Dmitry is right. The hilt is definitely Dutch, m1790 marinesabal pattern, but with a straight blade??? The Dutch marine swords usually have a curved blade, but the classic bird head grip, fish skin, raised capstan with offset screw securing the knucklebow is spot on for this model/pattern. It appears as if one of the hilt bars has been removed?
Interestingly enough, the late (great!) George Gilkerson surmised (along with other naval experts) in 'Boarders Away' that the m1790 pattern was exported to the United States during the 1790's to supply the newly formed U.S. marine corps. Evidence pointing to this distinct possibility is that the m1790 Dutch sabers used on the continent were all extensively marked with regimental marks, battalion marks, proofs, etc. whereas the ones shipped out bore no markings.
If we follow this logic, this could have been an export/prototype straight bladed naval saber/hanger for private purchase use. Just a thought. Very nice sword, in any case-