GB2229412A

GB2229412A - Device and method for reducing fouling of underwater features of ships

Info

Publication number: GB2229412A
Application number: GB9003230A
Authority: GB
Inventors: Patrick Alexander Fitzsimmons
Original assignee: BMT CORTEC Ltd
Current assignee: BMT CORTEC Ltd
Priority date: 1989-02-21
Filing date: 1990-02-13
Publication date: 1990-09-26
Also published as: EP0384655A1; GB8903928D0; JPH02247263A; GB9003230D0

Description

1 Device and method for reducing fouling of underwater features of ships

The invention concerns the problem of fouling of underwater features of ships and ccmprises a device and method of reducing fouling of such external underwater features as propellers, appendages and sonar dc[nes.

The fo=ation and development of marine growths on those parts of a ship which lie below the waterline are a n-ajor problem for all vessels and have a significant adverse effect on the efficiency of operation of a vessel. If such growths are allowed to build up, then they give rise to a frictional drag impeding movement of the vessel through the water, which in turn is manifested in reduced ship speed and/or an increase in fuel consumption. Various approaches to solving this problem have been adopted, ranging fram preventive measures such as anti- fouling coatings or electrolytic protective system to remedial cleaning treatments entailing polishing underwater surfaces using equipment of various types. However preventive system may prove to be scmewhat expensive and must be maintained regularly if they are to be effectivef while remedial treatments such as mechanical polishing, especially of propeller blades, my damage the propeller and in any case are liable to increase its surface roughness and thus enhance the drag.

Marine fouling occurs mainly when the ship is at rest or at lo wer ship speeds, such as when a ship is approaching or leaving port, which speeds my be encountered over as much as 20 or 30 per cent of the vnrking time of a ship in operation, and of course the adverse effects are felt mainly while a ship is at sea. Thus a system intended to reduce or prevent marine fouling must be effective during the lo wer -speed periods of a ship's operation in particular. It is an object of the present invention to provide a device and method which may readily be applied to the protection against marine fouling of underwater features of ships and which is effective during a ship's stay in port.

The device according to the present invention, for reducing fouling of propeller blades and similar projecting underwater features of ships, camprises a hollow sheath of flexible, water impervious material, said sheath being of such dimensions as to be able to enclose at least a major part of the surface of the underwater feature and having means to secure the sheath in fluid-tight position around that part of the feature.

1.

The method according to the invention rises placing a sheath as defined so as to enclose at least a major part of the surface of the underwater feature, displacing sea-water from the interior of the sheath and/or including a biocide within the sheath, and securing the sheath in fluid-tight position around the enclosed part.

The device of the invention is primarily intended for fitting as the vessel arrives in port and for subsequent removal as the vessel departs from port but, at least where the protected underwater feature is a non--iwving feature such as a sonar dome or stabiliser, it my be desired to leave the sheath in position for at least a part of the subsequent voyage. Even in the case where the protected feature is a propeller blade or similar moving feature, the device may be left to be shredded or thrown off by that feature during norn-al running of the vessel; however it is much preferred that the sheath be remved before the vessel leaves port.

Although the device and method are suitable for reducing fouling of various underwater features of ships such as those mentioned, they find their most important application in the protection of ships' propellers. Subsequent description herein will be directed to this irportant application but it should be en#asised that many of the conn-Lents made hereinafter are equally applicable to the use of the device and method for reducing the occurrence of fouling on other discrete underwater features of ships.

The material of which the sheath is made must be flexible and impervious to water. While it may be desired to use a stretchable material, either to assist entry of the propeller blade into the sheath or to give rise to a tighter fit of the sheath about the blade, any otherwise suitable flexible, waterimpervious material may be used, whether or not it is stretchable. Thus for exarnple, the sheath may be of natural or synthetic rubber or of another synthetic polymeric material. The n-aterial may advantageously be biodegradable.

