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Posts Tagged ‘Whitsunday Passage

Joshua Slocum in Google Earth: Whitsunday Passage to Cooktown

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Follow Joshua Slocum’s Sailing Alone Around the World at: http://www.hazelhurst.net/Slocum

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Captain Cook, taking Endeavour through Whitsunday Passage (named by him because 03Jun1770 was Whit Sunday), sailed through the night and arrived the following morning at: “a lofty promontory that I named Cape Gloucester”.

Joshua Slocum, a few days short of 127 years later, passes here on 26May1897. His charts show more accurately than Cook’s survey that the promontory is actually detached from the mainland and is now called Gloucester Island. The Spray hauls into the bay to the west of the island and anchors at Port Denison, close to the small town of Bowen.

Bowen at that time has a population of around 1,000; large enough to support a keen audience for Slocum’s story.

By 31May1897, the Spray, has carried Slocum safely through 350 miles of the Great Barrier Reef. Without anchoring anywhere, Slocum sails past many of the other capes, bays, and islands named by Cook:

  • Cape Upstart
  • Cape Cleveland
  • Cleveland Bay
  • Cape Richards
  • Rockingham Bay
  • Cape Grafton
  • Fitzroy Island
  • Cape Tribulation (“for here all my troubles began”)

Cook also named the Endeavour River, for it was here that H.M.Bark Endeavour was beached for repairs after she had struck a reef just north of Cape Tribulation (the reef was named unsurprisingly Endeavour Reef).

Cooktown was certainly in existence before the gold rush of the 1870s, when the settlement grew rapidly as a supply port, because Slocum reports visiting on the steamship Soushay in 1866; he didn’t see much of it at that time because he was ill with a fever.

The “lecture tour” continues when a meeting is arranged in the Presbyterian church and Slocum delivers his “story of the sea.”


The section of Joshua Slocum’s journey reported here opens Chapter XV of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:  http://www.hazelhurst.net/Slocum

Copyright © Colin Hazlehurst, 2012

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Joshua Slocum in Google Earth: South Solitary Island to Whitsunday Passage

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Follow Joshua Slocum’s Sailing Alone Around the World at: http://www.hazelhurst.net/Slocum

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After exchanging signals at South Solitary Island, Slocum continues north and on 19May1897 sails past Point Danger, named by Captain Cook after his encounter with shoals and strong currents there.

On the 20th, the Spray rounds Sandy Cape, a significant point that marks the beginning of the Great Barrier Reef. The light on Sandy Cape is visible for 27 miles and his next way point is the Lady Elliot Island light. This is important to find because Slocum is heading into a dangerous region shoals and reefs and all the charts in the world are of little use if you don’t know where you are. Lady Elliot Island is about 45 miles from Sandy Cape but it seems to take an endless time to cover that distance. Slocum concludes he is pushing against a strong current.

The Spray had sailed for hours in suspense, evidently stemming a current. Almost mad with doubt, I grasped the helm to throw her head off shore, when blazing out of the sea was the light ahead. “Excalibur” cried “all hands,” and rejoiced, and sailed on.

So he finds the light on Lady Elliot Island¹ and passes into the serene, but still risky, waters inside the Great Barrier Reef and is protected from the worst of the Pacific Ocean’s waves. Progress is good and the Spray averages 4.6knots over the next four days:

On the 24th of May, the sloop, having made one hundred and ten miles a day from Danger Point, now entered Whitsunday Pass, and that night sailed through among the islands. When the sun rose next morning I looked back and regretted having gone by while it was dark, for the scenery far astern was varied and charming.


The section of Joshua Slocum’s journey reported here concludes Chapter XIV of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:  http://www.hazelhurst.net/Slocum

Notes

1. The  technical challenge in this part of the presentation was to simulate the light from the Lady Elliot Island lighthouse. I wanted to create a beam of white light that rotates about the location of the lighthouse; furthermore, I wanted it to have the same characteristic as the current light, which is described on charts as: Fl.W. 7.5s. This code means that the light is white and flashes every 7.5 seconds.

To achieve this I needed two things:

  • A model to animate.
  • A TourMaker directive to generate the animation.

I created the beam of light by drawing a cone in Google Sketchup and colouring it white. The cone was about a mile long, oriented along the green axis, which is north when the model is exported to Google Earth, and its apex was placed about 100 feet above the origin.

In the KML file for this leg of Slocum’s journey, I added the model as a Placemark, positioning it at the latitude and longitude of the Lady Elliot Island lighthouse (at the south end of the island). I set the visibility of the Placemark initially to zero (invisible), because I wanted to ‘turn on’ the light at the instant in the narrative that Slocum sees it.

To simulate a rotating beam I would need to animate the model by changing its orientation. By placing the origin of the model at the position of the lighthouse, a change in its orientation would have the desired effect of a light sweeping round.

I measured the angle subtended by the model and found that the edges of the cone were 15° apart. To achieve a smooth rotation, I would want each new orientation of the model to be no more than 15° away from the last one. I also knew that the beam should sweep through 360° in 7.5 seconds, in other words its angular velocity should be 360/7.5 degrees per second, which  comes out at 48° per second.

I used this information to determine how many orientation changes per second would be required to generate a smooth animation at the required rotation rate. Quite simply, if each animation step rotates the model by 15° and we need to rotate the model at 48° per second, then we need 48/15 animation steps per second (3.2), so the duration of each animation step should be 1/3.2 seconds (0.312s).

All of this is easy to code, taking only a few hours of development and testing. To control this behaviour, I added a ‘Rotate’ directive to TourMaker, and its parameters identify which model to animate, the duration of the animation, the angular velocity required, and the delay until the animation should start. This last parameter allowed me to switch on the beam as the narration reads:

Almost mad with doubt, I grasped the helm to throw her head off shore, when blazing out of the sea was the light ahead

The animation starts at the word ‘blazing’; the Placemark is made visible, the light sweeps around for 30 seconds and the Placemark is then made invisible.

Copyright © Colin Hazlehurst, 2012

Captain Cook’s First Voyage Round The World

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The following slideshow and image gallery show screenshots taken from Captain Cook’s First Voyage Round The World, a presentation of Cook’s journal containing more than 15 hours of animation and audio.

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To view the presentation, point your web browser to http://www.hazelhurst.net/Cook/ and install the Google Earth plug-in if you don’t already have it installed.

Copyright © Colin Hazlehurst, 2012

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If you enjoyed Cook’s voyage, you might also like Joshua Slocum’s Sailing Alone Around the World, a similar virtual re-enactment of a famous sea voyage by the first single-handed circumnavigator; this presentation is still under construction.

 

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