The iPhone does so many things well and now it can help you on the water with many free and inexpensive apps. I own several of the apps described in this article and will also mention several that I do not own but you may want to try. If you have the new 3GS you have a head start with the Compass app. If you don't have the latest phone, you could download a compass app called MotionX. There is a lite version as well as a full blown one with many more options The lite version (free) works fine and will also allow you to create waypoints and give you all the info you would have on a handheld GPS. You can even set the compass to true and magnetic bearings. The one weakness here is that it does not show you where you are on a chart.
I was almost ready to buy a handheld GPS when the new iPhones came out last year. With GPS built in, I decided to upgrade and am very happy using the navigation software from iNavX. This a $50 app but it bets the heck out of buying a Garmin. Download the free NOAA raster charts and off you go. It can do waypoints as well as show your track on the charts. It's easy to zoom in and out by pinching the screen and I have found it to be a great help at night when sailing near the Berkeley Pier. It could come in very handy in the fog as well. This hand held chart plotter is constantly being updated and is an amazing app.
Next up is a tide and current app that is very helpful called Tides. There are several tide apps but this one is great because it also gives you current predictions. Easy to use and very straight forward. Wind Meter will give you good idea how fast the wind is blowing and is a steal at one buck. Wind Speed is one I do not own but it looks promising. If you would like to check the buoys in your area for weather data you may want to try Windbuoy.
There has been alot of chatter about Anchor Alarm. If you anchor alot, this is an app you want to have on your phone. The $10 app will give you piece of mind while you drift off in to a sound slumber. Be sure to set it past 20 meters so you donot have a false alarm.
For current wind conditions in your area checkout sailflow.com and dial it into you favorite waters. In the SF area, I use windandtides.com for a quick wind check and forecast before I go out.
Here is a list of apps you may also want to check out at your local app store:
Sailmaster (for the racer)
NOAA National Weather Service
Harry's GPS Sailor
Marine Rules and Navigation
Points of Sail
Marine Rules and Signals
Users assume all risk when using these apps at sea. If you have a favorite app that you want folks to know about, please leave a comment. Sail on!