The sheath is hollow and in many cases will be generally tubular. It may, for example, be so dimensioned as to cover the whole of a propeller blade or a major part of the blade or, in an alternative form, may be of such a size as to enclose the whole of the propeller. However it is particularly preferred to fit a separate sheath on each blade of the propeller, for example five such sheaths on a five-bladed propeller, each sheath being se cur ed in position in the region of the root of the corresponding blade.

The sheaths nay be shaped so as to fit closely to the profile of the blades or they my be relatively shapeless, open-ended bags, able to fit cemprehensively over a blade without any manoeuvring or stretching of the sheath.

The means for securing the sheath in fluid-tight position may be an integral feature of the sheath or bonded to it, or my be wholly separate from the sheath. For example, the sheath may be fonned with a stretchable resilient collar, adapted to fit closely around the root of the blade but to be c sufficiently extensible to pass over the blade during fitting and remval. As an alternative, a separate stretchable band may be provided to perform that function. As another alternative, a flexible non-stretchable band may be secured by buckles or other fastenings around the mouth of the sheath to hold the sheath in place. In yet another form of the invention, the sheath may be secured by means of a tubular collar, which may be inflatable by air or water and which may be integral with the sheath or a separate ccmponent.

In a further form of the invention, the sheath is open- ended so as to fit over a single propeller blade and conforms more or less closely to the dimensions of the blade, a watertight zip being fitted down the length of the sheath in the region of one or both edges of the blade.

The sheath protects the blade frcm fouling frem outside the sheath but it is necessary to prevent fouling occurring from within it. If the sheath is close-fitting and there is therefore little roem rewining within the sheath once fitted, then the preferred method is to use a sheath which carries a coating of a biocide on its inner surface. If, however, a more loosely fitting sheath is used, then either or both of two different approaches is preferred. Firstly, seme or all of the seawater which almost inevitably enters the sheath may be expelled with air or more preferably fresh water. Secondly, a quantity of a biocide in the form of a liquid or solid, for exanple one or more pellets, may be introduced to the sheath before the latter is secured and sealed in place.

It is envisaged that the fitting of the sheath(s) to the propeller will be carried out underwater by a diver when a ship arrives in port and that the sheath(s) will be removed by a diver before the ship departs. Depending upon the specific form of the sheath (for example, whether it is close-fitting or loose) and the manner of securing it in position, a ccinpetent diver can fit all the sheaths upon a single propeller within a period of a couple of hours and remove them all in about half of that tbw. Thus, for the expenditure of very little time and a modest amount of money, it beccuies possible to prevent fouling of a ship's propeller during the critical time in port, without recourse to the potentially damaging effects of mechanical polishing.

A further use of the device according to the invention is for protecting a propeller before and/or after the propeller is fitted to the ship. For ex"le, the sheath may be fitted at the works of a manufacturer or repairer before a new or repaired propeller is delivered to the ship for installation. Thus a propeller may be protected frcm paint splashes or similar contamination while the ship is in dock and fran fouling while the ship lies alongside during cutfitting prior to sea trials or re-entry into service. Such periods at rest may be of the order of months, extending even to a year in extrem cases, and the device is invaluable during these periods.

1 n The invention will now be further described with reference to the foregoing drawings, which illustrate four preferred in-ents of the device according to the invention, all in perspective view, and wherein: - Fig. 1 shows a first form of protective sheath, fitted to a single propeller blade; Fig. 2 shows a second form of protective sheath for a single propeller blade; Fig. 3 shows in combination individual blade sheaths and a sheath for the hub of the propeller; and Fig. 4 shows a further form of protective sheath, designed to fit over the propeller blades and hub in a single piece.

The blade protector 10 illustrated in Fig. 1 is made of a stretchable, biodegradable synthetic polymeric material and is shaped so as to be a close fit over a single propeller blade. The inner surface of the protector is coated with a biocide. The protector is presented to the blade in a rolled condition and is fitted by unrolling it from the tip of the blade towards the root. When the protector 10 has been fitted over the propeller blade, a retaining belt 11 is passed around the protector near to the root of the blade and secured in positio by means of a fastening clip 12. Similar individual protective sheaths (not shown) are fitted around the other blades of the propeller.

