You we will sleep on the boat and commute into work.

Being from the UK you get 90 days in the US, then you need to do a visa run out of the country and can then come back. I think as long as you are being paid by an non US business immigration don't mind.

Perhaps instead of a trip to Mexico or Canada a night on the boat would suffice?

Your residence and HQ is on a boat, but you can spend your days on mainland. If you're really into quick coffee meetings you can use one of those co-working spaces silicon valley has plenty of.