Originally Posted by Fenlander
>>>I'm planning on taking the girlfriend out on some fairly ambitious trips
Don't put her off for life!
This is good advice. Many a person has found their boating curtailed by a partner who just doesn't want to go after a bad experience. Starting short is a good idea (and getting to somewhere the other half will appreciate and is more easily reached by sea is a big help!). However the other thing is inspiring confidence in your crew: get trained, and have little "what if" plans in your head for as many cock ups as you can think of*. Stuff does go wrong with plans but the difference between an amusing anecdote and a terrifying adventure is mostly about having a sensible plan and appearing to be in control. She'll also probably feel more confident if she understands what is going on - so I'd encourage you to take her with you on the training. If you do it right before long she'll be encouraging you to take on longer passages.
* On the Thames that might be a good understanding of where you can get out and jump on public transport. But it can even be knowing where there is a cafe/pub to shelter from the rain in. Or some spare clothes in a dry bad. A forum-ite taught me that carrying a reasonable quantity of cash can be a useful idea as in a remote location as not only do many places not take cards but often cash can persuade someone to go out of their way to help you!