Webb Chiles : self-portrait in the present sea

From InThePresentSea

Webb Chiles was the first American to round Cape Horn solo.
He is the author of five books, has circumnavigated by sail four times, and has set numerous world records.


Links :

• FurledSails podcasts : part I / part II
  

Accuracy and reliability of charts versus confidence

The Island of California (Map, circa 1650) refers to a long-held European misconception, dating from the 16th century, that California was not part of mainland North America but rather a large island separated from the continent by a strait now known instead as the Gulf of California.

One of the most famous cartographic errors in history, it was propagated on many maps during the seventeenth and eighteenth centuries, despite contradictory evidence from various explorers.

From Mike Prince, Director of Charting, Australian Hydrographic Service

How accurate are nautical charts?
How much faith can be placed in them?

The Australian Hydrographic Service proposes a valuable guide which any skipper or navigator of a sailing vessel should be aware with.

Unfortunately, the answer is quite complex – far more complex than simply saying one chart is accurate whilst another is not.

However, having the necessary skills should be essential for any mariner venturing into unfamiliar waters.

All charts, whether paper or electronic, contain data which varies in quality due to the age and accuracy of individual surveys. In general, remote areas away from shipping routes tend to be less well surveyed, and less frequently, while areas of high commercial traffic are re-surveyed frequently to very high levels of accuracy, particularly where under-keel clearances are small.

It is quite accurate to consider a chart as a jigsaw of individual surveys pieced together to form a single image.
These surveys vary in age and quality, particularly due to changes in technology.

However, one fundamental truth remains – a hydrographic surveyor can typically only physically see a very small percentage of their survey area – the parts which rise above the sea surface; for the remainder they must have confidence in their systems and long-standing practices to accurately and confidently chart the seabed.

Because priority for surveying is given to the major shipping routes, an essential skill for mariners venturing into unfamiliar waters away from these routes is the ability to interpret the various quality indicators that are, or should be, on every chart.

These are the best guides available to mariners, whether on commercial vessels or cruising yachts, to help them decide how much confidence should be had in past and current surveyors and the technology available to them when surveying the different areas of each chart.

Indeed, a prudent mariner should be wary of any chart that does not show these indicators, irrespective of whether it is a traditional paper chart, a Raster Nautical Chart or one of the new Electronic Navigational Charts.

Finally, if in doubt, post a lookout, make your approach in daylight and good conditions, or go somewhere else – there is no such thing as a good grounding.

Links :

• MySailing : All you've ever wanted to ask the hydrographic-service
• AHS : the future of coastal navigation
• AHS : GPS Receivers and Chart Datums / Accuracy and Reliability of Charts
  

Old data guides mariners into risky waters

Flinders Islet off the New South Wales South Coast (Australia)

From Brisbane Times

Mariners may be putting their lives at risk by relying on electronic navigation charts that are not up-to-date, says the Australian Hydrographic Service (AHS).

The AHS’s director of charting services, Mike Prince said last week an outdated chart could have been the cause of the yachting tragedy last year that claimed the lives of two experienced sailors.

Veteran skipper Andrew Short, 48, and navigator Sally Gordon, 47, both of Sydney died after they were swept from the deck of PWC Shockwave after the yacht struck Flinders Islet off the New South Wales South Coast in October.

The 26-metre multimillion-dollar yacht broke up after the crash, which occurred about 3am as it was about to make the return journey in a 169-kilometre race from Sydney.

“A CYC (Cruising Yacht Club) report (read Navigation Systems Reliability chapter p.26 to P.31) to said they were using an electronic chart at the time of the crash and there is speculation that there could have been a problem with it,” Mr Prince said.

A yacht race inquiry in January heard some of the boat’s crew before the tragic race had observed errors on the chart plotter in Sydney Harbour and at Hamilton Island in Queensland.

The AHS is working with Yachting Australia and maritime services around the country to raise awareness of the limitations of the commercial charts used within chart plotters and software systems.

