I took the original photo (below) of these tankers on the Firth of Forth, from the harbour at Kinghorn, back in 2013, using my Nikon Coolpix L25 compact camera. The photo itself was okay, but nothing special. At this point in time, I used the black & white setting on the camera, not realising you get a much better photo by taking it in colour, then converting it to B&W, using post photo editing software.
To get the above image, I used the motion blur setting in Gimp, after first cropping the image to remove excess sea and sky, duplicating the cropped layer, and applying the blur to the top layer. Whilst on this layer, I applied a layer mask, and uncovered the underlying tankers (sharp) from the layer below. I must admit, I was quite pleased with the resulting image. If anyone requires more precise instructions, please let me know in the comments below.