Navigation of the Tides
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Which teaches how to know by the age of the Moon what the time is, or when High Tide is at any place where you know what delay that place causes on the Tide.
Now, by the age of the Moon, you may know the tidal flow at any hour, at any place where you know what Moon makes high water or high tide, which rule of thumb mariners call the shifting of the Sun and Moon; and there are many ways to do it.
Tidal Change each Day
The best way to know of the tides is to observe the Moon at high water, and then high water will only occur at the same position of the Moon, regardless of the time of day. And there being two tides a day, then high water will also occur half a day from this time.
The other way is harder, but it works during the day, and when the Moon is occluded by cloud or foul weather, and even if you are in your cabin. First, divide one hour into nine parts, and take eight of those parts, discarding the ninth. This figure serves as the amount to alter 24 hours. And the eight parts are 53 minutes and 20 seconds, and the ninth part of an hour is 6 minutes and 40 seconds. Each flood and ebb happens in a half day and four parts of an hour, or 12 hours 26 minutes and 40 seconds, later on average than its predecessor. And so each day the tide is eight parts, or 53 minutes 20 seconds later than the day before. For example, if a high tide occurs at midnight on a day, it will also occur at 53 minutes past midnight the next day, and so on, as shown below. For the course of the tides is nothing else but to add eight parts of an hour for every day of the age of the Moon, and by this you may at all times know at what time it flows, by putting to every flood and ebb, four parts of an hour, and to two floods and ebbs, eight parts. Now, as the Moon goes slower near the Auge, and faster in opposition, so these times are truly between three and five parts per tide, and so it can take between 26 and 30 days for the tides to return to their starting times, but this rule of thumb is enough to get by, for those that want only rough estimates or are looking few days ahead.
Tide Change or Moon Zenith
| Day | High Tide |
|---|---|
| 1 | 0:00 |
| 2 | 0:53 |
| 3 | 1:46 |
| 4 | 2:40 |
| 5 | 3:33 |
| 6 | 4:26 |
| 7 | 5:20 |
| 8 | 6:13 |
| 9 | 7:06 |
| 10 | 8:00 |
| 11 | 8:53 |
| 12 | 9:46 |
| 13 | 10:40 |
| 14 | 11:33 |
| 15 | 12:26 |
| 16 | 13:20 |
| 17 | 14:13 |
| 18 | 15:06 |
| 19 | 16:00 |
| 20 | 16:53 |
| 21 | 17:46 |
| 22 | 18:40 |
| 23 | 19:33 |
| 24 | 20:26 |
| 25 | 21:20 |
| 26 | 22:13 |
| 27 | 23:06 |
| 28 | -- |
| 29 | 0:00 |
How the Auge affects Tides
The Sun passes through the Zodiac in exactly 364 days, this being our year. But the Moon passes through the Zodiac far quicker, in but 26 days, the same time that the sun takes to move through one of the 14 signs. This means that in 26 days the Moon has not yet caught the Sun, for the Sun is still one sign further on; it takes two more full days for the Moon to catch the Sun, nearly two degrees into the next sign. So the time between each change of the moon is 28 full days, and so the moon changes from New to Full to New in these 28 days, and so it is throughout the year excepting that the Moon may change sometimes in less time, and sometimes more, as it moves faster or slower through the Zodiac. The Moon being in its Auge goes little more then 10°15' in 24 hours, and in opposition, as fast as 17°20' in 24 hours, and on average, 13°50'. So this is the reason why sometimes the Moon may change sooner or stay longer than 28 days. This point of Auge is moveable, and passes in a cycle through the Zodiac every 18 years, and it sometimes causes the Full Moon to happen sooner or later, and in like manner all the quarters of the Moon, and all the other aspects the Moon has with the Sun or any of the planers or Stars. But notwithstanding, I would not wish the common Mariners to trouble themselves with these matters, but follow their accustomed order, to allow for every day of the age of the Moon an extra 8 parts of an hour. But some Navigators will take it upon them to correct the Almanacs as concerning the change and quarters of the Moon, holding the opinion that every Moon ought to be equal in the number of days and hours, and the full moon to be just the half of this period, and the quarters in like manner, so that every quarter falls on a Moon day. Wherein they are notably deceived, as sometimes in the year you shall see the Moon rather than at some other time, for example, in Summer you shall see the Moon within 24 hours after the change, because she has North declination of the Sun, and makes a bigger arc than the Sun during New Moon, but in Winter you shall not see her until a full three days after the change, because her declination is to the South, but you may see her within 24 hours before her change.
Tides at any Place
There was going to follow a table of tides about certain places of this coast. However, given that those who travel regularly between certain ports will already know their timings with respect to the Moon, it is more useful to provide a method that can be used with some confidence to find the difference of tides between nearby places so that only the major ports need to be learnt, and with less accuracy to determine when it be high water at any port or coast without any local knowledge, and this shall work on any world which has a Moon and tides.
