How do I send a private message to the site administrator?
There's more than one administrator - it depends on what part of the site you want to contact someone about.
For the boat index, stoppages, forums, bug tracker, web server issues then you want me
For everything else you want Nick.
You can send messages to people using the messaging facility built into the main part of the site or, if its more appropriate, you can raise a Private Bug which can only be seen by the site administrators.