Alternation

When considering this technique, think Checkerboard.  Now, think three values instead of two.
 
For instance, look at the stern of the focal boat.  It's a midtone.  Next to it on the side is a light value.
Also next to it is a dark value, the reflection. 

Trying to keep that pattern going is like juggling; you have to keep track of all three balls--the two in your hands and the one in the air.

The key is to start with the lights.  Make a trail of linked light shapes by cutting around them with the midtones.  Then add a dark that is contiguous to one of the other two.  Checkerboard!

Here is another example of the same subject, both using alternation.