"The navigation channel runs westward from the wharf with a deviation of approximately 7° from due west."

Or "pier," "terminal," etc. for "wharf."
Or "to the west" for "westward."

What I'm not sure about, which perhaps is not a problem for this sentence, is whether the omission of "to the right (or left)" or "to WSW (or WNW)" is standard, and if its omission implies 7 degrees on each side, or a total range of 7 (3.5 on each side).


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Note added at 1 hr (2019-01-24 19:52:50 GMT)
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Dmitrii, I think you could add "to the right of," if you want to supply this info that is not in the original sentence. Maybe put it in square brackets? Except if you use "to the right," then it needs the preposition "of," whereas without that addition it is deviation "from."

I take it the action occurs in a real harbor, in the northern hemisphere? This would only be an issue in a text talking about standard allowable navigation deviations, say in airports, in which case you have to remember that in the southern hemisphere south behaves like north in the northern hemisphere, and therefore right from west would become left. But this doesn't matter, in a concrete example in the northern hemisphere, because north of due west will definitely be "to the right."