Basically there are four tide cycles per month that correspond with the phases of the moon. Neap Tides occur when the trough of the solar tide is aligned with the crest of a lunar tide. Spring Tides (the name has nothing to do with the season) occur when the crests of both lunar and solar tides are aligned. 

These illustrations are greatly exaggerated, of course. 


Spring Tide  New Moon

Neap Tide  1st Quarter Moon

Spring Tide  Full Moon

Neap Tide  Last  Quarter Moon

(Tides are measured as the water level added--or sometimes subtracted--to the average depth.  Thus, a place where the water is 8' mean depth will be 12' when the tide is 4.0 and 7' when the tide is -1.0.)

Below are actual tide tables taken from WXTIDE32, a superb freeware program.  Notice that the water movement is much faster on spring tides and mellow to slow on the neap tides.  For example, on the 21st of January, from the high tide at 10:42am to the bottom of the low tide at 6:02pm, there is 8.78 feet of moving water.  That's a fast moving tide!  Compare this with the following week, where the fastest water occurs between 5:00am and 11:42am, a slothful 3.91 feet.  

Wednesday 2004-01-21 
New Moon
High Tide: 12:14 AM  4.92
Low Tide:   4:47  AM  2.90
High Tide:  10:42 AM  7.05
Low Tide:    6:02 PM  -1.73

Wednesday 2004-01-28 
First Quarter Moon
High Tide:   5:00 AM  5.49
Low Tide:  11:42 AM  1.58
High Tide:   5:37 PM  3.72
Low Tide:  10:55 PM  2.03

Friday 2004-02-06 
Full Moon
High Tide:  12:52 AM   4.81
Low Tide:    5:40 AM   2.78
High Tide:  11:24 AM   6.15
Low Tide:    6:33 PM   -0.67



Friday 2004-02-13 
Last Quarter Moon
High Tide:   4:41 AM   5.99
Low Tide:  12:05 PM   0.45
High Tide:   6:42 PM   3.77
Low Tide:  11:11 PM   2.67