TABLE OF CONTENTS

APPENDIX

More about the construction

Tide table.

Execution of the multiple tide table.

Konst der Stuerlieden (art of navigation)

Operation and use

A typical complication

Accuracy

Afterthought

Captain's watch?

Digital assistent (PDA).

Notes

APPENDIX

In 2008 an unusual watch was discussed in the television programme "Tussen Kunst & Kitsch" (the Dutch equivalent of The Antiques Road Show). It concerned a golden² pocket watch, signed "G.J. Nauta, Leuwaerden", made c. 1720.

Gijsbert (Gijsbartus) Jacobus Nauta is known as a ‘celebrated’ clockmaker who worked around 1720. According to Ottema (Lit. 8) he is mentioned in deeds of sale from 1718 and 1725, in which he is the purchaser of such property as houses on the Oranje-Eewal. He died in or before 1757, as an advertisement in the Leeuwarder Courant of that year concerns the sale of a "curious silver pocket watch, made by the late Gijsbert J. Nauta". In 1946 Ottema saw a gold watch in a shagreen leather case, signed G. J. Nauta, in the Fries Museum. According to him it was a watch that showed the hour, the month, the date, the phases of the moon and the tides in Dutch and foreign ports on the European continent. It was thus a different watch than the specimen described in this article. Longcase and table clocks by Nauta are also known. (Morpurgo, Lit. 3)

The watch, described here in unrestored condition, is a relatively simple one. It has a Roman chapter ring with half hour divisions (French lilies) and quarter divisions. Along the outer edge of the chapter ring the names of the months with the corresponding number of days are indicated. Originally it had one hand, which probably had a 'tail'³.

The verge watch has a duration of c. 27 hours. It has a balance with balance spring and is from a constructional point of view simple. The spring feet, pillars and balance bridge are beautifully shaped, pierced and engraved, which was common practice in those days.
 

The movement is somewhat different from most watches of the same period. The motion work is not driven from the centre, but via a 16-leaf pinion, which is engaged with the great wheel (fusee arbor). For this reason the usual centre arbor, running between the plates, is not used here.

This 16-leaf pinion, which turns fully once every four hours, drives the central part in the dial, which revolves fully in exactly twelve hours.

This unusual central part carries the hand³. Engraved in it is a tide table, which indicates the times of high water at nine different locations. It consists of two superimposed discs turning around the same arbor. The two discs are the following, with their characteristics described respectively:

  1) A gilt brass disc with a semi circular aperture; along this aperture from right to left the Arabic numerals 6-12 and 1-6 are engraved. At one end of the aperture on the left the word "Hoogh" (High) is engraved and at the other on the right the word "Water". Opposite nine of the thirteen numerals a place name is engraved. The numerals indicate the times of high water when the moon is new (or full) at the corresponding locations. In addition the disc has a moon phase aperture and on the outer rim a moon date ring 1-29½. (Figs 6, 7 and 10)
  
  2)  A silver moon disc with the phases of the moon and a tide table with twice the division 1-12.

Both discs are toothed and engaged with each other via an 8-leaf pinion. The silver moon disc and the probably originally tailed hand³ are fixed on the hour arbor (Figs 6 and 10).

This arbor is supported in the front plate and is driven via a frictional connection with the hour wheel by the eccentrically placed great wheel pinion.

 

The phenomenon of tides (high and low water) is related to the position of the moon. The sun also plays a role but to a much lesser extent. The sun has for instance a reinforcing effect when it finds itself on the same side of the earth as the moon.
(spring tide and neap tide twice per lunar month).

Therefore a tide table is always put on a disc which also indicates the phases of the moon and/or the day of the lunar month.

The moon revolves around the earth in 27.32 days, which during this period (1/13 = 7.5%) runs a part of its orbit around the sun. It takes therefore 29.53 days until the moon has the same phase (position relative to the earth and sun).

On a moon disc of clocks and watches the month is approximated by 29½ days. Therefore after about two years and nine months an adjustment of one day is required.

In this process the earth revolves once around it axis every day (in 23 hours and 56 minutes). If the motion of the moon in relation to the earth is disregarded, then high water and low water occur twice a day with a 12-hour period in between. (˜12.4 hours when this motion is not disregarded)

The times of high and low water vary from day to day, so that after one month a 24-hour cycle is completed. The tide tables consist therefore of a scale of twice twelve hours, usually round the moon date ring(1-29½).

The only thing which is not yet established is the relative movement (position) of both scales in relation to one another. This movement is dependent on the place, for which the tides are given.

Amsterdam (Pampus) highwater, moonphase and age aperture on a 18th century Dutch longcase clock.

(Courtesy: Bernard Meier)

For example, for 'Pampus' - the sand bank at the approach of Amsterdam harbour - it is high water at 3 o'clock when the moon is new or full. For Harlingen, high water occurs at 9 o'clock, when the moon is new or full. Therefore, many tide tables on clocks from Harlingen and Leeuwarden have this indication.
 
A complication is caused by the closing off of the Zuyderzee (1932), which put an end to the tidal movement near Amsterdam and in the IJsselmeer, the name of the lake that was created. So for antique clocks and watches tide tables from the 17th and 18th centuries should be consulted.

