One of the great lines on the cult BBC show 'Red Dwarf' goes (approximately, from memory) like this:
Can't you go any faster, like so we're not being overtaken by stationary objects?
I'm sure my youngest sister would be able to correct the wording, and tell me immediately which episode it's from, who says it to whom (I think it's Rimmer to Kryten) and how many minutes and seconds it comes into the episode. Unfortunately (or maybe fortunately) I can't. But I've got the essence of it.
The line is amusing because one can't possibly go so slow as to be overtaken by something stationary. If that is happening, you are going the wrong direction, and speeding up will only make matters worse.
But, in a sense, it can be true. I was reminded of this last weekend when we (Karen, Benjamin and I) went sailing with some of Karen's friends on lake Rotoiti (the one next to Rotorua). I haven't been sailing for ages. But lake sailing provides an easy re-introduction - it removes the need to think about tides as well as wind. I learnt to sail a long time ago on Portsmouth Harbour where tidal currents can be vicious indeed. You have to pay close attention to where you are actually going. You might be moving along nicely along the surface of the water, but if the water is heading at 4 knots in the wrong direction you have a problem. Your actual velocity (e.g. as a GPS would record) would be the vector summation of your velocity relative to the water, plus the velocity of the water. The first might be just great [and you'll experience the exhilaration of the boat cutting through the water nicely, leaving bits of driftwood and plastic bottles (it is Portsmouth, after all) in its wake] . But the second could push you way off course. When you've got little wind it can become impossible to get where you want to be.
Then you really can be overtaken by stationary objects. There's nothing quite like the feeling of being out on the harbour at the end of a summer's day, when the sea breeze suddenly dies, and finding yourself being overtaken by a stationary buoy. At that point, grabbing hold of the buoy can be a good idea.
I am informed by someone with reasonable knowledge of the region that the 'Round the Island Race' (round the Isle of Wight) has been won on occasion by anchoring. (Obviously not for the entire race.) In other words, being stationary is as fast as you can possibly go.