Saturday, 20 September 2014

How to make a sketch chart

This post an article originally published in the magazine ‘Marine Quarterly’. Marine Quarterly is published by Sam Llewellyn and is fascinating, available only by subscription, but easily found via the web and any search engine

Any literary polish this article has is Sam’s work, as are most of the commas and all the semi-colons.

How to make a sketch chart

The joy of owning a small ocean going sailing vessel is that it allows me to cross oceans then poke into coastal byways that I could get to in no other way, carrying my home with me all while. A vessel for this sort of voyaging must be large enough to carry supplies for a long voyage and small enough to be sailed and maintained by her crew without outside help.

My compromise is Iron Bark, a thirty-five foot steel gaff cutter. She can be sailed by one person, and can carry enough supplies and equipment to be independent for many months and thousands of miles. She has a comfortable motion in a seaway, moderate draft and a strong hull. Her anchor gear is substantial and the rig capable of taking a great deal of abuse. I can repair anything critical that breaks with spares carried aboard. She is a fine vessel for exploring the less-travelled corners of the world.

A voyage from New Zealand to Chile and a winter exploring Patagonia and Tierra del Fuego promised to combine all I like most - a challenging voyage of 5000 miles through the Roaring Forties of the Southern Ocean to a wild coast with a multitude of channels and bays to explore. I cleared from New Zealand for Chile in November 2009 and arrived in Puerto Montt, Chile, after a rough passage of fifty-four days. Annie Hill, my frequent sailing companion, joined me in Puerto Montt for a two-month cruise. We pottered around Gulfs of Reloncaví and Ancud and as far south as Ventisquero (Glacier) San Rafael, the lowest-latitude tidewater glacier in the world. It is a fascinating place, pushing down to the sea through heavily forested hills alive with kingfishers, woodpeckers and humming birds.

After Annie left to fly back to New Zealand in early May, I set off for the canales, the wild glaciated channels that stretch 1800 miles south and east to Cape Horn. There is no road access to this part of Chile, and few settlements. The scenery is spectacular and the anchorages are deserted. Although the Chilean authorities restrict access to some areas, there are still a gratifyingly large number of blanks to explore. 

The canales are generally protected from ocean swell but are tormented by rachas, violent squalls tumbling down from high land. I hoped the colder weather of the approaching winter would bring calmer weather. The canales are deeply indented and it is usually possible to find a cove where a small vessel can lie snugly close under the trees with bow lines ashore and an anchor astern and sometimes stern lines ashore.

Chilean charts are of excellent quality considering the length of the coast and limited resources available to the Chilean Armada. There are accurate charts of all the channels used commercially; but off the main routes the charts are often little more than rough outlines, with few soundings and no detail of the smaller coves.  There are two good privately produced pilot/guide books for southern Chile, the Royal Cruising Club Pilotage Foundation’s Chile Guide and Rolfo and Ardrizzi’s Patagonia and Tierra del Fuego Nautical Guide. But there is still plenty left unexplored for anyone with visions of being a latter-day Cook.

We (Iron Bark and I) generally only travelled twenty or twenty five miles a day. There were many days when there was too much (or, more rarely, too little wind) to be worth moving at all. The low mileages were due to the short midwinter days and because it took me over an hour to get underway in the morning and the same to secure for the night. On arrival at an anchorage I launched the dinghy, motored in slowly, let go stern anchor, then let go bow anchor on short scope to hold the bow steady. It then became a race to get lines ashore before Iron Bark dragged the bow anchor ashore. I would leap into the dinghy with the end of a hundred-metre line tied around my waist and row to the windward shore with oars threshing like a steamer duck’s wings, heave the dinghy anchor into the scrub, scramble up the rocks and through undergrowth to find a strong tree to tie to, then back to the boat and get tension on the line. Repeat the exercise with the other bow line, then warp forward into the berth and run lines ashore from the stern if necessary. By this time the dinghy was filled with twigs and I was wet, scratched and in need of a whisky.

