I have patched a really bedraggled Zodiac successfully. The fabric
is Hypalon and there is only ONE glue that actually works. It is a two part glue: Part one is a liquid cleaner that also acts as a catalyst for the Part two, which is a colorless goop, and which is a sticky substance.
It takes some heat to form the bond under moderate pressure, such as from a very hot hair dryer. I did it while pressing with the hand against the edges of the patch. The glue sets up very quickly. Once it is done, if it is done right, it is a very strong and inseperable joint and it is as good as new. Minme lasted for years and then I sold it and it has been in use now for about 12 years since repair. The actual trade
name of the glue has been hard to find, but think that it is not polyurethane
I used a hypalon glue available from a dinghy patch kit specifically for hypalon dinks. As to patch overlap, I usually follow the rule
that the total area of the overlap be at least as big as the hole, and in no case should there be less than an inch and a half of overlap on each side of the cut or hole. By the way, Hypalon, when deflated, folded and stored in a locker or emergency
cannister, is perishable, especially in tropical conditions; the usual shelf life is about 5 to 7 years. If you see light-colored powdery spots appearing in blotches when you inspect it, then it is probably unsafe to rely upon it, as those spots will leak air quite quickly under moderate pressure. If it is a lifeboat, replace it.