Tide clock - wikipedia Tide clock Tide clock Tide clock Alunatime at Trinity Buoy Wharf, London A tide clock is a specially designed clock that keeps track of the Moon 's apparent motion around the Earth. Along many coastlines, the Moon contributes the major part ( 67 % ) of the combined lunar and solar tides. The exact interval between tides is influenced by the position of the Moon and Sun relative to the Earth, as well as the specific location on Earth where the tide is being measured. Due to the Moon 's orbital prograde motion, it takes a particular point on the Earth ( on average ) 24 hours and 50.5 minutes to rotate under the Moon, so the time between high lunar tides fluctuates between 12 and 13 hours. A tide clock is divided into two roughly 6 - hour tidal periods that shows the average length of time between high and low tides in a semi-diurnal tide region, such as most areas of the Atlantic Ocean. Traditional Mechanical Tide Clocks : The bottom of the tide clock dial ( 6 o - clock position ) is marked `` low tide '' and the top of the tide clock dial ( 12 o'clock position ) is marked `` high tide. '' The left side of the dial is marked `` hours until high tide '' and has a count - down of hours from 5 to 1. There is one hand on the clock face, and along the left side it points to the number of hours `` until '' the ( lunar ) high tide. The right hand side of the clock is marked `` hours until low tide '' and has a count - down of hours from 5 to 1. The number pointed to by the hand gives the time `` until '' the ( lunar ) low tide. Some tide clocks incorporate time ( using standard quartz movement ) and even humidity and temperature in the same instrument. Some tide clocks count down the number of hours from high or low tide, as in `` one hour past high or low tide ''. When the clock reaches the half way point ( `` half - tide '' ), it then counts the hours up to high tide or low tide, as in `` one hour until high or low tide ''. Generally, there is an adjustment knob on the back on the instrument which may be used to set the tide using official tide tables for a specific location at either high or low tide. Tides have an inherent lead or lag, known as the lunitidal interval, that is different at every location, so tidal clocks are set for the time when the local lunar high tide occurs. This is often complicated because the lead or lag varies during the course of the lunar month, as the lunar and solar tides fall into and out of synchronization. The lunar tide and solar tide are synchronized ( ebb and flow at the same time ) near the full moon and the new moon. The two tides are unsynchronized near the first and last quarter moon ( or `` half moon '' ). Also, in addition to the relative position of the moon and the elliptical pattern of the sun, the tide can be affected to some degree by wind and atmospheric pressure. All of these variables have less impact on the tide at the time of the full moon, so this is usually the best time to set a tide clock. If the tide clock is mounted on a moving boat, it will need to be reset more frequently. The best time to set the clock is at the new moon or the full moon, which is also when the clock can most reliably indicate the actual combined tide. A simple tide clock will always be least reliable near the quarter moon. Tide range is the vertical distance between the highest high tide and lowest low tide. The size of the lunar tide compared to the solar tide ( which comes once every 12 hours ) is generally about 2 to 1, but the actual proportion along any particular shore depends on the location, orientation, and shape of the local bay or estuary. Along some shorelines, the solar tide is the only important tide, and ordinary 12 - hour clocks suffice since the high and low tides come at nearly the same time every day. Because ordinary tidal clocks only track a part of the tidal effect, and because the relative size of the combined effects is different in different places, they are in general only partially accurate for tracking the tides. Consequently, all navigators use tide tables either in a booklet, computer or digital tide clock. Analog tide clocks are most accurate for use on the Atlantic coasts of America and Europe. This is because along the Atlantic coastline the moon controls the tides predictably, ebbing and flowing on a regular ( 12 - to 13 - hour ) schedule. However, in other parts of the world such as along the Pacific Coast, tides can be irregular. The Pacific Ocean is so vast that the moon can not control the entire ocean at once. The result is that parts of the Pacific Coast can have 3 high tides a day. Similarly, there are areas in the world like the Gulf of Mexico or the South China Sea that have only