OBSERVATION OF ENTRAINMENT AROUND A PROTRUDING BOW

It has often been observed that, when a ship is in the light condition, a water film climbs up over the exposed part of the bow blub; the film usually breaks up near the stem, and a large amount of air becomes entrained in the water. In a particular trim condition of a certain cargoship, underwater television revealed that a large quantity of air bubbles flowed into the propeller; tests on a 7-m model of this ship showed that these bubbles had been entrained at the bow. As a large quantity of air bubbles flowing into a propeller may be closely associated with excessive vibration of a ship, the phenomenon of air entrainment around a protruding bow should be carefully investigated with a view to its prevention. The Author, of Mitsubishi's Nagasaki Technical Institute, gives a brief account of such an investigation at the Mitsubishi Experimental Tank. Model tests showed that when a jet of water strikes, tagentially from above, a cricular cylinder representing a cross-section of the protruding bulb of a ship in the light condition, the jet adheres to the cylinder surface and a large number of air bubbles are transported to the other side of the cylinder; this is attributed to the Coanda effect. If such a water jet strikes each side of the cylinder, the air bubbles are transported to the bottom region of the cylinder. Further tests included observing the effect of attaching a spray strip to the nose of a model bulb; this scattered the water film which climbed the nost of the bulb, and no bubbles were observed in the vicinity of the propeller. The strip follows a streamline in the full load condition to avoid increasing the resistance. Order from BSRA as No. 52,296.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/0036603X
• Corporate Authors:

  Seehafen-Verlag Erik Blumenfeld

  Celsiusweg 15, Postfach 1347
  2000 Hamburg 50,   Germany 
• Authors:
  • Baba, E
• Publication Date: 1979-10

Media Info

• Features: References;
• Pagination: p. 851
• Serial:
  • Schiff und Hafen
  • Volume: 31
  • ISSN: 0036-603X

Subject/Index Terms

• TRT Terms: Bows; Bubbles; Dynamics; Propellers; Vibration
• Old TRIS Terms: Bubble dynamics; Bulbous bows; Model testing; Propeller vibration
• Subject Areas: Design; Marine Transportation;

Filing Info

• Accession Number: 00310794
• Record Type: Publication
• Source Agency: British Ship Research Association
• Files: TRIS
• Created Date: May 7 1980 12:00AM