US3512496A - Anti-fouling means for marine propellers - Google Patents

Description

* May 19, 1970 I 'SQHAWK'INS- 3,512,496

ANTI-FOULING MEANS FOR MARINE PROPELLERS Filed May 28, 1968 2 SheetsSheet 1 Mi I!" all Ill 5; m

INVENTOR SETH HAWKINS ATTORNEYS FIG 1 Filed May 28, 1968 y 19, 1970 s. HAWKINS 3,512,496

ANTI-FOULING MEANS FOR MARINE PROPELLERS Ill :HIIII .11

2 Sheets-Sheet 2 INVENTOR SETH HAWKINS ATTORNEYS United States Patent 3,512,496 ANTI-FOULING MEANS FOR MARINE PROPELLERS Seth Hawkins, Fairfax, Va., assignor to Robert Taggait, Incorporated, Fairfax, Va. Filed May 28, 1968, Ser. N0. 732,641 Int. Cl. 1363b 59/00 US. Cl. 115.5 11 Claims ABSTRACT OF THE DISCLOSURE A means for inhibiting fouling of an underwater propeller on a marine craft involving the turning of the propeller at no less than a certain speed while the craft is in stopped condition in the water.

This invention is directed to the elimination and prevention of marine fouling upon the surfaces of marine propellers.

Marine fouling, as usually defined, refers to undesirable plant and animal growths which occur on the surfaces of submerged objects. For many years various segments of the marine industry have been plagued by this problem in various forms: pier structures eaten away, buoys lost or constantly requiring maintenance, and ships being slowed down due to the effects of fouling. This invention is directed to the latter form of the problem, that is, the effects of marine fouling upon the propulsion characteristics of ships and other waterborne craft, specifically, insofar as said propulsion characteristics are affected by fouling of the ships propeller as distinct from fouling of the ships hull.

Marine fouling has been a problem with ships for hundreds of years. Not only were ancient sailing ships slowed down due to the added resistance as a result of fouling but their wooden hulls were often weakened or eaten away by marine borers. Early attempts to combat the effects of fouling took the form of sheathing the hull with copper plates. With wooden ships this proved to be an expensive but fairly successful approach to the problem. The advent of steel and iron ships and the use of paddle wheels and propellers, however, created a different situation which required alternative approaches towards a solution.

Much of what follows will be applicable to any type of marine vehicle (small craft, submersible, etc.). Therefore, it should be kept in mind that when the word ship is used, its use should be considered to mean any type of marine vehicle.

Marine fouling, as it relates to ships, consists of the growth of undesirable organisms on the underwater portion of the ship. In this respect, it should be established at the outset that the underwater portion of the ship means the hull and the propeller.

Heretofore, the attempts made in the marine industry to combat fouling have mainly been directed against hull fouling as distinct from propeller fouling. One reason for this discrimination perhaps is that the propeller, after all, comprises a very small underwater surface area relative to the hull. A more fundamentally important reason, however, is the fact that, on the whole, the industry apparently has not understood or appreciated the fact that propellers actually do foul or the true extent to which propeller fouling actually reduces the ships speed for a given shaft horsepower. Specifically, the industry generally has not been aware of the power loss caused by propeller fouling as compared to the power loss caused by hull fouling and it may be said that the present invention is based upon a recognition of the fact that the detrimental effects of propeller fouling constitute a much 3,512,496 Patented May 19, 1970 ice greater proportion of power losses than heretofore has been understood to be the case and, specifically, that in some instances propeller fouling may actually account for a greater power loss than does the hull fouling. This is not to say that the industry has completely ignored the importance of propeller fouling; however, the main thrust of thinking in the field has been centered on fouling of the hull.

Many factors influence the attachment, adherence and growth characteristics of marine organisms onto submerged surfaces, such factors including: geography, fluid motion, light and illumination, gravity, type of material, and the electrochemical characteristics of the environment, to mention a few.

Geographically, marine fouling organisms proliferate in tropical and temperate climates. In tropical waters most types of fouling can be expected to attach and grow throughout the entire year. In areas further away from the equator the fouling season, so to speak, will decrease somewhat in relation to the water temperature. Nevertheless, there are few if any sea coasts in the world where some form of fouling organism will not grow at least during one or two months of the year.

