The Dutch municipality of Flushing has digitized a vast collection of material related to the Scheldt shipyards, including plans, photos, and letters. The date range is approximately 1870-1950s.
Access to the archive (which I've pre-entered the search parameters for the Scheldt naval drawings) is here:
http://www.archieven.nl/nl/search-modon ... nv2#inv3t1Click "Inventaris" to display a drop-down of all the ships they have, then click each ship name to see what drawings they have available. The plus-in-box that are dark grey means they have digitized drawings you can access, white means they do not. Some are in PDF, some are in TIFF that you can download in extremely large JPG (click the dark grey bar along the bottom once you're viewing the preview) - here's an example of the destroyer Kortenaer:
http://i.imgur.com/ZJEscKZ.jpg (10048x4785 pixels)
There are several vessels on there that were not built there or were in Dutch service (e.g. that Soviet/Russian submarine rescue ship, Kommuna).