A butty boat is an unpowered boat traditionally with a larger rudder with (usually) a wooden tiller (known as an "elum", a corruption of "helm") as the steering does not benefit from the force of water generated by the propeller. The tiller is usually removed and reversed in the rudder-post socket to get it out of the way when moored. A few butty boats have been converted into powered narrowboats like NB "Sirius". The term butty is derived from the dialect word buddy, meaning companion.