QGIS water-lining fill style

I think this tutorial will be helpful:

Vintage maps with Qgis

Steps:

1. You have to create multiple buffers from coastline (with value in table corresponding with distance from the coast)
2. Merge all buffers into one shapefile. You'll have many lines with distance from coastline value in one shp.
3. Now You'll be able to manipulate this shapefile in the way You want to. QGIS has many interesting options in STYLE tab

Instead of creating buffers separately you can do this all dynamically with symbols alone.

You just need to add multiple symbol layers for the fill style. Set each to a "simple line" outline style, so that only the polygon border is drawn (ie, no fill). Then, use the "offset" option to progressively offset the outline out from the coast, so one symbol layer will have an offset of say 2mm, the next has an offset of 4mm, etc. It's a nice touch to make the lines either lighter or more transparent the greater this offset is.