On departure I started retrieving shore lines in the first cold grey of dawn, leaving the windward bow line until last, then hauled up the bow anchor from underfoot and warped back and broke out the kedge anchor. Once clear of the berth I pulled the dinghy on deck and lashed it on its chocks, coiled down several hundred metres of ice-stiffened rope and headed out.

As we pushed south, winter came in. The tree line became lower and lower, the weather colder. The rain turned to sleet, then snow. There was often a thin skin of ice in protected coves. As we travelled south this became too thick to break with a dinghy and difficult to break with Iron Bark. The general trend of the channels is south and east and the wind usually from the west, so we often had a fair wind even if it was mixed with snow or sleet. I tried to get to our night’s anchorage early enough to sound it for a sketch chart and to get ashore to cut firewood. Every five or six days I took a day off to do other domestic chores - water, washing and so on.

There is a huge satisfaction in finding a way through a rock-strewn passage into an uncharted nook where you can moor safely, protected from the worst gale.  But finding a passage is only half the job. Drawing a chart of it is the other half and few sailors will do this.

The first requirement for a good sketch chart is a base map with scale and geographic co-ordinates. Many modern charts have a reasonably accurate outline of the coast, even if they lack soundings. In this case all one needs to do is to enlarge the appropriate section of chart and fill in depths from the echo sounder. There are various ways of doing this, including scanning the original to a computer, enlarging to the appropriate size, then tracing it off to form the base map. With the base map on a clipboard, I note depths and coastal features as I go.  Each evening I make a clean copy of the day’s work and prepare a base map for the area I will cover the following day.

There are days spent puttering along in calm seas steering with one foot and sketching in details on the clipboard. There are others when sleet mixed with spray is whipping in horizontally across the cockpit. It is hard to use a clipboard in these conditions and impossible to use a computer. 

Some places - Canal Harriet in Patagonia for example - have no accurate base map and the only option is to use GPS-derived positions as a framework for a running survey, but this is slow and less accurate. The coast outline from a running survey can be improved using satellite photos such as those on Google Earth, but this requires internet access that Iron Bark lacks.

Poking along an uncharted passage requires a degree of caution, but with experience in an area you develop a feel for where the safe water is likely to be. I try to sound the safe water from Iron Bark and only use the dinghy in the really dodgy bits. The underwater topography is much influenced by the geological history of the area. Glaciated terrains like Patagonia or Greenland are quite different to Kimberleys of Western Australia, which is estuarine; but you soon get a feel for the differences. If the water is clear a lookout high in the rigging is useful, but this is a limited option with a crew of one or two; so I only con from aloft in thick ice or coral. 

A few years ago Annie and I did a running survey of the Nordre Sunds in Greenland. These are about 100 miles of unsurveyed fjords and sounds in about 72°N. Sometimes we could motor or sail at three or four knots, sounding and sketching as we went. But in places it took a week of patient sounding to make twenty miles. The water of Laxefjord, for instance, is milky with silt from the nearby icecap and the numerous banks are invisible. Here we nosed ahead until the water got too shallow for comfort then anchored; or Annie motored in circles while I went ahead sounding from the dinghy and buoying the channel. We sometimes made less than a mile in a long day before turning back to a safe anchorage to rest and draw up the day’s sounding. At that latitude in summer it is never dark so the only reason to stop was for rest.

There is a hand-held echo sounder that looks like a flashlight that is excellent for dinghy work. I have never been able to afford one so still use a lead-line from the dinghy. This is not ideal as it either tangles around the oars or I drift out of the channel before getting bottom. Sounding ahead from the dinghy is impossible when alone unless there is an anchorage nearby; so I did seldom did it in Patagonia.

