Singleness of purpose.
@Angela Jossy
First off I think the idea of a houseboat as an AirBnB is really cool. I would stay on it! But I think if you do what you're saying you want to do you will loose money.
I think you should decide whether it will be either A.) Tour boat, B.) AirBnB or, C.) Yearly/Monthly Rental . I don't see how you can combine any of the three very well unless you are AirBnBing unti you find a permanent tenant (if you can get permission from the Marina after waiting in line).
I would run the numbers on options A-C with very conservative maintenance and insurance estimates. Have you run the numbers already? What is your vacancy assumption for the AirBnB?
It sounds like you really like the idea of having a boat, having an AirBnB, and buy and hold investing - all three of which sound like fun or great ideas but maybe they should not be combined.
If it makes financial sense to add a boat to your tour company then I would say look at a variety of vessel options and pick the best option for that purpose - don't use a cruiser that's been converted into a tiny home as a tour vessel just because your friends have one for sale! Again it comes down the ROI.
Real estate investing is great because we're not necessarily re-inventing the wheel - not that there isn't a massive amount of creativity put into getting deals done - but the general mechanics are relatively straightforward and have been done thousands of times for centuries. When looking at any investment that veers hard off course and is pioneering new territory you have to assume that the amount of risk increases tenfold - therefore the potential return should compensate for that risk. If the reward doesn't match the risk, it's not worth doing. If everything goes as planned, which I would put as less than likely, is the reward/return great enough to risk losing your entire principal?
For example - What is the exit strategy? How many buyers are there for tour/airbnb/rental boats?