Confusion with Maine Harbor Tide Chart

[JFigliuolo]

I'll try.
1. The - means there is no PM low tide. The next low tide happens after midnight ie.
8/17 second high is 4:11 PM, the next low is 8/18 at 12:06 AM (a little after midnight)

2. The * means the second low tide in the series occurs in the AM, rather than the PM. ie.
8/18 first low at 12:06 AM, First High at 4:39 AM, second low at 10:42 AM. Normally the second tide would be in the PM, but for a few days a month, it is in the AM. Thus the *.

Hope this explains things a little.