Make yourself a custom brush in Photoshop. A brush that's just a line. Or you can squish a circle down to a line, whatever, depends on if you want just a straight line or a feathered tip. Now, set it up like this.

Spacing: as far apart as you want your lines.

Under shape dynamics:
Size jitter: Skip this if you want your lines to be the same size. If not, make it so that HALF of it when you test your stroke looks right. Personal choice, as much as you want the lines to differ in size.
Angle control: set it to "direction".

Now I'm assuming you have your coastline drawn. Make a new layer. Trace over it with your new brush. If you set up a size jitter, trace it so the coastline lines up about halfway through the stroke (and clean that up later by selecting your water layer and going back to the layer with the stroke and deleting it). This way your lines neatly overlap the coast.

Do you want the edges of the brush to fade away into little dots? When you make your custom brush, make the tip of it more opaque than the rest of the brush... say, fade it to 50%. Then, when you do it, you can set the layer style to dissolve and the more transparent parts will turn into little dots.

If you're super lazy and don't feel like manually tracing the outline of your continent, OR you don't happen to have a tablet, you can draw a vector path (just a path, not the one that fills itself in with color) too, select it with the path selection tool, right click and hit 'stroke path' (make sure the brush you just made is selected with the brush tool) and it'll automatically follow the path for you, following the "direction" rule. Then you can delete the path and your stroke will stay. You'll probably have to fix a couple of points by hand but it should work out pretty neatly.

Any questions, shoot me a PM and I can make a visual version of this. I'm not exactly a dedicated forumgoer.