The modern Puerto Rican Bordonúa has ten strings in five courses tuned from low to high as A, D, F#, B, E (with A, D and F# in octaves and B and E in unison pairs).

For example: 

  E4 |--------  .0?? gauge
  E4 |--------  .0?? gauge
  B3 |--------  .0?? gauge
  B3 |--------  .0?? gauge
  F#4|--------  .0?? gauge
  F#3|--------  .0?? gauge
  D3 |--------  .0?? gauge
  D4 |--------  .0?? gauge
  A3 |--------  .0?? gauge
  A2 |--------  .0?? gauge

Notice that this tuning is very similar to the way a guitar is tuned -- with the exception of the middle pair of strings which is a half step lower than the G on a guitar. Also, this is not the original "bass" tuning, but rather the melodic cuatro-like tuning proposed by Dr. Francisco López Cruz. In addition, Dr. López Cruz suggested using cuatro strings.

Another modern tuning for the Bordonúa is that of the Puerto Rican Tiple Doliente: E, A, D, G, C -- which is also very similar to that of the guitar (with the exception of the highest string which is a half-step higher than the B on the guitar).