doggie,
There are charter boats on block island, but I can't recommend any of them. You might also want to compare prices, Block island is nothing if not expensive. You might be better off having a boat from Pt. Judith or Montauk pick you up on the island. At that time of year there will be sharks around and maybe some school bluefin. If you want to go further there might be some longfin and yellowfin at the canyon.
There are charter boats on block island, but I can't recommend any of them. You might also want to compare prices, Block island is nothing if not expensive. You might be better off having a boat from Pt. Judith or Montauk pick you up on the island. At that time of year there will be sharks around and maybe some school bluefin. If you want to go further there might be some longfin and yellowfin at the canyon.