First, on the open ocean, and at any atolls or other small specks far from substantial amounts of land, high tide occurs at a South Moon, and has variance of but 1 ½ fathoms from ebb to flow. The position of the Moon at a high tide is sometimes named the tidal point, and so we shall call it. At any time there are two swells of high water on opposite sides of the globe, and these roll from East to West, one directly under the Moon, and the other opposite, so that high water at a Southeast Moon will also be at a Northwest Moon, except that a Moon to the Northwest is beneath the Horizon. These swells are slowed by land, and by being forced into narrow channels, or behind islands or peninsulas, or deep inland. All these features of harbours change or slow the tidal swell, and delay which Moon it is under, and so move the tidal point westwards. If from the Northeast to Southeast is all land, then add one point, and if it is from the North to the South, add another, and if from the Northwest through all the East to the Southwest is land, add a third point. If there is substantial land to the West, and none to the East, subtract a point. If the land lies roughly North-South and is vast with at least 500 miles between an East/West passage, then add or subtract an additional point as above. If the sea must pass through a channel at least three times narrower than long or steadily narrowing, add a point per 50 miles of channel. If the port is between an island of at least 20 miles in size and the coast, add a point. If the port is in a deep cove or harbour, add a point, and add additional points if the harbour is 20 miles long or branches over many mud banks. If there is open sea to the East, count each of these one less, but if the only sea is to the West, count them twice. If points have been added for any two of land, channel, and port, add another, and add again if all three rules have delayed the tide. Finally, if in an estuary or tidal river, then count an additional point per twenty miles inland, or if at Sea, strong winds from the West or East may add or subtract an additional point.
All these rules can be added together, to find the point of the compass where the Moon will be when it is high water. Nonetheless the tidal point will be more accurate if it is based on the point of a nearby location, modified by the difference in the points as listed above, and this is the recommended way.
Tidal Point
| Open Sea | South | ||
| Major Land Masses | |||
| Land Eastwards from Northeast to Southeast | +1 | ||
| Land Eastwards from North to South | +1 | ||
| Land Eastwards from Northwest to Southwest | +1 | ||
| Land to the West and not the East | – 1 | ||
| Above land is at least 500 miles North-South | +/– 1 | ||
| Narrow Seaways | |||
| Channel at least three times longer than wide (per 50 miles) | +1 | ||
| Sheltering Island of at least 20 miles and near coast | +1 | ||
| Harbours | |||
| Deep Cove or Harbour | +1 | ||
| Harbour is at least 20 miles long | +1 | ||
| Harbour branches, has many submerged banks | +1 | ||
| Only open sea to the West | double | ||
| Open sea to the East | – 1 | ||
| Other Rules | |||
| Any two of Land Masses, Seaways, Harbours delay tide | +1 | ||
| All three of Land Masses, Seaways, Harbours delay tide | +1 | ||
| Estuary or tidal river (per 20 miles) | +1 | ||
| Strong Westerly Winds if not in a Harbour | +1 | ||
| Strong Easterly Winds if not in a Harbour | – 1 | ||
Tidal Strength
And when the Moon has been found, the variance or strength of the tide may also be known. For high water at a South Moon, it varies by 1 ½ fathoms, and this increases by at least a foot for every point it is delayed until it be a West Moon which is also an East Moon, and decreased by a foot for each point from a South Moon to a South East Moon, and from a East Moon to a South East Moon it decreases by a full half fathom per point. And on a river or long harbour this variance is reduced by half, as it is in the eastern half of the inland sea, being the coasts of Azuria, Rokar, Arabie, Ellenia, and the Lunar Empire. And the tides are higher in the Spring streams than in the other quarters of the Moon, rising an extra foot in five, or if the Moon is in opposition, a foot in four. And on narrowing and gently shelving banks known as washes or in narrow channels between larger bodies of water the height of the swell may increase, so that I have heard of a bay at the end of a channel between two southern seas where the tidal swell is nearly 10 fathoms, and the rising tide cannot be outrun on foot but takes men under no matter how fast they be.
Special Rules
Now there is one special rule to note, which is that in a harbour or tidal river that has any distance to the Sea, it flows one point of the compass more in the Spring streams than in the other quarters of the Moon when there is neither rage of winds nor any other cause to hinder or further this effect. So, if the tidal point in a harbour is a South and by West Moon, then when the Moon is Full or in its change, it flows at a South Southwest Moon, for there is more water to move upstream and so it is delayed.
And near an island of some hundreds of miles North to South, then the tides work under different rules, for the tidal swell will go around this island, either anticlockwise if no other land is near, or in both directions, starting from the seawards side. And in either case, then only the difference of tides between nearby locations can be ascertained through this method, for it is too complex to give a general rule for. And Palestrina is one of these, as is Delph, Kinlu, and the Insel der Freiheit.
And if you sail to the Antipodes all the rules are the same, except that you must transpose South and North, so that features that delay the tidal flow move the tidal point clockwise, rather than anticlockwise, and likewise with the usual tidal flow around large islands, for the Moon is to the North. And under the Ecliptic, it may be either way, depending on the Dragon and the Auge of the Moon, excepting that the tidal flow around a large island be fixed, no matter where the Moon is.
Charts
Although all charts can be located in the Navigation Appendix, yet below is attached a copy of that chart which concerns the times of flood and ebb at various major ports across Alusia, being those for which I have observed a regular flow. And the special rules above for estuaries and long harbours are not part of this chart, but must be borne in mind by any good Navigator, along with the varying tidal strength due to the tidal point of the port and whether it is a Spring stream or no.