The invention relies upon the phenomenon that fluid motion in the area of a submerged object has a very definite eifect upon the degree of attachment and growth of marine organisms. If an object is placed in still sea water for a given period of time a specific amount of fouling will occur. However, if the fluid velocity in that environment is greater than zero, a greater amount of fouling will occur during the same period of time. This is somewhat akin to the well known fact that buoys in channels where tidal currents exist will foul more seriously than buoys in relatively still areas, primarily due to the increased supply of food brought about by the water motion.

Furthermore, the aforementioned increase in fouling in correspondence to increasing water velocity holds true only up to a certain critical water velocity, beyond which the degree of fouling progressively diminishes. This phenomenon manifests itself in accordance with the particular circumstances as follows:

(A) If a clean, completely unfouled object is placed in a body of water whose velocity is zero or higher, up to a first value, hereafter referred to as the sub-critical value, the rate of fouling will be higher in direct relation to the water velocity;

(B) If the same object is placed in a body of Water whose velocity is between said sub-critical value and a second higher value, hereafter referred to as the critical value, the rate of fouling relative to the fouling rate up to the subcritical value, will be progressively smaller roughly in inverse relation to the velocity level above the sub-critical value and, in fact, at velocities at or above the critical value no fouling at all will occur on the object;

(C) If a previously fouled object, such as the object exposed to condition (A) above, is placed in a body of water, the rate of further fouling thereon will increase in direct relation to the water velocity above zero and up to a second sub-critical velocity value which is higher than that mentioned in (A) for a clean object;

(D) If, however, the same object as in (C) above is placed in a body of water whose velocity equals or exceeds said second sub-critical value but is less than a second critical value which exceeds the critical value for a clean object, the fouling rate will be progressively less than the fouling rate which prevailed up to said second subcritical value, and at velocities at or in excess of said second critical value no further fouling will occur on the object.

In other words, the rate of fouling will increase in direct relation to the water velocity up to a particular velocity called the sub-critical velocity, and thereafter the rate of fouling will decrease in inverse relation to the Water velocity up to a higher velocity called the critical velocity, at which point all further fouling ceases, and the particular values of said sub-critical and of said critical velocities will be in direct relation to the extent of prior fouling which already exists on the object.

Generally the sub-critical water velocity for clean, complete unfouled surfaces is in the vicinity of one foot per second and the critical velocity for such clean surfaces is in the vicinity of 1.7 feet per second, these values, as aforementioned, being correspondingly higher for unclean surfaces which already have fouling accumulated thereon. In this regard, however, it should be noted that the actual sub-critical and critical velocity values will vary in accordance with factors other than the surface condition of the object in consideration, such factors including: depth of the object below the Water surface; texture of the object material; water temperature; water composition insofar as this may vary in different parts of the world and between rivers, lakes, and oceans; light and illumination to which the object is exposed while in the water; the effect of gravity on the object insofar as this may vary in accordance with different angular orientations of the object in the water and different geographical locations on the globe; and also the electrochemical environment of the object as determined by water composition and the nature of other structure in the vicinity of the object which is under consideration.

For example, the electrochemical environment is particularly applicable to ships propellers since they are made of metal. Metals can be classed in a galvanic series with respect to sea water, and various electrochemical potentials will exist between the metal and the water. These complex electrochemical properties have a definite influence upon the rate of fouling of a surface, that is to say, a given object constructed of a specific type of metal will foul heavily under some electrochemical conditions whereas it may not foul at all under other conditions.

As to combatting propeller fouling, the only respite has been recourse to the age-old expedient of periodic mechanical cleaning which usually entails dry-docking of the entire ship with its consequent expense and interruption in the ships operations.

It is an object of the present invention, therefore, to resolve the problem of marine fouling on underwater propellers in a manner which is more effective and longer lasting than solutions which have heretofore been known in the art.

It is a specific object of the invention to provide an expedient whereby propeller fouling can, at least, be greatly inhibited, and at best, be altogether eliminated.

It is a further object to provide a means for preventing propeller fouling which is easily applicable to propellers on all types of marine craft, whether large or small, regardless of function, and regardless of the power propulsion system employed thereon.

'It is a further object of the invention to provide a means for preventing propeller fouling, which means is relatively simple to incorporate in existing marine craft and does not require any significant structural changes or redesign ing of the existing propeller turning means.

