Hi Gray, I think you could be on a sticky wicket with this job !!!
You really need to know if the dingy is to stop inflated or does
your customer inflate it as required ? If is stays inflated then I think PVC
ink will do the job – but if it is inflated when used then you could try to locate the ink that is used to print balloons, it might work ?
The other problem is the type of water the dingy sails in ? fresh water doesn’t present a problem, but sea water is very searching and could cause more problems. I would leave the job to one of your competitors
and let him have the headache !!!!!!!, Brian.
I don’t know the answer to you problem either Gray !!
Just a thought though, have you tried to contact a company that makes these craft? I’m sure the manufacturer cant be that hard to find and they should be able to tell you. The RNLI use these craft over here and I am sure I have seen some of their inflatables with graphics on, do you have something similar over there?