As with any account that deals with maritime matters, much use is made of terms and phrases that may be somewhat unfamiliar to the non-nautical minded person. Furthermore, some terms and phrases used in 1912 differed from those that are used today. In particular, angular directions and helm orders seem to be the most confusing.
Angles and Bearings
References to angular directions were usually given in compass points or degrees. In all, there are 32 points in a circle (360°), with each point precisely separated by 11¼ degrees from the next point. Included in the set of 32 points are the four cardinal points: north (N), east (E), south (S), and west (W); four intercardinal points: northeast (NE), southeast (SE), southwest (SW), and northwest (NW); and eight secondary-intercardinal points such as north-northeast (NNE), east-northeast (ENE), east-southeast (ESE), and so on. There is one secondary-intercardinal point located between each cardinal and inter-cardinal point.
On a typical compass card of the period, points were marked in the shape of triangles of various sizes and diamonds. Marks for ½ points and ¼ points were also put on the compass card as well as tick marks for degrees, the latter marked on the outermost scale of the card. In 1912, degrees were specified by quadrant such north with so many degrees east or west, or south with so many degrees east or west. As an example, a heading of 265° would be specified as S 85 W, while a heading of 305° would be specified as N 55 W. A typical compass card of the period showing a heading of N 22 E (022°) is shown in Figure 1.
Because the axis of the earth’s magnetic poles are not aligned exactly with the earth’s axis of rotation, the direction of true north typically differs from the direction of magnetic north, depending on where you are on the earth’s surface. This difference is known as magnetic variation. In the area where Titanic sank in April 1912, magnetic variation was about 24° west. What that means is that north on a magnetic compass with no other errors would actually point 24 degrees to the west of true north. However, because magnetic compasses are also affected by the distribution of iron and steel within a ship, they are also subjected to errors know as deviation errors that varied with the actual magnetic heading that the ship was on at a given time. These deviation errors were tested and somewhat compensated for when a compass was last adjusted. Typically, the remaining deviation error was only a few degrees, and was marked in a table or on a diagram that gave the deviation error in terms of degrees to be added or subtracted from the ship’s heading that was read off of the compass card.
When a ship’s heading to steer by was given it usually was specified in degrees as marked on either the ship’s standard compass or on a steering compass. The standard compass, usually mounted on the upper bridge or on raised compass platform, was used to steady a ship on a desired magnetic courseline and also used to take magnetic bearings of celestial objects and landmarks when needed. The steering compass was the compass by which the helmsman, the man at the wheel, used to steer the ship. It was located in an enclosed wheelhouse or in an enclosed part of the bridge. The difference between the ship’s standard compass heading and steering compass heading was noted and both course headings were marked on a course board in the wheelhouse or on the bridge.
In modern times, courses are specified in 360-degree notation by three digits. For example, a ship heading due east true is said to be on a course heading of 090° T. With 24° west variation, the ship’s magnetic heading would be 114° magnetic. Since in 1912 the magnetic compass was marked in degrees by quadrant, a ship that was steadied onto a heading of 114° magnetic would be said to be heading S 66 E by standard.
Angular directions to objects were specified by bearings, either compass bearings or relative bearings. If a compass bearing was specified, it usually was given by reference to points. For example, an object sighted a half point to the west of the northwest (NW) intercardinal point on the compass would be said to be bearing NW ½ W. If sighted one full point to the west of NW, it would be said to be bearing NW by W. If sighted one and a half points to the west of NW, it would be said to be bearing NW by W ½ W. And if sighted two full points to the west of NW, it would be bearing on the secondary-intercardinal point of west-northwest (WNW). Similarly for other points of the compass.
If a relative bearing specified an angle to an object, it would be given in relation to the head of one’s own vessel. Unlike today, where relative bearings are a number of specific degrees measured clockwise from the head of the vessel to the object, relative bearings back in 1912 were almost always specified in points. For example, an object sighted exactly 22½ degrees to the right of the direction that the ship’s bow was facing would be said to be “2 points on the starboard bow.” An object sighted 45 degrees to the left of the direction that the ship’s stern was facing would be said to be “4 points on the starboard quarter” or “broad on the starboard quarter.”
The diagram below (Fig. 2) shows relative bearings in 1-point increments that were used at the time.
Helm Orders and Turning Directions
One area of great confusion to many people already familiar with most nautical terms such as “port” (left) and “starboard” (right) has to do with helm orders. In 1912 helm orders were the same as that which came down from the days of sail.
On a sailing vessel if one wanted to turn the vessel’s head to port (to the left) the tiller had to be put over to starboard (to the right). Thus the order would be given to starboard the helm. The tiller was firmly attached to the rudderpost, and putting the tiller over to starboard (to the right) would throw the rudder, which pointed aft, over to port (to the left). With the rudder over to port, the action of water running past it would create a force on the rudder that would cause the vessel’s stern to swing out in the opposite direction over to starboard (to the right). This in turn would cause the vessel’s head to turn to port (to the left), and the vessel would begin to turn in a circle to the left. Even when the steering gear of a sailing ship or a steamship was controlled by a wheel, to turn the vessel’s head to port the order would be given to put the helm, and thus the vessel’s tiller, over to starboard. To do this, the helmsman would turn the wheel to the left in a counter-clockwise direction. The opposite would apply to turn a vessel in the opposite direction.
