Based on some of the legal and technical aspects of what people have said here, I wonder if it might still capture some of the essence of what you’re trying for, to do a proper cremation and then have the ashes poured into a boat, possibly in a fancy or ceremonial way, that is then burned. Or the ashes could be in a burnable urn and placed into the boat.

I think there’s a lot that you could do with staging and design that would allow the event to have very similar gravitas despite the lack of a full body.