I just downloaded GWX today and haven't installed anything yet. I did take a not so quick glance at the manual though...there's a certain Kiel canal added in GWX (like it is in real life) which might help you conserve fuel.
It's a canal that leads from the Baltic Sea (Kiel) to the North Sea. If you have downloaded the GWX manual in pdf, instructions are on page 105 according to the document's numbering convention (in case you printed it), which translates to page 113 according to acrobat reader (due to the document not counting the cover/preface/contents/whatever pages).
The manual can be found here:
http://mysite.orange.co.uk/manual/GW...NUAL_EN_PF.pdf
Assuming you arrive at the exact correct starting point (or better yet plot a course directly to that point and let the AI navigate for better accuracy), you can have your navigator plot an automatic route through the channel.
By what i can gather, two of the originally included search patterns from the navigator's list of orders have been replaced by "Kiel Canal OUT" and "Kiel Canal IN". So, you just have to arrive at the correct starting point and give the appropriate order to your navigator, then kick back and let time compression do the job at ahead 1/3
