| WO1994007740A1 | 1994-04-14 | |||
| WO1989011343A2 | 1989-11-30 |
| BE1016624A3 | 2007-03-06 | |||
| US6193191B1 | 2001-02-27 | |||
| US20040126541A1 | 2004-07-01 | |||
| DE19631537A1 | 1998-01-29 | |||
| EP0340211A2 | 1989-11-02 | |||
| SE509857C2 | 1999-03-15 |
Claims
1 Procedure to reduce the friction between a hull and its surrounding water, characterized by the fact that from the ship's surface paint material mechanically is taken away so that after the taking away, the surface structure shows ribs closely to each other and parallel lengthways with the ship which have a height over the grooves between the ribs of less than 0.3 millimetre.
Procedure according to claim 1 , characterized by the fact that the height of the ribs over the grooves is less than 0.2 millimetre.
3 Procedure according to claim 2, characterized by the fact that the height of the ribs over the grooves is less than 0.1 millimetre.
Procedure according to claim 1, characterized by the fact that the height of the ribs is mainly the same as the distance between them.
Procedure according to claim 1, characterized by the fact that the grooves are made of grains applied to a driven endless band which along its whole width is pressed against the surface of the hull.
Procedure according to claim 5, characterized by the fact that the grains are applied in parallel rows on the band.
Procedure according to claim 5, characterized by the fact that the endless band is mounted on a device which can be moved along the ship in its lengthwise and closely lying parallel layers.
Surface structure on ships produced by a procedure according to any earlier claim. |
Procedure to reduce the friction between a hull and the surrounding water by creating ribs in the hull paint
The purpose of this invention is a process to reduce the friction between a hull and its surrounding water.
Surfaces which are lowered into the sea are immediately covered by growth. First a thin layer of biopolymers, bacteria and unicellular algae is formed followed by a thicker layer with invertebrates, for instance acorn barnacles and clams. Such growth or "biofouling" is a serious problem for shipping since the increased water resistance influences the fuel consumption.
The most common method to neutralize biofouling is applying poisonous paints to the surfaces which are to be protected. Commercial shipping often uses TBT paints (Tri Butyl Tin). An increased environmental consciousness about the risk with these very poisonous substances in the seas has resulted in local bans on use. Moreover a global restriction against the use of TBT paints for commercial shipping is expected to come into force in 2008. This has led to new effective and less poisonous paints being researched into which means that ships also in the future can be freed from biofouling.
It is since long known that a micro-ribbed surface structure can give less water resistance than a totally smooth surface. For example sharkskin shows ribs in its scales in the main parallel with the longitudinal direction of the body where the distance between the ribs can be 0.05 millimetre. On a sailing boat in America's Cup a film from 3M Inc. was attached to the hull with the intention to reduce the water resistance. This film on its outside had a structure of parallel micro-ribs with a cross section roughly like an equilateral triangle whose height was 0.064 millimetre. The foil does not prevent biofouling and attaching the foil is expensive and difficult particularly on curved surfaces.
The purpose of this invention is a process to make a ribbed surface structure directly on the surface of a hull.
The invention has the characteristics which will be evident from the patent claims and will be explained in detail by means of figures which in principle show an example of the procedure.
Figure 1 shows a tool on the hull of a ship seen from above.
Figure 2 shows the tool according to Figure 1 seen against the side of the hull.
1 indicates the outside of a hull and 2 and 3 cylinders on which an endless band 4 has been mounted. A pressure plate 5 presses the band against the surface of the hull. 6 indicates rows of grain attached to the band. The rows can be arranged in columns and in each column the distance between two rows can be for instance one millimetre. The distance between the top row in a column and the top row in an adjacent column can be for instance 0.1 millimetre. If each column includes 400 rows and there are 10 columns on the band a surface 400 millimetres wide can be treated with 4000 grooves. Depending on the speed of the band and the movement of the tool a grain row can come into the same groove several times. Even if the grains are not arranged in rows they can produce grooves separated by ribs yet of a more irregular appearance and length. The important thing is to produce a surface structure of very small ribs and grooves.
A tool according to the description above can for instance be attached to a contrivance according to the Swedish Patent 509 857 or to a carriage of a previously known kind where the carriage is kept against the hull by means of bands furnished with magnets and where the carriage is remote-controlled.
The procedure can be done on newly built ships when they are in a dock. It can be advisable to make the surface of the hull even by grinding off welding seams between the ship plates. The surface paint which is applied should be applied so that when ready it has relatively big thickness. As mentioned the paint should contain agents against biofouling. Also on old ships which dock it can be appropriate to provide them with a thick layer of new paint.
On ships lying in water the procedure can take place both above and under the surface of the water. If there is any biofouling it should be taken away before the procedure. This can also be made if a cleaner is attached to a device according to
the patent mentioned above so that this cleaner works before the tool which makes the grooves. If the ribs have been worn down by friction new grooves can be created by this procedure after the surface has been made smooth. Since the paint layer is thick several treatments can take place before it is time for docking again. It can also be so that the agent against biofouling is gradually emitted from the surface of the paint layer. Then the taking away of more inactive surface layers can make a more active surface layer appear.
It can be possible to, apart from the sides of the ship, heat its flat bottom.
It can be difficult to treat surfaces at the very front and the very back of a ship. The important thing is that a great part of the ship's surface under water gets the surface structure which reduces the friction. Even if the reduction of friction expressed in per cent or per thousand is small it can yet give a big saving of fuel for a ship which is in operation more than half the year.