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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

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The Spray is still the Spray

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

Now, it is a law in Lloyd’s that the Jane repaired all out of the old until she is entirely new is still the Jane…the Spray changed her being so gradually that it was hard to say at what point the old died or the new took birth, and it was no matter.

That’s what Joshua Slocum wrote about the reconstruction of his sloop Spray in 1892/3. Over a period of 18 months he replaced every timber with the stoutest, most durable woods he could find – pasture white oak, Georgia pine, and New Hampshire spruce. All was screwed and bolted together and caulked with cotton and oakum.

A similar transformation is taking place in the 3D models I’m using to reproduce Slocum’s voyage in Google Earth. The first image below is my very crude SketchUp model of the Spray.

Original Spray model in SketchUp

This was never intended to be more than a place-holder for a more sophisticated model, a model with which I could start the project. The next image shows the set of ‘guides’ I built up in SketchUp by taking measurements from printed copies of the Spray‘s lines and body-plan:

Spray Guides in SketchUp

The hull was created as a mess of triangles by joining the guides with lines. I shaped the sails with a ‘skin and bubble’ plugin and they are the best feature, but the superstructure is very rudimentary.

The other thing that has bothered me about this model is that it has a yawl rig whereas the Spray started the voyage rigged as a sloop. It wasn’t until Rio that Slocum converted her ‘in readiness for the tempestuous waters of Patagonia’.

After searching for a better model on TurboSquid and 3DExport – and there are some superb examples – I discovered that it would breach the End User License Agreement of those sites to deploy a model where it could be copied. Google Earth is one such place.

My next port of call, as it were, was PeoplePerHour where I searched for a modelling expert who could take my feeble effort as a starting point and create something that wasn’t embarrassing to show in close-up. I gave the work to Mike Halls of mesh-3D and he created:

Spray as a yawl after conversion in Rio de Janeiro

She is still a yawl, but what a difference!

All on my own, I took my shiny new Spray and removed the mizzen mast and sails and the semi-circular brace, all of which were installed in Rio and, using the Scale tool in SketchUp, I enlarged the mainsail.  This gives me a sloop:

Spray as a sloop

So now I have a sloop and a yawl to play with, and the beauty of the Keyhole Markup Language (KML) used in Google Earth is that’s it’s really easy to switch models:- unplug the old one and plug in the new one. In fact, on the leg of the voyage from Pernambuco to Rio, I have both the sloop and the yawl included in the KML and switch models in the middle of Rio bay. To watch this, go to  http://www.hazelhurst.net/Slocum, then select Chapter V followed by clicking on ‘Pernambuco to Rio de Janeiro’. Allow enough time for the models to load and click the ‘Play’ button when it appears.

The presentation is up to Chapter V and my project must now go in two directions: forwards to complete the remaining 18 chapters, and backwards to replace version 1 of the Spray with version 2. At least going forwards I can zoom in more often to show the model in detail and fire the imagination.

Happy sailing!

The Spray

Copyright © Colin Hazlehurst, 2012

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