Saturday, February 27, 2010

Trial of a prototype daggerboard

An addition to the kayaking kit - a carbon fibre blade.

Slot for blade retro-fitted to the Greenlander Pro.

View of the blade housing within the cockpit.

A crowded deck.

  Sailing to windward.
The blade improves the kayak's ability to sail higher into the wind and transfer that wind energy into lift. However on this trial run I found that despite bringing the V-sail in as tight as she would go the sail and mast system still tended to collapse before the kayak was pointing as high as I would like. 

Fltyng downwind under two sails.

Gullwing formation under a combined sail area of 2.5sqm in 12 to 15 knots of breeze.

The deep blade prevents the "yawl" effect that a large sail area generates when travelling directly downwind.

The blade.

Sunday, February 21, 2010

Ancient topography

Paddling seaward on a Port Jackson ebb tide.
And look who is paddling in the other direction ... Peter heading up-harbour and against the draining tide of the Port Jackson / Parramatta River valley.
A knot of tidal current gently sweeping around South Head and out to sea.

Mid-way between South and North Head a robust Bonito drags Tony's kayak backwards.

Today's destination : the rock platform at Salmon Cove.
This small section of the rock platform serves as a good analogy for the ancient sub-surface topography of Sydney Harbour.
In simple terms the harbour is formed by the erosive path that the Parramatta River has carved on its journey out to sea through its base of Hawkesbury sandstone and into which has flown the rising sea since the last ice age.
The image below shows a bathometric chart describing the path that the Parramatta River created for itself in the last ice age, when the sea level was much lower and the coast was consequently much further eastward ~15 or more kms.
The Parramatta River turned to the south at the Heads, travelling down to meet the "Bondi River" and then reorienting itself towards the east and before emptying into the ancient sea.
In the last ice age the view towards the eastern horizon from a position standing on either of the Heads would have been not unlike the present view from Katoomba towards the Jamison Valley. That is, sheer sandstone cliffs falling vertically into a cool climate forest v-shaped valley at the bottom of which travelled a modest river.

Source : Cainozoic Morphology of the Inner Continental Shelf near Sydney, NSW.
A.D.Albani et al. 1988

The chart above describes the path of the "Bondi River"which has been interpreted as the original way in which the Parramatta River found its way eastward - through what is now the Rose Bay Golf Course - before silting itself up and precipitating the carving of the modern river's path out to sea via the Heads. (See an earlier post on this topic).

There are other intriguing geological phenomenon that are observable above the current sea level along this section of coastline.
When east Gondwana began to break up under techtonic forces brought about by under-plate felsic intrusions around 120 million years ago there occured a series of near vertical "strike-slip" movements in the techtonic plates. In Sydney these strike faults took place along a north-northeast direction. The strike faults belonging to the "Watsons Bay Fault Zone" are clearly visible on the surface of the lower rock platform on the left side of the image shown above.
The southerly extent of this fault zone is visible at South Era Beach in the Royal National Park (see coloured chart below). This fault swarm is also clearly visible at Bottle & Glass Island and Shark Island.
Subsequent to the faults breaking up east Gondwana, igneous dykes exploited the weaknesses of the north-northeast strikes about 50 million years ago. A number of these dykes, including the examples at Salmon Cove and North Bondi, travel at an opposing angle to the faults - in a north-west orientation.
"Source : Timing of brittle faulting and thermal events, Sydney region: association with the early stages of extension of East Gondwana" D.J.Och et al (2009)

The strike faults passing through Sydney Harbour.

With the nor-easter filling in and the tide turning, we hoisted our sails and cruised back up the flooded ancient valley of Sydney Harbour.

Sunday, February 14, 2010

February = Furneaux

It's February and the kayak tribe had intended on spending much of this month exploring the 52 islands of the Furneaux Group, Eastern Bass Strait. However a combination of work, study and family responsibilities has seen us postpone this adventure until February 2011.
(Twelve months to hone our abalone, cray and scallop hunting techniques.)

Wednesday, February 10, 2010

Before dawn

This mid-week morning we were lone travellers on the harbour.
While Sydney's residents restlessly slept through the final chapters of their mortgaged dreams we were paddling under a starry sky and beneath a crescent moon, across a velvety blue-black field with ribbons of phosphorescence peeling off our bows.

Past the rhythmic bell tolling of the channel marker.

Stretching legs at Obelisk Bay - mercifully free of its usual prowling creatures.
Heading for home: Peter paddling towards the ledge of North Head.

Tony and the harbour city.

Luke and Bo-am-billy.