The silver moon disc fig.6 2) is - like the hand³ - fixed to the hour hand arbor and therefore revolves fully once every twelve hours.

The superimposed gilt disc fig.6 1) is not fixed to the hour hand arbor but revolves around it. (see also Fig. 10)

The silver tide table is visible through the semi circular aperture in this gilt disc. fig6 1)

Noon in Ostende on the day when it is new moon.
The forecast of the high water times in other places can be read simultaneously. The second, probably later hand has been removed (simulation)

When the moon is new (or full) the hour numerals on the silver tide table 2) correspond with the ones engraved opposite the locations along the semi circular aperture. (Fig. 7)

To find out which locations are actually meant, two versions of the "Kunst der Stuurlieden" can be consulted (Lit. 1 & 2): the first "'t Vergulde Licht der Zeevaart" by Claas Hendriksz Gietermaker dated 1677, the second "Schat-kamer ofte konst der Stuurlieden" by Klaas the Vries dated 1777. They were published before and after the Nauta watch was made.

Fig. 8. Two manuals for navigating sailors. They were published before and after the Nauta watch was made.

(Maritiem Museum Rotterdam)

Both books include a "Tafel" (table), in which 16 times of high water are mentioned (every 45 minutes) and a number of "plaatsen and kusten" (places and coasts) where these high tides occur.
(Fig. 9) In addition the times of high water for al these locations on the days after a new or full moon are mentioned, namely every day 48 minutes later (See also Fig.12).

click the pages below to enlarge
 
    1777    1677
Page: 14-15   Page: 16
Page: 16-17   Page: 17
Page: 18-19   Page: 18
 Page: 20-21                 
 Page: 22-23                 


fig 9. 1777 en 1677 book tables.

In the table below, the high water data of
the Nauta watch are compared with the
relevant data in the book tables.
 

Click here to view the relevant North Sea map section.

  OPERATION AND USE.

How the watch operates is quite simple. As the silver moon disc 2) which has 58 teeth, engages with the same pinion as the superimposed moon date disc 1), which has 59 teeth, the upper disc will lag behind at every 12-hour turn by 1/59. (Fig. 10)

After two turns the hand³ will indicate the moon date a day later and the times of high water will be indicated 24/29½ hour = ˜ 49 minutes later.

The months and the corresponding number of days, engraved along the outer rim of the chapter ring, can serve as an aid when converting lunar days to calendar days.

For the tide table to work correctly, it is strictly speaking necessary to set the hand on the right starting time when the moon is full or new, in other words when the hour numerals on the scales correspond perfectly (fig. 7) without turning the silver moon disc.

The maximum error that might occur owing to an incorrect setting of the time, is six hours⁴, which would result in a deviation of the tide table by ˜12 minutes (0.2 uur) (6/24 x 49 minutes).

This required resetting of the time is a typical complication of a multiple time table.
The right time set varies from location to location, for instance 12 o'clock for Ostende (Fig. 7) or 3 o'clock for Amsterdam etc. This 'norm location' could be called the 'home port' in this context.

For setting purposes there is an angle of 45° between the two "squares" on the hour hand arbor, to which the hand and the silver moon disc are attached. (Fig. 10) In this way the hand can be set in eight positions (times) which differ by 1.5 hours. This cannot really be done without the help of a qualified clockmaker.

Setting the watch for stationary use in one particular location is in fact feasible. For mobile use (onboard), however, it would be necessary to set the watch according to the local time of the 'home port' to maintain a correct time table.

The scales which turn gradually (constantly) in relation to each other provide a correct reading of the phases and age of the moon at any moment.
 

 

However, for predicting the next time of high water, this time must be shown by a jumping action comparable to calendar indication mechanisms in clocks, and is to remain fixed during a set period of time. Therefore, on this permanently turning scale, which does not jump, the reading is correct only once per period between two "high waters".


Because of this 'imperfection' this repeating error is largest shortly after the previous time of high water, viz. ≈25 minutes (0.4 hours) on average too early. The times of high water established when the moon is new (such as 12 o'clock for Ostend, 3 o'clock for Amsterdam etc.) have an error of ≈1 hour, so +0.5 and -0.5 hours. The accumulated error can therefore be ≈0.9 hours (0.5+0.4).

The scales which turn gradually (constantly) in relation to each other provide a correct reading of the phases and age of the moon at any moment.

• Captain's watch?

Whether this pocket watch in this case could be worn on deck at rough seas with lots of "spray" is doubtful. After all, it is not a waterproof "Omega Seamaster". A dry spot in the captain's cabin seems to be a minimum condition for longer use. The movement does not show traces of excessive corrosion as a result of wet conditions.
(Click here to view case details)

As not only the tides do cause high and low waters but also the direction of the current and its strength, accurate tidal data are extremely important for safe and successful navigation at sea.

The doubtful seaworthiness and possible inaccuracy of ≈0.9 hours, perhaps justifies the question of whether this watch was not mainly used on land (by a ship owner or a trader?) to be able to estimate the times of arrival and departure of a ship in various ports (?). Moreover it was for example important for the market price of fish to know whether the fishermen were be able to go out fishing once or twice a day. (Lit.7)
 

click here to enlarge

Fig. 12.
"to find the time of high water,
on the basis of the age of the moon."