Living aboard does make making modifications difficult, so i am just putting together ideas at the moment.

My 10hp diesel engine is currently out of commission, and i want to replace it with an electric equivalent. 10 hours of power will be more than adequate for where i am as it will only be used for rivers and getting in and out of harbour and short trips with no wind. My boat has been pushed by a 5hp outboard and is good for up to 12 (maybe more)

hp watt kwh for 10 hours

Horse powerWatt Equivalantkwh (10h use)12v amp hours

I could safely halve the time (for at least 7hp) which i still meed to find 25kwh (2100ah 12v) of storage, with very few scraped ev's in the uk right now)