. It can be done on a phone or tablet, so even the smallest vessel can use it.  This method is particularly valuable to those who sail or paddle in the same area, as you can set it up once and then just turn it on the next time without any set up.

The trick is to set up a fake route (waypoint 1 to waypoint 2) marking the center of the separation zone and then just monitor the XTE to that fake route as we sail in the vicinity of the lanes. Below is an outline of the process, followed by a video illustration.

Step 1. Set up a route on the echart along the center of the separation zone between the inbound and outbound lines. Lock and save the route.

Step 2. Measure the perpendicular distance from that route to the boundary of both the separation zone and the outer limit of the lane. In Puget Sound the lanes are about 0.5 nmi across with about 0.25 miles of separation zone between them. Thus the outer distance is 0.62 nmi and the inner distance is 0.12.

Step 3. Activate  the route as if you were sailing toward one of the end points. This is not the case, so distance and time to the waypoint, and so on will be nonsense (just don't display these), but the cross track error (XTE) will still be right. That display then tells you precisely were you are.  The COG and SOG, total time and distance sailed will be right, so these could be useful displays as well, but for this exercise it is the XTE we are focusing on.

XTE > 0.62 you are outside of the lanes

XTE < 06.2 you are inside the lane
XTE < 0.12 and you are in the separation zone.

The values and what they mean are the same on either side of the lanes, but the XTE display will change labels, such as R going to L, or >> going to <<, etc. The directions will depend on the order you have for the waypoints, but routes can always be reversed so that does not matter.

I will add here phone and tablet apps that work well for this as I find them. Here is one:
memory-map navigator, which has versions for iOS, Android, and Windows mobile. This is excellent inexpensive product, but I am sure there are others.