Mr Prince estimated that one million Australian boaties used unofficial electronic charts.
‘‘Sailors should use the charts to support navigation, not totally rely on them,’’ he said.

In another case, Timothy O'Neill, 39, died after his motorboat doing 25 knots crashed into a seawall at the mouth of the Brisbane River in 2007.
The boat’s electronic charts had not been updated to show the seawall had been built on reclaimed land. (see Maritime Safety Queensland SeaScape p. 4 saying the accident was partly to blame due to an over-reliance on an outdated GPS system / Office of the State Coroner - Findings of Inquest)
In 2008, a $1.7m yacht Asolare hit a reef 200 nautical miles east of Cairns and two crew members who had been clinging to the boat’s hull were winched to safety by rescue helicopter.
“The skipper said the reef wasn’t on his electronic chart but it was on the paper chart so he obviously hadn’t updated it,” he said.

The AHS publishes fortnightly updates new and altered information that could affect safety at sea on the Australian Notice to Mariners. It is up to mariners to apply the updates to their charts.

“If people don’t update them they could be ignorant of hazards or dangers that could affect their safety,” he said.

Makers of commercial electronic charts are not legally required to regularly update their charts because they are marked “not for navigation” or “aid to navigation only”.

These unofficial charts might only be updated every few years.

The AHS has published fact sheets to tell mariners how to use official and unofficial charts safely.

Links :

• Sailingmates : your GPS can kill you (required reading for every sailor who uses a GPS)
• MAIB Safety Bulletin : Collision between Ash and Dutch Aquamarine south-east of Hastings in the Dover Traffic Separation Scheme (2001)
  

It’s time to zone the seas

From NJToday by Amy Mathews Amos

With the Deepwater Horizon oil spill doing long-term damage to commercial fishing, wildlife, and tourism, perhaps the bubble of our ocean fantasies has finally burst.

We’ve always thought of the seas as free, wild, and infinite.
A place we go to get away from rush hour traffic and office cubicles.
We picture waves rolling under the bow of a boat, sails full, sun bright.
Or white breakers crashing on lonely stretches of beach.
To most of us, the ocean seems unimaginably big. Vast. Endless.

But it’s not.

The tar balls washing up on Gulf of Mexico beaches remind us that it’s getting pretty crowded out there.
And not just with oil rigs.
Walking the shore, we can’t readily see the fierce competition underway for pipeline routes, mining sites, sewage lines, communication cables, fishing fleets, and more.
But in reality, things are bumping into each other much more often at sea, whether it’s oil and water, cables and corals, or ships and whales.

Often literally colliding: A 90,000-ton container ship can kill a 100-ton right whale when it hits it. Ship collisions are the biggest source of human-caused death for these endangered cetaceans. The second biggest is entanglement in fishing gear.

To bring order to the seas, it’s time to take our cue from the land.

For decades communities have used zoning to reduce land-use conflicts and protect property values.
In 2008, Massachusetts became the first state to apply this idea to the ocean.
With 400 years of seafaring behind it, Massachusetts entered the 21st century struggling to balance modern demands like fish farms, sand mining, and wind farms with declining fisheries and thriving tourism.
With the state’s passage of a comprehensive ocean “zoning” law, it now has a framework to identify which offshore areas are appropriate for which uses, and to flag potential conflicts in advance.
The Obama Administration wants to do the same thing in U.S. ocean waters and the Great Lakes.

Called “marine spatial planning,” this concept is rooted in conservation.
Australia pioneered it in the 1980s to protect valuable coral reefs, seagrass beds, and mangroves in its world-renowned Great Barrier Reef National Park.

Protecting special places in U.S. waters isn’t new either.
Just as our national parks preserve special areas on land, national marine sanctuaries protect resources like the sunken wreck of the Civil War ship USS Monitor off the North Carolina coast, and the country’s northernmost coral reefs in the Flower Garden Banks of the Gulf of Mexico.