It is a further object to provide a propeller anti-fouling means which is of relatively small initial expense to install either in new or in existing marine craft and which requires a minimum of expense and of supervision to operate once installed.

Other objects are those which are inherent in the herein presented disclosure.

The present invention is based upon an awareness and a consideration of two very important factors which have been heretofore mentioned herein, namely:

(a) An awareness of the relative importance of propeller fouling as compared to overall power efficiency losses 4 and, specifically, as compared to the importance of hull fouling; and

(b) An awareness of the particular relationship which exists between fouling and the water velocity past a submerged surface.

Applicant has, in view of the foregoing factors, conceived of an expedient whereby, at least, propeller fouling can be significantly inhibited and whereby, at best, such fouling can be completely eliminated.

It is evident from the foregoing that no fouling of a ships propeller occurs whenever the ship is underway since the propeller at such times rotates through the water at a speed considerably in excess of the aforementioned critical speed. Fouling, however, normally occurs whenever the ship is in port, anchored, or otherwise stopped while afloat, and, in its simplest terms, the invention calls for continuously or intermittently turning the ships propeller so that the velocity of water flow past its blade surfaces will be of sufficient magnitude to either prevent or at least greatly inhibit marine fouling whenever the ship is in said stopped condition.

Intermittent turning of the propeller is also effective in this regard since marine growths do not develop instantaneously upon a submerged surface but, instead, require a measurable period of time in which to become attached. Such growths, therefore, will not develop provided that the propeller is turned at the speeds set forth herein at least periodically at intervals and for periods of time which will vary in accordance with the many variable factors already mentioned herein which influence the attachment, adherence, and growth characteristics of marine organisms onto submerged surfaces. The cycle of such running and stopped intervals will, therefore, depend upon the specific environmental conditions and can be ascertained through experiment and practice.

In this regard, it should be noted that such continuous or intermittent turning of the ships propeller(s) will not compromise the ships ability to remain stopped since the required turning velocity does not result in sufficient thrust to overcome the restraining force of the ships anchor chain or the lines or hawsers which tie the ship to a dock. In any event, the problem of thrust does not arise in the case of variable pitch propellers.

In the case of an anchored vessel, the fact that the device can rotate the propeller in either direction eliminates one problem which might arise. When anchored the device would usually be used to rotate the propeller in an astern direction.

For other conditions, such as when moored to a pier, quay, wharf, etc., a qualitative measure of the practicality of the patented method would be to calculate the forces generated by the propeller and to compare these to environmental forces which might be encountered by the ship.

The following table presents, for a wide range of waterborne craft, a comparison of equivalent wind velocities which would result in forces along the longitudinal axis of the vessel equal to the thrust which would occur from use of the fouling prevention device. For the purposes of this presentation it has been assumed that the propeller(s) will be rotated such that a point at the 0.3 radius is moving at 1.7 feet per second.

EQUIVALENT WIND VELOCITIES SUCH THAT WIND FORCE EQUALS PROPELLER THRUST 1 Wind velocity assumed to be acting along centerline of vessel.

It can be seen that the forces developed by propeller( s) operating at reasonable r.p.m.s for the purpose stated herein, produce thrusts which are equivalent to wind forces which would be encountered a good deal of the time in most parts of the world.

The mechanical means whereby the propeller is so turned may comprise a power device arranged according to any of the following:

(a) One which turns the propeller directly,

(b) One which turns the propeller shaft which in turn rotates the propeller,

(c) One which turns the reduction gears or transmission which in turn rotates the shafting and propeller,

(d) One which turns the connecting shafting between the prime mover and reduction gears, or transmission, or between the reduction gears of transmission and propeller shafting, thus turning the propeller,

(e) One which turns the prime mover which in turn rotates, either through a transmission or gearing system or not, the propeller shafting and propeller,

(f) One which, in any of the cases (a) through (e), can rotate the propeller in either direction, and

(g) One which, in any of the cases (a) through (f), can be used either during the entire time the vessel is stopped or during any portion of such time.

The term device, as used herein, can be a mechanical device comprised of a motor or engine and the necessary gearing, of any type and arrangement, or it can be a device comprised of a mechanical arrangement of piping which feeds small amounts of steam, gas or other vapors into a turbine prime mover of any type, excluding the presently used systems for providing fiow of motivating vapors to a turbine as they exist in practice today. For instance, one could run a small by-pass around the turbine throttle valve for the purpose of accomplishing the aims of this invention.

