This was self evident to me fourdecades ago and the only question to me was why it was not been done. The only reason that made much sense was thatcompressor technology itself stunk. Itstill stinks, but a 500,000 ton container ship can afford to use jet engines toget the job done along with a simple conduit along the hull to allow escapement.And yes, parallel thin strips may help in slowing layer losses.
At worst a portion of the naturalfriction will be released.
Even better may be to simply deal withthe bow itself to reduce its drag and allow normal momentum entrainment to keepthe rest of the hull happy. It is not asif these displacement hulls have any plans for increasing actual speed.
Actually placing a pair of bow propsinside a driving channel could also be beneficial inasmuch as it wouldaccelerate bow water under the hull and eliminate much of the bow wave drag. On the other hand, I do not think it issignificant enough, and air bubbles may be easier and cheaper.
At least they are paying attentiontoday to the possibilities.
Airships of the sea
Naval architecture: Blasting a cushion ofair bubbles under a moving vessel’s hull can reduce its fuel consumption
Dec 9th2010 | from PRINT EDITION
IF YOUblow a lot of air bubbles under a ship, and keep them coming, “good things willhappen”, says Steven Ceccio, an expert on bubbles at the
Universityof Michigan’s mechanical-engineeringdepartment in .When air is pumped rapidly out of small holes in a ship’s hull, the swarmingbubbles will quickly join together and coat the hull with a layer of air acentimetre or two thick. This reduces drag, because air offers far lessresistance than water. Ann Arbor
As theship moves forward, the layer of air slides back and out from under the hull.But blowing more bubbles to replenish it does not require much energy, so fuelsavings of 5-10% are within reach, says Dr Ceccio. He studies air-lubricationsystems, as the field is known, for the American navy, even though warshipsgenerally have V-shaped hulls, which facilitate fast travel but are unfriendlyto bubbles. Almost all cargo vessels, by contrast, have flat bottoms, whichallow a larger volume to be kept buoyant for a given amount of hull metal.Bubbles work well on these and, since the cost of fuel is often more than halfof a cargo ship’s total operating expenses, the potential savings are huge.
Bubblesare wont to slip past the edges even of flat hulls, but efforts to hold them inplace are paying off, says Uwe Hollenbach of the
,a facility that tests new naval technologies. One trick is to trap the blanketof air between two ridges that protrude a few centimetres downward from theport and starboard edges of the hull. Another is to shape the vessel’s stern ina way that stops air being sucked into the propeller, where it would reducethrust by lessening the propeller’s grip on the water. It is also possible todesign hulls that include air-trapping recesses a couple of metres deep. Hamburg Ship Model Basin