The owner of every vessel or float of timber shall be answerable to the undertakers for any damage done by such vessel or float of timber, or by any person employed about the same, to the harbour, dock, or pier, or the quays or works connected therewith, and the master or person having the charge of such vessel or float of timber through whose wilful act or negligence any such damage is done shall also be liable to make good the same; and the undertaker may detain any such vessel or float of timber until sufficient security has been given for the amount of damage done by the same: Provided always, that nothing herein contained shall extend to impose any liability for any such damage upon the owner of any vessel, where such vessel shall at the time when such damage is caused be in charge of a duly licensed pilot whom such owner or master is bound by law to employ and put his vessel in charge of.