CYCLONE ILSA

With respect to finding the wreck of RMS Koombana I have consistently held the view that the site will approximate an oil patch / slick discovered by Captain Upjohn late 2 April, 1912, almost a fortnight after Koombana went missing. Note that an oil slick was used to locate the wreck of the Derbyshire (https://en.wikipedia.org/wiki/MV_Derbyshire) and Clan Ranald, 1909. The exact location of the oil patch was dependent on Captain Upjohn's coordinates which were susceptible to period calculation errors. We have his broader guidance of 27 to 28 n miles northeast of Bedout Island. 

Wreckage was discovered approximately at the same time, a fortnight later, in various locations (see image below) including an awning spar and one of the planks in close proximity to the oil patch (not marked on image). In order to substantiate a theory that the oil patch marked the location of the wreck it could be postulated that the distribution of wreckage supports a starting point in the broader vicinity of this oil patch - a current, post cyclone, predominating in a generally westward direction (see a previous post, Analysis of Wreckage Distribution).

 

1. Stateroom door; painting stage; small pieces of board. SS Gorgon  
19 10 S, 119 06 E

2. Motor launch starboard bow plank (with insignia). SS Bullarra   
19 15 S, 119 06 E

3. Small wreckage; (life) boat tanks; lifebelts; panel from saloon / smoke room ceiling. SS Bullarra

(see: https://koombanarevisited.blogspot.com/2019/11/sufficient-warning.html) 
19 15 S, 119 06 E

4. Bottom board from (life) boat; white painted board. Lugger McLennan.  
19 22 S, 119 05 E 

5. (life) boat mast and small wreckage (rising from bottom). SS Una   
19 07 S, 118 53 E

6. Miscellaneous wreckage. SS Una  
25 miles NW Bedout Island. 

7. Miscellaneous wreckage. SS Una.  
28 miles NW Bedout Island.

(see https://koombanarevisited.blogspot.com/2019/10/captain-rantzau.html)

8. Cabin paneling. Lugger Mina.  
19 30 S, 118 55 E

9. Smoking room cushion; cabin door. SS Minderoo.  
19 36 S, 117 53 E 

10. Straw envelopes (Leech's fortune). SS Minderoo and SS Gorgon.  
55 miles NNW Port Hedland.
(see:  https://koombanarevisited.blogspot.com/2019/11/sufficient-warning.html)

11. Bottom boards (lifeboat); drawer; small teak panel. SS Minderoo.  
19 32 E, 118 09 S

(courtesy Annie Boyd)

I have taken a closer look at the most recent Cyclone Ilsa which made landfall between Port Hedland and Wallal Downs, a cyclone very similar in size and behaviour to the Balla Balla Cyclone of 1912, albeit north not south of Port Hedland. My intention is to document the daily surface currents in the vicinity of Bedout Island over a period of roughly a fortnight (when wreckage was first discovered, assumed to be rising from the wreck, as absolutely no wreckage was discovered during extensive searches prior to this) and observe whether a generally westward trending current in the vicinity of Bedout Island does in fact follow a direct cyclone hit in the Pilbarra during the late cyclone season of March and April.

Also important to note in retrospect how little impact was felt at Port Hedland and Broome. Being of similar size and targeting Balla Balla, the 1912 hurricane also did not not impact Port Hedland and Bedout Island to any significant degree.

Cyclone Ilsa path, north of Port Hedland,

Diameter, roughly 100 miles, similar to size of the 1912 Balla Balla cyclone.

courtesy The Age
https://www.theage.com.au/national/western-australia/cyclone-ilsa-live-updates-wa-coastline-to-be-rocked-by-category-5-cyclone-red-alert-imminent-20230413-p5d06k.html

13 APRIL - Bedout Island is roughly where the two 'll's' of Wallal Downs appear on the graphic. Note the predominantly westward surface current trend in the broader area. This is prior to cyclone Ilsa moving in.

Shipping cleared in path of Cyclone Ilsa (late 13 April)

courtesy VesselFinder.

14 APRIL - as Cyclone Ilsa made landfall between Port Hedland and Wallal Downs, note the distinct changes in the surface currents. Bedout Island experienced a record sustained wind speed of 218 km/hour.

15 APRIL - 1 day post cyclone - a distinctly counter, 'northeastward' trending surface current in the vicinity of Bedout Island.

16 APRIL - westward current around Bedout Island, 're-established'.

17 APRIL - unchanged, westward

18 APRIL - unchanged.

19 APRIL - unchanged.

20 APRIL - unchanged.

21 APRIL - unchanged.

22 APRIL - unchanged.

23 APRIL - unchanged.

24 APRIL - unchanged.

25 APRIL - unchanged.

26 APRIL - still generally westward current, but 'further out'.

27 APRIL - as above - general westward trend persists.

28 APRIL - unchanged.

29 APRIL - unambiguous, westward trending surface current.

In conclusion it appears that there is a generally westward trending surface current post cyclone that persists for up to a fortnight and which, more importantly, supports a flotsam drift theory with Captain Upjohn's oil patch as the starting point.

courtesy:

Google Earth

http://www.bom.gov.au/oceanography/forecasts/idyoc300.shtml?region=NWWA&forecast=SSTCur