General Ship Knowledge

Content of this section is divided into boxes for each area of study. These are just my nautical science study notes compiled in one place. I'm still learning...

more about this page + disclaimer I am studying to be a licensed canadian mariner, largely by following the curriculum set out in publication TP2293-E, the Examination of Seafarers. I have no intention of sailing internationally and my knowledge and experience are contained within canadian coastal waters. The intention of this page is just to serve as an archive for my notes leading up to my eventual 'final exam', an oral examination on seamanship with the federal transport authority. There are so many different terms and acronyms used in the marine world that it can be tough to keep track of everything. I am sharing my notes publically because I have great interest in the archival and sharing of information. I want to create a sort of encyclopedia of modern watchkeeping-related information for myself.

General Seamanship

As much as I hate to admit it- some of the best guides out there to study are government publications. Transport Canada put out TP10038-e in 2003, the small fishing vessel safety manual which I could consider as the baseline for the bare minimum seamanship considerations to be had onboard a vessel of any size. You could view this publication as a sort of primer for the watchkeeping mate curriculum; as all of the topics covered in this publication are studied in greater depth by watchkeepers. (also available offsite here)

Chartwork and Pilotage

Definitions

Longitude: an anglular measurement which is based off of the Prime Meridian. Meridians of longitude run 'vertically' between the north and south pole, but represent distances either east or west of the prime meridian. The distance between lines of longitude will change depending on the latitude (ie. distances between meridians at the equator will vastly differ from distances between meridians at the polar latitudes). All lines of longitude are considered great circles. (wikipedia)
Latitude: a geographic representation of position north or south of the equator. Lines of latitude run 'horizontally' but measure north and south, and are called parallels as opposed to angular measurements because they run parallel to one another measuring northerly or southerly positions. Parallels of latitude (other than the equator) are not great circles because they do not pass through the center of the earth. Latitude is used in chartwork for measuring distances because there is no chart distortion in distance when working with mercator charts. (wikipedia)
demonstration of a great circle
Great Circle: the largest circumfrence which can be drawn on any sphere- which in navigation applies to the spherical shape of the earth. A great sphere must divide the earth into 'halves' by passing through the center of the sphere. All lines of longitude are great circles (as they pass from pole to pole), but lines of latitude other than the equator are not great circles. The shortest route possible across the circumfrence of the earth is to follow along the curvature of a great circle. (wikipedia)
all of the curved lines on this diagram are meridians and great circles
Meridians: lines which run from pole to pole connecting areas of equal longitude. Because the earth is considered a sphere (it is an 'oblate spheroid') and all meridians conjoin at the north and south poles, the distance between meridians is not equal everywhere (which is mostly relevant when measuring distances on the chart itself). There is one meridian of particular note, called the Prime Meridian, which is where all angular measurements of longitude are referenced from (as in easterly or westerly of the prime meridian). The prime meridian is located near Greenwich in the United Kingdom, which is also where GMT (Greenwich Mean Time), the international time standard, originates. Because of the way both time and longitude are measured, they have a close relation to one another. (wikipedia)
Rhumb Line: a line that cuts across all meridians at the same angle and maintains a constant true direction. Using the Mercator projection, rhumb lines appear as straight lines. To follow a true heading in a straight line irregardless of the meridians is to follow a rhumb line course. If you drew a rhumb line from one pole and followed it all the way to the other, it would form a spirallic loxodrome. (wikipedia)
demonstation of mercator map distortion
Mercator Chart: the standard kind of map that is used almost universally because of its simplicity for navigating in small areas. The mercator map represents the world as if it were a rectangular shape rather than a spherical one, and thereby distorts areas at extreme latitudes (this is why antarctica appears giant on world maps), making them appear much larger than they actually are. The mercator chart is straightforward for navigation because drawing a straight line between two points will give a direction to follow to get to your destination. On larger scale maps, this is a problem because the earth is spherical; but for navigating on the coast and at non-extreme latitudes, mercator charts are the best choise.

