Hi Jack.
Just because I have a fast boat now, don't think that I always do that. I have had some plodders in my time.
A few years ago, I bought the Yardmaster's boat from Nelson. The Nelsons were a a good range of boats, often used by Harbourmasters and Tug crews etc. Real workhorses.
It had a 50HP Perkin Elmer diesel. The tank was full when I got it and was pretty much full after about 800 miles later. It did about 8 kts.
It bobbed up and down a lot in rough seas, but I knew it was safe.
But one of my favourite boats was "Petit Bluer". It was 14ft, with a 4HP outboard. I could launch it from a trailer on the back of my car and be off within a few minutes, having parked the car. I went all over the Solent and round the Isle of Wight in that, at about 4kts all the way.
It was basically just a big rowing boat. Sometimes (when I ran out of fuel 10 miles from home) I rowed it long distances.