The Portugieser Yacht Club Moon & Tide features a tide display that keeps you informed about the next high water. It is possible thanks to a special wheel train that translates the rhythm of the hours into the constantly shifting chronological sequence of high and low water. The Greek mariner Pytheas recognized the link between this natural phenomenon and the moon as early as the fourth century B.C. It is particularly noticeable at the coast that the moon visible at high tide is almost at the same place in the sky again at the next but one high tide. In 1609, the German astronomer Johannes Keppler first outlined a theory according to which the moon attracts the water in the oceans and thus causes the tides. Indeed, the tides are caused by a complex interplay of gravitational and centrifugal forces between the Earth, the moon, and the sun. On the side of the Earth facing the moon, the moon’s gravitational pull attracts the water, creating a bulge that causes the tides. But a similar bulge of water also forms on the side of the Earth facing away from the moon. This is caused by the centrifugal forces that arise due to the rotation of the Earth, much like the clothes in a spin dryer, the masses of water are pushed outwards by these centrifugal forces.

The Earth rotates on its own axis once every 24 hours and, within that period, moves under the two bulges of high tide and two areas of the ebb tide. For human beings, who do not notice the rotation of the Earth, this gives the impression that the water is receding from the coast and then rising again. But why does high tide occur at a different time each day? During the time it takes the Earth to complete a rotation, the moon progresses a little bit further. So, on Earth, it takes 24 hours and 48 minutes for the moon to be in the same position. The time between two high tides, then, is always exactly 12 hours and 24 minutes. If, for example, it is high tide at midnight, the next ones will occur at 12:24 pm and 12:48 am, respectively.

The tide display on the Portugieser Yacht Club Moon & Tide now shows the slightly shifting times for high tide
on the dial. During the 12 hours and 24 minutes between two high tides, the display rotates by around 24 minutes on the 12-hour scale. The energy required to turn it is channeled by the basic movement’s hour pinion. The challenge facing the designers was to convert the rapid hourly rhythm into the much more leisurely rotation of the tidal disc. A reducing gear comprising three precisely calculated cogs slows the rotation to the point where the tidal disc rotates around its axis once in exactly 14.76 days. The tidal display module is integrated into the IWC calibre 82835 and contains just 49 individual parts. The automatic movement provides a power reserve of 60 hours and is visible via the display case back.

Because the display rotates continuously, it always shows the approximate time of the next high tide. If the arrow points to 12 o’clock at 10 o’clock in the morning, the next high tide will be a little later than 12 o’clock
because, in the next two hours, the tidal disc will also move a little further. On the opposite side, you can
also, read the approximate time for the next low tide. The exact times for high and low tide depending on the
longitude. As a result, the display needs to be calibrated once using the tide tables for a specific location, such as New York, Lisbon, or Sydney. The display works reliably on all coasts with two equally strong high and low tides per day.

Another special feature of the Portugieser Yacht Club Moon & Tide is the double moon phase display. It has
been extended to include a special inscription and also provides information about the strength of the current tides. At full and new moon, the Earth, moon, and sun are in a direct line. In this constellation, the tidal forces are cumulative and generate a spring tide —a particularly strong high tide. At half-moon, however, the sun and moon are at right angles to each other. The result of this is a weaker high tide, or “neap tide”. Exactly how high the water rises depends on the geographical location and the exact physical nature of the coast. While the tidal swell on the open sea is only about 30 centimeters, the sea level during high tide rises by up to 20 meters in the Canadian Bay of Fundy. So, anyone in charge of a boat would be well advised to take a look at the dial of their Portugieser Yacht Club Moon & Tide.

The Portugieser Yacht Club Moon & Tide ref. 344001 is the first watch from IWC to sport the newly developed
tide indication cased in a 44.6 mm 18K 5N gold case with blue dial, the watch is delivered with a blue rubber strap with textile inlay.

Sticker Price $33,100 USD. For more info on IWC click here.