Scuba Doctor Dive Maps - correcting the "corrections"

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packo
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Scuba Doctor Dive Maps - correcting the "corrections"

Postby packo » Tue, 26 Feb 2019 12:02 pm

***** Scuba Doctor Dive Site Maps - correcting the "corrections" *****

The Scuba Doctor's Dive Site Maps were updated just recently (Feb 2019) with a number of new sites being written up. That is very good to see and thanks to those who have chosen to share their knowledge for everyone's benefit.

However this post is trying to rectify bungled "corrections" to the GPS coordinates of two dive sites that were made some time ago. I have to own up to one of the bungles, back in 2016, as being primarily my fault! It needs to be corrected.

The other, in Jan 2018, is primarily the fault of Lloyd who owns and controls the website content. Hopefully both dive sites can be properly corrected so the database is improved for everyone.

While I have been frustrated in the past in trying to get useful corrections made, I do acknowledge that Lloyd's rigorous "moderation of suggested GPS coordinate changes" is far better than none at all!

The world wide web has quite a number of unmoderated GPS lists for dive sites and fishing spots where users can freely enter their own site coordinates without any oversight. Invariably these websites eventually spiral downwards to "junk status" with numerous wildly contradicting sets of coordinates for supposedly the same location. It is surprising just how many things can seem to go wrong when GPS coordinates are observed, recorded, passed around, and then published later on.

So there does need to be some control, both in adding new site entries and correcting old ones. The question is how stubborn should the moderator be? (Lloyd is right up there!)


***** Packo's Correction Blunder for the "Devil's Drop Off" Site *****

Ok back to the bad Scuba Doc info that I am now taking the blame for!

I have a pretty good eye for spotting unlikely GPS coords, and late in 2015 I quickly identified a number of sites in the SD dive site list that were way out of place due either to typos or some other number mishandling. Some of the errors were inherited from the forerunner VSAG/BSAC dive site lists, but others were entirely new. The database was growing so rapidly around that time that such problems were hard to avoid. Some of these position errors were rather big in the 1km - 5km range and so very easy for me to spot.

Some time back I also had experienced the frustration of wasting a dive looking for a SD dive site (Rosebud Reef), the coordinates of which had a typographical error of one unit in the longitude minutes. This placed me in a featureless sand desert 1.5km west of the reef's real position. I know many others did much the same thing over several years before the error was corrected. Prompt corrections are needed to avoid "ghost-netting" divers on bad coordinates, and also to try to limit the spread of the bad numbers over the internet.

When I spied the original Scuba Doctor coordinates for "Devils' Drop Off" of 38 19.602 S, 144 38.658 E, I knew this placed it way outside the Heads and where I knew a 20m to 40m drop didn't exist. Wondering if a simple typo in the minutes of Lat or Long could be to blame for the bad position, just as for Rosebud Reef, I looked at some trustworthy bathymetric data to see if any simple single digit change in coords could land me back on a drop off somewhere along the edges of the entrance canyon at the Heads.

I soon found that a simple 2 minute change in the latitude (17.602 S rather than 19.602 S) put me smack bang on a 20m to 40m drop off. This spot is not too far from the dive site named as "The Abyss" and is closer to Pt Nepean than to Pt Lonsdale.

My BLUNDER here was in thinking that having this simple change lead smack bang to a similar depth canyon wall was so unlikely to happen by pure fluke that it must be the correct explanation. WRONG! - I failed to notice that the description of this site claimed it was on the Lonsdale side of the canyon! If the descriptive text was right, then BOTH the original Lat & Long numbers must have been wrong!

(However note "The Abyss" dive site page also claims it to be on the Lonsdale side but I know it isn't. I think the similar wording in these descriptive texts comes from a Dive Vic generic "copy & paste" about wall sites, so the text isn't always reliable unless it is a first person account and avoids any copy & pastes from other site descriptions.)

Anyway in an email to the dive shop I included this simple suggested "fix", along with noting a half-dozen or so other sites where the coordinates had gone a bit crazy. Most amendments to the Scuba Doctor's list were made in mid 2016, including my suggested "fix".

Now, several years later, I had a large "oops moment" when I stumbled on several other descriptions and some video that confirm that the "Devil's Drop Off" is a site somewhere along the Lonsdale Wall. This means both the original SD coordinates were wrong, and my so called "fix" was just a pure fluke substitution of a different canyon wall for the intended one.

My apologies to all for my role in this misinformation. At least anyone diving those numbers would have had a drop off to dive on, but possibly not up to the standard of the real "Devil's Drop Off" site. I hope Lloyd or anyone else can discover the correct coordinates for the "Devil's Drop Off" site and then get the database corrected.


***** Lloyd's Correction Blunder for the "Lonsdale Wall" Site *****

Ok I have harped on about this a number of times and even threatened to give up and let the bad info stand. However it is far too important a dive site to let it rest at that!

I also harbour some guilt in that if I had kept my mouth shut in the first place about trying to get a minor coordinate change done, we would all have been better off. That course of action would have at least stopped a fairly small error from being turned into a much bigger one!

The Lonsdale Wall is an iconic and quintessentially "Port Phillip Heads" dive site(s) and wall system. It has national recognition and even some international recognition. We just shouldn't have one of the dive shops that support private boat divers visiting this area putting out misinformation and directing these divers to the wrong spot!

So here I am trying yet again for a fix. The muck up was triggered by a large knee-jerk response to my minor complaint back in late 2017 that the then "Lonsdale Wall" Scuba Doctor coordinates of 38 17.522 S, 144 37.833 E (WGS84 from a previous VSAG list) were in rather deep 50m+ water about 80m southeast of the actual Wall lip.

