Abstract:
The composition for coating marine watercraft has the property of reducing kinematic friction and includes a polymer comprising a polyhydroxystyrene of the novolak type. In a preferred embodiment the composition further comprises an antifouling agent. One of the methods entails coating an outer surface of a marine watercraft with the composition. Preferably the composition is applied in a solution in an appropriate solvent, for example, a low-molecular-weight oxygenated hydrocarbon such as an alcohol or ketone. The coated surface is smooth and free of tackiness and thus is not fouled by common water debris such as sand and weeds. The coating is insoluble in water and resists abrasion, giving a functional lifetime that has been estimated to be a few years of continuous use. An application of the composition of the present invention to a water-submersible surface results in a hydrophilic surface having a considerably reduced contact angle. Thus the use of the coating is beneficial on watercraft to increase the speed thereof and/or to improve the fuel utilization.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to surface coatings, and, more particularly, to such coatings for use in a marine environment. 
     2. Description of Related Art 
     Marine coatings for application to moving watercraft and static underwater structures are known for use to preserve surfaces, improve their appearance, and reduce drag for moving watercraft. Such watercraft may comprise, but are not intended to be limited to, movable boats such as sailboats, yachts, inboard and outboard motor boats, rowboats, motor launches, canoes, kayaks, waterskis, surfboards, sailboards, waterbikes, ocean liners, tugboats, tankers, cargo ships, submarines, aircraft carriers, pontoons for sea planes, and destroyers. Underwater static structures may include, but are not intended to be limited to, wharves, piers, pilings, bridges, and other structures that may comprise wood, metal, plastic, fiberglass, glass, or concrete. 
     Some coatings known in the art include those described in U.S. Pat. Nos. 3,575,123; 5,488,076; and 5,554,214. Antifouling compositions have also been known to be used against such organisms as barnacles, algae, slime, acorn shells (Balanidae), goose mussels (Lepodoids), tubeworms, sea moss, oysters, brozoans, and tunicates. 
     Coatings may be hydrophilic or hydrophobic, the latter incurring friction between the moving surface and the water and including Teflon-like, paraffin wax, and fluorocarbon/silicone materials. The former maintains an adhering layer of water, the kinematic friction occurring with the water through which the craft moves. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method of reducing kinematic friction between a marine watercraft and the water through which the watercraft moves. 
     It is an additional object to provide a coating for a marine watercraft for reducing kinematic friction. 
     It is a further object to provide such a coating that is hydrophilic. 
     It is another object to provide such a coating that also possesses antifouling properties. 
     It is yet an additional object to provide a new use for a novolak-type polymeric composition. 
     An additional object is to provide a composition and method for improving fuel efficiency in marine craft. 
     These objects and others are attained by the present invention, a composition and method for coating marine watercraft having the property of reducing kinematic friction. The composition comprises a polymer comprising a polyhydroxystyrene of the novolak type. In a preferred embodiment the composition further comprises an antifouling agent. 
     A first embodiment of the method of the present invention comprises applying the composition as described above to an outer surface of a marine watercraft to achieve a coating thereof. Preferably the composition is applied in a solution in an appropriate solvent, which may comprise a low-molecular-weight oxygenated hydrocarbon such as an alcohol or ketone. The coated surface is smooth and free of tackiness and thus is not fouled by common water debris such as sand and weeds. The coating is insoluble in water and resists abrasion, giving a functional lifetime that has been estimated to be a few years of continuous use. 
     A second embodiment comprises a method for increasing the kinematic efficiency of a marine watercraft, including applying the composition to a submersible surface of a marine watercraft. 
     A third embodiment comprises a method for making the composition, including blending the polyhydroxystyrene in a low-molecular-weight oxygenated hydrocarbon solvent. 
     An application of the composition of the present invention to a water-submersible surface results in a hydrophilic surface having a considerably reduced contact angle. For example, when the composition is applied to a fiberglass/polyester surface with an initial contact angle of approximately 60° with water as determined by the tilting plate method (see N. K. Adam, The Physics and Chemistry of Surfaces, Oxford Univ. Press, 1941), the contact angle is reduced to about 15°. Thus the use of the coating is beneficial on watercraft to increase the speed thereof and/or to improve the fuel utilization. 
     The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     THE FIGURE illustrates the laboratory apparatus used to test the effect of the coating of the present invention upon the speed of an object falling through water. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description of the preferred embodiments of the present invention will now be presented with reference to the FIGURE. 
     A preferred embodiment of the composition comprises polyhydroxystyrene dissolved in methanol as a 5-20 wt/vol % solution and an antifouling agent also present at 5-10 wt/vol %. The antifouling agent comprises at least one compound selected from the group consisting of copper powder, copper oxide, zinc oxide (Kadox 911), titanium oxide (Degussa P-25), and tin oxide. A pigment may also be included. 
     A copolymerization of the polyhydroxystyrene with at least one other hydroxylated polymer such as polyhydroxylethylmethacrylate and polyhydroxymethylene or with another hydrophilic polymer such as polyallylamine, polyaminostyrene, polyacrylamide, or polyacrylic acid allows a variation of the coating without reducing the solubility of the copolymer in the solvent, while also not increasing the solubility of the dry coated polymer in water. 
     Test Apparatus 
     A laboratory apparatus 10 used to test the effectiveness of the coating of the present invention on a plastic bob 12 to affect the speed with which the bob 12 drops 1.3 m through sea water under the influence of gravity. An exemplary bob 12 comprises a plastic hydrophobic pointed cylinder approximately 1.26 cm in diameter and from 7.62 to 25.40 cm in length. 
     The apparatus 10 includes a glass tube 14 1.52 m long and having an inner diameter of 3.5 cm filled with artificial seawater 11. The bob 12 was allowed to fall from an initial position 20 to a second position 22 1.3 m apart. A photoelectric detector 16 at the initial position 20 starts a digital electronic timer 18. A second photoelectric detector 24 at the second position 22 stops the timer 18. The time recorded, typically in the second range, depending upon the size and mass of the falling bob 12, represents the time taken for the bob 12 to fall from the initial position 20 to the second position 22. 
     The bob 12 also has a thread 26 attached to its top end, which enables the bob 12 to be raised after resetting the timer 18 to ready it for another test. The initial position 20 should be set carefully in order to achieve reproducible results with a low standard deviation from the mean when ten identical, or as close to identical as possible, tests are averaged. 
     Exemplary Test Results 
     Tests undertaken on the apparatus described above have shown that the falling time, which ranges from 1.5 to 6 sec depending upon the size and mass of the object, decreases by 100-300 msec when a coating of the present invention has been applied (Table 1). 
     