But the idea of ocean zoning goes far beyond conservation.
The Obama Administration sees it as a way to promote economic development too.
Identifying areas suitable for various economic, industrial, or conservation uses in advance can help reduce conflicts and facilitate compatible uses.

This includes energy development, which increasingly drives how we use the ocean.
In Massachusetts, conflicts over the location of liquefied natural gas terminals, tidally-driven energy facilities, and wind farms fueled change.
At the national level, intense pressure for offshore oil and gas drilling leases adds to the urgency.

The catastrophic BP spill in the Gulf forces the question: what areas should be off limits to oil and gas drilling, and where can we develop more sustainable, renewable energy sources so these disasters don’t happen in the future?

Not surprisingly, the idea of flagging parts of the ocean for specific uses raises hackles.
To many, this simply doesn’t fit the romantic image of a free ocean.
Recreational fishing interests in particular are opposed to anything that might restrict fishing access.

Dr. Elliott Norse, president of the nonprofit Marine Conservation Biology Institute and a leading thinker and supporter of marine spatial planning, likens the idea of a free and open ocean to a “sacred value.”
According to psychologists, sacred values are concepts that defy rational decision-making, based solely on strong emotion.
No promise of practical benefits can easily sway someone away from a sacred value.

But clinging to outdated notions of what we want the oceans to be could do irreversible harm. We’re placing tremendous new demands on the seas and need a more thoughtful approach to managing them.

The time for marine spatial planning has come.
If there was any doubt before, surely those doubts should have sunk with the Deepwater Horizon.

Links :

• UNESCO : UNESCO initiative on marine spatial planning

Moon image : scenic phenomenon

Full moon at Perigee and Apogee

From Perseus

A common misconception is that the moon is larger when it is near the horizon than when it is high overhead.
However, this optical illusion is not true, for the apparent size of the moon is virtually the same when it is rising or setting near the horizon or when viewed overhead (in fact, it is very slightly smaller when viewed near the horizon due to refraction as well as the greater added distance in observing across the earth's radius).
This illusion has been wrongly attributed to landmarks near the horizon, such as homes and trees, supposedly giving a sense of perspective and whereas the same perspective is lost when looking at the overhead moon bathed in an empty sky.
As noted by Donald E. Simanek and Carl J. Wenning, the real reason behind this trick by our brain is the perception of the moon being against a "close" or "distant" foreground and which is lucidly described by the above two references.

In contrast, it is puzzling that when a physical change in the apparent size of the moon does occur, due to its elliptical orbit around our planet, the change in the apparent diameter which can be up to 14% between apogee and perigee, is not noticed at all.
In fact, the change in the apparent diameter of the moon is a monthly phenomenon and is something that could be discerned quite easily during any given lunation by looking very carefully at the full moon and the waning crescent thirteen days later (or observing a waxing crescent thirteen days earlier)!

At apogee, the moon is approximately 406,500 km away from earth with an apparent diameter of about 29.5' whereas, at perigee, it is approximately 356,500 km away and is characterized with an apparent diameter of about 33.6'.
This difference of 50,000 km between apogee and perigee leads to the dramatic change in the apparent diameter as illustrated by the two full moons below which were strategically selected during 2010 so as to have the full moon as near to its minimum possible perigee and maximum possible apogee as possible when crossing the local meridian.

Furthermore, the apogee full moon below, captured during late summer, was slightly muted in colour when crossing the southern meridian due to its relatively low altitude during each summer and in contrast to the sun when the latter is at its highest during the same season.
These relative positions between the sun and the moon are juxtaposed six months later and during mid-winter with the (perigee) moon at a much higher altitude relative to six months earlier (note the absence of muted colouration due to atmospheric effects and sharper image) as well as relative to the sun.
The sun is now also much lower in the sky as compared to six months earlier (see here).

Note: The change in the apparent diameter of the sun due to perihelion and aphelion is fully documented elsewhere on this website (see here).

Links :

• Wikipedia : Kepler's laws of planetary motion