Hi Fernando,
The blade does appear to be a rapier blade, and blades of this form seem consistant with blades sent to Spains colonies to be mounted during the latter 17th century. I have seen blades in similar condition stated to have come from shipwrecks of that period, in this case marked 'Jesus' on one side in the fuller and 'maria' on the other side in the fuller. Since rapiers were typically not made in the colonies it may be presumed that these would be replacement blades for those broken.
While the corrosion on the examples I have seen was extensive, it is difficult to imagine how they could survive at all underwater as typically, unless encased in coral etc. they rust away. The only thing I can think of would be in shallow water under silt, but I'm no underwater archaeologist
In any case, lots of blades were sent to the colonies over considerable time and by the latter 18th, early 19th century large quantities of the so called 'dragoon' type broadsword blades typically with the 'Spanish motto' were sent to Mexico. The blades often were literally in bundles as far as quantity, which is why they turn up so prolifically in various swords.
I am sure that Marc will add to this !
All best regards,
Jim