Hi Fred,
That door is a score. Where did you find it? Looks like teak, yes? With a bi-fold open you can still get out of the helm while it's open, I wouldn't change a thing. Because it has an astragal (the lip that lays on the port frame), you could keep it closed with a single hasp, barrel, or slide bolt placed vertically on the left stile of the starboard door, just right of the hinge any of the following would do the trick:
http://www.sailboatstuff.com/cb_latchasp.html
You could also use a lock like you see on filing cabinets and truck boxes
http://cgi.ebay.com/ebaymotors/_RV-T...4506.m20.l1116