Restricted access at The Rip looks bad for the PoMC
Port of Melbourne Corporation’s 20th July Notice to Mariners, imposing new restrictions on shipping when transiting the Rip looks like their dreams of "all tide access" for 14 metre draught vessels has come crashing down!
The Notice advises that tankers of 11.6 metres draught or more can now only transit when flood and ebb tides are 3 knots or under.
All other vessels over 12.1 metres draught are restricted as follows:
· Inbound, when flood and ebb tides are 5 knots or more
· Outbound, when flood tide is 5 knots or more
· Outbound, when ebb tide is 4 knots or more.
Interestingly, 12.1 metres draught was the previous upper limit for ships able to transit the Rip prior to channel deepening.
The Notice suggests these restrictions will only apply for “short” periods of high tidal flow. However, an examination of the tidal stream tables for The Heads indicates that there are many days all through the year when tidal flow (current speed) regularly exceed 3, 4 and 5 knots. So, on that basis alone, the constraints imposed could have major impacts on shipping schedules- and hence the economic justifications for the Channel Deepening project.
When tides are at their strongest – Spring tides- which occur when the moon is in its New or Full phase, tidal flow at The Rip can be 7 or 8 knots. So, for half of every month, shipping could be greatly restricted, causing delays in departures and arrivals in Port. In fact, even on Neap tides - when the moon is in its Quarter phases - current speed can often be at least 3 knots.
Tides change twice every 24 hours, so there could well be many hours in each 24 hour period when Flood (water flowing in) and Ebb (flowing out) current speed exceeds the new restrictions.
So- what’s changed and why?
Old tide tables (from before The Entrance was deepened during the channel deepening exercise), also show many days when current speed was predicted to be in excess of 3, 4 and 5 knots. No doubt the tide has been flowing in and out at those speeds for thousands of years, so why has it become more dangerous to enter and exit Port Phillip Bay, even for some vessels that pre-channel deepening may not have been so restricted? Eg: In 2004 an 11.6 metre draught oil tanker had no restrictions on entry or exit at any height or speed of the tide. Now it has to wait for a current speed of 3 knots or less.
At the 2004 Channel Deepening EES, PoMC was adamant it required 24 hour a day access through the Rip for all vessels up to 14 metre draught through all stages of the tide. We were asked to believe that any delays –even of a few hours- caused by deeper draught ships having to wait for high tide before transiting the Rip was a major economic burden for the shipping industry and thus the raison d’être for the deepening of the Entrance.
Now for some reason PoMC is happy to impose significant constraints on all vessels over 12.1 metres draught and any tanker of 11.6 metres draught or more. That’s certainly not “all tides access” - to use PoMC’s own terminology to describe what they said they would achieve with the Channel Deepening project.
There’s no denying these new parameters are significant restrictions compared with the PoMC’s free wheeling visions back in 2004 of fully laden 14 metre draught oil tankers and container vessels plying the Bay without restriction.
Perhaps insurers have decided for some reason that the Rip now presents as a greater risk for them?
(One expert we’ve talked to observes that the PoMC’s separation of vessel types into tankers and all others over 12.1 metres draught doesn’t make sense. Both tankers and bulk carriers - which could carry anything from cement and grain to coal - are slower, less manoeuvrable vessels. So, if oil tankers are restricted to 3 knots through the Rip, so should other bulk carriers. Either way, a grounding of an oil tanker or a bulk carrier full of cement would be a messy event with major economic and environmental consequences.)
If this Notice to Mariners means what we think it does, it is certainly starting to look like the $1 billion Channel Deepening project has been a giant white elephant – leaving us with a toxic dump in the Bay forever and a buggered beach at Portsea – all for nothing. Ah yes, Portsea beach……..
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