Coffs Castaway

Craig Brokensha
Swellnet Analysis

If you've had cause to check the Coffs Harbour and Batemans Bay waverider buoys, you'll notice something is amiss. Both buoys have currently gone AWOL off the East Coast.

The reason for the buoys - which are owned and operated by Manly Hydraulics Laboratory (MHL) - breaking their moorings is unknown, there's been no large swells to break their fastenings, but nor are the buoys completely lost.

Since going adrift on the 12th of November, MHL have been tracking the Coffs buoy via satellite and they've provided a plot of its journey thus far. The plot makes visible the East Australian Current (EAC).

The EAC is a western boundary current (falling on the western side of the Pacific Ocean and abutting the Australian continent) and feeds tropical water south from the Coral Sea down the NSW coast, usually taking a turn east towards New Zealand from a position south of Seal Rocks. At this junction we also see warm water eddies spawning and seperating from the main flow.

When at its strongest the East Australian Current pushes down past the southern NSW coast and can even impact Tasmania. We're seeing this occur more frequently with continued warming of the world's oceans due to climate change.

Overlaying the track of the drifting Coffs Harbour buoy with the observed current path and speed provided by the Integrated Marine Observing System website (below), we can see an almost perfect match, as expected.

The buoy has travelled approximately 700km in 20 days, that being 35km/day, 1.5km/hour or 0.41m/s. Looking at the chart above we can see the strongest sections of the EAC are currently flowing at about 1.5m/s (black arrows).

Currently the buoy is located east-southeast of Jervis Bay and looking at the current path from here, we can expect to see the buoy hooking due east and then back north-east into the Tasman Sea. The MHL have stated they're “monitoring the drifting buoy and will attempt recovery if it moves close to the coast.”

This appears unlikely to happen.

Unike the Coffs buoy, the Batemans Bay buoy isn't communicating with MHL, however as we know how the EAC is moving we also know the approximate path of the buoy. Depending on when it went adrift, the Batemans buoy could currently be anywhere from eastern Bass Strait to up near where the Coffs Harbour buoy is drifting, which would be very handy indeed.

Comments

thermalben's picture
thermalben's picture
thermalben Friday, 4 Dec 2020 at 7:22am

I was in Riverton many years ago (southern end of NZ's South Island), and had a conversation with the local deep sea fishos, who showed me a waverider buoy belonging to the Qld EPA, that had been a drift for a long time and eventually washed up on their shores.

thermalben's picture
thermalben's picture
thermalben Friday, 4 Dec 2020 at 7:25am

Interesting reading in the MHL 2017-2018 report too:

GPS tracking units supplied by Pivotel are currently being attached to Waverider buoys to check their position once per day. The successful operation of the tracking units and software has resulted in the successful recovery of five Waverider buoys that have gone adrift since the tracking units were introduced in November 2015. During 2017–2018 the GPS tracking units facilitated the recovery of three Waverider buoys:

• the Crowdy Head Waverider buoy went adrift on 29 September 2017 following damage to the mooring system. The buoy was recovered on the same day drifting about 3 km off Crowdy Beach

• on 29 March 2018 the Coffs Harbour Waverider buoy went adrift after the mooring was severed by a ship propeller. The buoy was recovered drifting about 12 km off Sawtell on 31 March 2018

• the Coffs Harbour Waverider buoy went adrift on 27 May 2018 after the mooring was severed by a large vessel. The buoy drifted south in the East Australian Current covering about 160 km in two days before it was recovered 21 km south-east of Laurieton on 29 May 2018.

dazzler's picture
dazzler's picture
dazzler Friday, 4 Dec 2020 at 8:19am

41m / s. Far out, I wonder how that compares to horror sweep on GC points?

You wouldn’t want to fall off the back of a trawler at night, be out of sight & earshot in seconds.

Craig's picture
Craig's picture
Craig Friday, 4 Dec 2020 at 8:22am

Dazz, that's 0.41m/s, not 41. Ha, that would be rapid!

dazzler's picture
dazzler's picture
dazzler Friday, 4 Dec 2020 at 8:32am

Just re-read the article....oops!!

