If you have a pair of boats you make the tea steering the motor
In the mean time you partner who has less steering duties makes the butties.
At an appropriate bridge you drop off the motor pass your beloved the tea and are rewarded with your butties.
Hence butty boat. I was informed of this absolute fact on purchasing a butty in the 1980s by an old boater who said ‘ with a butty you will never go hungry’.
Sadly he was proven wrong, the advent of a butty meant many cups left congealing in bridge holes whilst the steerer starved, and the butty steerer got dehydrated.
Mobile phones made it worse , texting do you want branstone pickle while making butties and steering the butty lead to a number of fishing match related incidents, and a discussion of tea or coffee, lead to a succession of traumatised hirers.
In the end we gave up and bought a boat with a kitchen.
Butties were abandoned with the boat.