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Responsibilities Between Vessels:
Understanding Rule18

By Jim Austin


You are powering or sailing happily along with just a few boats in your vicinity, to which you pay little attention. As one vessel draws closer, it appears to remain in about the same position relative to a stanchion, edge of the doghouse or whatever, and about that time your mind starts to drift towards “wonder what she’s going to do” or “let’s see, am I supposed to do something”, or more likely – both. The first thing to consider is the nature of the other vessel.


Affectionately referred to “The Pecking Order”, Rule 18 seeks to establish order out of potential chaos by designating a hierarchy of “privilege”. This privilege (for want of a better term) is determined by the work or function of the vessel at the time (as opposed to relative position as in meeting, crossing or overtaking) and applies only when in sight (as in eyeballs) of each other. Detection of the presence of another vessel by radar or fog whistle therefore does not meet the criteria.


What does the above phrase “work or function at the time concerned” refer to? An example would be a trawler not fishing – perhaps proceeding to or from her area. Although she is a fishing vessel, she is not considered a “vessel fishing” for purposes of priority status. She would be simply a power driven vessel.


Having said that, the order as generally listed (in decreasing rank) is:


1a) Not Under Command (NUC)

1b) Restricted in Ability to Maneuver (RAM)

2) Constrained by Draft (ColRegs only*)

3) Fishing

4) Sail

5) Power Driven Vessel

6) Seaplane / WiG**


*  The ColRegs are the “International Rules for the Prevention of Collisions at Sea”, as distinguished from the Inland Rules.


**  “WiG” stands for “Wing-in-Ground”,  a craft added to the Rules last September. The abbreviation refers to the aerodynamic effect enabling it to employ a cushion of air to facilitate flight, thus giving it the same priority status as a seaplane).


To start with, any applicable requirements of Rules 9 (Narrow Channels), 10 (Traffic Separation Schemes) and 13 (Overtaking) take precedence over Rule 18. An example is the requirement of Rule 13 that “any vessel overtaking any other shall keep out of the way of the vessel being overtaking.” Thus, a sailboat overtaking power does not have the right of way.


If life were that simple! In reality, there are several nuances:


a)      As noted above, one vessel that outranks all of the above is ANY VESSEL BEING OVERTAKEN. Thus in that one situation, relative position supercedes function.


b)      NUC does not have priority over RAM – even though they are often listed in the above relative position – implying a priority. Some time ago, NAVSAC (The Navigation Safety Advisory Council) was asked to clarify – they declined, stating only that if those two vessels find themselves in risk of collision, Rule 2(b), the General Prudential Rule, should be employed. A question on the USCG exam relating to those two has been repeatedly challenged, the misinterpretation being a consequence of the way they are listed in (i), (ii) fashion – implying an order. Clarification is still refused for reasons know only to God and the USCG. So – both are obligated to stay clear of each other.


c)      In listing “Constrained by Draft”, the complete phrase given in the definition (Rule 3) clarifies the intent of the Rule – indicating that it’s the “draft in relation to the available depth AND WIDTH of navigable water...”. Thus, courts have declined to look with favor upon a vessel claiming such constraint because of depth limitation when more than adequate water of the same depth was available laterally. Note that this category exists under ColRegs only.


d)      “Fishing” priority continues to be claimed by some small pleasure boats out on a Sunday afternoon trolling. The test applied is “fishing with nets, lines, trawls or other fishing apparatus which restricts maneuverability”, otherwise that craft with a line dangling over the side is just another power driven vessel according to the rules. As small craft go and their relationship to the rules, this is perhaps the least understood and the most often violated causing a maritime version of “road-rage.”


e)      A sailboat, sails up and drawing but under power is a power driven vessel for purposes of the rules (thus affecting signals, lights and priority).


f)        For those taking the Rules portion of the Coast Guard exam, look for certain trigger phrases. For Not Under Command it’s “due to some unusual circumstance”, for Restricted in Ability to Maneuver it’s “due to the nature of her work”, and for a Vessel Engaged in Fishing it’s “with nets lines, trawls or other fishing apparatus which restricts maneuverability”.


g)      And to be complete, one vessel that falls within the Restricted in Ability to Maneuver category but has her own specific lights and shapes is the Minesweeper (while sweeping). Definitely not a vessel to approach!




Author bio:

Jim Austin, M.D. is a graduate of the US Naval Academy, later serving the Navy as a navigator and OOD on destroyers. He earned a medical degree from the University of Vermont, holds a 100-ton master's license with a radar observer endorsement, and for many years has taught sailing and navigation in Massachussets and Vermont.