If you like water sports and activities that involve the water, then San Francisco should be at the very top of your must visit list. There are so many water activities in San Francisco your head will spin. In fact, bring your suit and prepare to spend a great deal of time enjoying the water and the great recreation that the water has to offer.
If you like the water but have little real experience at manning the wheel of a boat or navigating narrow straights, you will probably be best served by chartering the services of experts rather than attempting a go of it on your own. The good news is that there are plenty of ways to do this. One of the most common ways is to take a ferry out to Alcatraz or Angel Island. You get the benefit of time on the water with no work involved whatsoever. You also get the added benefit of a tour of some sort on the other end of your trip. Many visitors each year enjoy this means of water travel and it is both an economical way to travel by water and a low stress way to do so.
You can also elect a sunset or sightseeing cruise around the bay on a chartered sailboat or motor sailor that is fully crewed. Some of the charter companies...