It was not just helm orders that reflected the terminology that came down from the days of sail. When a vessel was seen turning to port (to the left), it was described as being “starboarded.” Think of it as describing the direction in which the vessel’s stern was swinging as a vessel was being turned. Similarly, if a vessel was seen turning to starboard (to the right), it would be described as being “ported.” The diagram below (Fig. 3) shows all this.
Tonnage, Volume and Displacement
Another area of confusion is the topic of ship tonnage. Tonnage was usually expressed in gross registered tons and net registered tons. Gross registered tonnage (GRT) represented the total internal volume of a vessel, not its weight. One register ton is equal to a volume of 100 cubic feet. RMS Titanic was listed as a 46,328 GRT vessel. Her total internal volume was 4,632,800 cubic feet.
Net registered tonnage (NRT) represented the internal volume of the ship that was available for passengers and cargo expressed in register tons, where one register ton is equal to a volume of 100 cubic feet. NRT is obtained by subtracting the volume of non-revenue earning spaces (i.e., spaces not available for carrying passengers or cargo) from the ship’s GRT. RMS Titanic had an NRT of 21,831 tons.
A ship’s weight is specified by her displacement, which equals the weight in long tons of the volume of water that is displaced (i.e., pushed aside) by the vessel’s underwater volume when afloat. The weight of the displaced water equals the total weight of the vessel. RMS Titanic displaced 52,310 long tons of seawater at load draft. One long ton of seawater occupies a volume of about 35 cubic feet and weighs 2,240 pounds (lbs).
Lengths, Distances and Depth
Large distances were expressed in nautical miles (usually referred to simply as miles). Shorter distances were referred to as cables, yards or feet. One nautical mile is 6,080 feet, and one cable is 608 feet, or exactly 1/10 of a nautical mile. Since there are 3 feet in a yard, one cable is a little over 200 yards.
Depth was usually express in fathoms or feet. One fathom is equal to 6 feet. The depth of water that was marked on a chart was usually given in fathoms for some average state of tide, such as mean low tide. These length relationships are shown in Figure 4 below.
Speed and Knots
Finally there is the concept of speed. The speed of a vessel was, and still is, expressed in terms of knots, with 1 knot equal to 1 nautical mile per hour. For a steamship, the average speed through the water was approximately proportional to the average number of revolutions per minute (rpm) carried on her engines, which in turn, were usually connected directly to the ship’s propellers by means of shafts and thrust collars. The conversion from revolutions per minute to speed in knots was a function of the pitch of the propellers (the ideal travel distance that the propellers would move in one revolution if there were no slippage through the water) and the amount of slip produced by the propellers at a given rotational speed (the difference between the ideal travel distance and the actual travel distance in one revolution of the propellers). The amount of slip depended on a number of things, including the resistance of the ship’s hull, which itself was a function of how clean the ship’s bottom was.
A table, called a slip table, showing the expected speed of the vessel as a function of revolutions per minute would be posted in the chartroom once that was worked out by measuring how long it took for the ship to advanced some known distance (for example a measured mile or other known distance) while carrying a given number of revolutions.
Another measure of a ship’s speed through the water was by means of the patent log. The patent log ideally measured the distance traveled through the water over some specified time interval. On White Star Line passenger vessels, the log was usually reset at noon every day, and the ship’s quartermasters took readings of the log every two hours. The patent log used on Titanic was a Walker’s Patent Neptune Taffrail Log that was mounted on the rail of the docking bridge near the stern of the vessel.
The small dial on the left rotated once every nautical mile and was marked in tenths of a mile. The large dial in the middle rotated once every 100 nautical miles and had 100 units marked around the dial. The small dial on the right rotated once every 500 nautical miles and was marked in 100 mile increments.
Although calibrated in nautical miles, what the taffrail log actually measured was the number of revolutions of a finned rotor that was attached to the end of a long line as it was pulled through the water by the moving vessel. Its accuracy in recording nautical miles depended on how well it was calibrated at different speeds, when it was calibrated last, and its overall condition, including the attached log line and all internal parts.
It must be emphasized, that speed through the water was not necessarily the same as the actual speed-made-good of a vessel. For example, if a vessel was traveling at 15 knots through the water against a 1 knot head current, its speed-made-good would actually be 14 knots, something that would be noted by comparing the actual distance traveled relative to known landmarks or navigational fixes over a given period of time.
Today, the term “knots” has only one exclusive meaning, and that is nautical miles per hour, a measure of speed. Unfortunately, many seafarers back in 1912 erroneously used the term “knots” when referring to distances in nautical miles. Even in printed engine-room log books as late as the 1930’s you may see a column marked “Knots Run” to mean nautical miles traveled by the ship over a specified interval of time, or another column marked “Knots by Propeller” where someone would record the distance traveled in nautical miles based on the propeller’s pitch and the total number of propeller revolutions that were counted over a specified interval of time. Sometimes you may also hear sailors use the erroneous term “knots per hour” when referring to speed. Despite some of these misuses of the term “knots” by some seafarers, their true meaning can easily be obtained from the context of what they were saying.
(Reprinted from: Appendix-A, Strangers on the Horizon: Titanic and Californian – A Forensic Approach, Kindle Direct Publishing, 2019)