This invention relates to a ladder cleaning device, in particular an au tonomous offshore ladder cleaning device using the movem ent and motion of the sea, as well as a system incorporating such a device.

Access to an offshore wind turbine, or other offshore structures, is gained by climbing a ladder attached to the transition piece such as of the monopile of a wind turbine. The lower part of this ladder is submerged in wa ter half of its life, due to the rise and fall of the tide. Due to the ladder being in and out of the water, there is a large issue with algae, sea weed and other m arine growth on the ladder rungs, which in time makes it extrem ely slip pery, causing safety issues whilst clim bing the rungs at a low tide.

One current solution to this problem is cleaning the ladders with a high pressure washer at a low tide. This solves the issue in the short term but not long term , and due to the weather offshore, it is very hard to keep on top of this work on a day to day basis.

Other systems of ladder cleaning have also been proposed. WO201 7/088886 discloses a propelled crawler adapted to clim b a ladder, de tecting the rungs and cleaning them using water jets from nozzles. EP3045652 proposes an autonomous buoyant ladder cleaning device adapted to move up and down the ladder with tide and waves and clean the ladder rungs by means of protruding brushes while doing so. None of these pro posals seem to have gained any success.

Based on this prior art, it is the object to provide a system for clean ing a ladder, in particular an autonomous system for cleaning a ladder in stalled offshore.

According to a first aspect of the invention, this object is achieved by a ladder cleaning device, said ladder cleaning device comprising a number of rings, where the rings are adapted to be arranged around rungs of a ladder, a cord passing through a hole in each of said rings, and at least one attach m ent device adapted for attaching said cord to the ladder.

According to a second aspect of the invention this object is achieved by a kit of parts for providing a ladder cleaning device, said kit of parts com prising a cord, at least one attachment means for attaching the cord to a lad- der, and a num ber of ring segments.

According to a third aspect of the invention, this object is achieved by a cleaning system comprising a ladder, and a ladder cleaning device ac cording to the first or second aspect.

According to a first preferred em bodiment, the attachm ent device is associated with a stringer of the ladder. Associating the attachment means with one of the normally two stringers of a ladder, e.g . by mounting it direct ly thereon or in close proxim ity thereto, such as on a rung, allows the clean ing device to easily be cleared away by a person to clim b the ladder.

According to another preferred embodim ent, the attachm ent device is adapted to attach the cord to a rung of the ladder. The rungs of the ladder typically have smaller cross-sections than the rest of the ladder and the at tachm ent device may be made sm all and handy.

Furthermore, when , according to a further preferred em bodiment, the ladder cleaning device of the invention com prises two attachm ent devices arranged at a predeterm ined distance from each other along said cord, it be com es intuitive to place the attachm ent devices with the correct spacing, as they may sim ply be attached to the first vacant rungs after those on which the rings are arranged.

This is in particular the case, when according to another preferred em bodiment, the predeterm ined distance is so adapted to the num ber of rings and the distance between the rungs around which the rings are to be arranged that the rings may move horizontally along the rungs. Allowing the rings to move horizontally allows the rings to move along the rungs with the waves and currents so as to clean the entire length of the rungs.

According to yet another preferred em bodim ent , the hole through which the cord passes is the central hole of a ring. This hole is comparatively large and allows the cord to move relatively freely. This for one allows all rings to move along the length of the rung on which they are arranged. For the other it allows the rings all to be easily drawn into line above each other by a person pulling som ewhere along the cord. The rings and the cord m ay thus easily be pulled aside to clear the way when a person needs to clim b the ladder.

According to a further preferred em bodiment, the cord is, as seen in a direction upwardly from the bottom , threaded through the rings in a direc- tion away from the stringer associated with the attachm ent m eans. This is in particular the case when , according to a further preferred em bodim ent , the rings comprise a scraper blade arranged on the exit side of the cord through the rings. Moreover, when pulling the cord to clear the way for passage of the ladder, the pull will tilt the rings away from the scraper side, and thus make it easier to pull the rings towards the stringer. On the other hand, when left on their own the rings will experience less friction when sliding to the scraper side due to the tilt causing loss of contact. This, in turn , ensures that the rings move away from the stringer to which they have been pulled and back onto m iddle of the rung where cleaning is needed most, because that is where persons clim bing the ladder tread. Consequently, the cleaning effect is greatly improved where it is needed the most.

