The gateway is about 50 miles wide at it narrowest, and rather elevated in the middle, much less convenient than Panama. Canals are unfortunately out of the question, which means that most cargoes get unloaded there, which makes it more exotic than if most stuff just traveled directly through.
For the "ripples" i use Photoshop's "outer glow" effect. Instead of a single color, i set it to a gradient. "Technique" must be set to "precise".
The gradient fluctuates between opaque and transparent portions see attached.