All I was suggesting was a slight pruning of Lat & Long back to the wall lip itself: Say to 38 17.487 S, 144 37.797 E which would be pretty close to the lip and is a shift of about 80m. This would also be fairly close to another VSAG/BSAC 2014 location called "Lonsdale Wall Shallow" at 38 17.479 S, 144 37.788 E where the wall started in only 12m and dropped away to 50m+. (I assume the term "shallow" here was in reference to the relatively shallow starting depth.)

Although this correction might sound straightforward, there were added complications because of some additional site confusion. In 2007 & 2008 the Dive Vic charter Group took Lloyd and a few VSAG bods to a location some 0.5km further to the north that was also called "Lonsdale Wall Shallow". (This time the term "shallow" was a suitable description because the entire depth range was only around 13m to 22m)

Furthermore because this site was almost exactly due north of the pre-2018 Scuba Doctor "Lonsdale Wall" site, the longitudes of both these sites were almost identical. This may have also played a hand in the mix-up.

One more factor to muddy the waters was that in the early VSAG/BSAC documentation, the conversion of "google" longitude coordinates (decimal degrees) into degrees and decimal minutes was wrong. So in that format the pre-2018 Lonsdale Wall sites appeared to be in about the middle of Pt Lonsdale's main street! (I think this stemmed from a rogue "copy & paste" of the pre-2018 "Lonsdale Arches" numbers - but only the Lats were subsequently re-edited after the paste, leaving the original Longs uncorrected.)

So all this baggage set the stage for a bungled correction whereby instead of a 80m shift of GPS coordinates towards the wall lip as I was suggesting, we got a whopping 500m shift north into Victory Bight. This replaced Lloyds own "Lonsdale Wall Shallow" site with the "Lonsdale Wall" name, but kept the more northern latitude coordinate. I have been trying for over a year to get this undone but without success. The following set of 3D & 2D style images at successively higher levels of zoom and accuracy show the current situation, and the need for it to be repaired:-


***** Image #1 *****
Image
An oblique aerial view looking into the Rip from the southwest along the main channel leads. This is a PoMC image from the channel deepening planning phase (2004 - 2007). In the central region the sea has been "peeled back" to show their seabed depth data. The deep entrance canyon is shown in dark blue with the shallower areas in lighter blues, greens and yellows. The red hatched areas show the Rip Bank and Nepean Bank dredging targets.

The dive sites numbered 1 -> 8 are marked as closely as possible to their respective positions. The GPS coordinates (WGS84), names, and sources used are as follows:-

Code: Select all

1 -> 38 17.153 S, 144 37.839 E  = "Lonsdale Wall" from 2018+ Scuba Doctor list (formerly "Lonsdale Wall Shallow").   
2 -> 38 17.522 S, 144 37.833 E  = "Lonsdale Wall" from pre-2018 Scuba Doctor list (now removed).
3 -> 38 17.479 S, 144 37.788 E  = "Lonsdale Wall Shallow" 2009 - 2014 VSAG/BSAC site list.
4 -> 38 17.425 S, 144 37.885 E  = "LONWAL" from 2005 Getunder dive club site list.
5 -> 38 17.479 S, 144 37.813 E  = "Packo's drop off" from 1976 horizonal sextant angles converted to WGS84.
6 -> 38 17.447 S, 144 37.851 E  = "Party Point" from 2019 Scuba Doctor site list.
7 -> 38 17.447 S, 144 37.899 E  = "Paradise Wall" from 2019 Scuba Doctor site list.
8 -> 38 17.404 S, 144 37.977 E  = "Spot G" from 2019 Scuba Doctor site list.

So you see site #1 from the Scuba Doctor's 2018+ list is a long way from all the other sites clustered along the "Lonsdale Wall" side of the entrance canyon.


***** Image #2 *****
Image
The base image is a small section around Lonsdale Wall derived from PoMC multi-beam echo sounder surveys with the waters less than 10m showing in various shades of red. This copy is from a "Dive Vic Group" image that appeared some years ago on their old website. The square place markers are DVG's work and attempt to show the positions of some of their dive sites. The ones included here are OK, but the underlying PoMC image used a rather tricky projection that makes it quite distorted with changing map scales across the whole image and where most bearing lines are actually curves.

All this means it is quite hard to correctly identify the GPS co-ordinates of features in the image (and vice-versa). In parts of the image not shown here, DVG's placement of markers for their other dive sites ranged from dangerously-misplaced, through to roughly-OK, and then on to plain laugh-out-loud silly!

They took the image down after just a few days to avoid embarrassment to the dive shop. It is all rather a pity really because apart from some of their misplaced markings, it was a lovely clear and colourful display of just what's down there! The resolution of their original posting was good enough so features of just 10m across were discernible.

After a lot of work to understand and verify the image distortions, I have good confidence that each of the circular dive site markers from 1 --> 8 is within 30m of its GPS coordinates as given earlier. These show that the current Scuba Doctor "Lonsdale Wall" mark (site #1) is quite a long way from where the real action is and doesn't feature dramatic deep drop offs.

Also note my original complaint that site #2, the "Lonsdale Wall" location in the SD list prior to 2018, is in deep water rather too far from the edge of the wall. Note also the square #3 site marker from Dive Vic was listed as "Devil's Drop Off". This may give some guide as to the necessary correction. (refer to "packo's bungle" at the top of this post.)


***** Image #3 *****
Again the base image is from the PoMC's survey work, but this time a biological survey. It is at a slightly larger scale than the previous one and uses yet again another different colouring scheme for water depths. The only distortion here is a straight forward North-South squash of about 20%. This makes one tenth of a minute of Latitude (185m) appear the same size as a tenth of a minute of Longitude (145m).
Image

I have overlaid a red grid of decimal minutes (WGS84) because it is more convenient to check positions from it rather than the original black minutes & seconds markings. The grid looks square rather than the usual rectangular one because of the map distortion. The white numbered circles are the same dive sites as given earlier except that site #1 is well out of the picture at this larger scale.