According to yet a further embodim ent, the hole is adapted to the cross-sectional shape of the rung on which it is to be arranged. This allows the rings to follow and at least engage the cross-sectional shape of the rung so as to ensure cleaning of a large part of the surface thereof.

According to another preferred em bodiment , each ring com prises at least two segm ents, adapted to be assem bled around a rung to form said ring . The rings may thus be easily assem bled around the rungs and the cord.

According to yet another preferred em bodiment, the at least two segm ents comprises m utually adapted engagement m eans so as to be as sembled without the use of tools. This facilitates the offshore installation which m ay take place under difficult circum stances, leaving possibly only one hand free to do the installation .

According to yet a further preferred em bodiment, the rings have a lower density than sea water. They will then have a buoyancy forcing them towards the underside of the rungs when subm erged, thus allowing them to clean the underside of the rungs, when subm erged as well as the upper side of the rungs on which the hang when not subm erged. Preferably the rings have internal buoyancy cham bers in order to achieve this.

The invention will now be described in greater detail based on non lim iting exem plary em bodim ents and the drawings on which :

Fig. 1 a shows a cleaning system com prising a cleaning device ac cording to the invention in the operating position,

Fig. 1 b shows the cleaning system with the cleaning device drawn aside to allow passage of a person on the ladder,

Fig. 2 shows two ring segments for the use in the cleaning device ac cording to the invention ,

Fig. 3 shown the two ring segm ents in an installed position around a rung of a ladder and a cord,

Fig. 4a shows a ring of the cleaning device hanging on a rung out of the water,

Fig. 4b shows the ring of Fig. 4a held down by the rung in a sub m erged position .

Turning first to Fig . 1 a cleaning system according to the invention is shown. The system comprises a ladder 1 which is partially submerged below the sea surface 2. The ladder comprises two stringers 3 and a number of rungs 4 connecting the stringers 3. Since the level of the sea surface 2 nor m ally changes with waves, tides, currents, atmospheric pressure etc. , there is a zone where rungs 4 are sometim es submerged and prone to growth of e.g. algae while at other tim es they are out of the water and m ust serve their purpose as steps for persons clim bing the ladder. Perm anently submerged rungs below that , if any, will normally not be used, and rungs above that will generally be dry and little prone to overgrowth . The zone in use and prone to growth is in the following referred to as the critical zone, as overgrown rungs will norm ally be slippery and pose a hazard for persons using the ladder, e.g. for offshore transfer. The sam e will of course also apply to other partially submerged ladders, such as safety ladders 1 in harbours and the like, and the system of the invention is also applicable in such places and not only off shore. Around each of the rungs 4 in the critical zone a ring 5 is arranged. As can be seen, the ring 5 is not necessarily circular or toroidal but m ay, as best seen in Fig. 3, be generally polygonal, in particular square, albeit with round ed corners, and have a likewise generally square cross-section of the body form ing the ring 5. The central hole 6 of the ring is likewise preferably square with rounded inside corners 7. As can be seen from Figs. 3, 4a and 4b, the shape of the central hole 6 and the radius of the rounded corners is adapted to the rounded corners of the rungs 4, i.e. the cross-sectional shape of the rungs 4, so that the inner surfaces of the ring 5 m ay lie flush with the surfac es of the rung to be cleaned. I f the rungs 4 were circular in cross-section and not square as shown, the radius of the corners 7 would correspond to the radius of the cross-section of the rungs 4.

