I had used a texture map initially, based on a segment of the picture first posted. But the blue was too pale and thats how I got thinking about other techniques, I also experimented with ripples and a parametric mapping to rotate them 45°.

I think my problem is actually because the rope is a vector object and there are some splits in the sides which means that the UV mapping does not work too well, I should have 1 rectangle and 2 circles but I've got 4 rectangles.

So thanks for the words of experience, I'll switch back to a black and white texture map as a mixer for the colours I want and as you've done I'll also put it in the bump channel.