re: Patch dinghy while inflated?
If it's polypropylene, you normally want to have it deflated to allow the roll out of air bubbles and to place a weight on it to ensure adhesion. The weight isn't 100% needed,but I prefer to be safe. I used to patch inflatables for the Navy so my experience may not apply to your application or it may... We had a pretty solid process for repair
1) locate leak and circle it in chalk
2) allow to dry
3) cut patch 1 inch larger than damaged area - scallop the edges
4) apply polypropylene glue to the patch and inflatable in a vertical motion
5) allow to dry
6) Scuff the damaged area and patch
7) paint raft and patch with tolulene to reactivate the rubber surface
8) Apply glue to patch and inflatable in a horizontal motion
9) allow to dry till tacky and place the patch on the raft
10) roll out any bubbles and place a weight on the patch
11) allow to cure 24 hours
12) test to ensure all leaks are repaired.
Very seldom had a repeat leak or patch fail. Hope this helps