Thus when due to wind, waves, currents etc. the rings 5 move back and forth along the rungs 4, parts of the inner surface 8 including som e of the corners of the ring 5 will slide along the m atching surface 9 of the rung 4, and scrape off or inhibit beginning growth , thus keeping the rungs 4 clean and safe. I n order to maxim ize the scraping the rings 5 m ay have a scraper, such as a scraper blade 1 2. The scraper blade 1 2 in one embodim ent is a rubber washer or ring generally matching the shape of the ring 5 itself but with a sm aller central hole than the central hole 6 of the ring 5, so that pro trudes inwardly over the ring 5. The scraper blade 1 2 is in that case prefera bly made of a rubber m aterial. Preferably, there is only one scraper blade 1 2 affixed to one side of the ring 5 as illustrated in Fig. 3. Thus, when pulling the cord 1 0 to clear the way for passage of the ladder 1 , the pull will tilt the rings away from the scraper side, and thus m ake it easier to pull the rings 5 to wards the stringer 3 without experiencing the increased friction from the rub ber. On the other hand, when left on their own the rings 5 will experience less friction when sliding to the scraper side due to the tilt causing loss of contact . This, in turn , ensures that the rings 5 move quickly away from the stringer 3 to which they have been pulled and back onto m iddle of the rung 4 where cleaning is needed most , because that is where persons climbing the ladder 1 tread.

I n another embodim ent the scraper blade 1 2 may be m ade from a hard plastic material, e.g. the sam e material as the rings 5 are made of. This, in turn, allows the scraper blade 1 2 to be integrally form ed with the ring 5 in the sam e manufacturing process, e.g. injection moulding . The scraper blade 1 2 m ay, however, also in this case be a separate part attached to the ring 5.

As an alternative to the scraper blade 1 2 protruding inwardly over the ring 5, a scraper in the form of a com b or brush like structure could be used. That is to say, a plurality of rigid elongated protrusions protruding in wardly, the protrusions e.g . being arranged in a line as the teeth of a com b, or covering an area like the bristles of a brush . These protrusions could be m ade of the same material as the ring 5, and preferably moulded integrally therewith, but harder materials, such as m etal, or softer material, such as rubber, could also be envisaged. Evidently, any harder m aterial should not be so hard that it dam ages the protective coating on the rungs 4. Preferably, as can be seen from com parison between Figs. 4a and 4b the rings 5 have a density lower than sea water so that when subm erged, their buoyancy will keep some of the rounded corners 7 and parts of the in ner surfaces 8 in engagement with the surfaces 9 of the underside of the rungs 4, allowing these parts to be cleaned. Conversely, when they are not submerged the rings 5 will hang suspended on the rungs 4, allowing the up per surfaces 9 of the rungs 4 to be cleaned. The desired density can be achieved by suitable material selection or by incorporating buoyancy cham bers in the rings 5.

Turning now to Figs. 1 a and 1 b it can be seen that a cord 1 0 is passed through the rings 5, preferably through the central hole 6 thereof. The cord 1 0 is attached to the ladder 1 by m eans of at least one attachment device 1 1 . The attachm ent device 1 1 m ay be fitted on the cord 1 0 prior to the installation of the system at sea, e.g . during m anufacture, or it may be fitted in-situ. Preferably, there are two attachm ent devices 1 1 fitted on the cord 1 0 in manufacture, thereby defining a predeterm ined length of cord 1 0 between them . The distance defined between the attachment devices 1 1 along the cord 1 0 is adapted to the number of rings 5 and the distances D between the rungs 4 around which the rings 5 are to be arranged and to the attachment points of the attachments devices 1 1 on the ladder 1 , so that the rings 5 m ay move horizontally along the rungs 4, preferably along the entire length of the rung 4 on which they are arranged. The attachm ent devices 1 1 are preferably also adapted to be attached to the rungs 4, so that it becom es intuitive where to mount them and not run the risk that the cord 1 0 is not loose enough to allow the horizontal movem ent of the rings 5. This will nor m ally be on the first rung 4 above the ones on which rings 5 are arranged and the first rung 4 below them . I t is of course not excluded that the attach m ent devices 1 1 attach the cords 1 0 to the stringers. I t is, however, currently preferred to use a sim ple clam p as attachm ent device 1 1 clam ping on to a rung 4. This will m ake a sm aller and less com plicated attachm ent device 1 1 than if it were to be adapted to be attached to e.g. a stringer 3.