For the purposes of this invention it is desired to establish a velocity of propeller rotation as follows:

(A) Screw propellersthe angular velocity of the propeller should be such that the velocity of a point on the propeller located at the two-tenths radius (0.2R) will be in excess of one foot per second.

(B) Vertical axis propellersthe angular velocity of the propeller should be such that the velocity of a point located at the blade roots will be in excess of one foot per second.

This invention is intended to apply to any propeller on a vessel of any type including auxiliary maneuvering devices such as how and stem thrusters of any type which may be subject to fouling of the propeller, and also including propellers on vessels of any size and function such as large commercial vessels, naval vessels of all types, and small pleasure craft, tugboats, fireboats, submersibles, etc.

The accompanying drawing illustrates various applications of the invention. In said drawing,

FIG. 1 is a schematic showing of a ship propulsion means wherein the invention comprises a special turning device coupled to the propeller shaft;

FIG. 2 is a schematic showing of the invention as applied to a marine propulsion means wherein the prime mover comprises a generator-motor combination;

FIG. 3 is a schematic showing analogous to that of FIG. 1 but showing the invention as comprising a throttle by-pass line adapted to feed the pressurized motive gas to the turbine while the throttle is closed; and

FIG. 4 is a schematic showing of the invention as applied to an inboard motor type of propulsion means such as found in small craft.

With reference to the drawing, wherein the same reference characters have been used in the respective figures to indicate identical parts, PM indicates the prime mover which in FIGS. 1 and 2 could be either a steam or gas turbine, any internal combustion engine, a reciprocating steam engine, or any other known type of prime mover. In FIG. 1, the prime mover PM is shown as driving a propeller shaft S through a coupling means C which can be a clutch (as in the case when PM is a Diesel engine),

or a reduction gearing (as is the case when PM is a turbine) or simply a direct fixed connection. In any event, the invention resides in the provision of an antifouling drive means P which is connected to shaft S through a disengageable coupling means C such as a clutch, disengageable gearing, etc.

The drive means F most conveniently is an electrically driven motor which may be run off the ships main switch board, or have its own independent drive means such as a small Diesel or gasoline engine, or even be battery powered.

The drive means F is not to be confused with the well known jacking engines which are found in conjunction with reciprocating steam engines and particularly in conjunction with steam turbine drives in marine vessels. Such jacking engines, also referred to as jacking gears, are used in the case of steam turbines, on vessels and also in shore installations, to rotate the turbine rotor in order to permit it to cool immediately following a shutdown of said turbine without said rotor distorting under its own weight.

'In the case of turbo-electric ship drives, the jacking gear drives only the turbine without having any effect on the propeller shaft. In the case of geared-steam-turbine ship drives, the jacking gear is usually connectable with one of the gears in the reduction gear train between the turbine and the propeller shaft and thereby said jacking gear necessarily turns the propeller shaft at the same time that it turns the turbine rotor. Said known jacking gears, however, turn the propeller shaft at speeds usually in the range of 0.1 to 0.5 rpm. which is much too slow relatively to the speed required according to this invention. The minimum rotational speed resulting from operation according to the invention will be over one r.p.m. in the case of most propellers. Operation at the slower speeds provided by known jacking gears may actually enhance marine growth on the propeller rather than inhibit it, in accordance with the previously given explanation relative to the fouling elfects of water velocities which are below the sub-critical velocity. Furthermore, it should be noted that conventional jacking gears are employed only while the stream turbine or engine is cooling down and that they are stopped after the engine or turbine has cooled down.

-In the ship propulsion means of FIG. 2 the prime mover PM drives an electric generator G which in turn provides electric power through circuitry means E to the main propulsion motor M which, in turn, is coupled to propeller shaft S through coupling means C. The anti-fouling drive means F in this case is engageable with shaft S through a disengageable coupling means C.

FIG. 3 shows a turbine propulsion means wherein turbine T drives shaft S through coupling means C, said turbine being fed with pressurized fluid through inlet line L which includes throttle valve V. The invention in this instance includes the relatively small lay-pass line 1 which is controlled by valve v and which serves to by-pass fluid from the inlet line L to the turbine around throttle valve V when this latter is closed. The size of by-pass line 1 is such as to permit suflicient fluid to flow to the turbine to result at least in a speed of propeller P as required herein to inhibit fouling of said propeller.

