The ATSB report into the grounding and total destruction of the pilot launch P V Corsair at Port Phillip Heads has been released and is available at:-
www.atsb.gov.au/publications/investigation_reports/2025/report/mo-2023-003An interesting read, with the lesson that just because you have safely come through the Heads many times before, you still need to pay great attention to navigation, particularly at night. Electronic nav screens aren't just decorations!
Perhaps naming the reasonably new Pilot Launch after a notorious PPH submerged rock was just looking for trouble.
The report also has a good discussion on the "four fingers west" route used by many yachts, and the even further west routes used by many power boats to escape the worst of the ebb stream.
Big scale chart snips, clear pictures of the onshore navigation aids and their layout might be of interest to some.
Since I'm a tide nerd, I'll put my spin on some points not in the report:-
a) Seems a large contributing factor was to rendezvous with the ship a fair way to the west of the usual point. (So coming back in on a compass heading rather than relying more on the chart plotter beggars belief.)
b) The reason for the more westward meeting point noted in
a) was because during the outward trip a viscous ebb tide was running out into a stiff southerly. This produced very bad sea conditions along the outward route to the normal pilot transfer point. Further to the west avoids the worst of it, but the return trip needs much care as you are way off any of the usual leads.
c) The reason for the strong ebb in
b) is because PPH is a long distance from either of the real "deep oceans" (Southern Ocean & Tasman Sea), which means the strongest tides at the Heads don't occur until around 5 days AFTER a Full or New Moon. It is an inertia effect of all that Bass Strait water having to slosh back and forth many times to build up maximum amplitude.
With a Full Moon around 5 days before the accident, strong tides were predicted, unfortunately with the night time peak ebb flow occurring a little before the outward journey of the Pilot Launch.
d) The late evening ebb stream strength predictions for October 4th & 5th were -6.53 and -6.28 knots respectively. Although we often say that the Heads tide streams can be "up to 6 knots", it is fairly rare for the predictions to equal or exceed that number. A quick scan of the BoM predictions shows these rates were the highest for the whole year.
e) The reason for those high numbers is that the peak of the 18.6 year long lunar declination swing cycle happened to occur in late 2023 and early 2024 ( and we still have a pretty high North/South declination swing for 2025). The next time we get this is in 2032 / 2033.
All mariners will be aware of the East-West phasing of the Sun and Moon's apparent positions that gives us the fortnightly spring and neap tide amplitudes. However there is also a North-South cycle of the Moon's declination that is important in producing enhanced tides in areas that have a strong diurnal tidal component (like PPB).
Not only did the Moon's declination hit a peak of 28.3 degrees north on the 5th of October, but the Moon was also much closer to the Earth than usual in the days prior. Tide wise, it seems like Russian roulette with too many bullets in the chamber.
f) A few times the report has phrases that indicate they think slack water at PPH occurs when the "inside" and "outside" levels "equalise". This isn't true, but is widely believed to be so. It is a myth that has a detrimental effect on safety. I'm tackling Ports Victoria (again) on this myth, and also ORCV, but I am meeting resistance - Grrr!
It seems they want simplicity over safety, but in my book you shouldn't be telling "little white lies" when there are adverse consequences. ( I would appreciate any ORCV members out there to give their safety committee a nudge. ORCV are about to run another one of their very popular "Rip Tours", but some of their web pages about PPH are still plugging this myth.)
Any PPH regulars still in doubt should browse:-
jake-h5.neocities.org (Post #1 to start with, and there is a brand new Post #3 on measured sea surface slopes. You don't have to read it all - just skim to the images and animations in the posts and you should quickly get the point. Reply back here if you are still skeptical and want to slug it out! Alternatively take the link near the end of Post #1 to see CSIRO's work. Post #2 looks at two other "bad boy" myths that risk lives.)
cheers,
Jake
