Piloting – Navigation Instruments

Piloting – Navigation Instruments Ordinary Requirement 9 Part III

Description • The presentation covers Pelorus, Speed Logs and Soundings • See also • 9a – Piloting - Compass and Relative bearings • 9b – Piloting - Dead Reckoning Ordinary 9 - Piloting

Learning Objectives • Explain the degree system of compass direction. Explain variation and deviation, and show how corrections are applied to correcting and uncorrecting compass headings assigned by your consultant. • Name relative bearings expressed in both degrees and points. Be able to report objects in view and wind directions with respect to the boat, and know the duties of a lookout. • Name three kinds of devices used aboard ship for measuring speed and/or distance traveled and, if possible, demonstrate their use. • Make a dead reckoning table of compass and distances (minimum three legs) between two points, plot these on a chart, and determine the final position. Ordinary 9 - Piloting

The Compass • The compass is one of the simplest and most useful navigation instruments to be carried aboard a vessel. • A competent navigator, up-to-date charts, a timepiece, and a good compass are the only real requirements for a safe and efficient voyage. • Columbus was able to navigate even without good charts or timepieces! Ordinary 9 - Piloting

Compass Development – Antiquity • Pole Star (Polaris) served as the seaman's lodestar • lodestar = star that shows the way • Magnetic stone used to magnetize a compass needle was therefore called a lodestone. • The magnetic, direction-finding property of the lodestone had been discovered in China as early as the twelfth century. • Early Chinese compasses were said to point South, as this was considered a more noble aspect. Ordinary 9 - Piloting

Compass Development – 1500s • By the time of Columbus, the compass was well-developed. • Mariner's compass was made with a magnetized soft iron wire • bent to a lozenge shape and attached to the underside of a circular compass card • suspended at the center on an upright needle. • Iron wire tends to lose its magnetism over time • each ship carried a good lodestone to re-magnetize the wire by rubbing when it weakened. Ordinary 9 - Piloting

Compass Development – Modern • By sixteenth century, mariner's compass evolved into something similar to the compass of today. • The case in which the compass itself is housed was made of wood or ivory in the early days. • Later, brass came into use since it does not affect the magnetic needle. • Modern liquid-filled compass dates back to the 1850s • Developed and patented by E. S. Ritchie of Boston, Massachusetts. • Company founded by Ritchie is still in business today. • We use Ritchie compasses on our yachts Ordinary 9 - Piloting

Parts of the Compass • The compass has evolved into a functional, easy-to-read, convenient, and relatively inexpensive navigational instrument. • A lightweight dial or compass rose is graduated in degrees • Increasing in a clockwise direction from 000 degrees to 359 degrees to indicate compass heading. • The increments shown on the compass dial can be 1 degree, 2 degrees, or, more typically for compasses used on small vessels, 5 degrees. Ordinary 9 - Piloting

Compass Details Ordinary 9 - Piloting

Compass Numbering • Cardinal points (north, south, east, and west, or abbreviated N, S, E, and W) are indicated on the dial. • Arrows or other marks are sometimes used to designate the intercardinal points (e.g., NE, SE, SW, and NW). • Numbers are typically spaced every 30 degrees Ordinary 9 - Piloting

Pelorus • The pelorus is a moveable compass card with a sighting apparatus, through which an observer may take a bearing relative to the ship’s LOP. • Instructions for making one is in the Sea Scout Manual p. 205 Ordinary 9 - Piloting

Speed Logs Ordinary 9 - Piloting

Dutchman’s Log • A log is a device for measuring the speed or distance covered by a vessel. • The term ‘log’ comes from the wood chip or ‘Dutchman’s log’ thrown over the side of the boat and used to measure the time to pass from a marked point on the bow to a marked point on the stern. Ordinary 9 - Piloting

Example • The distance between the two points is 29 feet (6,080 feet in a nautical mile). • The time between marks is four seconds (3,600 second in an hour). (29 / 4) × (3,600 / 6080) = 4.3 knots • A knot is 1 nautical mile per hour, a rate of speed not distance S = D / T Ordinary 9 - Piloting

Speed Tables Ordinary 9 - Piloting

Considerations • Great care must be taken to sight to the water vertically and to mark the time accurately, preferably with a stopwatch Ordinary 9 - Piloting

