For the record, a vinyl sticker DOES NOT stick to a hypalon base.
I tried sticking it on and the sticker came straight off. It ruined the glue on the sticker. What I did then was to put a thin layer of SikaFlex on the sibyl sticker and then stick this onto the boat.
The good thing is the boat and SikaFlex is both black, so it looks OK from a distance. If you go close, you can see the extra glue on the pontoon.
Thanks all for your comments. I added photos of the name and number on the boat.