25 years working in finance I should be across numbers, but what’s a decimal point or 2 amongst friends!

thermalben's picture
thermalben's picture
thermalben Friday, 4 Dec 2020 at 9:24am

If I had a financial adviser, I sincerely hope his name would be 'dazzler'. How can you not go wrong!

seaslug's picture
seaslug's picture
seaslug Friday, 4 Dec 2020 at 7:22pm

Haha Ben, I'd run for the hills

Howie66's picture
Howie66's picture
Howie66 Saturday, 5 Dec 2020 at 9:23am

This guy is doing my tax return this year, should be a good one!

freeride76's picture
freeride76's picture
freeride76 Friday, 4 Dec 2020 at 9:37am

the strength of that current can easily put those bouys underwater and maybe snap moorings.

Craig, I think the vast bulk of the EAC water is South Pacific in origin, not Coral Sea.

Craig's picture
Craig's picture
Craig Friday, 4 Dec 2020 at 11:20am

Yeah correct you are, equatorial western Pacific.

seaslug's picture
seaslug's picture
seaslug Friday, 4 Dec 2020 at 7:25pm

Yes FR, surface mooring bouys for example can be pushed underwater to a depth where they implode.

Fatigue and/or snap loading on the mooring system can cause the components to fail

freeride76's picture
freeride76's picture
freeride76 Friday, 4 Dec 2020 at 11:22am

I always find it somewhat ironic that it is considered low nutrient and biologically poor but contains within it so much pelagic life, both adult and larvae.

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 4:00pm

A lot of water between fish and it’s basically a highway between destinations.

fitzroy-21's picture
fitzroy-21's picture
fitzroy-21 Friday, 4 Dec 2020 at 10:25pm

I believe it is the upwellings from interaction with the cold currents that support such incredible food source and life FR.

Jamyardy's picture
Jamyardy's picture
Jamyardy Friday, 4 Dec 2020 at 3:16pm

Good stuff Craig. I seen in the paper earlier this year that UWA deployed two "drifting buoys" in WA. One off Rotto, and the other off the south coast. I think they lost one recently, but the other is currently to the NW of Exmouth. Interesting, given the Leeuwin current travels in the opposite direction. I wonder if its that the freo doctor is more powerful than a surface current on a free floating object.

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 4:03pm

Predominant winds are Southerly in WA even the convection winds and the Leeuwin is weaker .....I think.

One of the resident weather nerds will be along to contradict this guess shortly.

Jamyardy's picture
Jamyardy's picture
Jamyardy Friday, 4 Dec 2020 at 4:26pm

Cheers Blowin. yes definetly a lot more south winds than north over here, all year. As for Coffs, the buoy appears to be following the current, unless the predominant winds over there are Northerly this time year ?

seaslug's picture
seaslug's picture
seaslug Friday, 4 Dec 2020 at 7:35pm

Need also to analyse the windage area of the buoy (above water level) compared to current area (below water). Same applies to vessels, watch how they respond differently to wind, wave and current forces (which are not necessarily collinear) when fully loaded compared to ballasted.

Legrope's picture
Legrope's picture
Legrope Sunday, 6 Dec 2020 at 4:34pm

Once offshore around 10 nautical miles the Leeuwin current is very strong. In a strong southerly off WA, our cray pot floats were being pulled south with the last float punching straight into a strong southerly wind chop. Completely opposite to what you’d expect in strong winds. Maybe the bouy was further out to sea in deeper water beyond the pull of the current?

Thegrowingtrend.com's picture
Thegrowingtrend.com's picture
Thegrowingtrend.com Friday, 4 Dec 2020 at 4:05pm

I guess the bow line undid.

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 4:15pm

Imagine the bull dollies lurking under that Coff’s bouy ....