Chartwork

Video Lessons and Refreshers: Content covering practical chartwork is difficult to understand when written out and presents better as videos to show the different steps. When I was learning chartwork I watched video tutorials extensively. My favorites are Northeastern Maritime Insitute Lessons (playlist covering basic chart plotting into plotting with current, wind, and tide. tide calculations, compass corrections), and Refresh Maritime has a great running fix tutorial and explaination of chart datums.
example of the navigation triangle. A-B is the heading line (CTS), B-C is the direction and forces of set, and A-C is the course actually travelled (CMG) due to the forces of set.
Dead Reckoning: the process of calculating the current position of an object by using a previously determined position to create a fix (position-fixing). Distance travelled is equal to speed multiplied by time elapsed (which is measured either in hours or minutes), so any two out of these three kinds of information present in a problem will allow the last one to be found. Dead reckoning begins with a known position, such as 1 nautical mile abeam of a waypoint at a certain time- and from there a line of position (LOP) is created in a heading direction (which can be either transferred from or measured by using the parallel ruler to measure off of the nearest chart compass rose). To obtain distance travelled on the chart, the navigation dividers are used to measure incriments of Latitude on the side of the chart (1 degree is equal to 1 minute, and 1 minute is equal to 1 nautical mile), which are transferred onto the line of position. A line of position or fix without time noted is useless; time must always be indicated when plotting on the chart because time is a crucial part of the distance=(speed)x(time) formula. (wikipedia)
Current and Tide: the direction of tidal push, called the set, is expressed as a degree measurement on the compass, referencing the direction tide is pushing (a northerly tide would push towards north). The speed of tidal currents is called the 'rate', and the distance that elapses under tidal effects is called 'drift'. The heading of set is expressed on the chart as an LOP with three arrows in the middle, pointing the direction of travel.
Wind and Leeway: wind measurements are expressed as the cardinal direction they originate from (ie. a northerly wind comes from the north and blows the direction of south). Wind is accounted for mathematically in calculations, but is not plotted at the chart because it is subject to rapid change.
a triangle of velocities is constructed to help determine forces affecting the vessels heading
Course Made Good (CMG) and Speed Made Good (SMG): to be 'made good' refers to the actual speed or course which is travelled, as opposed to information which is assumed like the course steered or vessel speed. Because a vessels speed is subject to tidal forces, the speed through the water (STW) is different than the speed made good, which can only be measured by finding a distance travelled to reference against the STW. A course made good is in reference to a vessels heading under environmental forces like tide, which can create a difference between course to steer (CTS) and course made good. A vessel could be steering a course of 180 degrees, but due to the force of tide setting to 170 could be pointing towards 180 (CTS) but travelling in the direction of 170 (CMG). In chartwork, the LOP which represents course made good is expressed with two arrows marking the direction of travel. The CTS heading is marked with one arrow pointing in the direction of travel.
diagrams of the nav triangle from Bowditch - Chapter 10
The Navigation Triangle: To create a reprentation of forces affecting navigation, a triangle of velocities or 'nav triangle' can be drawn to measure them. A navigation triangle typically represents either a period of 60 minutes (vessel speed and tidal drift will give a true distance travelled over 60 min) or a period of 30 minutes (all information measured hourly, like speed, must be halved in this case), but can be scaled up or down to represent larger or smaller periods of time. The diagrams shown here represent different orders that the triangle is created in to determine different info, always drawn in the order of A-B, B-C, C-A.
Allowing Current: when allowing the effects of the current to push the vessel, the work order is as such:
  • the vessels heading (CTS) is noted and converted into a true bearing (from a gyro, magnetic or compass bearing). Gyro error, or deviation and then variation are accounted for (heading is converted into true bearing),
  • gyro error, or deviation and then variation are accounted for (heading is converted into true bearing),
  • with the ships heading now converted to a true bearing, the effects of leeway can now be accounted for mathematically,
  • with leeway now sorted, the CTS can be plotted on the chart. Track through the water is drawn,
  • Tidal effects are accounted for,
  • Course over the ground (CMG) is determined. (bearing is converted to true and can be plotted on the chart)
Counteracting Current: when countering the effects of the current to maintain a particular heading, the work order is as such:
  • The desired course over the ground is noted and plotted on the chart,
  • the direction of current/tidal push is noted,
  • course to steer is determined by 'closing' the navigation triangle, (giving a true bearing to be converted later on)
  • leeway/wind direction is accounted for at the start of calculations, and is not plotted
  • ships heading (CTS) is converted into a compass or gyrocompass heading, gyro error, or variation and deviation are calculated,
  • A course to steer is determined (bearing has been converted to a compass heading for the navigator's use)
Position Fixing: it is important for the navigator to take regular fixes to determine and confirm their position. There are many different ways to fix position depending on what information and tools are available to the navigator at the time. It is most common to determine position by drawing two lines of position from diffent known objects (static objects marked on the chart), creating a 'fix' where they intersect that determines the position of the vessel. It is not always possible to have two reliable objects to fix position from, in which case the running fix is used.

