Air Cavities in hulls

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JK
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Air Cavities in hulls

Post by JK »

This is a very promising development using a cavity in the hull to trap air to reduce fuel consumption. It will be interesting to see what kind of compressors are required to supply the air to the cavities.
http://www.marinelink.com/news/resistan ... 41787.aspx

Present Air Bubbler systems have large, low pressure rotary air compressors driven by power hungry motors which require special interlocks on the electrical board. The air is delivered via valved manifolds to nozzles at the hull. The compressor runs constantly as the air is vented through the nozzles. The valves are operated remotely allowing different ranges to be turned on and off, directing the flow of air. It can be used as a bow thruster by directing the air to one side of the ship only. There is a large blow off on deck if the ranges are shut off completely by incorrect operation of the range valves.
The air piping cannot go through fuel tanks as the pipe does erode from the passage of the water entrained air, which can lead to fuel spills. There is also the problem of air leakage into ship side tanks and the requirement for venting that will prevent over-pressurization.
The bubbler nozzles that pass through the hull, that I have dealt with, was 4-5" mechanical tubing. This tubing had 1" walls was a long lead item for ordering and required special welding and testing as it is considered part of the hull. The associated expense makes it very specialized for ice breaking lubrication of the hull.
On ships like the MV Arctic, which was fitted with bubblers in the 80's, the rigid nozzles passed through a flexing hull which led to cracking. This suggests that similar problems would be found on other commercial vessels.
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