Yes it will mess with the tides and that would be positively moon like. The tidal chaos could potentially cause massive floods. Have you ever seen two waves coming from opposite directions meet one another. the resultant wave is often a very sharp jump up in shallow depths. That could really be quite nasty. Not Tsunami like, but very fast very high tides. So fast moving that many estuary channels would reshape themselves and low lying flats surrounding these estuaries would become inundated.
There is also the possibility of the ship eclipsing the sun. That is most likely to drive the wildlife nuts. It could potentially disturb mating habits at a stretch. And if the ship eclipsed the sun often enough it could cause Global Cooling. But it would have to find a way to position itself in front of the sun on purpose regularly to do that. Which is difficult if you want to stay in orbit.
As for the moon, the ship and the moon would be gravitationaly attracted. So potentially it could dramatically alter the moons orbit, but what that would look like in real terms I couldn't say with certainty. I suppose it would give the moon a more elliptical orbit which could cause a catastrophic collision with the earth(?). But that seems a little far fetched.
The most logical orbit I can think of for this half moon mass ship would be half the distance between the moon and the earth away from the earth.