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Posts Tagged ‘Sandy Cape

Joshua Slocum in Google Earth: Mauritius to Port Natal

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

Fully provisioned and rested, Slocum sails from Port Louis, Mauritius on 26Oct1897. At first the winds are light and he draws away from the island slowly. By the next day he is passing the island of Réunion. The sea is too rough to consider landing, but a pilot comes out of Galets on the north-west corner of the island when Slocum hands over a Mauritius paper.

A course is set to Cape St. Mary, the southernmost point of the island of Madagascar. The trade winds are weakening now and by 30Oct1897 Slocum finds himself becalmed:

The sloop was now drawing near the limits of the trade-wind, and the strong breeze that had carried her with free sheets the many thousands of miles from Sandy Cape, Australia, fell lighter each day until October 30, when it was altogether calm, and a motionless sea held her in a hushed world. I furled the sails at evening, sat down on deck, and enjoyed the vast stillness of the night.

On the following day, a light breeze carries the Spray past Cape St. Mary. About one week later and for the rest of the voyage to Port Natal (Durban) strong gales batter the yacht and heavy thunderstorms were prevalent¹.

Here the Spray suffered as much as she did anywhere, except off Cape Horn. The thunder and lightning preceding this gale were very heavy.

It takes the Spray 18 days to cover the 800 miles between Madagascar and Durban, an average of 45 miles per day made good. This is less than half the distance per day that she is capable of. In reality, the course is not a straight line because the “succession of gales of wind…drove her about in many directions.” So, the Spray is sailing as fast as ever, but on some crazy zig-zag course dictated by the winds².

Slocum stays in Port Natal for four weeks; he meets all the members of both yacht clubs and sails on the crack yacht Florence; he meets Henry Morton Stanley, the Welsh-born naturalised American who is a renowned explorer of Africa; and he encounters a trio of men who believe that the world is flat. They visit Slocum actually expecting to find information that will support their hypothesis. He must disappoint them:

With the advice [to them] to call up some ghost of the dark ages for research, I went ashore, and left these three wise men poring over the Spray‘s track on a chart of the world, which, however, proved nothing to them, for it was on Mercator’s projection, and behold, it was “flat”.

The Spray sails from Port Natal on 14Dec1897 and is once more: “off on her alone,” as they say in Australia.


The section of Joshua Slocum’s journey reported here concludes Chapter XVII 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. Thunder and lightning or rather lightning followed by thunder was a fresh challenge to my animation skills. Again, I used models created in Google SketchUp to represent the effect of lightning; I added to this a couple of thunder tracks from the WavePad sound effect library. Normally I would try to enhance TourMaker by adding a directive that would generate the thunder and lightning automatically. This time I hand-coded it. Each lightning model flashes on and off twice (by setting visibility=1 then visibility=0 ) with each period of visibility lasting about 100ms. A few seconds later the thunder-clap audio is output.

2. I realised that a better animation of a rolling yacht would result from oscillating the angle of roll about the current ‘Roll’ setting, rather than about the vertical. This would create the effect of the yacht being heeled over in the wind while  waves introduce an additional periodic rolling motion. I have amended TourMaker accordingly

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 in Google Earth: Point Danger to Bustard Bay

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Endeavour in BustardBay

Today, I added a leg of Cook’s exploration of the Australian coast to my Google Earth tour which presents his first voyage round the world. The screenshot above shows Endeavour anchored in Bustard Bay on 23May1770 after travelling north from Point Danger.

If you use Google Earth I can strongly recommend version 6.2 which, to my mind, has dramatically improved imagery.

Copyright © Colin Hazlehurst, 2012

If you would like to follow Cook’s voyage, you will need to install the latest version of Google Earth on your computer; then go to the Captain Cook blog  and click on the links on the right-hand side of the page, under the ‘Google Earth’ heading. After the animation is loaded in Google Earth, you need to expand an entry in the Table of Contents. You will see a ‘Play’ icon which you double-click to start the animation. Don’t forget to enable your speakers to hear the spoken journal.

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