                       TABLE 1______________________________________Contact angles of water on various surfaces beforeand after coating with a solution of PolyhydroxystyreneSurface     Contact Angle Before                      Contact Angle after______________________________________Polyethylene       56             16Stainless Steel       42             20       61             18Aluminum    70             15Fiberglass/polyester       53             22       60             17Silicone rubber       48             18Plexiglass  60             12       63             14Polystyrene 58             15Wood (oak)  33             18______________________________________ 
    
     This represents an improvement in the speed of 2-8%. The maximum speed at which these tests were performed correspond to the equivalent of about 2.5 knots. This is far below the 9-20 knots of ocean tankers or the 20-30 knots of passenger ships and ocean cargo vessels. However, the results of Table 2(b) show that the degree of improvement of the coating increases as the speed of the moving object increases for a fixed suface-to-water contact area. 
     It has been shown that an application of a 5-20% solution of polyhydroxystyrene in methanol changes a hydrophobic surface into a hydrophilic one. The contact angle of flat metal, plastic, and wood surfaces were determined by the tilting plate method before and after application of the coating. The results are given in Table 2, where the contact angles are the averages of the advancing and receding angles. These data show that the coating causes a significant decrease in the contact angle of water with the surface. Similar data obtain when an antifouling agent such as listed previously. 
     
                       TABLE 2______________________________________Some typical results showing (a) the effect polyhydroxystyrenecoatings on bobs of various materials by a determination of the timefor the bob to fall (in milliseconds, ms), and (b) the effectof speed on the improvement due to the coatings for a fixed______________________________________surface.           Anti-   Time (ms)                           Time (ms)                                   Percentage           fouling Before  After   Improve-(a) Material*   Agent   Coating Coating ment______________________________________1.  Polyethylene           ZnO     3869.4 ± 44                           3567.0 ± 30                                   7.9%2.  Nylon       None      4283 ± 79                             4179 ± 41                                   2.4%3.  Nylon       ZnO     3098.2 ± 26                             2988 ± 27                                   3.5%4.  Polyvinylchloride           ZnO       4561 ± 38                             4404 ± 34                                   3.4%5.  Polyvinylchloride           None    1519.3 ± 13                           1489.0 ± 10                                   2.0%______________________________________Mass of Bob          Time (ms)   Time (ms)                               Percentage(b)  Grams     Before Coating                      After Coating                               Improvement______________________________________6.   32.9      5047.6 ± 56                        4959 ± 72                               1.8%7.   34.2      2011.7 ± 27                      1947.6 ± 20                               3.2%8.   38.3      1711.3 ± 21                      1664.4 ± 12                               6.0______________________________________ *1 &amp; 3 were in distilled water with ZnO at 10% wt/vol %. All others were in sea water. 4 ZnO was at 15 wt/vol %. 6, 7, 8 the bob was a hollow polymethylmethacrylate pointed cylinder to which weights were added to make the bob fall faster. 
    