FIG. 4 shows the invention applied to a type of small marine craft such as a pleasure boat, river boat, etc., wherein the prime mover comprises an internal combustion engine 10 which drives propeller P through a transmission s'hafting S, which could also be a straight shafting. The anti-fouling drive means F in this instance comprises an electric motor which is powered from battery B or any other electrical source such as shore power and which is connectable to shaft S through disengageable coupling means C".

It is to be understood that the details given herein relative to specific disclosed embodiments and modes of realization of the invention are for illustrative and not 7 liniitative purposes, the scope of the invention being limited only by the claims as allowed herein, whether originally filed or presented subsequently by Way of amendment, said claims being intended to cover all changes, substitutions, or equivalents which are obvious or within the purview of one skilled in the art.

What is claimed is:

1. A method for inhibiting marine fouling on a propeller of a waterborne marine craft, comprising: turning the propeller in either direction at a rotational velocity corresponding to a water velocity of substantially one foot per second past the 0.2 radius of the propeller, said turning being carried out substantially during the entire time that the craft is in stopped condition in the water.

2. The method of claim 1, wherein the propeller is turned intermittently at said rotational velocity in accordance with a repetitive schedule of running and stopping periods of time, the latter of which are shorter than that necessary for marine growths to be able to develop upon the propeller surface.

3. The method of claim 1, wherein said rotational velocity corresponds to a water velocity of at least 1.7 feet per second at the 0.2 radius of the propeller.

4. The method of claim 1, wherein the propeller is turned continuously at said rotational velocity during substantially the entire time that the craft is stopped in the water.

5. A method for operating a propeller-driven water craft in a manner so as to inhibit marine fouling of the propeller means thereof, comprising:

(a) during running conditions rotating the propeller means at the rotational velocity required to maintain the required craft speed; and

(b) during stopped conditions while afloat, continuing to rotate the propeller means at a rotational velocity which corresponds to a water velocity of substantially one foot per second past the 0.2 radius of the propeller.

6. An arrangement for rotating a propeller on a propeller-driven marine craft, comprising: a propeller and a prime mover for rotating said propeller during running conditions of the craft through the water, an anti-fouling drive means for rotating said propeller during stopped conditions of the craft, said anti-fouling drive means being especially designed to rotate said propeller at a rotational velocity which corresponds to a water velocity of substantially one foot per second past the 0.2 radius of said propeller, said anti-fouling drive means being adapted to being de-activated relative to said propeller While the prime mover is driving the propeller to propel the craft through the water.

7. The arrangement of claim 6, wherein said propeller is mounted at one end of a propeller shaft, and including a reduction gearing drivingly connecting said prime mover to said shaft, said anti-fouling drive means comprising an electric motor which is selectively drivingly engageable with a gear of said reduction gearing, said motor being operable at a speed such that it can drive said propeller through said gear at least at said rotational velocity.

8. The arrangement of claim 6, wherein said prime mover is a turbo-electric plant comprising an electric motor directly coupled to the propeller shaft, said antifouling drive means comprising an electric motor which is selectively drivingly engageable or disengageable with said shaft.

9. The arrangement of claim 6, wherein said prime mover is a geared-turbine type of propulsion means which includes a steam turbine having a steam inlet line leading thereto and a throttle valve in said line, said antifouling drive means including a by-pass steam line around said throttle valve, said by-pass line having a steamcarrying capacity sufiicient to permit said turbine to be driven at a speed which corresponds at least to all points on said propeller being driven at the critical speed necessary to prevent fouling of all points on the propeller blades.

10. The arrangement of claim 6, wherein said prime mover is an inboard internal combustion engine on a small marine craft, said anti-fouling drive means comprising a battery powered electric motor.

11. The arrangement of claim 6, wherein said antifouling drive means is adapted to turn said propeller at least at 1 rpm.

References Cited UNITED STATES PATENTS 1,181,988 5/1916 Breitung 1l50.5 2,378,589 6/1945 Slack et al. 37 XR 3,170,434 2/1965 Ewing 115-.5 3,361,108 1/1968 Hobbs 11534 ANDREW H. FARRELL, Primary Examiner U.S. Cl. X.R.

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