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    Re: Navigation Rules
    From: Trevor Kenchington
    Date: 2002 Jan 13, 1:22 PM

    Lu Abel wrote:
    
    > Respectfully, my copy of the (US) Navigation Rules does not mention
    > anything about their "not applying to vessels in fog so dense that one
    > cannot be seen from the other."  Rule 6 (both International and US Inland)
    > clearly requires vessels to "at all times proceed at a safe speed so that
    > she can take proper and effective action to avoid collision..."  To me this
    > says that if the fog is so thick two vessels can't see each other, they are
    > both obligated to slow down or stop!
    
    Rule 6 is part of Section I -- Conduct of Vessels in Any Condition of
    Visibility. The priority of sail over power, however, comes under Rule
    18 and that of starboard tack over port in Rule 12. Both Rules 12 and 18
    are in Section II -- Conduct of Vessels in Sight of One Another. Those
    Rules do not apply when vessels cannot see one another on account of
    poor visibility, which is as it should be since (as Herbert pointed out)
    if you can't see a nearby vessel you have no way of knowing whether she
    is under power or not, let alone what tack a sailing vessel may be on.
    
    As to what to do when close to another vessel in fog too thick to see
    her, it is not a matter of simply extrapolating from Rule 6 but of
    obeying Rule 19 -- Conduct of Vessels in Restricted Visibility. In the
    case of the radar-plotting exercise that started this thread, Rule 19(d)
    would apply -- if visibility was assumed to be poor for the purposes of
    that exercise. "Ownship", having determined by radar that she was in a
    constant-bearing situation, with respect to the target ship, would be
    obliged to take avoiding action in ample time. Considering that the
    target ship was forward of "ownship's" beam (Relative Bearing 322 or Red
    038) and that "ownship" was overtaking the target, Rule 19(d) would
    allow "ownship" to alter course in either direction -- though, following
    the common principle, an alteration to starboard would be preferred
    unless there was compelling reason to turn to port.
    
    In reality, "ownship" could expect to sight the target's stern light
    well before a collision occurred, making her subject to Rule 13 before
    the situation was resolved. (The plotting exercise only brought the two
    vessels to a distance of 5.4 M apart.) "Ownship" could, however, make
    the same alteration of course to comply with both Rules.
    
    Meanwhile, Rule 19(e) would require "ownship" to slow to the minimum
    speed that would give her steerage way until such time as she could
    determine that no risk of collision existed. (No doubt there is case law
    that defines how much reliance can be placed on the radar plot in making
    that determination but I am not aware of what it says.)
    
    Putting those together and considering the courses of the two vessels,
    "Ownship" might do best to slow down, turn sharply to port, and pass
    under the target's stern before resuming her own course. Naturally, it
    would be best to communicate that intention to the target vessel over
    VHF before altering course.
    
    
    Trevor Kenchington
    
    
    --
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
    
                        Science Serving the Fisheries
                         http://home.istar.ca/~gadus
    

       
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