Establishing the Headings of Seaway ll (Julian Joy Report)
In establishing whether risk of collision exists, the important features are the compass bearings of the 2 vessels in relation to each other & the distances apart.
For collision to exist, the compass bearing must remain constant & the distance must be decreasing.
(‘Similar triangles’ is the geometry behind his process)
Both of these criteria must exist ie. If the compass bearing is changing, no risk of collision exists; if distance is not decreasing, no risk of collision exists.
To establish compass bearings, I first needed to establish the actual headings of Seaway using the photos & the positions established from them & from that I am able to establish the relative & compass bearing of Classique from Seaway at the time of each photo. It is not possible to so easily measure the relative bearings of Seaway from Classique but I have made estimates, using her course of 80*T
The following photos are those taken by Seaway, enlarged & cropped to remove all but the band of horizon ahead of Seaway ll.
The lines drawn from the vessel are the heading point at the time of the photo.
4 lines are drawn where possible to establish accuracy :
1. Aligning the white structure
2. Aligning the hull deck structure
3. Aligning the edge of the ramp
4. Aligning the yellow painted line on the ramp
Lines 1,2 & 3 give a very good accuracy as they meet at a point in the distant perspective. Line 4 is at a slightly different alignment because the ramp is not horizontal, its reliability is therefore very much reduced due to this angle & I have not used it for that reason. It is only here because it is the line that Mr Young used.
Using these lines show that :
In Photo 1, Seaway is heading just slightly to the right of Sentinal Building in Takapuna.
In Photo 2, Seaway has clearly turned to starboard. If Seaway had maintained course, she would still be heading at Sentinal building, which is now behind Classique’s forestay.
If Seaway had maintained its 286* course since Photo 1, Classique would now have crossed ahead clear by 0.6 nmile
In Photo 3, Seaway has clearly turned further to starboard. Sentinal is not in this photo, it is a distance off to the left of the photo frame.
Classique has crossed ahead with clearance of up to 80 mtrs.
If Seaway had maintained its 286* course since Photo 1, Classique would now be 150 mtrs away on the starboard beam of Seaway having crossed about 1100 mtrs in front
Therefore is shown a clear & unmistakeable progressive turning of Seaway to starboard in these 3 photos.
Quantifying the amount of turning is accomplished by establishing the compass heading of Seaway at each photo.
From the above analysis & plotting the positions on the charts I have established that the headings in Photos 1,2 & 3 are close to : 287*T, 292*T & 297*T
There is clear & unmistakeable gradual alteration of course by Seaway towards the North, which is to starboard. The overall change is 11 degrees.
The effect of this on the incident is very significant. The sketch diagram below, not drawn to scale, indicates how the effect is greater than appears in the photos because of the progressive movement of Seaway to the North. The offset distance from the actual curved track to the projected line of the original track (287) appears less in the photos as Seaway has moved further northward between photos, which show only the additional offset, not the cumulative offset which is the important one.
Photo 2 – Classique is ahead of port bow or 2* from
centre line about 0.35 nmiles or 650 mtrs away.
If Seaway had kept to 286*, Classique would by now be
5* on Seaway’s starboard bow 650 away, having
crossed ahead at 0.6 nmile or 1100 mtrs away
Photo 3 – If Seaway had kept to 286* since photo 1,
Classique would now be 150 mtrs away on the starboard
side of Seaway & Classique would have crossed
about 0.6 nmile or 1100 mtrs in front of Seaway.