Each evening I transfer the day’s sounding to the base chart at the same scale as I intend to make the final chart, and write up the notes. Omissions or gaps become obvious and can be filled in from memory or by going back before leaving the area. A hand-drawn chart is quicker to produce than one on a computer unless you have specialised software and experience using it. (Annie transferred all our Greenland surveys to computer-drawn charts, and found it a slow job.)  If the charts are intended for use in a guidebook, the publishers will redraft it into their own format and would probably rather work from a hand-drawn chart, which is a generation closer to the original survey.

Every chart should have:
  • A scale, preferably yards, metres or nautical miles. Avoid cables; surprisingly few people know what they are.
  • A north pointer. Do not assume that north is up - put it on the chart.
  • A geographical reference. Now we all have GPS, latitude and longitude is the obvious one, but distance and bearing to a prominent point is often better. When giving latitude/longitude, give the datum. If it is WGS 84, say so.
  • The units of depth and height (metres, fathoms, feet)

Every chart should have, in a title box or in a corner where it will not be reproduced if the chart is to be included in a guide without redrafting:
  • The source any outside data. Eg “Outline adapted from Chilean Chart 10372”
  • Who compiled it
  • Date of survey

A good sketch chart will tell most of what there is to say, but a brief set of written notes is worthwhile. Apart from navigation data - “leave the drying rock in the centre of the channel to port on entry” - this is the place for information that is not apparent from the chart: quality of holding, susceptibility to williwaws, availability of water and firewood and so on. If your notes are intended to supplement a particular guide or pilot, it is sensible to use their layout and style. A high-level oblique photograph of an anchorage is useful and easy to get in places like Labrador or Greenland where the vegetation is sparse, but nearly impossible in much of Chile or the New Zealand fjords, because of the dense forest.

Although there is nothing intrinsically difficult about any of this, it does require preparation and persistence, especially if the weather is bad. As an example, to produce a sketch chart of Seno Pia in Tierra del Fuego took me two days. Fiordo Pia runs into Beagle Canal and has two large glaciers flowing into it, and several anchorages that sounded feasible. I decided to spend a couple of days there, starting off by getting a line of soundings down an unnamed, unsurveyed bay extending southwest from the main the fiord. After preparing a base map by enlarging a Chilean chart, I motored into the fjord and fixed a waypoint to safely cross the old terminal moraine. The unnamed bay was covered with hard ice about 50mm thick, near the limit that Iron Bark can break. We crunched slowly through it to the head of the bay taking soundings, then turned back to find an unfrozen anchorage for the night. The ice was too thick to break from a standing start and turning around took a while and cost a lot of paint.

The pilot books described a possible berth in the western arm of Fiordo Pia. This proved to be a bleak, rocky slot but would have to do as it was too late and too windy try elsewhere. There was insufficient swinging room to anchor and getting lines ashore before Barky was driven on to the rocks required quick work. Both the dinghy and I were knocked about, one leaking the other bleeding. That night the wind backed to the southwest and eddied into the caleta as violent squalls, bringing in large amounts of glacier ice. Most of the ice was no more than large brash, but there were some rafts weighing as much as Iron Bark. These snagged on the mooring lines, imposing large strains on them, as well as being noisy and hard on the paint. To borrow a quote from Tilman, in bad weather it is ‘a berth to be chosen from necessity and not with any expectation of tranquillity’.

After a worrying, uncomfortable night the wind eased and the ice dispersed. I took the opportunity to leave and motored over to the eastern arm of Fiordo Pia. This appeared to be a better berth, but I had had enough of Fiordo Pia so after taking soundings for a sketch chart, made use of a fair wind to sail along the Beagle Canal to Caleta Olla. I secured there with three lines ashore and two anchors astern and spent a pleasant week making final drafts of the sketch charts and notes and catching up on the domestic tasks of wood, water and washing. Some of the most enjoyable times when cruising in remote places are in a safe haven with the stove glowing and the wind howling outside.

When dealing with South American bureaucracy became too wearing, I left Chile and sailed to the Falkland Islands, then on to Trinidad. Only a small, seaworthy vessel gives its own the sort of freedom that the gods should envy.

1 comment:

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