one high tide a day. Mechanical tide clocks used on the Pacific Coast must be adjusted frequently, often as much as weekly, and are not useful in diurnal areas ( those with one tide per day ). Digital Tide Clocks : Digital tide clocks are not married to the 24 hour 50.5 minute tide cycle and thus track tides beyond the Atlantic coast. Smart digital tide clocks can work across all locations in North America without any adjustments. This is achieved by storing all the variations of tides at numerous locations. Given a particular location and date / time, a digital tide clock can display the previous tide, next tide and current absolute tide height. Thus, they are able to track semi-diurnal, diurnal and mixed diurnal tides. Notes Jump up ^ http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide07b.html Jump up ^ Why are Time and Tide Clocks Best Used on the Atlantic Coast ?, Weems & Plath Jump up ^ How does a digital tide clock differ from a traditional mechanical tide clock ?, WeND External links Wikimedia Commons has media related to tide clocks. Tide Clock Tips Physical oceanography Waves Airy wave theory Ballantine scale Benjamin -- Feir instability Boussinesq approximation Breaking wave Clapotis Cnoidal wave Cross sea Dispersion Edge wave Equatorial waves Fetch Gravity wave Green 's law Infragravity wave Internal wave Iribarren number Kelvin wave Kinematic wave Longshore drift Luke 's variational principle Mild - slope equation Radiation stress Rogue wave Rossby wave Rossby - gravity waves Sea state Seiche Significant wave height Soliton Stokes boundary layer Stokes drift Stokes wave Swell Trochoidal wave Tsunami megatsunami Undertow Ursell number Wave action Wave base Wave height Wave power Wave radar Wave setup Wave shoaling Wave turbulence Wave -- current interaction Waves and shallow water one - dimensional Saint - Venant equations shallow water equations Wind wave model Circulation Atmospheric circulation Baroclinity Boundary current Coriolis force Coriolis -- Stokes force Craik -- Leibovich vortex force Downwelling Eddy Ekman layer Ekman spiral Ekman transport El Niño -- Southern Oscillation General circulation model Geostrophic current Global Ocean Data Analysis Project Gulf Stream Halothermal circulation Humboldt Current Hydrothermal circulation Langmuir circulation Longshore drift Loop Current Modular Ocean Model Ocean dynamics Ocean gyre Princeton Ocean Model Rip current Subsurface currents Sverdrup balance Thermohaline circulation shutdown Upwelling Whirlpool World Ocean Circulation Experiment Tides Amphidromic point Earth tide Head of tide Internal tide Lunitidal interval Perigean spring tide Rip tide Rule of twelfths Slack water Tidal bore Tidal force Tidal power Tidal race Tidal range Tidal resonance Tide gauge Tideline Landforms Abyssal fan Abyssal plain Atoll Bathymetric chart Coastal geography Cold seep Continental margin Continental rise Continental shelf Contourite Guyot Hydrography Oceanic basin Oceanic plateau Oceanic trench Passive margin Seabed Seamount Submarine canyon Submarine volcano Plate tectonics Convergent boundary Divergent boundary Fracture zone Hydrothermal vent Marine geology Mid-ocean ridge Mohorovičić discontinuity Vine -- Matthews -- Morley hypothesis Oceanic crust Outer trench swell Ridge push Seafloor spreading Slab pull Slab suction Slab window Subduction Transform fault Volcanic arc Ocean zones Benthic Deep ocean water Deep sea Littoral Mesopelagic Oceanic Pelagic Photic Surf Swash Sea level Deep - ocean Assessment and Reporting of Tsunamis Future sea level Global Sea Level Observing System North West Shelf Operational Oceanographic System Sea - level curve Sea level rise World Geodetic System Acoustics Deep scattering layer Hydroacoustics Ocean acoustic tomography Sofar bomb SOFAR channel Underwater acoustics Satellites Jason - 1 Jason - 2 ( Ocean Surface Topography Mission ) Jason - 3 Related Argo Benthic lander Color of water DSV Alvin Marginal sea Marine energy Marine pollution Mooring National Oceanographic Data Center Ocean Ocean exploration Ocean observations Ocean reanalysis Ocean surface topography Ocean thermal energy conversion Oceanography Pelagic sediment Sea surface microlayer Sea surface temperature Seawater Science On a Sphere Thermocline Underwater glider Water column World Ocean Atlas Commons Retrieved from `` https://en.wikipedia.org/w/index.php?title=Tide_clock&oldid=783211225 '' Categories : Clocks Hidden categories : Commons category with local link different than on Wikidata Talk About Wikipedia Français 中文 Edit links This page was last edited on 31 May 2017, at 20 : 37. 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Question: how long does it take for the tide to come in
Answer: 6-hour