Navigation by a Sun Compass

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In which is shown the making and use of a Sun Compass for those navigating a vessel powered with Cavorite, which is of particular relevance to Wordsmith, Loxi, and the Elven Captain of the Princess Blade.

The Sun Compass

In Hydrographic Navigation, it is rarely most necessary to know at every instance of the day in what manner the Sun shines over the vessel, at what declination and degree. And when it is needed, the Sun being in the sky then its very shining makes its position clear to the Mariner, except when obscured by cloud or storm. However in some forms of Cosmographic Navigation, wherein the ship flies through the air or over the water, the exact position of the Sun matters as much or more than the quarter of the wind. One design of flying ship is the Aeir Ship, which can be propelled by the use of deflected Cavorite panelling being attracted to or repelled from heavenly bodies, primarily the Sun but also the Moon and other distant planets, and the vessel can make considerable way by using this force. Wherein the course set by the ship under Cavorite steerage can vary only slightly from the arc of the Sun, and the alternate method of propulsion of an Aeir Ship, being Sinusoidal, is both much slower and hard on those of faint constitution or flighty temperament, it is essential to know whether Cavorite deflection is best able to hold and carry the course, or whether a Sinusoidal course need be invoked, and the Sun Compass shall provide this knowledge. And the Ship's way, being difficult to measure at altitude, can also be read from the Sun Compass when under Cavorite steerage.

Making a Sun Compass

Whereas the Equinoctial Dial may be made of wood, the Sun Compass requires curves in all directions like a globe, and is thus best cast in brass to be true. The half Sun Compass consists of a vertical Needle, which casts a shadow onto a partial dish etched with various arcs and markings. The shape of the dish is a semi-hemisphere, cut from a globe first horizontally to form a bowl, and then vertically which gives easy access to the inside. Next the inside of the dish is etched with a central dividing line, and two series of nine parallel and even lines, each marking the surface into ten areas. The first line initially runs vertically before curving straight down to the base of the dish, and divides the dish into two equal parts. The next nine lines are seen as straight when the dish is viewed from directly above, and are equally spaced, with the vertical cut and the tangent of the bowl being lines ten and eleven also equally spaced; these lines, when viewed from the side, will curve downwards to different extents, the least being widely spaced down the side, and the most closely spaced near the bottom. The last nine lines are seen as straight when the dish is viewed from directly to one side, and each touches the lowest point of its contrary upright line at its further extent being the initial vertical line, making them unevenly but precisely spaced. Furthermore, at the nine points of intersection the percentile numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 are to be etched, with 0 etched at the centre of the bowl, and 100 at the lip. And the rim of the bowl should be marked with the degrees 10, 20, 30, 40, 50, 60, 70, 80, 90 on each side of the rim, with the centre being 0 degrees and the two corners being marked as 90 degrees; and in addition the middle horizontal line being similarly marked, or whichever line as is deep but still easily read. Finally, a wire or rod of the same height at the bowl is affixed to the centre as the Needle, and is made to stand vertical so that its tip is aligned with the bowl's lip. And the full Sun Compass is constructed as above, except that the dish is not cut vertically, or is made from two half compasses affixed together, so that nineteen vertical lines are etched rather than nine and the horizontal lines are etched in a full circle not half.

Mounting a Sun Compass

And as it is most important that the lip of the dish is level with the Horizon at all times, the dish is then fastened with a pin at its centre on a flat base of wood or brass so that it does not tilt or roll, but that it may rotate sideways about the centre point. And two pins are inserted in the base at the leeway bearings on either side, the leeway being the course deviation that the Navigator can coax from their ship from the direct line of the sun, and is in the order of 1 point or 11 degrees, but also varies due to the skill of the Navigator or Pilot and the shape and configuration of the ship, thus allowing the compass to be turned either way by this deviation, for uses as explained later. When installing the Sun Compass on board a ship, the base is best fixed with pins and hung from a gymble, so that it is flat and level howsoever the ship pitches and plunges, this being even more common on aerial than aquatic vessels.

