Black Trireme Replacement Wake Streamers

So, I noticed that the tail end of the keel was missing on my 1/700 scale Zaphnora when I got it, so I decided to make a replacement piece.  The piece in question is called a "wake streamer," which is not a rudder, as it is fixed in place.  Its only function is to improve the airflow underneath the ship, largely for the purpose of keeping the stern from twisting while at cruising speed (which is quite fast - the Zaphnora and her sister ships have a top speed of 130 knots).