Buoyage

Buoys: Buoys are a type of floating aid to navigation, and are part of the aids to navigation system, along with fixed navigation-aids like lighthouses and electronic aids like RACONS. Buoys, like all aids to navigation, come in many different shapes like nun (cylindrical with conical top), can (cylindrical), cone (conical shape), pillar (frame with solid parts) and spar (a nail-like shape). Buoys are typically a combination of multiple differend aids to navigation, typically being outfitted with bells (audible aids), lights (visual aids), and topmarks (daybeacons). As useful as they are, buoys are not as reliable as fixed navigation aids because their position could potentially shift in heavy weather; therefore heavy reliance on buoys for navigation may open the navigator up to danger (such as using buoys as waypoints as opposed to fixed aids, or sailing too close to buoys that may be displaced from their hazard). Online chart viewers can be helpful in visualizing the buoyage systems around the world.
Buoyage Systems: the world is split into two buoyage systems, IALA A (europe, australia, africa and west asia), and IALA B (north and south america, japan and the phillipines). In IALA A, a port hand lateral buoy will be red, matching the red port-side light of the vessel. In IALA B, a port hand lateral buoy will be green. A saying regarding IALA B regions is 'red, right, return,' to signify keeping a red starboard-hand lateral buoy on the starboard or right-hand side of the vessel, when returning to harbour or proceeding upstream (the direction of which is assumed North on the west coast, and south on the East coast). It is of great importance to be aware of the buoyage system in an area when passage-planning. IALA has a digital dictionary of international aids to marine navigation, which is extremely useful for studying the technical definitions of particular equipment that pop up in examinations (like diaphone horns, occulting light characteristics, etc.).
a general idea of the buoyage system
Lateral Buoys: starboard and port hand buoys indicate which side they should be kept to while passing them, and are colored either red or green (or a combination of both), have either a triangle or a square topmark, and either a red or green light (matching their color). In IALA B, a port-hand lateral buoy is green and should be kept to the port side; and similarily a starboard-hand buoy is red and should be kept to the starboard side when passing. A starboard hand buoy flashes red 1 time every 4 seconds. A Port hand buoy flashes green 1 time every 4 seconds. Bifucation buoys indicate a split into a main and secondary channel or passage. To use the main channel indicated by a bifurcation buoy or marker, the buoy must be kept to the side it primarily indicates; a port-hand bifurcation marker indicates a primary channel to port and a secondary channel to starboard, and a starboard bifurcation would indicate primary channel to starboard and secondary to port. The 'shape' indicating starboard is a triangle (Triangles have 3 points, which make them odd. Starboard contains 9 letters, which makes it odd. Starboard is always associated with odd numbers onboard the vessel and starboard buoys will always be odd-numbered). The 'shape' indicating port is the square (Squares have 4 points, making them even. Port has 4 letters making it even; and it is always associated with even numbers. Port buoys are always even-numbered). This section of TP10038-E clearly explains the IALA B lateral buoys. (wikipedia)
it is difficult to see the topmarks of a buoy unless close to it
Cardinal Buoys: buoys and markers which indicate that safe water exists in a cardinal direction relative to their position. Cardinal buoys are colored yellow and black, have white lights, and have black triangle-shaped top marks. The topmarks on a cardinal buoy will point with their triangular 'arrows' towards the black part of the buoy to identify it as a north, east, south, or west cardinal buoy. The lights on cardinal buoys are associated with the numbers on the clock; north will flash 1 time every 1 second, east 3 times every 5 seconds, south 6 times with 1 long flash every 10 seconds, and west flashing 9 times in 10 seconds. (wikipedia)

