Piloting Navigation Instruments

1
Piloting Navigation Instruments

• Ordinary Requirement 9
• Part III

2
Description

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

3
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.

4
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!

5
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.

6
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.

7
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

8
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.

9
Compass Details
10
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

11
Pelorus

• The pelorus is a moveable compass card with a
  sighting apparatus, through which an observer may
  take a bearing relative to the ships LOP.
• Instructions for making one is in the Sea Scout
  Manual p. 205

12
Speed Logs
13
Dutchmans 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
  Dutchmans 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.

14
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

15
Speed Tables
16
Considerations

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

17
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

18
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 473" 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.

19
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.
20
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.

21
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

22
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.

23
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.

24
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 232 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.

25
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 !

26
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.

27
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

28
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.

29
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.

30
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

31
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.

32
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.

33
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.

34
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

35
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.

36
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.

37
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.

38
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.

39
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.

40
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.