The groups of coloured circles labeled A, B, C, & D are the "Lonsdale Wall" sampling sites as determined by the marine biologists doing the survey. These circle groups mark various survey transits down the canyon walls between depths of 27m (blue circles) and 57m (red circles). They seem to show less interest in the shallower parts of the wall.

Most of the sites favoured by recreational divers are closer to the middle and northern end of the Lonsdale wall structure. Sadly, and for unknown reasons, the image does not show the depth colouring along the upper reaches of the Lonsdale wall section of the canyon. This makes that section all look a bit drab and unexciting. From other data, I have marked in a pink line as a "best guess" of the wall lip contour (at say 14m).


***** Image #4 *****
This shows a similar area to the previous image but has a nicer depth colouring scheme and shows the Lonsdale Wall lip a little better. Again the base image comes from PoMC work but used MGA coordinates. This means the overlaid red WGS84 grid is slightly angled but is otherwise undistorted. The same numbered dive sites as before have been plotted onto the image.
Image

Note the round site markers cover bottom terrain about 15m across which gives some guide as to the separation between sites. (Note there is some suspicion about the latitude of site #7 which is given in the SD list as identical to site #6 even though it is some 80m further east, and over that distance the wall lip has crept some 30m further northwards.)


***** What was/is trying to be achieved here???? *****

The green arrow in the image above shows the shift I was originally suggesting some 15 months ago to move site #2 (ScubaDoc's old "Lonsdale Wall") about 80m over to the actual wall lip at suggested site marker #9 shown in green. The new coordinates I'm suggesting are 38 17.487 S, 144 37.797 E [with VSAG attribution because it was between their original "Lonsdale Wall Shallow" (#3) and their deeper "Lonsdale Wall" site (#2)].

It all seemed sensible to me but instead Lloyd went off on some narcosis induced tangent, shifting site #2 way up north to take on the coordinates of his own (and different) "Lonsdale Wall Shallow" (this was site #1 and visible only in the first two images). The "shallow" part of the name was then dropped, and of course the GPS coordinates of both the old VSAG "Lonsdale Wall" sites fell out of the database.

Along with the large position shift, this "revamped" list entry now also inherited the old "read more" links including linked videos from the real Lonsdale Wall site. It also acquired a 12m to 38m depth rating even though there is no water deeper than 25m anywhere within several hundred metres of this new "Lonsdale wall" site.

In the long run, publishing such misinformation can only result in disappointed divers when the site fails to live up to the hype about the iconic "Lonsdale Wall" system. I've tried half a dozen times to get this situation fixed but get rebuffed every time.

At the time this change happened, in early 2018, the only comments Lloyd made about it are quoted below:-

"I've updated the Lonsdale Wall location with a mark from a better source. (It's what was the Lonsdale Wall Shallow mark.)"


- Perhaps the better source should have been the old VSAG/BSAC "Lonsdale Wall Shallow" as it was just 20m to 30m from the lip of a genuine 12m to 50m wall almost due east of the Lonsdale lighthouse.

"Not sure how that other location got in there."


- The old "Lonsdale Wall" coords previously in the list were inherited from VSAG/BSAC folk long ago, they are in the right area but perhaps were just a little too far off the wall for safety.

"The mark for Lonsdale Wall, -38 17.153, 144 37.839, is what is/was used by the dive charter operators."


- No it isn't/wasn't any charterer's mark for "Lonsdale Wall". However one charterer used to take divers there and they clearly referred to it as "Lonsdale Wall Shallow". (Possibly this site was used as being suitable for divers with only a basic OW qualification.) It was dropping the word "Shallow" that caused the problem and allowed this more northern site to masquerade as the real "Lonsdale Wall".

The old Dive Vic Site Maps clearly show their "Lonsdale Wall" as being almost due east of the Lonsdale Lighthouse whose latitude is somewhere around 38 17.5 S. Many charts and other sources also put the middle of the wall near that latitude.

The latitude of the new ScubaDoc mark (38 17.153 S) is over 0.5km north of the real Lonsdale Wall position that has been documented since "forever". I started diving Lonsdale Wall in 1976 after finding it with the help of a large scale Ports & Harbours chart. Not many boats around back then but its popularity steadily grew.

Nowadays the most favoured spots tend to be around the northern end of the wall where the deeper section turns to the east. Some like to go just beyond the Marine Park boundary where crays can be taken. We can all argue over where the "absolute best spot" is, but it is all pretty good, and it also depends slightly on what you are into.

However almost all regular visitors would have to agree that the myriad of "Lonsdale Wall" sites don't start until southward of latitude 38 17.400 S, so the SD latitude minutes of 17.153 S is a bit of a fly in the ointment.

So in my view an iconic VIC dive location(s) that might be in the sights of visiting boat divers, or the next generation of locals, has had a lesser site substituted! This situation can only lead to disappointments.

Each time I try to fix it I get rebuffed with Lloyd saying he wants verified coordinates from more high profile divers before he will change anything. (Pity the same rigour wasn't applied to vetting the "giant leap north" early in 2018!)

So come on high profile divers, do your bit and post here or drop Scuba Doctor an email. The aim is simply to make sure any private boat divers don't get led astray. I note in the recently added new sites that both Graham Ellis and JL have stepped up to offer up several marks for new sites. Maybe these gents could be contacted again to help finally sort this issue out?

Let's not be too stubborn on this one! Although the back-story is rather confusing, the needed outcome is pretty clear cut. If nothing is done for yet another year, then the dive shop, some of its customers, and some of its website readers will continue to be the losers.


