This black-and-white real photo postcard of the Miami Beach Show Boat was produced by EKC. The stamp box on the back indicates it was published sometime between 1930 and 1950 (according to playle.com). And the note written in cursive on the back gives us a nice pinpoint of when it was used: "Boat Jim & I went on a sightseeing tour on while in Miami Florida In Sept. 1945."
If you click on the postcard to make it larger, you can read all of the text on side of boat. But I've also transcribed it here for you...
1. The text across the top of the boat states: "WORLD'S LARGEST GLASS IN BOTTOM BOAT — UNDERWATER ILLUMINATION."
2. On on the side, the larger text states:
CHAMBER OF COMMERCE DOCK MIAMI BEACH PH 5-9200
MOONLIGHT CRUISE DANCING MARINE BAR SHOW 9-12PM $1.00
I can't find much in the way of additional history on this Miami Beach Show Boat. It would be great to hear some memories of traveling on this, but, depending on how long it remained in service, it might just be too many decades ago for us to have first-hand tales.
I did, however, find (on Pinterest) this nifty vintage brochure for the Miami-based glass-bottom boat Mermaid.
That led me to the amazing history-and-ephemera blog Old Florida, authored by Rick Kilby, and his 2012 post titled "Mid-century mermaids in Florida." You should check it out and dive into all of the cool stuff on Kilby's blog, which has nearly 450 posts on Florida history.