Electronic Positioning Systems

Systems

Global Navigation Satellite Systems (GNSS): satellite systems considered to have global satellite coverage. There are 4 main systems active as of 2024; GPS (USA), GLONASS (Russia), BDS (China), and Galileo (Europe), and each system has a different number and configuration of satellites globally. The satellite 'waves' which transmit info to ground-based stations work via line of sight; so a clearer line of sight with a satellite will mean more accurate information. Satellite transmissions are subject to many errors, such as distortion due to the troposphere, reflection off of targets, and most importantly a difference in time (time=lag). Multiple satellites will work together to draw 'lines of position' onto a target- the accuracy of which is measured through Dilution of Position (DOP). The higher the DOP number, the less accurate the position fixing is due to greater errors affecting the signal. The GNSS System has land-based systems (GBAS), such as radio towers, which either transmit or recieve information from satellites or other ground stations in order to augment the satellite (SBAS) and air-based (ABAS) systems within GNSS.
Automatic Identification System (AIS): obtains vessel position info based off of information fed to it via GPS, rather than the vessels actual position in the world. AIS transmits different classes of information about a vessel; static and dynamic (and voyage information in class A models). The static information transmitted are things such as a vessels name, its characteristics (length and width), and what kind of ship it is. Dynamic information includes the position and speed. While only class A transponders (fitted on passenger and large ships) will transmit voyage information, that will include information like the destination headed, the number of people onboard, or the cargo. Most vessels will carry a class A transponder- the class B type are often carried by yachts and pleasurecraft. AIS is highly useful for collision avoidance (so long as the vulnerability of gps-based collision avoidance is not overlooked), search and rescue and vessel tracking. It is also integrated into the Aids to Navigaton system and there are AIS-specific navigation aids which exist digitally but not physically. You can view AIS online to see the extent of the system and how useful it is for keeping track of vessels. (wikipedia)

