1.35 liters of propane has the energy of 1 liter of gasoline. I don't know what kind of dink engine
you have, but we go through a tank (11 liters) of gasoline pretty fast. Your whole 3 gallon propane tank would be equivalent to only about 2.5 gallons of gasoline. How long would that last you? How much does propane cost where you fill up? Is it as easy to buy and lug propane tanks as it is to buy gasoline, in your area?
For us, it's a no brainer. Gasoline is much, much more efficient in terms of cost, storage
and transportation, for us.
Now if they'd just come up with a super lightweight, two-stroke diesel
outboard -- wow, that would be t**s.