On a boat the rudder is technically the blade that cuts through the water and the tiller is the thing that gives you enough leverage to apply force to control t

On a boat the rudder is technically the blade that cuts through the water and the tiller is the thing that gives you enough leverage to apply force to control the direction of the rudder as it passes through the water; sometimes quite a lot of force is needed! Only quite small boats have tillers that you can directly manipulate. Larger boats typically have a wheel which controls hydraulic rams which manipulate the ‘tiller’