Tide heights and times for UK ports and harbours
Visit http://www.tidetimes.org.uk, click on the location of your choice, click on the RSS feed icon, copy the URL from the feed e.g. for Brighton Marina the value for tideurl is http://www.tidetimes.org.uk/brighton-marina-tide-times.rss
Not anymore. It was disabled in oik version 1.11
uk-tides currently only works for the UK since the information is obtained from http://www.tidetimes.org.uk If you can point us to a resource for other locations then it should be possible to develop a very similar solution.
For saltwater tide times and heights for the US see US-tides WordPress plugin
YES. See http://www.tidetimes.org.uk/widgets But you may find the output harder to (re)style.