     The coating was also applied to a test boat having an onboard computer to monitor the power, speed, and rpm. The characteristics of this exemplary test boat are given in Table 3, and the results of three tests under different conditions of speed and rpm for the uncoated and coated boat are given, respectively, in Tables 4A and 4B, with a summary given in Table 5. For fixed power, the coating effected an increase in speed of 8%, and the fuel savings was approximately 10% when the boat was fully in the water, i.e., prior to planing. The coated boat tended to plane at lower throttle speed and felt more slippery in the water than the uncoated boat. 
     
                       TABLE 3______________________________________Boat Characteristics______________________________________Gas Test Number   Test 1Boat Model        26 Nova SpyderBoat Number       WELP 340 E788Engine Manufacturer             Mercruiser TwinEngine Model      350 MagnumStem Drive Model  Alpha OneGear Ratio (X:1)  1.50:1Propshaft Hp      500Stbd Idle Timing  8 Degrees BTDCPort Idle Timing  8 Degrees BTDCStbd Adv Timing   32 Degrees BTDCPort Adv Timing   32 Degrees BTDCRpm Range         4400-4800 RPMX&#34;Dimension       51/4 (11/4&#34; Above)Fuel Load         60.0 Gallons                        4900 Lbs AftFuel Capacity     120 Gallons                        2800 Lbs FwdBoat Weight at Test             9011 Pounds                        7700 Lbs TtlCenter of Gravity 104.7 Inches                        24.00 Ft. Dist.Trim Tabs         Bennett 9&#34; × 12&#34; (Performance)Exhaust System    Thru-transom                        100 Pounds GearDriver            Willie Petrate                        200 PoundsPassengers        Don, Ken, Lee                        640 PoundsLocation          Sarasota BayWater Conditions  Lite ChopWind Conditions   Northwest @ 10 MPHRadar             StalkerFuel Flow Meter   Floscan 7000G&#34; Meter          Vericom 2000rPropeller Model   QuicksilverProp Material     Stainless SteelWellcraft PN      1405====Manufacturer&#39;s PN 48-163184Number of Blades  Three RhDiameter          133/4&#34;Pitch             21&#34;True Pitch        22.0 InchesHull Constant     280,6633Minimum Rpm to Maintain Plane             2400 RPMBoat Position Angle at Rest             4 DegreesBoat List Angle at Rest             0 DegreesBow Measurement (Inches)             N/A InchesTransom Measurement (Inches)             N/A InchesNMMA Boat Maneuverability Test             OKBackdown Test     Use CautionSight Anti-ventilation Plate             Well DefinedTotal Fuel this Test             12.0 GallonsTotal Engine Time this Test             One HourRecommended Cruising Rpm             3500 RPMAcceleration Test Test   Seconds FeetTime to plane     1      4.10    600-20 Mph          2      4.17    61Drive Trim 100% dn             3      5.00    74             Avg    4.42    65Recommended Propeller             Yes______________________________________ 
    
