As early as the Seventeenth Century the possibility of developing a propulsive thrust by the use of a submerged helicoidal, or screw, propeller, had been vaguely recognized, and during the following, or Eighteenth Century, the same idea had been brought forward.  It had been viewed in this connection, however, merely as a curiosity, and led to no immediate results.  Later, in 1804, Francis B. Stevens, of New Jersey, in an experimental boat on the Hudson, operated twin screws, and demonstrated their applicability to the requirements of marine practice.  These propellers, in fact, had a form far more nearly approaching the modern screw-propeller than did those which came somewhat later, and which marked the real entry of the screw-propeller into actual and practical service.

Again, in 1812, Ressel, a student in the University of Vienna, began to study the screw-propeller, and his first drawing dates from this time.  In 1826 he carried on experiments in a barge driven by hand, and in 1827 an Austrian patent was granted him.  Two years later he applied his screw to a boat with an engine of six horse-power, and a speed of six miles per hour was said to have been attained.  Then came a bursting steam-pipe, and the police put a stop to the experiments, which seem to have had no further results.

Likewise in 1823 Captain Delisle, of the French Engineers, presented a memorial to his Government in which he urged the use of the submerged propeller for the propulsion of steam vessels.  No especial attention was given to the suggestion, however, and it was apparently forgotten until later, when the propeller had become a demonstrated success.  Then this memorial was remembered, and its author brought forward to receive his share of credit in connection with the adaptation of the propeller to marine propulsion.

These various attempts to introduce the screw-propeller seem curiously enough to have had no lasting result.  They were not followed up, and in the mean time had to some extent passed out of memory, or, if remembered, the absence of result can hardly have acted as an incentive to fresh effort.  At the same time it must be admitted that the screw-propeller as a possibility for marine propulsion was known in a vague way to the engineering practice of the day, and it is at this time of course quite impossible to say how much may have been known by Ericsson, Smith, or others concerned in later developments, or to what extent they may have been dependent for suggestion on what had preceded them.  The question of who invented the screw-propeller in the absolute sense is entirely futile and without answer.  No one could ever have reasonably advanced any such unique claim.  At the best it is simply a question of the relative influence in the introduction, improvement, and practical application of what was the common property of the engineering practice of the day.