Have to say that the ones I Remember on the Thames in London were not steam powered but maybe there were other types.
Hope the following links will help.
Here is a link to info on the 1912 prototype.
**LINK**
This might be a useful contact for info on Slipper Launches.
**LINK**
Edited By V8Eng on 31/01/2019 22:25:21
Edited By V8Eng on 31/01/2019 22:30:52
Edited By V8Eng on 31/01/2019 22:31:23