The Canal to the coast is barely completed - it will probably be at least 5 years before you can move anything larger than a small barge or a rowboat from the coast to New Oceanus. At the same time, trying to cut a harbor out of the coastline is going to continue to take time and resources. It may be about 7 years before you can get the coastline dredged enough to allow a warship or merchantman into the harbor at all, even if the canal is completed first.
When it's done (and feel free to correct me if I remember this incorrectly) the actual port will be in New Oceanus, with a canal/manmade river allowing vessels to approach the city proper.
Alternatively, you could do something similar to what the ancient Athenians did and build the port on the coast (which removes the cost and time of the canal) and then build a wall on either side of the road from the city to the port.
All that being said, you now control several port cities, including: Dwarfsport, Crisoth, Krosport, and Sylvanus. Though you don't have many (any) dedicated warships, you have access to the foundries at Khaz Modan, and there are dry dock and shipbuilding facilities at all of the ports I mentioned above.
At the very least, it should be possible to purchase and arm merchant vessels, or at least issue letters of marque to merchant captains who may wish to try their hands at bloodying the draconids' collective noses. I'd recommend doing both.
As of the current moment, the Draconid Ironclad is unarmed (you used its cannon on the walls at New Oceanus) but it could be rearmed with dwarven cannon or any number of other potential weapons.