The cord 1 0 in practice form s a loose linking of the rings 5. This link serves two different purposes which will be understood from Figs. 1 a and 1 b. Turning first to Fig. 1 a, it can be it can be seen that when one ring 5, say the one most exposed to wind waves and currents, moves under the influence thereof it will pull sideways on the cord 1 0, which will then transm it forces to the other rings 5 thereby moving them too, so that not only the exposed ring 5 perform s cleaning sweeps along a rung, but at least to some extent, so do also the other rings 5, in particular the neighbouring rings 5. For the optim al functioning of the cleaning device it has shown im portant that the cord 1 0 is threaded through the rings 5 in correct way. Referring specifically to Figs. 1 a, 1 b and 3 this correct way is as follows. Starting from the bottom attachment 1 1 at the left-side stringer 3 going upward, the cord 1 0 threaded through the central hole 6 of each ring 5 entering from the left- hand side and exiting from the right- hand side. The orientation of the rings 5 arranged on the rungs 4 is likewise important for the proper cleaning function . More specifically, the scraper blade 1 2 is to be located on the exit side of each ring 5, which , still as seen in relation to a cord 1 0 threaded through from the bottom attachment and upward. So, the cord 1 0 is threaded through the rings 5 away from the stringer 3 when going upward. Of course if the attachments were associated with the right- hand stringer 3, the arrangem ent would be a m irror image, but the cord 1 0 would still be threaded through the rings 5 away from the string er 3 as seen when going upward.

Turning now to Fig. 1 b, it can be seen that by grabbing the cord 1 0 between two rings and pulling (as indicated by the arrow) all rings may be brought into alignm ent with the attachment devices. I f, as illustrated, the attachm ent devices 1 1 are attached at or close to one of the stringers 3, preferably on the far side thereof, the pull will move all rings 5 as well as the cord 1 0 itself to one side of the rungs 4, and provide an unhindered passage for a person to climb the ladder 1 . Unlike the prior art devices, the cleaning device and system of the present invention will not obstruct the purpose of the ladder 1 , i.e. to be clim bed safely. This is in particular the case when as m entioned above, the attachments are on the far side of the ladder 1 , i.e. the side facing away from the person climbing the ladder 1 .

The cleaning device of the invention is adapted to be retrofitted to an existing ladder 1 to provide a cleaning system according to the invention, and m ay thus come as a kit of parts, comprising the cord 1 0, the suitable number of rings 5 for the length of the cord 1 0, and the attachm ent devices 1 1 , fitted on the cord 1 0 or not. The rings 5 are preferably provided as ring segments 5a, 5b that m ay be assembled to rings 5 around the cord 1 0 and a respective rung 4 without the use of tools. Thus, as can be seen in Fig. 2 a ring 5 may com prise two com plem entary ring segments 5a, 5b with m utually interlocking snap acting means, such as protrusions 1 2 engaging in recesses ( not visible) in a well-known m anner under the elasticity of the ring segm ents 5a, 5b. This inter alia avoids the need for tools for assem bling the rings 5 in situ, where conditions may make it difficult to sim ultaneously hold on to the ladder 1 , ring segm ents 5a, 5b, the cord 1 0 and a tool. Removing the tool m akes one less thing to consider and thus the installation easier. I rrespective of this, however, the skilled person will understand that the construction of the rings 5 inherently allows them to be placed individually around the rungs 4 inde pendently of each other, e.g. more than one ring 5 around the sam e rung 4, as well as without the use of the cord 1 0 linking them together.

The rings 5 m ay com prise more than the illustrated two segments 5a, 5b. The ring segments 5a, 5b are preferably made from a plastic m aterial suitable for the harsh offshore conditions, e.g. by injection moulding. I f the plastic material itself does not have the desired buoyancy, buoyancy cham bers m ay be provided inside or outside thereof during manufacture. I nside buoyancy chambers are, however, preferred over outside ones in order not to have unnecessary protrusion on the outside of the rings 5.

With the invention, a sim ple autonomous cleaning device and system retrofittable on existing ladders is provided. The skilled person will realize that num erous variations and deviation from the above exem plary embodi m ents in term s of shapes, materials, dim ensions are possible without deviat ing from the inventive idea and the scope of the claims.