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 even offer team-building activities if you are traveling to San Francisco on business. Sailing is a great way to build a team and bond them like nothing else on earth. If you've never been sailing before, I highly recommend chartering a boat for an outing even if it's only for a small period of time. It's a great way to find out if you have sea legs that's for sure. In addition to finding out if you have sea legs, a short tour will either leave you knowing this isn't for you or hungry for more-in which case, you might wish to take sailing lessons and consider purchasing a sailboat of your own someday.
Sailing lessons are a great thing to give yourself while on vacation in San Francisco as well. The bay offers a protected, or at least relatively protected area in which to learn the finer aspects of sailing and there are many schools locally that can offer excellent instruction in the finer points of sailing and navigation. Sailing however requires more than an afternoon of lessons in order to have any degree of competency but a few lessons while on vacation is a great place to begin and an even better excuse to return.
If you have some experience with navigation and sailing, there are some companies that will allow you to rent a boat for a day or even a weekend. This allows you to be your own "Master and Commander" and can make for a great family day for the entire family. I firmly believe there are few things on earth that are better than tasting the salt of the sea while feeling the wind in your face, but I've always felt more at home on water than on solid ground so I am more than a little biased towards enjoyment of water based activities.
Which brings me to my next suggestion. Some are not content to merely ride the waves but would rather create waves of their own. For those who prefer a more hands on and muscle powered trek through the water, perhaps a rowboat or paddleboat rental would be in order? There are places in Golden Gate Park where this is easily achieved and the lake is an ideal setting for these kinds of boats. And of course there are kayak rentals that seem to abound in the San Francisco area which offer a whole new level of fun for all involved.
No matter how you look at it, there are some great ways to spend a day on the water in San Francisco. Come found out why so many people have left their hearts here and enjoy the peaceful serenity of a day 'at sea'.