The treasure hunt begins

20th of May,
We sailed many days North West toward the island of Cuba with many stops at islands along the way. Me crew is getting restless wonderin where be this treasure of Blackbeard’s. I cannot tell the men that I do not yet know where the island lies, for they would mutiny for sure. But it is on no charts that I can see. I have decided me crew and I are going to take the fine Brigand that lies in port at Havana. This should distract the men for awhile and give me more time to puzzle over the strange clues Blackbeard left upon his map. When we got to Havana it was mid-day. The brig was in port so we went to the Dancing Bear Inn and while we were there I found out that the ship was to set sail tomorrow. What luck! I gave the men their liberty for the night to spend their money on drink. All except Josh Wright who I took back to the Cutlass with me. There I showed him the map and the clues which were left on it, in hopes that he would be able to help me figure it out, clever fellow that he is.
I showed him the scriptures written on the edges.
Here they be:
Psalm 23 The Lord is my Shepherd there is nothing I shall want.
Psalm 42 As the deer longs for streams of water, so my soul longs for You, oh God.
Psalm46 God is our refuge and our strength, an ever-present help in distress.

Why would Blackbeard have written psalms on the map?

And here is the poem- it seems to warn against a shipwreck off the island:
80 sailors lost their lives,
On the 24th of May,
29 fathoms depth, says I,
Are the graves where they lay.

I only hope Josh and I can figure out the clues and the location of the island before the men mutiny and I lose it all.