I agree with this being a fighting dirk as it is larger than sword blades of course, but notably larger than typical knives. With the profound connection of dirks to maritime themes it is natural to presume that distinction, however that cannot always be an exclusive definition. The weapons often used aboard vessels in various situations were often not specifically 'naval'.
I think the 'Spanish' feel noted may be well placed as this blade does seem to resemble the size and character of what are regarded as Central American dirks (Levine 1985) those these typically had an unusual finger ring in the hilt. 'That blade may indeed be quite old, perhaps even turn of the century or slightly earlier.
Knife fighting was a common matter among sailors and those situated in ports of call throughout the 'Spanish Main' , which of course remained alive and well long after the familiar 'Golden Age of Piracy' throughout the Caribbean, and especially the Gulf and colonies in Central and South American coastal regions. In the early 19th century there was a profusion of weapon styles that evolved using earlier blades and components in these Caribbean and coastal regions in the Americas.....and as always, piracy
As well known with the case of Jim Bowie, New Orleans was virtually a hot bed of knife fighting and dueling in the early 19th century, which while epitomized there, was actually prevalent as noted throughout the ports frequented by vessels of all sorts.
As always, weapons were often refurbished with the whims of the owner or as they changed hands. This may be the case here, and in accord with Marks assessment of the present hilting character.