August 22, 2021 — 10:00 am – 4:00 pm
Avoiding both the Cheval d’Frise and Shoals — Piloting the Delaware
Explore the challenges of piloting an 18th century vessel up the narrow and shallow Delaware River. Michael Carver will discuss and demonstrate how large vessels navigated around known obstacles in these challenging waters..
In addition to the Cheval d’Frise placed in the river, there are shallow flats, currents, and other hazards when sailing up the river. It is the work of the harbor pilot and marine surveyor to ensure that safe passage is obtained.
Knowing the depth of the river at any point is vital if you want your ship to not run aground. A sounding line or lead line is a length of thin rope with a plummet, generally of lead, at its end. in order to avoid repeatedly hauling in and measuring the wet line by stretching it out with one’s arms (one fathom), it is common practice to tie marks at intervals along the line. These marks are made of leather, calico, serge and other materials, and so shaped and attached that it is possible to “read” them by eye during the day or by feel at night. Traditionally the marks were at every second or third fathom: at 2, 3, 5, 7, 10, 13, 15, 17, and 20 fathoms. The “leadsman” called out the depth as he read it off the line. If the depth was at a mark he would call “by the mark” followed by the number, while if it was between two marks, he would call “by the deep” followed by the estimated number; thus “by the mark five,” since there is a five-fathom mark, but “by the deep six,” since there is no six-fathom mark. Fractions would be called out by preceding the number with the phrases “and a half,” “and a quarter,” or “a quarter less”; thus 4 3/4 fathoms would be called as “a quarter less five,” 3 1/2 as “and a half three,” and so on. Where the depth was greater than 20 fathoms the line would commonly be marked with a single knot at 25 fathoms, two knots at 30, and so on.
In peacetime, we mark hazardous places along the river with buoys. Ships sail up the safe channel between the buoys in the same manner as you drive in a lane along the highway. In wartime, however, this defeats the advantages of sunken hazards like the cheval d’frise and shoals. We want the enemy to wander upon these and be stuck but we also want our shipping to pass safely. This is the role of the harbor pilot. Most harbor pilots managed their progress up the river by deductive reckoning (aka dead reconning). Dead reckoning involves estimating a current position based on a past position. Dead reckoning factors in speed, time, and direction of travel.
Piloting relies on fixed visual references to determine position. This is probably the most familiar type of navigation. With this technique, the pilot must be able to recognize visual markers or identify them using maps or charts. If the pilot misidentifies the markers, he or she could take the vessel off course.
Since the safe channel in the river was necessarily narrow and circuitous, a combination of dead reconning, pilotage, and basic compass navigation employing known landmarks along the river and triangulation, was needed to safely traverse the obstacles in the river.
- Sounding line: a line weighted with a lead or plummet and bearing marks to show the length paid out, used for measuring depths.
- Chip log: an apparatus consisting of a small weighted wood panel that was attached to a rope, and a time measuring device. the chip log rope had knots tied at equal distances. Sailors would throw the wood panel into the sea, behind the ship, and the rope would start unwinding. The faster the ship was moving forward the faster the rope would unwind. By counting the number of knots that went overboard in a given time interval, measured by the sand glass, they could tell the ship’s speed. This is the origin of the nautical speed unit: knots.
- Sighted Compass: a circular brass box containing a magnetic needle which swings freely over a brass circle which is divided into 360 degrees. The horizontal angle is measured using a pair of sights located on north – south axis of the compass.
- Nautical Chart: Nautical charts are the sailing equivalent of road maps. A nautical chart provides an aerial view of a waterway with its landmarks, bridges, water depth, and a variety of other important navigational information.
- Sand Glass: an instrument (such as an hourglass) for measuring time by the running of sand.