****** Anything more? *****

I don't think I can do much more except to show a final compilation of parts of three images from the Scuba Doctor's own "Scuba Diving Downloads" page. It shows position info for "Lonsdale Wall" dives in these downloadable maps that is at odds with the GPS numbers in the website's Dive Site List.

***** Image #5 *****
Image

Final note: When Parks Vic corrected their Port Phillip Heads Marine National Park Map, they not only altered its URL but inserted a "waffle page" ahead of the map itself. Pity they couldn't just correct the map and leave it as a 1-page pdf. (Heritage Vic can also move stuff about with no thought of those who might have linked to it.)

So at the moment the SD website features a number of broken links to the Parks Vic website:-
http://parkweb.vic.gov.au/__data/assets ... ds-MNP.pdf [BROKEN]

In the Scuba Diving Downloads section there is a link to its own internal copy of the old map:-
https://www.scubadoctor.com.au/download ... ds-MNP.pdf [Link WORKS but with GPS errors]

Perhaps SD might think about taking a new copy of just page 2 of the corrected version from:-
https://parkweb.vic.gov.au/__data/asset ... l-Park.pdf
and using it to update the download area file and then directing the other broken links back to SD's own (new) copy.

cheers,
packo



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Thu, 14 Mar 2019 9:07 am

packo wrote:[color=#0000ff]So at the moment the SD website features a number of broken links to the Parks Vic website:-
http://parkweb.vic.gov.au/__data/assets ... ds-MNP.pdf [BROKEN]

In the Scuba Diving Downloads section there is a link to its own internal copy of the old map:-
https://www.scubadoctor.com.au/download ... ds-MNP.pdf [Link WORKS but with GPS errors]

Perhaps SD might think about taking a new copy of just page 2 of the corrected version from:-
https://parkweb.vic.gov.au/__data/asset ... l-Park.pdf
and using it to update the download area file and then directing the other broken links back to SD's own (new) copy.


I've created a one page PDF of the updated Parks Victoria map. As best as I can tell, all of the broken links now point to the new map. Thanks for the heads up Packo.

Best regards, Lloyd Borrett.



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Thu, 14 Mar 2019 9:15 am

packo wrote:***** Packo's Correction Blunder for the "Devil's Drop Off" Site *****
At least anyone diving those numbers would have had a drop off to dive on, but possibly not up to the standard of the real "Devil's Drop Off" site. I hope Lloyd or anyone else can discover the correct coordinates for the "Devil's Drop Off" site and then get the database corrected.


Nothing really for me to do until I have a verified set of coordinates for Devils Drop Off.

Best regards, Lloyd Borrett.



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Thu, 14 Mar 2019 9:19 am

packo wrote:(However note "The Abyss" dive site page also claims it to be on the Lonsdale side but I know it isn't. I think the similar wording in these descriptive texts comes from a Dive Vic generic "copy & paste" about wall sites, so the text isn't always reliable unless it is a first person account and avoids any copy & pastes from other site descriptions.)


So, do we currently have the correct coordinates for The Abyss?
https://www.scubadoctor.com.au/divesite ... =The-Abyss

How does the description need to be changed to be correct?

Best regards, Lloyd Borrett.



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Thu, 14 Mar 2019 9:38 am

packo wrote:***** Lloyd's Correction Blunder for the "Lonsdale Wall" Site *****

Ok I have harped on about this a number of times and even threatened to give up and let the bad info stand. However it is far too important a dive site to let it rest at that!

I also harbour some guilt in that if I had kept my mouth shut in the first place about trying to get a minor coordinate change done, we would all have been better off. That course of action would have at least stopped a fairly small error from being turned into a much bigger one!

The Lonsdale Wall is an iconic and quintessentially "Port Phillip Heads" dive site(s) and wall system. It has national recognition and even some international recognition. We just shouldn't have one of the dive shops that support private boat divers visiting this area putting out misinformation and directing these divers to the wrong spot!

So here I am trying yet again for a fix. The muck up was triggered by a large knee-jerk response to my minor complaint back in late 2017 that the then "Lonsdale Wall" Scuba Doctor coordinates of 38 17.522 S, 144 37.833 E (WGS84 from a previous VSAG list) were in rather deep 50m+ water about 80m southeast of the actual Wall lip.

All I was suggesting was a slight pruning of Lat & Long back to the wall lip itself: Say to 38 17.487 S, 144 37.797 E which would be pretty close to the lip and is a shift of about 80m. This would also be fairly close to another VSAG/BSAC 2014 location called "Lonsdale Wall Shallow" at 38 17.479 S, 144 37.788 E where the wall started in only 12m and dropped away to 50m+. (I assume the term "shallow" here was in reference to the relatively shallow starting depth.)

Although this correction might sound straightforward, there were added complications because of some additional site confusion. In 2007 & 2008 the Dive Vic charter Group took Lloyd and a few VSAG bods to a location some 0.5km further to the north that was also called "Lonsdale Wall Shallow". (This time the term "shallow" was a suitable description because the entire depth range was only around 13m to 22m)

Furthermore because this site was almost exactly due north of the pre-2018 Scuba Doctor "Lonsdale Wall" site, the longitudes of both these sites were almost identical. This may have also played a hand in the mix-up.

One more factor to muddy the waters was that in the early VSAG/BSAC documentation, the conversion of "google" longitude coordinates (decimal degrees) into degrees and decimal minutes was wrong. So in that format the pre-2018 Lonsdale Wall sites appeared to be in about the middle of Pt Lonsdale's main street! (I think this stemmed from a rogue "copy & paste" of the pre-2018 "Lonsdale Arches" numbers - but only the Lats were subsequently re-edited after the paste, leaving the original Longs uncorrected.)

