Page 16: of Maritime Reporter Magazine (January 2014)

16 Maritime Reporter & Engineering News • JANUARY 2014

EYE ON DESIGN

For the fi rst time an investigation into

Voith Schneider Propulsor-induced hull-pressure fl uctuations has been car- ried out. This investigation was part of a New York City Department of Trans- portation (NYCDOT) study to retrofi t the Molinari Class Ferries, which op- erate to the world-renowned Staten Is- land, with Voith Schneider Propulsion (VSP).

One of the objectives was to investi- gate the modifi cation in terms of energy effi ciency.

The Staten Island Ferry carries more than 21 million passengers annually be- tween Staten Island and Lower Manhat- tan. The three sister ships, Guy V. Mo- linari, Sen. John J. Marchi and Spirit of

America, can carry 4,427 passengers and have a crew of 16. The double- ended ferries have a propeller gondola, conventional propulsion system and one center skeg at both ends.

The study started by adapting the cur- rent hull lines for a propulsion arrange- ment consisting of four VSP26R5 units.

After the lines were optimized, a 7.3 m long ship model was manufactured and a model test program for the opti- mization of the Voith Schneider propul- sor arrangement was carried out in the

Shallow Water Towing Tank.

The goal of these tests was to deter- mine the best propulsor confi guration, which requires the lowest shaft power at design speed, focusing on the best di- rection of rotation, thrust vector direc- tion and power distribution between the fore and aft VSP units.

With the selected confi guration, pro- pulsor cavitation observations and mea- surements of the propulsor-induced hull pressure fl uctuations were carried out in the Depressurized Wave Basin. Cavita- tion observations and measurements were performed on the portside aft pro- pulsor, with all four VSPs active.

It was concluded that the level of the measured hull excitation caused by the two active aft VSPs is low.

The highest levels are measured on the center line of the ship, which is due to interaction between the portside and starboard VSP units.

This observation resulted in recom- mendations for a minimum spacing be- tween the two aft propulsors.

The main advantage of the tested con- fi guration, compared to the existing set up, is the increased maneuverability of the vessel.

These results supported the NYCDOT in its decision-making for future devel- opments of the Staten Island Ferry.

Voith Schneider Propulsor

The Maritime Research Institute Netherlands undertakes the fi rst-ever investigation into VSP-induced hull-pressure fl uctuations

BY RIEN DE MEIJ, MARIN

MARIN’s Depressurized Wave Basin was the site for a test of the best propulsor confi guration for the Staten Island ferries.

MR #1 (10-17).indd 16 1/7/2014 10:29:17 AM