1. Field of the Invention
The present invention relates to bow sinkage and vessel drag. More particularly, the present invention relates to apparatus for reducing bow sinkage and vessel drag.
2. General Background of the Invention
A large number of barges and offshore structures such as jack-ups and liftboats have rectangular hulls with square, blunt bows. A large amount of power is used when these vessels are towed or self-propelled.
Careful observation of the bow flow shows a large eddy forms at the bow corner and water is pushed ahead as the vessel moves.
See also Gorbanxe2x80x2, V. and I. Gorbanxe2x80x2, xe2x80x9cDynamics of vortices in near-wall flows: eigenfrequencies, resonant properties, algorithms of controlxe2x80x9d, NATO AGARD Report 827, xe2x80x9cHigh Speed Body Motion in Waterxe2x80x9d, AGARD-R-827, September 1997, which, with all references it cites, is incorporated herein by reference (see particularly FIG. 11).
The following U.S. Patents are incorporated herein by reference:
U.S. Pat. Nos. 661,303, 2,378,822, 3,680,517, 3,934,531, 4,003,325, 4,041,885, 4,377,123, 4,513,679, 4,569,302, 4,776,294, 5,090,352, 5,117,882, 5,787,832 6,324,480, 6,213,824.
U.S. Pat. No.4,513,679 discloses a drag-reducing device for barges that is placed at the bow of the barge.
U.S. Pat. Nos. 4,377,123; 4,041,885; and 5,787,832 disclose attachable devices that stabilize and break through the plane of the water when the bow cuts through the water.
U.S. Pat. No. 3,934,531; 4,003,325; 3,680,517; and 4,569,302 disclose methods of reducing friction and drag for large barge-like cargo ships or boats.
U.S. Pat. Nos. 5,117,882 (see especially FIG. 11); 5,090,352; 661,303; and 2,378,822 disclose vertical structures placed ahead of the bow to reduce drag.
The prior art patents mentioned above include:
a) five patents (U.S. Pat. Nos. 3.934,531; 4,003,325; 4,041,885; 4,377,123; 4,776,294) with a horizontal plate/foil submerged below the water surface;
b) six patents dealing with air injection drag reduction materials;
c) One patent for stern skegs (rudders); and
d) One patent for stabilizer floats.
Main conclusion:
The patents do not disclose or suggest the bow plate concept of the present invention. Specifically:
1. The bow plate of the present invention is mounted verticallyxe2x80x94the patents have horizontal plates.
U.S. Pat. No. 4,513,679 discloses a flexible mat which conveys air under the barge bottom, while the bow plate of the present is rigid and is mounted ahead of the bowxe2x80x94there is no contact between the bow and bow plate of the present invention.
U.S. Pat. No. 4,041,8 85 is a vertical submerged horizontal hydrofoilxe2x80x94the bow plate of the present invention is mounted ahead of the bow, not directly attached to the bow.
U.S. Pat. No. 5,787,832 is a floatation element,xe2x80x94the bow plate of the present invention is thin and does not contribute to the floatation of the hull.
2. The bow plate of the present invention is mounted at the waterlinexe2x80x94the patents have submerged horizontal plates.
The bow plate of the present invention reduces hull drag by reducing the bow sinkage.
U.S. Pat. Nos. 3,934,531 and 4,003,325 disclose a submerged horizontal bow plate which reduces the bow wave resistance similar to the bulb below for a cargo vessel hull.
The bow plate of the present invention is for a blunt box bow.
U.S. Pat. No. 3,680,517 discloses an air ejector for drag reduction.
U.S. Pat. No. 4,569,302 discloses barge stem skegs (rudders)xe2x80x94not applicable to the present invention.
3. The bow plate of the present invention reduces the bow sinkage and drag of full blunt hulls.
U.S. Pat. Nos. 5,090,352 and 5,117,882 and others disclose an air ejector system mounted on or ahead of the fine ship bow. This reflects the observations that for thin streamline ship bows, the flow streamlines form a bit ahead of the bow so the air will be more effective when ejected in this position. However, the ejectors are thin like the bowxe2x80x94the bow plate of the present invention is wide and only extends partially below the water surface in contrast to FIG. 11.
The following Table A contains the inventor""s comments:
Table A Summary of Patent Review by Dr. R. Latorre
Comments on patents:
The state of the art covers vertical plates, air ejectors but does not deal with the bow plate reduction of blunt bow trim and drag as the speed increases.
The patents disclose the working elementxe2x80x94plates/hydrofoils submerged below the water surfacexe2x80x94the working element of the bow plate of the present invention cuts the surface and is offset from the bow. The bow plate of the present invention preferably also covers the entire bow width rather just than the bow stem.
The present invention is an attachable vertical bow plate set a distance ahead of the existing bow. This plate preferably extends above and below the water surface. Its lower edge is preferably set at a depth corresponding to the depth where the existing bow begins to have its cut away. The plate preferably extends upwardly at least the distance it extends downwardly into the water when the boat is under way.
The present invention includes a preferably flat plate attached to a barge or other vessel having a substantially flat front surface, the flat plate being attached such that the plate, when the vessel is underway, is partially above and partially below the waterline. The plate preferably has a width which is 70-120% of the width of the vessel, and more preferably 90-110% of the width of the vessel. The plate preferably has a depth, when the vessel is underway, which is 10-30% of the depth of the vessel when the vessel is underway, taken from water surface. The plate preferably extends at least as far above the water surface as below the water surface, when the vessel is under way. The vessel can be an armored personnel carrier.
Configuring the bow plate like a cow catcher on a steam engine can be useful in operation in river areas with floating debris. The flat plate is attractive for retrofits.
The bow plate can be wedge shaped. The hull can have scallops in the comers of the leading end. The bow plate and scallops in the hull enhance side eddy cancellation.
Hull roughness, wind and wave conditions can impact the effectiveness of the bow plate of the present invention.
The bow plate invention of the present invention can be used on lift boats, jack-up rigs, in oil and gas industry applications, cargo barges, and military applications. The drag reduction technology of the present invention developed for lift boats can be used for other vessels such as the M113 Armored Track Vehicle, the Lockheed-Martin Troop Carrier, and other military vehicles under development by Lockheed-Martin.
The invention was developed by Professor Latorre at the University of New Orleans (UNO). UNO has an undergraduate and graduate naval architecture offered by the School of Naval Architecture and Marine Engineering. The development of the bow plate was done using the 125 ftxc3x9715 ftxc3x977 ft deep model towing tank. This facility enables xc2xc to {fraction (1/60)} scale models of ships and offshore structures to be tested in both calm water and sea wave conditions.