So all this baggage set the stage for a bungled correction whereby instead of a 80m shift of GPS coordinates towards the wall lip as I was suggesting, we got a whopping 500m shift north into Victory Bight. This replaced Lloyds own "Lonsdale Wall Shallow" site with the "Lonsdale Wall" name, but kept the more northern latitude coordinate. I have been trying for over a year to get this undone but without success. The following set of 3D & 2D style images at successively higher levels of zoom and accuracy show the current situation, and the need for it to be repaired:-


***** Image #1 *****
Image
An oblique aerial view looking into the Rip from the southwest along the main channel leads. This is a PoMC image from the channel deepening planning phase (2004 - 2007). In the central region the sea has been "peeled back" to show their seabed depth data. The deep entrance canyon is shown in dark blue with the shallower areas in lighter blues, greens and yellows. The red hatched areas show the Rip Bank and Nepean Bank dredging targets.

The dive sites numbered 1 -> 8 are marked as closely as possible to their respective positions. The GPS coordinates (WGS84), names, and sources used are as follows:-

Code: Select all

1 -> 38 17.153 S, 144 37.839 E  = "Lonsdale Wall" from 2018+ Scuba Doctor list (formerly "Lonsdale Wall Shallow").   
2 -> 38 17.522 S, 144 37.833 E  = "Lonsdale Wall" from pre-2018 Scuba Doctor list (now removed).
3 -> 38 17.479 S, 144 37.788 E  = "Lonsdale Wall Shallow" 2009 - 2014 VSAG/BSAC site list.
4 -> 38 17.425 S, 144 37.885 E  = "LONWAL" from 2005 Getunder dive club site list.
5 -> 38 17.479 S, 144 37.813 E  = "Packo's drop off" from 1976 horizonal sextant angles converted to WGS84.
6 -> 38 17.447 S, 144 37.851 E  = "Party Point" from 2019 Scuba Doctor site list.
7 -> 38 17.447 S, 144 37.899 E  = "Paradise Wall" from 2019 Scuba Doctor site list.
8 -> 38 17.404 S, 144 37.977 E  = "Spot G" from 2019 Scuba Doctor site list.

So you see site #1 from the Scuba Doctor's 2018+ list is a long way from all the other sites clustered along the "Lonsdale Wall" side of the entrance canyon.


***** Image #2 *****
Image
The base image is a small section around Lonsdale Wall derived from PoMC multi-beam echo sounder surveys with the waters less than 10m showing in various shades of red. This copy is from a "Dive Vic Group" image that appeared some years ago on their old website. The square place markers are DVG's work and attempt to show the positions of some of their dive sites. The ones included here are OK, but the underlying PoMC image used a rather tricky projection that makes it quite distorted with changing map scales across the whole image and where most bearing lines are actually curves.

All this means it is quite hard to correctly identify the GPS co-ordinates of features in the image (and vice-versa). In parts of the image not shown here, DVG's placement of markers for their other dive sites ranged from dangerously-misplaced, through to roughly-OK, and then on to plain laugh-out-loud silly!

They took the image down after just a few days to avoid embarrassment to the dive shop. It is all rather a pity really because apart from some of their misplaced markings, it was a lovely clear and colourful display of just what's down there! The resolution of their original posting was good enough so features of just 10m across were discernible.

After a lot of work to understand and verify the image distortions, I have good confidence that each of the circular dive site markers from 1 --> 8 is within 30m of its GPS coordinates as given earlier. These show that the current Scuba Doctor "Lonsdale Wall" mark (site #1) is quite a long way from where the real action is and doesn't feature dramatic deep drop offs.

Also note my original complaint that site #2, the "Lonsdale Wall" location in the SD list prior to 2018, is in deep water rather too far from the edge of the wall. Note also the square #3 site marker from Dive Vic was listed as "Devil's Drop Off". This may give some guide as to the necessary correction. (refer to "packo's bungle" at the top of this post.)


***** Image #3 *****
Again the base image is from the PoMC's survey work, but this time a biological survey. It is at a slightly larger scale than the previous one and uses yet again another different colouring scheme for water depths. The only distortion here is a straight forward North-South squash of about 20%. This makes one tenth of a minute of Latitude (185m) appear the same size as a tenth of a minute of Longitude (145m).
Image

I have overlaid a red grid of decimal minutes (WGS84) because it is more convenient to check positions from it rather than the original black minutes & seconds markings. The grid looks square rather than the usual rectangular one because of the map distortion. The white numbered circles are the same dive sites as given earlier except that site #1 is well out of the picture at this larger scale.

The groups of coloured circles labeled A, B, C, & D are the "Lonsdale Wall" sampling sites as determined by the marine biologists doing the survey. These circle groups mark various survey transits down the canyon walls between depths of 27m (blue circles) and 57m (red circles). They seem to show less interest in the shallower parts of the wall.

Most of the sites favoured by recreational divers are closer to the middle and northern end of the Lonsdale wall structure. Sadly, and for unknown reasons, the image does not show the depth colouring along the upper reaches of the Lonsdale wall section of the canyon. This makes that section all look a bit drab and unexciting. From other data, I have marked in a pink line as a "best guess" of the wall lip contour (at say 14m).


***** Image #4 *****
This shows a similar area to the previous image but has a nicer depth colouring scheme and shows the Lonsdale Wall lip a little better. Again the base image comes from PoMC work but used MGA coordinates. This means the overlaid red WGS84 grid is slightly angled but is otherwise undistorted. The same numbered dive sites as before have been plotted onto the image.
Image

Note the round site markers cover bottom terrain about 15m across which gives some guide as to the separation between sites. (Note there is some suspicion about the latitude of site #7 which is given in the SD list as identical to site #6 even though it is some 80m further east, and over that distance the wall lip has crept some 30m further northwards.)


