Assessment of the Risk of Collision – Seaway ll (Julian Joy Report)
Under the International Collision Rules & the Maritime Rules Part 22 Collision Prevention, which is the NZ rule & applicable here, the only defined methods for assessing whether risk of collision exists are the use of compass bearings or radar.
Before specifying compass & radar however, the rules specify that “all available means” must be used. It is important to note that there is no limitation on the methods to be used, in any NZ or International rules.
Extracts from Maritime Rules Part 22 Collision Prevention
Rule 22.7 Risk of Collision
(1) Every vessel must use all available means appropriate to the prevailing circumstance & conditions to determine if the risk of collision exists …follows with (2) (3) & (4)a & b
It is important to note that use of all available means includes using radar, AIS & anything else without limitation
In general, ‘constant compass, decreasing distance’ means a risk of collision exists as shown in the sketch. The ships are following paths along similar triangles. Any movement of the relative bearing indicates that ships would not reach collision point at the same time, therefore there would be no collision.
For a collision to occur there must be a decreasing distance & a constant compass bearing.
Mr Bolton used 2 methods – 1: Relative Bearing ie. lining up other vessel with part of own ship structure.
2: Line of Sight to Background referred to as a rule of thumb of which Mr Young said “that method is wrong …the collision regulations clearly say that you’ve got to watch the compass bearing of an approaching vessel to assess the risk of collision”
Mr Bolton agreed & said “The Relative Bearing has its failure in that it depends on the keeping of a straight course.
The Line of Sight method can be used in situations where either there is no compass or compass use is impractical”
My opinion (J Joy) is that mariners in smaller boats do use these methods described by Mr Bolton & I do myself. In common with practical techniques in any discipline, methods are combined to ensure a reasonable assessment. In harbour situations, this is a very practical combination.
An important point here also is that the Line of Sight method used by Mr Bolton has seen him navigate around the world, charter for many years in the Caribbean & America’s Cups in Fremantle, Sandiego & NZ & navigate in other extremely busy environments without incident.
It is noted also that during the lead up to the incident, neither vessel used the compass or radar, both used only the ‘eyeball’ techniques.
Measuring the distance for collision risk is not easy at sea without using radar or similar systems. It is always difficult to estimate distances across water due to a lack of suitable benchmarking objects. For a relative perspective in the distances involved during the incident, the total width of Waitemata Harbour from Devonport wharf to the container terminal is 0.5 nmile (About 900 mtrs) The width of the channel between Browns Island Beacon & Illiomana Rock Beacon on Rangitoto is 1 nmile (about 1850 mtrs)
The vessels first saw each other at distances well over 2 nmiles ( over 3,3700 mtrs) however that distance is not of significance to this analysis, as within the range of available water, visibility range was not a factor of limitation & manoeuvring to avoid collision would not be necessary, expected or normal at that distance.
It is important to point out that the situation & local conditions mean there is no fixed distance specified in any rule. In these harbour waters, passing distances between vessels including ferries are frequently less than 100 mtrs & can be easily so without any danger.
My analysis shows that had Seaway maintained a straight course, safe distances would have been experienced & no ‘incident’ would have occurred.