Chip Log • Of course, one could only drop a chip of wood overboard so many times before exhausting the supply of wood aboard. • This was remedied by attaching a length of light twine or line to the log; the same log could then be retrieved and used repeatedly. • Marks were added to the line to allow for a more accurate speed reading. • Well suited for use on small boats from 2-10 knots Ordinary 9 - Piloting

Chip Log • The final refinement consisted of: • a large reel, with free-turning handles at either end of the reel, capable of holding... • 500' of light line, marked at 47‘3" intervals, with... • 6" lengths colored cotton twine,... • a flat wooden drag or drogue "log"... • and a small hourglass, with enough sand to measure 28 seconds. • This setup will allow a measurement of up to 15 knots; few sail-powered ships can travel at higher sustained speeds. Ordinary 9 - Piloting

Making a Chip Log • The drogue is made from a 1"x12"x12" board; • the type of wood is less important than the shape. • A quarter-circle of 12" diameter is measured from one corner, scribed and cut. • 3/8" diameter holes are drilled near each corner. • Along the curved edge, about 1/2" in from the edge, 5-7 1" diameter holes are drilled almost through Melted lead is poured into the equally-spaced holes for ballast. Ordinary 9 - Piloting

Making a Chip Log • At one end of the 500' line, unlay about 12-14" of the strands and securely seize the line where the strands part company. • Take two of the strands and thread them through two of the holes at the corners of the drogue; tie a figure-of-eight or overhand knot in the bitter end of each. Ordinary 9 - Piloting

Making a Chip Log • From a piece of scrap pine, carve a peg with a 3/8" taper at one end, and a large enough flat area on the other end to drill a 3/8" hole through. • Thread the third strand through the hole in the peg, bring the end back to itself and and securely seize an eye, trapping the peg in the eye. • Press the peg firmly into the remaining hole in the drouge. • When completed, the drouge should lie perpendicular to the axis of the line Ordinary 9 - Piloting

Making a Chip Log • Measure 47 ¼ feet from the drogue, and force open 2" of the strands with a marlinespike or small fid. • For the first "tag", tie one figure-of-eight knot at one end of the tag, and weave the other end into the line, leaving the last 2" of the tag exposed. • Measure another 47 ¼ feet, unlay the line, and insert another tag, but this tag will have two knots tied 1/2" apart, at the exposed end of the tag. • Continue this process, adding one more knot in each succeeding tag, until the entire line is so marked. Ordinary 9 - Piloting

Making a Chip Log • The exact construction of the reel is not important, only that the following features are adhered to; • that the reel be long and of small diameter, to allow the reel to be held comfortably aloft over the head without the reel touching the head, and • that the handles, or the axle of the reel be free-spinning, to allow the line to pay out without friction. Ordinary 9 - Piloting

Making a Chip Log • The glass is made from a 3 min. egg timer. • One end of the glass is carefully opened with a Dremel tool with a dental burr or drill. • This is extremely difficult, as too much pressure will break the glass. • Get a stopwatch and a piece of clean paper. • Invert the timer and pour out 2:32 worth of sand. • Stop the watch as the sand finishes flowing; you should have left 28 seconds. • Turn over measure remaining sand. If too long, pour off more sand, if too short, add sand back. Ordinary 9 - Piloting

Using a Chip Log • To use the log requires two scouts; one to hold the reel aloft, facing aft at the taffrail, and one to drop the drogue overboard, turn the glass, and stop the line when the sand runs out. • The reason for the odd amount of sand in the glass is that after stopping the line, the number of knots payed out is the speed of the ship; Hence the use of the term ‘knot’! (47 ¼ / 28) * (3600 / 6080) = 1 knot ! Ordinary 9 - Piloting

Using a Chip Log • To retrieve the drogue, rather that reeling it in against the dead drag of the upright board, just give the line a quick, very sharp tug, and the peg, snugly fitted into the drogue, will pop out, letting the board flip parallel to the flow of the water and allowing for easy retrieval as it skips across the surface of the sea. Ordinary 9 - Piloting

Ground Log • A ground log is a simple form of log for use in shoal waters. • It consists of a weight on one end of a hand line. • The distance and time are recorded as in the chip log • 15 seconds is easy to time on a wrist watch, in which case, knots could be tied every 24’ 4” Ordinary 9 - Piloting