The Celestial Compass

And for those planning a voyage amongst the stars, they will require the Celestial Compass, which is of clear crystal and perfectly round like a full globe or sphere, allowing the sunlight or starlight to enter from any angle and shine through the central cross hairs onto the markings etched on the inside of the surface in all three directions. And the vertical lines are now circles, and twice the number of horizontal lines, being nineteen, is required, and the central vertical wire is replaced with three wires in a knot, so that each end of wire stands at 90 degrees to four others, forming a star suspended centrally in the sphere. Furthermore, the device is to be suspended above the deck, such that it can be turned in any direction and locked in place. But the making of this device is for the shapers of glass, and is outside my knowledge as a Navigator.

The Use of a Sun Compass

The Sun Compass is used to know at what speed the ship travels under Cavorite propulsion, and in which direction, and how much the course is making good, this being the speed at which the ship is travelling towards the assigned port. And by knowing what way is made under Sinusoidal passage, it is possible to know whether a course held under Cavorite is faster although indirect than the slower but direct course, given the possible amount of course deviation.

Relative Direction of the Sun

To know the relative direction of the sun, the Sun Compass being fixed fore and aft so it can be read from behind, merely observe where the shadow of the Needle falls and read it off the lower of the two sets of degree marks. And if the Sun is coming from forward of the compass, it should be turned 180 degrees, and the reading made. And in any case, do not stand between the Sun and the Compass, but instead read it from one side or other, as otherwise your shadow will prevent all readings, as may your sails, masts, or idle deck passengers, none of which may easily be moved.

Determining your Speed

When travelling via attraction or repulsion of the Sun (or other heavenly bodies) by Cavorite shields, your speed is fastest when the Sun is directly behind or in front of the ship, and lies upon the Horizon, wherein the Sun Compass Needle lies on the 100 percentile marking. And when the Sun is at a different bearing or higher altitude, the ship speed is reduced, both in its seeming speed, and in its way made good. To know your best speed, you should lay out a course that is aligned with the setting sun, and is of a fixed or known distance, and then cover this ground at your best speed just before dusk, accounting for the time until completion. And this course should again be run using only sinusoidal movement, and this speed recorded, along with the ratio of the two speeds as a percentile number.

And to know the speed across the ground when travelling with the Sun, find the point marked by the Needle, and run your eye across the Compass, following and staying between the horizontal lines, until you find the percentile numbering, and this is your speed across the ground relative to your best speed. Moreover, to know the speed made good against the course set, turn the Sun Compass until it is aligned with the desired destination, and then find the point shadowed by the Needle, and run your eye along staying between the vertical curving lines, until you find the percentile numbering, and this is your speed made good, relative to your best speed, which will always be less than your speed across the ground unless you can hold your desired heading.

Determining your Course

Whereas any Cavorite ship may be moved through the air by the use of the attraction or repulsion of the Sun, or by the use of Sinusoidal movement, each being at a different rate of travel and in a different direction, and the speed and direction of two of these being dependant directly on the position of the Sun, which is ever changing as observed previously, it is necessary for a Navigator or Pilot to know which form of travel is the best for their ship at any time, and without resort to tables for calculation. And only one of the pair of repulsion or attraction need be measured, for the sun's shadow for one falls within the half Sun Compass only when the other does not; and that which does not fall within the Compass would provide retrograde motion and not be of any use in progression. And as a truer course can be steered by coaxing a point or more of leeway from the ship, the compass may be turned away from the destination by the amount of this leeway, so the speed made good is better than it may otherwise be. And whereas the percentile of the sinusoidal motion against the best speed is fixed and known, and the percentile speed made good of the vessel by attraction or repulsion be easily and rapidly found by turning the compass to your destination still allowing for leeway, and taking a single reading, it is easy for the two values to be compared, and the bigger of the two is the faster method, and the best course.

And this method works at any Latitude, and for any declination or bearing of the Sun, and at any altitude from the earth, for the speeds are relative to each other in the same circumstances. Furthermore, to reset them for another world, you may simply determine your best speed by Cavorite attraction and by Sinusoidal travel, and use the new percentile number as your mark of comparison.