***** What was/is trying to be achieved here???? *****

The green arrow in the image above shows the shift I was originally suggesting some 15 months ago to move site #2 (ScubaDoc's old "Lonsdale Wall") about 80m over to the actual wall lip at suggested site marker #9 shown in green. The new coordinates I'm suggesting are 38 17.487 S, 144 37.797 E [with VSAG attribution because it was between their original "Lonsdale Wall Shallow" (#3) and their deeper "Lonsdale Wall" site (#2)].

It all seemed sensible to me but instead Lloyd went off on some narcosis induced tangent, shifting site #2 way up north to take on the coordinates of his own (and different) "Lonsdale Wall Shallow" (this was site #1 and visible only in the first two images). The "shallow" part of the name was then dropped, and of course the GPS coordinates of both the old VSAG "Lonsdale Wall" sites fell out of the database.

Along with the large position shift, this "revamped" list entry now also inherited the old "read more" links including linked videos from the real Lonsdale Wall site. It also acquired a 12m to 38m depth rating even though there is no water deeper than 25m anywhere within several hundred metres of this new "Lonsdale wall" site.

In the long run, publishing such misinformation can only result in disappointed divers when the site fails to live up to the hype about the iconic "Lonsdale Wall" system. I've tried half a dozen times to get this situation fixed but get rebuffed every time.

At the time this change happened, in early 2018, the only comments Lloyd made about it are quoted below:-

"I've updated the Lonsdale Wall location with a mark from a better source. (It's what was the Lonsdale Wall Shallow mark.)"


- Perhaps the better source should have been the old VSAG/BSAC "Lonsdale Wall Shallow" as it was just 20m to 30m from the lip of a genuine 12m to 50m wall almost due east of the Lonsdale lighthouse.

"Not sure how that other location got in there."


- The old "Lonsdale Wall" coords previously in the list were inherited from VSAG/BSAC folk long ago, they are in the right area but perhaps were just a little too far off the wall for safety.

"The mark for Lonsdale Wall, -38 17.153, 144 37.839, is what is/was used by the dive charter operators."


- No it isn't/wasn't any charterer's mark for "Lonsdale Wall". However one charterer used to take divers there and they clearly referred to it as "Lonsdale Wall Shallow". (Possibly this site was used as being suitable for divers with only a basic OW qualification.) It was dropping the word "Shallow" that caused the problem and allowed this more northern site to masquerade as the real "Lonsdale Wall".

The old Dive Vic Site Maps clearly show their "Lonsdale Wall" as being almost due east of the Lonsdale Lighthouse whose latitude is somewhere around 38 17.5 S. Many charts and other sources also put the middle of the wall near that latitude.

The latitude of the new ScubaDoc mark (38 17.153 S) is over 0.5km north of the real Lonsdale Wall position that has been documented since "forever". I started diving Lonsdale Wall in 1976 after finding it with the help of a large scale Ports & Harbours chart. Not many boats around back then but its popularity steadily grew.

Nowadays the most favoured spots tend to be around the northern end of the wall where the deeper section turns to the east. Some like to go just beyond the Marine Park boundary where crays can be taken. We can all argue over where the "absolute best spot" is, but it is all pretty good, and it also depends slightly on what you are into.

However almost all regular visitors would have to agree that the myriad of "Lonsdale Wall" sites don't start until southward of latitude 38 17.400 S, so the SD latitude minutes of 17.153 S is a bit of a fly in the ointment.

So in my view an iconic VIC dive location(s) that might be in the sights of visiting boat divers, or the next generation of locals, has had a lesser site substituted! This situation can only lead to disappointments.

Each time I try to fix it I get rebuffed with Lloyd saying he wants verified coordinates from more high profile divers before he will change anything. (Pity the same rigour wasn't applied to vetting the "giant leap north" early in 2018!)

So come on high profile divers, do your bit and post here or drop Scuba Doctor an email. The aim is simply to make sure any private boat divers don't get led astray. I note in the recently added new sites that both Graham Ellis and JL have stepped up to offer up several marks for new sites. Maybe these gents could be contacted again to help finally sort this issue out?

Let's not be too stubborn on this one! Although the back-story is rather confusing, the needed outcome is pretty clear cut. If nothing is done for yet another year, then the dive shop, some of its customers, and some of its website readers will continue to be the losers.


That's all great information and I can certainly appreciate the time and effort put into it. But no solution is proposed.

Seems one solution would be to rename the current Lonsdale Wall back to Lonsdale Wall Shallow and update its description appropriately.

Then add a new Lonsdale Wall site with the current description. But where to place it?
Would the Getunder mark do, or should it be somewhere else?
4 -> 38 17.425 S, 144 37.885 E = "LONWAL" from 2005 Getunder dive club site list.

Best regards, Lloyd Borrett.



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Thu, 14 Mar 2019 9:41 am

packo wrote:The dive sites numbered 1 -> 8 are marked as closely as possible to their respective positions. The GPS coordinates (WGS84), names, and sources used are as follows:-

Code: Select all

1 -> 38 17.153 S, 144 37.839 E  = "Lonsdale Wall" from 2018+ Scuba Doctor list (formerly "Lonsdale Wall Shallow").   
2 -> 38 17.522 S, 144 37.833 E  = "Lonsdale Wall" from pre-2018 Scuba Doctor list (now removed).
3 -> 38 17.479 S, 144 37.788 E  = "Lonsdale Wall Shallow" 2009 - 2014 VSAG/BSAC site list.
4 -> 38 17.425 S, 144 37.885 E  = "LONWAL" from 2005 Getunder dive club site list.
5 -> 38 17.479 S, 144 37.813 E  = "Packo's drop off" from 1976 horizonal sextant angles converted to WGS84.
6 -> 38 17.447 S, 144 37.851 E  = "Party Point" from 2019 Scuba Doctor site list.
7 -> 38 17.447 S, 144 37.899 E  = "Paradise Wall" from 2019 Scuba Doctor site list.
8 -> 38 17.404 S, 144 37.977 E  = "Spot G" from 2019 Scuba Doctor site list.