     
                       TABLE 4A______________________________________BOAT TEST REPORTMARINE ENGINE FUEL INJECTIONTEST NUMBER: Test 1Normal Hull______________________________________1000  RPM                          ZERO  LIST______________________________________slip % 48.4%     1       7.7  mph   83    DBmpg   1.99      2       6.6  mph   4.25  BPAtrim  100% DN   3       7.2  mph   3.6   GPHplates None      avg     7.2  mph   227   RANGE______________________________________1500  RPM                          ZERO  LIST______________________________________slip % 55.4%     1       9.9  mph   85    DBmpg   1.45      2       8.7  mph   6.5   BPAtrim  100% DN   3       9.3  mph   6.4   GPHplates None      avg     9.3  mph   156   RANGE______________________________________2000  RPM                          ZERO  LIST______________________________________slip % 66.4%     1       10.5 mph   86    DBmpg   0.77      2       8.0  mph   7.75  BPAtrim  100% DN   3       9.5  mph   12.2  GPHplates None      avg     9.3  mph   87    RANGE______________________________________2500  RPM                          ZERO  LIST______________________________________slip % 21.4%     1       27.0 mph   87    DBmpg   1.72      2       27.6 mph   3.75  BPAtrim  100% DN   3       27.3 mph   15.9  GPHplates None      avg     27.3 mph   196   RANGE______________________________________3000  RPM                          ZERO  LIST______________________________________slip % 20.8%     1       32.6 mph   88    DBmpg   1.73      2       33.4 mph   3.75  BPAtrim  20% UP    3       33.0 mph   19.1  GPHplates None      avg     33.0 mph   197   RANGE______________________________________3500  Cruise RPM                   ZERO  LIST______________________________________slip % 15.5%     1       40.7 mph   90    DBmpg   1.74      2       41.4 mph   3.50  BPAtrim  35% UP    3       41.1 mph   23.6  GPHplates None      avg     41.1 mph   193   RANGE______________________________________3500  RPM                          ZERO  LIST______________________________________slip % 15.5%     1       40.7 mph   90    DBmpg   1.74      2       41.4 mph   3.50  BPAtrim  35% UP    3       41.1 mph   23.6  GPHplates None      avg     41.1 mph   193   RANGE______________________________________4000  RPM                          ZERO  LIST______________________________________slip % 14.7%     1       47.8 mph   91    DBmpg   1.51      2       47.0 mph   3.25  BPAtrim  60% UP    3       47.4 mph   31.4  GPHplates None      avg     47.4 mph   172   RANGE______________________________________4500  RPM                          ZERO  LIST______________________________________slip % 14.5%     1       54.0 mph   95    DBmpg   1.35      2       53.4 mph   3.00  BPAtrim  70% UP    3       53.0 mph   39.5  GPHplates None      avg     53.5 mph   154   RANGE______________________________________4760  MAX RPM                      ZERO  LIST______________________________________slip % 14.3%     1       56.0 mph   97    DBmpg   1.22      2       57.2 mph   3.00  BPAtrim  80% UP    3       56.8 mph   46.6  GPHplates None      avg     56.7 mph   139   RANGE______________________________________ *PHS = Polyhydroxysterene 4750 RPM STBD ENGINE 4820 RPM PORT ENGINE 0 RPM SINGLE ENGINE 
    
     
                       TABLE 4B______________________________________BOAT TEST REPORTMARINE ENGINE FUEL INJECTIONTEST NUMBER: Test 2Hull Coated with PHS______________________________________1000  RPM                          ZERO  LIST______________________________________slip % 48.2%     1       7.6  mph   83    DBmpg   2.06      2       6.8  mph   4.25  BPAtrim  100% DN   3       7.2  mph   3.5   GPHplates None      avg     7.2  mph   235   RANGE______________________________________1500  RPM                          ZERO  LIST______________________________________slip % 52.5%     1       9.7  mph   85    DBmpg   1.52      2       10.1 mph   7.00  BPAtrim  100% DN   3       9.9  mph   8.5   GPHplates None      avg     9.9  mph   174   RANGE______________________________________2000  RPM                          ZERO  LIST______________________________________slip % 61.2%     1       10.0 mph   86    DBmpg   .90       2       11.5 mph   8.25  BPAtrim  100% DN   3       10.8 mph   12.0  GPHplates None      avg     10.8 mph   102   RANGE______________________________________2500  RPM                          ZERO  LIST______________________________________slip % 15.1%     1       29.2 mph   87    DBmpg   1.84      2       29.7 mph   4.25  BPAtrim  100% DN   3       29.5 mph   16.0  GPHplates None      avg     29.5 mph   210   RANGE______________________________________3000  RPM                          ZERO  LIST______________________________________slip % 14.1%     1       36.0 mph   88    DBmpg   1.85      2       36.4 mph   4.00  BPAtrim  20% UP    3       35.0 mph   19.3  GPHplates None      avg     35.8 mph   211   RANGE______________________________________3500  Cruise RPM                   ZERO  LIST______________________________________slip % 13.6%     1       42.1 mph   90    DBmpg   1.79      2       42.6 mph   3.50  BPAtrim  35% UP    3       41.3 mph   23.5  GPHplates None      avg     42.0 mph   204   RANGE______________________________________3500  RPM                          ZERO  LIST______________________________________slip % 13.6%     1       42.1 mph   90    DBmpg   1.79      2       42.6 mph   3.50  BPAtrim  35% UP    3       41.3 mph   23.5  GPHplates None      avg     42.0 mph   204   RANGE______________________________________4000  RPM                          ZERO  LIST______________________________________slip % 12.5%     1       49.0       91    DBmpg   1.54      2       48.7 mph   3.50  BPAtrim  60% UP    3       48.1 mph   31.5  GPHplates None      avg     48.6 mph   176   RANGE______________________________________4500  RPM                          ZERO  LIST______________________________________slip % 12.4%     1       55.0 mph   95    DBmpg   1.37      2       54.5 mph   3.50  BPAtrim  70% UP    3       54.8 mph   40.1  GPHplates None      avg     54.8 mph   156   RANGE______________________________________4785  MAX RPM                      ZERO  LIST______________________________________slip % 12.4%     1       58.0 mph   97    DBmpg   1.25      2       58.2 mph   3.25  BPAtrim  80% UP    3       58.5 mph   46.5  GPHplates None      avg     58.2 mph   143   RANGE______________________________________ *PHS = Polyhydroxysterene 4750 RPM STBD ENGINE 4820 RPM PORT ENGINE 0 RPM SINGLE ENGINE 
    
