Pleasure cruises and tipping

[Cruella 66]

Okay, here's another place to post this question and see if anyone answers. We are going on the GG Pirate Fireworks Cruise next week. I did this same (and I highly recommend it) fun cruise last June with my Girl Scout troop. At that time we didn't tip the pirate captain...just didn't occur to me. However, my sister will be going this time too and wanted to know how much to tip the pirate guide???? Help!!! Any opinions from dis'ers who've done one of the 'pleasure' cruises???? Cindy