Sorry, Tim. Apparently, I was wrong in attributing this knife to the Luba.
In 'Rare African Short Weapons' by Manfred A. Zirngibl (1983) I found a picture of a sword almost identical to yours. Based on the handle, the author attributes this sword to the Medje or Makere. The length is 48 cm.
This is what he writes :
This knife with its highly original blade shaped like a snake comes from the Zande or Mangbetu region. Although various museum records as well as several design characteristics such as the engravings on the blade and the relatively heavy-looking ivory handle indicate that it is a Medje or Makere product, it is not possible to classify the piece accurately
All that is certain however is that the knife - based on the shape of its blade - could not have functioned as a weapon. In spite of the sharp cutting edges, it could only have been used as a cult or ornamental knife.
Does your knife blade has any engravings ?