Should we be adding Packos Drop Off as a site?

If so, how about a description?

Best regards, Lloyd Borrett.



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby packo » Sat, 16 Mar 2019 12:50 am

Hello,

Thanks Lloyd for reading & replying to the original post. Sorry I had to nag you into it but the Lonsdale Wall area is too important to let sleeping dogs lie.

In reply Lloyd wrote:-

That's all great information and I can certainly appreciate the time and effort put into it. But no solution is proposed.

Seems one solution would be to rename the current Lonsdale Wall back to Lonsdale Wall Shallow and update its description appropriately.

Then add a new Lonsdale Wall site with the current description. But where to place it?

I believed I did put forward a clear solution: use site #9 coords of 38 17.487 S, 144 37.797 E for a resurected "Lonsdale Wall" entry (because that is about the closest part of the wall to the original sites #2 & #3 from the VSAG/BSAC list days.)

What to do with the current SD "Lonsdale Wall" location / former SD "Lonsdale Wall Shallow" location? Since the only reference to this northern site that I have seen or heard of is in your own dive log, I was leaving it entirely up to you as to what to do with those coords and what descriptive text is appropriate.

The comment section in your log seems to suggest it was a nice dive, but then goes on to say that you could hardly wait to do Lonsdale Wall proper. Make of that what you will.

Lloyd I know you are struggling to accept my numbers, possibly because of our past history or possibly because with sites #2 & #3 dropping out of the database you have some doubts about their authenticity. Perhaps this image of your previous work on the BSAC dive site list (captured in 2014) might restore some confidence in them. The grab is of the "all things Lonsdale" from the list at that time:-

Image

Note the last two entries (Wall Dives) and the dates and originator at right. These two locations stood in that list for 7 years, and I believe were both transferred into the SD list. The first remained intact in the SD list for a further 4 years until a change shifted it north (to site #1) in Jan 2018. The second may have lasted in the SD list for a shorter time, but all I can establish for sure is that by March 2016 it also had moved some 600m north to morph into site #1.

Note the red numbers correct the minutes format of Longitudes of those two sites. It seems these errors arose from an incomplete copy/paste/re-edit "time saving" manoeuvre, with the 36.744 value displayed for both sites being uncorrected copies of the old "Lonsdale Arches" site longitude just visible at the top of the list. [This also took a fair hike (westward) in Jan 2018, but that is another story for another day. :)]

My argument is that the old sites #2 & #3 that Lloyd recorded in 2007 had some pedigree and for a long time represented "Lonsdale Wall" GPS numbers once that technology arrived. This was the section of the wall that was most popular in the late 1970s, 1980s, & 1990s, and is definitely close to where the early charter outfits used to go.

The later shift to favour the slightly more northern sites (eg. The Getunder site), and the surrounding ones with ever more flowery names is no reason to distort the history. There are already plenty of SD sites squashed into that area and we don't really need another one there! People need to explore much larger sections of the wall to see which they like best.

A mistake I may have made was to assume the Lonsdale Wall site in the above snippet, which is about 80m off the wall and in quite deep water, was sourced from scuba divers. This may not have been the case as I now see its source is listed as "unknown". I have seen those identical numbers published by "Seamus" a local fisho as a "kingfish location".

I had assumed he/she may have grabbed the coords from early diver's lists. However it now seems that a more sensible explanation is that the transfer went the other way around. This may explain the "too far off the wall" location. If this were true, it would leave the original old site #3 as the better "diver mark" for the the early days Lonsdale Wall site, and site #2 should be ditched as being dangerously far off the wall and not a useful mark for divers.

However I do believe site #3 is just a little too far "inland" for its coordinates to be useful for either anchor or shot-line placement. (Wasted bottom time, risk of getting lost and not finding the wall, risk of not re-finding shot or anchor.) Thats why site #9 much closer to the wall lip seems a better bet while still paying homage to the early Lonnie Wall divers.

Nearby site #5 (a "packo 1970s site") I used to enjoy as it features a fairly abrupt drop with twin rocky pinnacles starting at about 110 feet on the wall and rising 20 feet or so upwards. Behind them are good undercuts and a fairly claustrophobic "15m long tunnel swim-though". Its ceiling was adorned with numerous small gorgonian fans of every conceivable colour. Good torch and nerves needed!

The GPS coords listed for that site were obtained by using the horizontal sextant angles I was using back in that era and then "reverse engineering" them back into into today's WGS84 numbers. Nothing at all wrong with these calculations, but the sextant was a home-made plastic one and I can't really vouch for the degree markings being any better than 0.1 degree accurate. This leaves some metres of uncertainty.

In more recent times I find that like AB, "heads-up" navigation using old visual transits allows better placement accuracy than by using screen numbers from the GPS while in a cross-current. The net result is that I never got round to confirming how close the given GPS numbers are to the wall directly above the twin rock formation. On that basis I won't offer it up as an SD listed site at this stage. Realistically it is only short swim from site #9. Even "return to the shot-line" style divers will easily range several times that distance along the wall in one dive.

***** The Abyss *****
Lloyd also wrote:-
So, do we currently have the correct coordinates for The Abyss?
How does the description need to be changed to be correct?

I think the coords are ok, but haven't actually dived this site. Ran the sounder over it a few times though. Your numbers agree fairly well the old DVG maps and the PoMC dive sites map and other charting info.