Equipment

Magnetic Compass: During the process of construction, ships are made to have magnetic properties through external forces (magnetism flowing from one pole to the other, welding in the vicinity, etc.) as they are built primarily with ferromagnetic materials, like steel. A ship during construction will obtain permanant, temporary, and induced magnetic characteristics, all of which will contribute to magnetic deviation effecting the magnetic compass (causing it to point other directions than north). Deviation is one of many compass errors that the magnetic compass may be subject to, along with magnetic variation, which is the annual shifting of magnetic north away from 'true north' (geographic north). While the magnetic compass is typically not the primary navigational compass used in the modern age because of the errors it is subject to, it is still an effective piece of equipment as it does not require any power to function. Modern ships will normally use a gyroscopic compass or fluxgate compass for navigation, but must carry a magnetic compass as backup. Nauticalsite.in has a really fantastic article about magnetism, compasses, and compass work/course conversions used in chartwork. To minimize the effects of magnetic interference, the magnetic compass is stored in and viewed through a binnacle. In cases where the binnacle is stored outside of the wheelhouse, it can often still be read through a periscope.
a free gyroscope can spin any direction
Gyro Compass: a non-magnetic compass which operates under the forces of gyroscopic precession and gravity, allowing it to be made to point towards true north with a high degree of accuracy, and to continue to hold that position despite both vessel movement and rotation of the earth. A gyrocompass will take a few hours to spin up and point north but this process can be sped up via damping, which is the provision of precession to the gyrocompass to nudge it towards being north-facing. There are a lot of complicated principles that allow the gyrocompass to function, and the nauticalsite article on gyro compasswork does a great job of explaining some of it. There is an archived service manual for the 1994 sperry mark 14 gyro-compass, which explains how the compass works. The modern gyrocompass is much more compact than this model. The gyrocompass is typically hooked up to compass repeaters, which allow the heading to be read off of the repeater and feed heading information into the bridge systems.
Radar: one of the most important modern devices onboard the ship. The radar works by sending out RF energy waves, which reflect off of targets and return to the transponder; indicating the position of whatever they reflect off of. Certain materials are more reflective than others- water and steel are highly reflective; whereas wood tends to absorb the signal more. There are different types of radar antennae that serve different purposes; an 'open-array' style radar is not compatible with ships that have extensive rigging overhead- where a compact 'radome' style antennae is a far better choice. In operation of the radar it is crucial that the pulee length allows time for the signal to return- otherwise the signals will intercept one another and produce a false reading. There are two types of radar bands, X-Band ('extra-close') and S-Band. The 'X-Band' uses a lower frequency signal, and is better for collision avoidance, and close range coastal navigation. The 'S-Band' signal travels further and is better used for long range detection, for weak signals, and in the rain. It is important to scrutinize radar information and in order to detect and account for errors like 'ghost echoes', gyro misalignment and yawing. What the radar excels at is range detection- its bearing detection may not be considered accurate because multiple targets can 'merge together', but the range is subject to little error and is highly accurate. In collision avoidance radar is a crucual aide by providing distance and approximate position, in addition to giving speed information which allows the navigator to plot a relative bearing and closest point of approach using the ARPA system.
Autopilot: the autopilot system works by maintaining a set heading, as opposed to manual or hand-steering where a dedicated quartermaster is necessary to achieve this purpose. It operates either in heading (holds set heading) or track mode (follows a pre set route and alters at waypoints), and in either follow-up (rudder will automatically move to hold course) or non follow-up mode (rudder will move only under control). The autopilot is not to be considered as a replacement for the quartermaster and it must be possible to switch from auto to manual steering 'immediately', which is technically defined as 3 seconds. In close quarters and collision avoidance scenarios it is unacceptible to use to autopilot system. It is important to note that the autopilot system is considered one of the various steering systems onboard, and in the event that control is lost elsewhere it can always be tested as a back up method (as in, in addition to the emergency hydraulic controls from the steering flats). In rough weather the autopilot may not be the best choice as the yawing motion can allow it to swing between courses, causing a greater rolling motion.
Echo Sounder: an underwater device which sends out soundwaves, which are then reflected back to provide a depth reading. It works by using the difference in time between when the signal was transmitted and when it was recieved, if at all, to measure the depth travelled. As with all radar devices it is important that the pulse repetition rate and pulse repetition frequency are balanced in order for the signal to travel uninterrupted to minimize error. It is of utmost importance to always be aware of the depth of water underkeel and the echo sounder is an important device that changed depth sounding forever and phased out the lead line. If placed in an unstable position vulnerable to vessel fore-and-aft pitching, the echo sounder can also give false readings because it is moving from the position where it originally sent out its signals. The sounder should be placed perferably midships (depending on characteristics of course) and with as close to a 90 degree vertical beam projection as possible. The salinity of the water will have an effect on signal strength; meaning that in low salinity a depth reading may present as greater because the signal moves faster through the water, and in high-salinity may present as shallower beacuse the signal moves slower. The echo sounder is not a single unit; it is a system made up of different units to generate, transmit, and recieve the signals it deals with. The pulse generator generates the signals, the transducer recieves and transmits signals, the amplifier enhances the signals recieved, which is then recorded to produce a reading.
Doppler Log: a device for measuring the vessels speed by using the doppler effect. The log will transmit a signal to the seafloor, and the time difference between the transmission and retrieval is used to measure speed. A doppler log consists of multiple systems like the echo sounder. Most importantly to the navigator, the doppler log will provide a reading of speed through the water as opposed to the speed over the ground reading that GPS provides.