     
                                           TABLE 5__________________________________________________________________________SO-BRIGHT INTERNATIONAL TEST RESULTSTest One - Prior to Chemical ApplicationTest Two - After Chemical Application   TEST NR        Test 1            Test 2                Changes                     Test 1                         Test 2                             Changes                                  Test 1                                       Test 2                                            Changes__________________________________________________________________________20 Nova Spyder   RPM  MPH MPH IN MPH                     MPG MPG IN MPG                                  RANGE                                       RANGE                                            IN RANGEMercruiser   1000 7.2 7.2 0.0  2.0 2.1 0.07 227  235  7.6350 Magnum   1500 9.3 9.9 0.6  1.5 1.5 0.07 166  174  8.0Alpha One   2000 9.3 10.8                1.4  0.8 0.9 0.13 87   102  15.1Sarasota Bay   2500 27.3            29.5                2.2  1.7 1.8 0.12 196  210  14.2Quicksilver   3000 33.0            35.8                2.8  1.7 1.9 0.13 197  211  14.5Stainless Steel   3500 41.1            42.0                0.9  1.7 1.8 0.05 #8   204  5.4Three Blades   4000 47.4            48.6                1.2  1.5 1.5 0.03 172  176  3.8RH(2)21&#34;     4500 53.5            54.8                1.3  1.4 1.4 0.03 154  158  3.84760    4785 56.7            58.2                1.6  1.2 1.3 0.04 121  124  3.6ACCELERATION (0-20 MPH):          Test 1               Test 2SECONDS TO PLANE:           4.4  3.9FEET TO PLANE: 65.0 57.0__________________________________________________________________________ Notes: The purpose of this test was to demonstrate the improvements we found (if any) in the performance of the boat described above. To do this we tested the boat prior to and immediately after a chemical application to the boats hull bottom. Test 1 shows results prior to and Test 2 shows results after. 
    
     The results clearly show that a boat coated with the composition of the present invention moves faster than an uncoated boat under substantially identical power consumption; similarly, for the same speed the coating reduces the rate of fuel consumption or increase the distance the boat will travel on a full tank of fuel. The difference varies with speed or power of the boat, and Table 5 shows that in the tests the maximum improvement of 17% at 2000 rpm corresponded to 10.8 miles/hour. At higher speeds the boat started to plane, resulting in less boat surface area in contact with water, and therefore a reduced beneficial effect of the coating is observed. For the case of ocean liners, cargo boats, or sailboats, which do not plane, it is expected that the beneficial effects of the coating of the present invention would continue to increase with an increase in power and speed since the surface-to-water contact area would not change under these changing conditions. 
     Therefore, it can be seen that the composition and methods of the present invention represent a significant increase in speed and fuel efficiency, thus conferring concomitant ecological and economic benefits. 
     It may be appreciated by one skilled in the art that additional embodiments may be contemplated, including analogous compositions having similar hyrophilic polymeric elements. 
     In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the apparatus illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction. 
     Having now described the invention, the construction, the operation and use of preferred embodiment thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.