What Time Should I Leave?

“You may not operate boats under power or sail between sunset and sunrise.”  The sentence in the club manual is such a simple statement, and yet there is so much confusion over it.

It’s March 21, 2014, and I just received a call in the office that got me to thinking.  The questions asked were “What time is sunset tonight?” and “What time do I need to leave Pier 39 to get back in time?”

Unfortunately, I wasn’t able to give a good answer off the top of my head to either question.  The answers require a bit of research and planning.  An effort that I recommend each captain (yes, that’s you and me when we take a boat out) complete prior to leaving the slip for a day’s sailing.

According to the Tide Tables (yes, it’s there … look at the last page) sunset on March 20 was 1922.  On March 25, it will be 1926.  A bit of simple math in my head tells me that sunset today will be approximately 1923 … as “observed from sea level at the Golden Gate Bridge.”  That’s a great starting point; however, if you arrive back in Marina Bay at 1923, it will be well past sunset.  First, Marina Bay is about 7 miles east of the gate, so the sun goes down earlier.  Second, and more important, there are mountains that are well above sea level between Marina Bay and the horizon.  Sunset, according to the club rules, is when the sun goes down behind those mountains.  Today, it was more like 1910.  As far as the time to leave Pier 39, its 8.3 miles from Pier 39 to Marina Bay.  At an average speed of 5 knots, that’s 1:40.  However, what are the currents doing?  With a flood it may take less than that.  While ebbing, you can easily add an extra 45 minutes to the trip.  Max flood today was 2.8 knots at 1452.  By 1600 to 1700, there won’t be much current to help, so 1:40 still seems about right.  Leaving at 1700 to 1715 should work.

What about wind.  During normal wind conditions on the bay, you are going to be in the “shadow” of Angel Island for a good portion of the trip.  More than once, I have found myself going backwards because I was sailing slower than the current was flowing.   Motoring at 5 knots wouldn’t be a problem.  Sailing might require extra time.  If you average 2 knots speed over ground, 1:40 just became 4:10 minutes, and you needed to be underway before 1500!

A good skipper takes all of this into consideration and plans accordingly.

Note from Matt: Consider clean-up time as well. As a general rule, to stow a boat properly it takes about 1 minute per foot of boat per day that you spent on it. When we have one of those rare conversations with members about not cleaning up after themselves properly, it’s quite often because they tried to do it in the dark!

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