Ian, prior to the official launch I used to wait until SHMBO went out 'shopping' fill the bath and test and adjust ballast to trim the levels, you can also carefully run the motor and check the prop shaft and rudder shaft for leaks
I have to admit getting inpatient some years ago due to bad weather and testing a Windermere steam launch indoors, I was having such a great time, but didn't appreciate the oily tide mark of evidence, eek
