Hi Katana,
You are really busy! and acquiring some most interesting examples!
As Tim has very astutely observed, this very heavy blade does appear to be a naval cutlass blade. It would seem this blade most likely from a French naval cutlass, probably the M1792, though the blade is interestingly a bit more parabolically curved. It would not be surprising for suppliers to the French after the Egyptian campaigns to have been inclined to such feature.
See "Boarders Away" , William Gilkerson , R.I.1991 (p.78, fig's #20,21) for examples of this pattern, typically mounted with three branch guard.
Obviously, during the 19th century, the coasts of West Africa were heavily colonized by the French, and these naval blades found thier way into native armouries. The blades were of course remounted many times, well into the 19th century. The history of these regions, the tormenting and unfortunate tragedies of the slaving, and the rich culture later imbued into the Americas does indeed include romantic tales.......and it seems quite likely this blade in its more recent mounts most probably has some of its own!!!
Now, what was that about sanity?
All the best, from another romantic,
Jim