A tide clock in Puget Sound has a harder job than simply counting the hours between one high tide and the next. The Sound’s long basins, narrow entrances, sills, islands, and side channels reshape the ocean tide as it travels inland. A useful display must know both the time and the place.
Puget Sound has mixed tides
Many traditional tide clocks are built around an ideal semidiurnal pattern: two similar high tides and two similar low tides during a lunar day of about 24 hours 50 minutes. Puget Sound is generally mixed semidiurnal. It still usually has two highs and two lows, but the two highs may differ and the two lows can differ dramatically. Mariners commonly distinguish higher high water, lower high water, higher low water, and lower low water for that reason.
The familiar clock dial suggests a smooth, symmetrical rise and fall. The actual curve may spend unequal amounts of time rising and falling and may show a modest low followed later by a much deeper low. A mechanism that repeats the same average cycle cannot reproduce that daily inequality.
The tide changes as it moves inland
The Pacific tide enters through the Strait of Juan de Fuca, passes constrictions such as Admiralty Inlet, and spreads through several connected basins. Coastline shape, water depth, friction, and narrow passages change both its range and its timing. NOAA research describes areas with fairly steady amplitude and phase separated by channels where both change rapidly. The range generally grows again toward the southern end of Puget Sound, while the wave also arrives later as it moves away from the ocean.
That means a tide clock calibrated for Port Townsend is not a dependable Seattle clock, and a Seattle setting is not automatically right for Tacoma or Olympia. Even two nearby locations can use different prediction stations because a narrow channel or embayment changes the local response.
Choose the station, not just the region
NOAA publishes predictions for harmonic stations, where observations support a set of local harmonic constants, and subordinate stations. A subordinate station borrows the prediction from a designated reference station, then applies measured corrections to the times and heights of high and low water. This gives boaters far more useful local information than a single “Puget Sound” setting.
A tide display for this region should therefore identify an appropriate station and follow that station’s predicted curve. It should not merely be set once to the next high tide and allowed to repeat forever.
A tide clock that can travel
NautiKron uses GPS to determine its location and selects the nearest supported NOAA station from more than 2,400 station datasets stored in the clock. Its tide calculation uses the data for that place instead of assuming one universal lunar cycle. No Wi-Fi connection is required.
This matters aboard a cruising boat. Sail from Port Townsend into the San Juan Islands, continue through Admiralty Inlet, or move south through the Sound, and NautiKron can change to the appropriate local prediction without being recalibrated at every port. Set the time zone, give the clock a view of the GPS sky, and the location-dependent work happens automatically.
Tide height is not tidal current
One final Puget Sound distinction is essential: the time of high or low water is not necessarily the time of slack current. In constricted passages, currents can be strong and their relationship to water level can be complex. Use official current predictions for navigation through places such as passes and narrows. A tide clock is a clear view of predicted water level; it is not a substitute for a current table, chart, weather report, or prudent seamanship.