They’d be gathered like pasty white Aussie punters at the Bumiminang

seaslug's picture
seaslug's picture
seaslug Friday, 4 Dec 2020 at 8:36pm

2 beautiful catches there

Craig's picture
Craig's picture
Craig Friday, 4 Dec 2020 at 4:30pm

Jamyardy, the Leeuwin Current is strongest during the winter months and weakest through summer. Do we know when it was deployed off Rotto?

The constant southerly wind regime through the summer months could have sent it on its way north.

Jamyardy's picture
Jamyardy's picture
Jamyardy Friday, 4 Dec 2020 at 4:50pm

Hi Craig, I don't know when they deployed them. UWA on June 1st reported that one of the buoys was 500km SW of cape Leeuwin and the other 350km NW of Gero. The same article says it was the Rotto buoy that went to the South and the Bremer Bay Buoy went West then North up past Gero ! I think they were probably deployed last year, but could have been earlier this year.

https://www.news.uwa.edu.au/archive/2020060112125/research/new-data-reve...

freeride76's picture
freeride76's picture
freeride76 Friday, 4 Dec 2020 at 4:31pm

been dollies on the FAD here for two months.

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 4:36pm

Spoke to a fella in the surf who reckons a 22 kilo freak was caught off here the other day

freeride76's picture
freeride76's picture
freeride76 Friday, 4 Dec 2020 at 4:49pm

that would have been fun to subdue when bought on board.

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 5:12pm

I’ve never caught one.

Bucket list. This season etc etc

Heard a marlin was caught in close too. Looks like a nice temp spike coming. Probably as I drink tooheys new and type this AKA this arvo.

freeride76's picture
freeride76's picture
freeride76 Friday, 4 Dec 2020 at 5:31pm

I pulled one in on a handline trolling behind a yacht about 25nm south of Hawaii.
Massive bull mahi-mahi that went absolutely ballistic when we brought it on board.

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 6:01pm

And you’re a more interesting person for it.

We are diamonds and every experience is another facet.

fitzroy-21's picture
fitzroy-21's picture
fitzroy-21 Friday, 4 Dec 2020 at 10:33pm

If you have an occy strap handy, one end hooked in the mouth and the other end wrapped around itself on the tail subdues them pretty quick!

BigZ's picture
BigZ's picture
BigZ Friday, 4 Dec 2020 at 5:44pm

Way back in 1847 a transport schooner named Selina was on its maiden voyage from Brisbane northwards.The Selina was found the following year on the Capricorn Coast , it was later determined that the Selina floated for thousands of miles in a huge circle near the Victorian coast before heading across the ditch towards NZ and then back to where it more or less started. The place where its journey ended being called Wreck Point, maybe a place where future lost wavebouys end up.!

Blowin's picture
Blowin's picture
Blowin Friday, 4 Dec 2020 at 5:58pm

That’s not far from poetry

BigZ's picture
BigZ's picture
BigZ Friday, 4 Dec 2020 at 9:03pm

Poets day and did not know it Blowin!

uncle_leroy's picture
uncle_leroy's picture
uncle_leroy Friday, 4 Dec 2020 at 10:37pm
see.saw's picture
see.saw's picture
see.saw Saturday, 5 Dec 2020 at 9:07am

That’s a big fish for that chick to be carrying like that! Is it a real photo? Her biseps are hidden. Maybe they’re like Arnies.

see.saw's picture
see.saw's picture
see.saw Saturday, 5 Dec 2020 at 9:07am

That’s a big fish for that chick to be carrying like that! Is it a real photo? Her biseps are hidden. Maybe they’re like Arnies.

Justonemore's picture
Justonemore's picture
Justonemore Saturday, 5 Dec 2020 at 9:39am

Maybe she has those things called (biceps)

udo's picture
udo's picture
udo Sunday, 6 Dec 2020 at 4:43pm

Keep a look out Kiwis...could be heading to your Shores
A hard to see colour in the Ocean

https://www.gumtree.com.au/s-ad/queenscliff/surfing/100-dollar-reward-gu...