Patent Log • A patent log is a mechanical device designed to measure a ships speed or distance, or both. It usually consists of: • A metal rotator (propeller) with blades that vary as the speed of the boat varies • A line several hundred feet long attached to the rotator and a wheel on an instrument on the boat • A dial that registers the speed of rotation of the wheel • Best known type is called a taffrail log. Ordinary 9 - Piloting

Speedometer • A speedometer is often called a log • It differs from a tachometer that measures engine revolutions • Many speedometers utilize a pitot tube, which measures changes in water pressure due to changes in speed. Ordinary 9 - Piloting

Considerations • Any speedometer or log (with the exception of the ground log) shows only relative or approximate speed over bottom. • Wind and current must be considered to get an accurate reading. • A speedometer also gives a check on performance of the boat • A drop in speed could indicate propeller damage, trimming is needed, or excessive bottom growth Ordinary 9 - Piloting

The Sounding Lead • The hand lead or “blue pigeon” as sailors call it is one of the most useful instruments on board a ship. • Two leads are employed: the deep sea lead weighing 28 lb., and a hand lead weighing 14 lb or less. Ordinary 9 - Piloting

Preparing a Sounding Lead • We will look at a small, easily constructed line suitable for instructional and light duty use. • To prepare a lead line, assemble the strips of material, a 3-8 lb. lead weight, and 25 fathoms (150 ft.) of 3/8" cotton or manila line. Ordinary 9 - Piloting

Preparing a Lead • If you are unable to obtain a lead you can cast your own. • Carve each half of the mold from pine 2x12's • Splice the eye of the weight to one end of the line. • Flatten the base of the lead with a hammer or, saw the base flat with a hacksaw, then drill a shallow hole for the tallow in the center. Ordinary 9 - Piloting

Preparing a Lead Line • At each point, measured from the weighted end, use a fid or marlinspike to open the strands of the line. • Insert the appropriate strip of material, so that the strip extends equally from both sides of the line. • Allow the strands to return to their normal position, trapping the strip in the line • Place a whipping immediately at either side of the mark to hold the strands Ordinary 9 - Piloting

Preparing a Lead Line • The line used for a hand lead is 25 fathoms long, and is generally marked as follows: At 2 fathoms, Leather, with two lobes3, Leather, with three ends with 3 "lobes" 5, White calico. (2" wide x 6"long strip)7, Red bunting. (same size as above)10, Leather, with hole through it at each end13, Blue serge.(same as above)15, White calico.(same as above)17, Red bunting.(same as above)20, Strand of light line, with two knots in it at each end. Ordinary 9 - Piloting

Using the Lead • By the different feel of the materials used you can tell what mark is in one's hand in the dark. • The tagged depths are called “marks”; the areas between the marks are called "the deeps". • Thus, at five fathoms, the leadsman calls, " By the mark five," • In eleven fathoms,"By the deep eleven.“ • He also calls halves and quarters of fathoms • i.e.," And a half six,'' for six and a half fathoms, "A quarter less six," for five and three-quarters. Ordinary 9 - Piloting

Using the Lead • To take soundings while under way, the leadsman would take his place at the bow of a small boat, or at the forward chain plates on a large ship, secured from falling overboard by a "breast band", a wide strip of canvas used like a seat belt tied between two shrouds. • The leadsman could then lean forward against the band to swing his lead in the clear. He would then swing the lead round and throw it as far forward as possible, so that the lead would be resting on the bottom and the line tight, when the vessel is directly over the lead. Ordinary 9 - Piloting

Using the Lead • If the lead is hove properly, so that the line pays out with a little tension as it passes through the hands, it is easy to tell when it has reached the bottom by the sudden slack felt in the line. • When sailing in shoal waters, soundings can be taken much quicker with a pole or boathook than with a lead. Ordinary 9 - Piloting

Using the Lead • There is a hollow at the base, or "heel" of the lead which can be filled, or "armed", with tallow or beeswax; • A specimen of the bottom (mud, sand, or shingle) is brought up with the lead, and this, by referring to the chart, which generally marks the nature of the bottom, may help find your position precisely. Ordinary 9 - Piloting

Electronic Depth Sounders • This is an instrument for measuring the time required for a transmitted electronic impulse to reach the bottom and return. • Sometimes called depth finders, echo sounders, fathometers, etc. • Consists of two elements, an indicator and a transducer • The transducer is a combined receiver and transmitter, located in or just above the hull. Ordinary 9 - Piloting

Piloting – Navigation Instruments