. The Artizan. and called pitch. It was really a screw with an increasing pitch, as given in thefollowing table:— Description of screw on Steam Tug Dagmar. Radius. 171411 Width of Blade. 10 121211 Angle. Pitch. ft. in. 8 0 6 6 5 0 4 6 Pigs, 2 and 3 explain the apparatus that was used for ascertaining the angleof the deflected currents below the centre line of the screw. A is the screwpropeller above described ; B the steiT of the tug-boat; C, a light shaft set ver-tically, and left free to turn in any direction; it could also be raised to anydesired position behind the sc
. The Artizan. and called pitch. It was really a screw with an increasing pitch, as given in thefollowing table:— Description of screw on Steam Tug Dagmar. Radius. 171411 Width of Blade. 10 121211 Angle. Pitch. ft. in. 8 0 6 6 5 0 4 6 Pigs, 2 and 3 explain the apparatus that was used for ascertaining the angleof the deflected currents below the centre line of the screw. A is the screwpropeller above described ; B the steiT of the tug-boat; C, a light shaft set ver-tically, and left free to turn in any direction; it could also be raised to anydesired position behind the screw; D is a vane of ten square inches area, at-tached to the spindle C, and having its centre 6in. from C; E, an index fingerupon the deck, about 9in. long, with a set screw for holding the square shaftC, and having a pin upon it, E, set 6in. from the centre, and therefore exactlycoinciding with the centre ot pressure of the vane, J); P is an arc, graduatednto degrees; and G is a small spring balance. After ascertaining each deflection it was very desirable to know somethingabout the pressures exerted by these reverse currents; so, to accomplish thispoint, the index finger, E, was turned at right angles to them, that is, into theline 0, Z, and held in that position by the spring balance, G. Whatever pres-sure became indicated is the pressure of the reverse current upon an area of tensquare inches ; and it varies in a most remarkable manner. It should be mentioned that there was at times very considerable vibrationupon the index finger, but the mean indication was taken. There were fourblades to this screw, and while the experiments named in the table were madethe four blades were all perfect; but on another occasion, when these experi-ments were tried with the same boat and the same screw, while propelling itselfalone and not towing a flat, the vessel got on a sandbank, and amongst therocks ; three of the blades were broken off, but no noticeable change took place int
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Keywords: ., bookcentury1800, bookdecade1840, booksubje, booksubjecttechnology