The second form of protective sheath 13 illustrated in Fig. 2 is also designed to protect a single blade against fouling. This form of sheath iray be made of flexible nonstretching synthetic polyrreric material if desired as it does not need to stretch to enable it to be fitted. The sheath 13 is designed to follow closely the shape of the individual propeller blade and has a waterproof zip 14 running from the end associated with the blade root towards the tip of the blade. The sheath is applied to the blade with the zip in its fully open condition and the zip is closed to fit the sheath around the blade. The sheath 13 is then secured in place by ireans of a retaining belt 15 and clip 16. Sin-d-lar sheaths (not shown) are fitted in a similar manner to the remaining blades.

Fig. 3 shows a fo=n of the present invention by means of which the whole of the propeller, including the hub, is protected from fouling. The blades are covered by individual sheaths 17 to 20, which resemble the sheath 13 of Fig. 2 but extend slightly at the root end on to the adjacent hub area. A further protective cover 21, having a nr of zips 22 corresponding to the number of blades, which zips extend from the open end 23 of the sheath to the respective blade roots, is fitted over the propeller hub. The Cover 21 overlaps the sheaths 17 to 20 in the region of the blade roots and thereby assists in retaining these close- fitting sheaths in place.

Finally, Fig. 4 illustrates a unitary sheath 24 Which encloses the whole of the propeller. The sheath 24 is fo with a generally tubular section 25 of such a size and shape as to fit closely over the propeller hub and with blade sections 26 to 29 to cover the individual blades. Zips 30, of a number corresponding to the number of blades, extend from, the open end 31 of the sheath 24 to the region of the tip ends of the respective blades. This forn of the protector according to the invention is particularly suitable for application to propellers of a relatively smaller size.

-10

Claims

CIAIMS

1. A device for reducing fouling of propeller blades and similar projecting underwater features of ships, rising a hollow sheath of flexible, water-inipervious material, said sheath being of such dimensions as to be able to enclose at least a major part of the surface of the underwater feature and having mans to secure the sheath in fluid- tight position around that part of the feature.

2. A device as claimed in clai:rn 1, wherein the sheath is formed of stretchable material.

3. A device as claimed in either of the preceding claim, wherein the sheath is formed of a synthetic polymeric material.

4. A device as claiued in any of the preceding claims, wherein the sheath is formed of a biodegradable material.

5. A device as clain-ed in any of the preceding claims, of such diniensions and shape as to fit closely over a single blade of a propeller.

6. A device as claimed in any of claims 1 to 4, of such divensions and shape as to fit closely over a whole propeller.

7. A device as claimed in any of the. preceding claims, wherein the securing imans coirprises a water-tight zip extending along the sheath.

1 C

8. A device as claired in any of the preceding claims, wherein the securing mans cmprises a flexible band securable by buckles or other fastenings.

9. A device as claimed in any of claims 1 to 6, wherein the securing weans comprises a stretchable resilient collar formed integral with the sheath.

c

10. A device as claimed in any of claim 1 to 6, wherein the securing weans comprises an inflatable tubular collar.

11. A device as claimed in any of the preceding claim, wherein the sheath carries a coating of a biocide on its inner surface.

12. A device for reducing fouling of propeller blades 'and sin-Lilar projecting underwater features of ships, said device being substantially as hereinbefore described with reference to, and as illustrated in, any of Figs. 1 to 4 of the accompanying drawings.

13. A nethod for reducing fouling of propeller blades and similar projecting underwater features of ships, comprising placing a device as claimed in any of the preceding clahrs so as to enclose at least a major part of the surface of the underwater feature, displacing sea water fron the interior of the sheath and/or introducing a quantity of a biocide to the sheath, and se cur ing the sheath in fluid-tight position around the enclosed part.

Published 19K. &.ThePalen.0!f,.,-e Stat. H c: _st 6E - Hign H Lorid::r WC1 R 4TP 5Les St Max; Cray Kent BR5 3Rr Printed by Multl.-,'ex tecrriq,.ies ltd. St Mazi Cray. Kent Cc.n. It'