The National Oceanic and Atmospheric Administration (NOAA) - provides us with a nice set of tables predicting the high and low tide times and heights. I've taken that data and made a tide clock. The brown triangle shows the low tide time (brown for muddy) while the blue triangle shows the high tide time. Water height is given by the variables on the bottom. This tide data is for Bangor, Maine - you can get tide data for other areas in the USA from the NOAA website. This is only data for 2013 - new data will have to be loaded every year. I have applied a time offset to the NOAA data to better reflect my personal observations - this can be removed by editing the Local Offset Minutes variable and setting it to zero.
Added the new Current blocks so the clock is now self-setting. Also added in the tide predicting stuff. Thanks to NOAA for the free tide table. Bangor Tide data was obtained from this page http://tidesandcurrents.noaa.gov/noaatidepredictions/viewDailyPredictions.jsp?Stationid=8414612 using the "annual TXT" format option. Tabs were then converted to blanks using the ConTEXT text editor.