The universal calculation of the pull or the strain; a tugboat is capable, when towing. Unlike in ground vehicles, the statement of installed horsepower is not sufficient to understand how strong a tug is - this is because other factors, like transmission losses, propulsion type, propulsion system efficiency, have an influence as well. Bollard pull values are stated in tons. They are an indication of the maximum pulling force that a ship can exert on another ship or an object