The website contains properly researched info about how, why, & when, "Slack Water" occurs at Port Phillip Heads. There are three posts available at the moment.
Many water based recreational pursuits often use the low current period as the tidal flow reverses to keep participants safe.
This also applies to locations just outside the entrance, as well as up to 20 km inside it, where significant tidal currents can still be felt.
Nearly 50 years of various water-based recreations in this region has shown me that many folk's understanding of "Tidal Things" isn't up to scratch.
These misunderstandings increase their level of risk in this potentially very dangerous area.
The motivation for improving my own understanding is to keep me a bit safer as my body's strength declines with age. I am happy to share the insights gained but it can get a bit technical.
A particular bugbear of mine is a few "slack water myths" still in circulation, that have no evidence base whatsoever. If followed, these can be from mildly to very dangerous.
Decades ago, while sailing homeward in strong tide-against-wind conditions, I changed course slightly just to reduce the glare from the soon to set Sun. After nearly a mile on this "pure fluke new course" I encountered a drowning "myth victim". He was right at death's door and in an otherwise rough and lonely sea. It was a difficult and emotional rescue in the conditions. Ten days of hospital treatment and he was OK. I hate those bloody groundless myths!
I have wrapped three of these bad myths up in a second post, hoping the text is enough to kill them all off!
Almost equally irritating is the apparent lack of will from the port authorities and other safety bodies to effectively act to eliminate such "bad tidal information" wherever it crops up.
This post looks into the sea surface slopes that drive the tidal streams at Port Phillip Heads and across the rest of the Bay. A time series of sea height plots using the Bay's tide gauge network show how the down and up slopes develop over the distance from outside in Bass Strait to all the way up to Melbourne. These plots cover a full day of tides.
Also covered is a method of accurately measuring the surface slopes at slack water both at the entrance, and at various distances inside the Heads. These "point results" are then compared to the earlier large scale results.
Finally we look at work by Ports Victoria that commenced in early 2024 and has the longer term goal of providing mariners with near-real-time measurements of the actual entrance current, rather than the present situation which relies only on prediction algorithms for current speed information. The algorithm's response to "weather effects" has not been well validated. Success in this ambitious project will be of great benefit to those boaters operating at or near the Heads.
The posts are a mix of "pictures", diagrams, animations and text, glued together with my kindergarten level HTML coding.
They are best viewed on a desktop or laptop computer screen with a wide browser window, rather than on a tablet or mobile phone screen.
This allows an image, and the text that discusses it, to fit within the same screen.
The first post might be a bit of a slog, but if you frequent PPH it should be a worthwhile investment.
"Skim readers" should find plenty of interesting images to flick through.
Readers with an even lower level of interest are recommended to look at just the first two and last two screens of Post #1. This captures much of the point of that post but without the how and why detail.
POST #1 link is:- Port Phillip Heads Slack Water Quiz:- And The Winner Is:
POST #2 link is:- Port Phillip and 3 "Bad Boy" Slack Water Myths
POST #3 link is:- Sea Surface Slopes in Port Phillip