The site is about 1.3km NW of Pt Nepean with the wall here roughly 20 to 40m and facing NE. Some distance off the wall lies a very large bommie over 100m E-W and perhaps 40m N-S.

Not real sure of the separation between the main wall and the bommie wall (perhaps 30-40m?), but in good vis maybe you can see both sides of the drop as you sink down into "The Abyss" between the two structures.

The one thing that does need correction however is the descriptive text. It claims this site is on the "Lonsdale side" of the entrance. Taking the centre of the Heads at roughly longitude 144 38.000 E, it is clear that "The Abyss" at 144 38.626 E is nearly 900m on the Pt Nepean side of the centre line.

Seems to me that this text is in fact a copy and paste of Dive Vic's old description, which in itself also seems to be an inappropriate "copy/paste/failure to re-edit" from one of their other sites. Not only is the "side" wrong, but the depth is a little understated, and it also claims a large flat area which is at odds with "The Abyss" name and several sources of depth surveys.


***** Devils Drop Off *****

Currently the SD list has this site within swimming distance of "The Abyss". As mentioned in the original post the given coords are bad - in part this was my fault for offering up a change to the original very whacky coords without realising BOTH the original Lat & Long values were whacky. It was not just a case of a simple slip-up in one digit of the latitude minutes as I first thought.

I think I got sucked in here thinking it was a "devilish drop off", appropriately quite close to the evil sounding "The Abyss" site. I've recently come to my senses and realised from numerous other references that this is actually on the Lonsdale side, and it is not "devil" as in Satan, but "devil" as in Blue Devil fish.

Don't know the exact coords but possibly quite close to the Lonsdale Wall sites 3,5, & 9 discussed earlier. I know Chimney Rock Charters has a site they call "Blue Devil Wall" which I think is in that vicinity.

Not sure Lloyd's comment ...

Nothing really for me to do until I have a verified set of coordinates for Devils Drop Off.


… is quite the way to go here. The site's descriptive text is totally at odds with the given coordinates including the rather shallow minimum depth.
So the info presented is self contradictory.

Maybe this site should be "pulled" until someone authoritative coughs up the proper GPS numbers. This may take a while as many divers are unwilling to let their marks see the light of day.

In the meantime browsing the internet will throw up plenty of items suggesting that site is along the Lonsdale Wall and not across the water near "The Abyss". One such item I found was from the RedBoats charter operation itself:-

"On Sunday 5th of November 2017, Red Devil performed her maiden voyage carrying Scuba Divers from Portsea and Queenscliff to the aptly chosen dive site of “Devils Dropoff”, which is a fantastic section of Lonsdale Wall famous for its Blue Devil fish."

So if the RedBoats and the old DVG mob (image #2 original post) both claim its along the Lonsdale Wall who am I to argue, and should SD continue to be suggesting otherwise with its current coordinates?

Another descriptive item found was:-

"Devil's Drop Off"
One of the most popular dive sites on Lonsdale wall, this site begins with a huge dropoff from 12 to 30m and continues with a series of ledges, overhangs and swim-throughs and then gently slopes to 55m+. This is also the habitat of the Southern Blue Devil fish which can be spotted all along the wall here. Their placid nature and vibrant blue colour also makes them great for photography. You will also come across many other species of marine life here as the site lies in the Marine Park. At 27m there is a long overhang to follow covered in a large variety of soft corals and small fans. A spectacular dive site with something for everyone."


The description is very "lonnie wall like" in both depth and site character. The mention of its Marine Park location also rules against the current SD location using that name. I'll leave it for Lloyd to chew over how best to react, and I'll keep my ear to the ground should accurate coordinates come my way. Others are invited to chip in by registering and replying here, or by dropping the dive shop a line.

Keep up all the good work and improvements Lloyd, it is becoming a great site.

cheers,
packo



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Sat, 16 Mar 2019 11:20 am

G'day,

We now have Lonsdale Wall and Lonsdale Wall Shallow, hopefully with appropriate descriptions.

We now have The Abyss with a more appropriate description.

We await the correct coordinates for Devils Drop Off, which has been renamed from Devils Dropoff.

Best regards, Lloyd Borrett.



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby packo » Sun, 17 Mar 2019 10:15 am

Thanks Lloyd for those changes. I am sure it is for the best, and I promise not to hassle you for awhile .......

...Except that I think I may have made a bad suggestion about just updating the ParksVic map (without a filename tweak).

I now find that from my desktop computer (which has visited that part of your site before), I still get the old map with errors. However on my tablet (that has never visited the downloads section before), I get the error free new map!

I'm guessing (but don't really have a clue!) that it might be due to caching of that old copy at my end? I don't really understand browser caching that well and I thought they would look at both filename and creation date to decide whether to reload from the internet or grab from the cache.

Apparently my ancient version of firefox doesn't. Not sure whether other browsers do this or not? (If I use an equally old version of safari on the desktop I get the new map, but this is no real test because that browser probably hasn't visited the SD website before so there would be nothing relevant in the cache.)

Anyway you will understand the problem way better than me, and it might just be my old out of date tech! However I thought if others might also experience this, a fix could be needed - such as a very slight tweak to the filename of the new map.

Sorry if all this causes you any extra bother!

cheers,
packo



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Re: Scuba Doctor Dive Maps - correcting the "corrections"

Postby lloyd_borrett » Sun, 17 Mar 2019 2:53 pm

packo wrote:I'm guessing (but don't really have a clue!) that it might be due to caching of that old copy at my end? I don't really understand browser caching that well and I thought they would look at both filename and creation date to decide whether to reload from the internet or grab from the cache.


It is browse caching. If you hold down the Ctrl key and click on the refresh icon in your browser you should get the new version.




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