My two pennies!
I have used various oils in the past in car engines, you must have the correct type of fuel pump, on a car it was the Bosch, anything made by Lucas will end in tears, maybe not at first but give it time and it will go pete tong!
I have used Cod liver oil, Evening primrose oil, Shark liver oil, Flaxseed oil and even flavoured oils such as lemon oil, orange oil and fruits of the forest oil... If it had oil it in i would pour it in.
In the winter you are advised to mix with Diesel or petrol to thin it out, i have used neat all through the winter of 2011/2012 but only due to commuting 240 miles a day for work, starting the engine was hard, most mornings i had to jump start it.
For me it was worth it, i covered over 30k miles in 6 months and would never have been able to afford the fuel, but it caused some issues with my old BMW and in the end did go boom in a big way.
Knowing what i know, i would not run a narrowboat engine on the stuff, its just not worth the hassle.
Plus it gets everywhere and smells, trying to keep things clean when using oil is not easy!
Hope this helps!