CA1044089A - Hydrophilic polymer coating for underwater structures - Google Patents

Abstract

Abstract of the Disclosure Hydrophilic polymers are applied to the under-water portions of surfaces which move through water or sur-faces against which water is flowing in order to reduce drag.

Description

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The present invention relates to drag reducing coatings for surfaces moving through water or surfaces against which water is flowing.
It is an object of the present invention to reduce the resistance or drag developed on moving watercraft through water.
Another object is to develop novel anti-foulant compositions.
A further object is to provide watercraft and underwater static structures with an improved anti-foulant coating.
Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiment of the invention, are given by way of illustration only3 since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
It has been found that these objects can be obtained by using coatings comprising film forming polymers which have the ability to absorb water, but which are insoluble in water, and remain intact, swollen on the surface thereby coated, as coatings at least for the underwater por~ion of ;' watercraft and underwater static structures.
Accordingly the invention provides a marine structure which is a j;
watercraft having an adherent continuous exposed coating consisting essentially of a water insoluble hydrophilic polymer which is swellable to an extent of .-at least 10% in water wherein the hydrophilic polymer is selected from the group consisting of hydrophilic cellulose esters, hydrophilic cellulose ethers, hydrophilic polyurethanes, hydrophilic vinyl lower alkyl ethers, vinyl alcohol group containing polymer, polyvinyl pyrrolidone, partially hydrolyzed poly~
acrylonitrile, ethylene-maleic anhydride copolymer, styren~-maleic anhydride copolymer, proteins, high molecular weight polyalkylene oxides, and phenoxy resins wherein the coating is sufficient to reduce the drag of the watercraf~
when in ~ater.
Many conventional water-soluble polymers are useful in the practice ,~
of this invention3 if, after application to the surface they are crosslinked to render them insoluble. The optimum amount of water absorption to obtain maximun drag -,: ".
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~ ', :., reducing effect varies somewhat with the composition of the polymer, film thickness, etc., but in general the polymer must absorb a minimum of about l~/o by weight of water to be effective. Preferably, it should absorb 20% of water to 12~/~, and it can absorb even more, e.g. 500% or 2/00~/o by weight.
The term marine coating is used in the present ap-plication and claims to cover both coatings for watercraft and underwater static structures~ The term watercraft in-cludes movable boats of all kinds, including, but not limit-ed to sailboats, yachts, inboard and outboard motor boats, rowboats, tor launches, canoes, Kayaks, water skis, surf-boards, ocean liners, tugboats, tankers and other cargo ships, submarines, both of the atomic and conventional vari-eties, aircraft carriers, destroyers, etc. Underwater stat-ic structures include, but are not limited to wharves, piers, -permanently moored watercraft, pilings, bridge substructures, ` ;
underwater oil well structures, etc. The underwater surface can be made of wood, metal, plastic, fiberglass, concrete or other material.
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The anti-foulant compositions are useful as marine -coatings to render the structure (moving or static) resis-tant to fouling by marine organisms such as barn`acles, algae, `
slime, acorn-shells (Balanidae~ goose mussels ~Lepadoids), tube-worms, sea moss, oysters, brozoans, tunicates, etc~
It is critical that the hydrophilic polymer, e~g, acrylic resin, be water insoluble, or rendered water insol-uble, since otherwise it will not be permanently affixed to the underwater surface.
The coatings of the invention effectively reduce the "drag" or resistance developed on moving the coated sur-face through water.
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If it is desired to employ the coating solely to effect friction reduction on racing or pleasure craft, for example, which do not remain static in water for extended periods, it is not necessary to incorporate an antifouling agent.
-While not being bound by any theory it is believed that the mechanism of friction reduction is two-fold. The coating absorbs a substantial percentage of water and the `
water swollen coating exhibits a low contact angle with the water n In addition, the swollen coatings are soft, (partic-ularly if a linear polymer is employed) and th~ softness can !,~'. ' provide a hydrodynamic dampin~ effect and reduct turbulence of the flow.
As stated in our Canadian Patent Applica~ion No.076,719 15 filed March 6,1970, preferably the hydrophilic monomer employed ;
is a hydroxy lower alkyl acrylate or methacrylate or hydroxy lower alkoxy lower alkyl acrylate or methacrylate, e.g. 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, diethy-lene glycol monoacrylate, diethylene glycol monomethacrylate, 20 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3- ` -hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, dipro-pylene glycol monomethacrylate and dipropylene glycol mono-acrylate~ The most preferred monomers are the hydroxyalkyl acrylates and methacrylates, particularly 2-hydroxyethyl ~-25 methacrylate.
There can also be employed polymers of acrylate, methacrylamide, n-alkyl substituted acrylamide and meth-acrylamide such as ~-propylacrylamide, ~-isopropyl acryla-mide, ~-isopropyl methacrylamide, ~-propyl methacrylamide, 30 ~-butyl acrylamide, N-methyl acrylamide and ~-methyl meth-acrylamide, diacetone acrylamide, I~-(2-hydroxyethyl) acryl- , B :

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amide and ~-(2-hydroxyethyl) methacrylamide.
Likewise, there can be employed copolymers of these monomers with each other or with other copolymeriz-able monomers. In fact, if the hydrophilic monomer gives a product which is water soluble, e.g. polyacrylamide, it is necessary to employ a copolymerizable monomer to render it only water swè~l~ble, rather than water solubleO The co-polymerizable monomer can be used in an amount of 0~05 to 50%. Preferably, comonomers include methyl acrylate, ethyl acrylate, isopr~pyl acrylate, propyl acrylate, butyl acry-late, sec. butyl acrylate, pentyl acrylate, 2-ethylhexyl ;:
acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, sec. butyl methacrylate, pentyl methacrylate, lower alkoxy-ethyl acrylates and methacrylates, e.g. methoxyethyl acry-late, methoxyethyl methacrylate, ethoxyethyl acrylate and `~
ethoxyethyl methacrylate, triethylene glycol acrylate, tri-ethylene glycol methacrylate, glycerol monoacrylate and glycerol monomethacrylate. ;
Thère can also be used unsaturated amines8 P-aminostyrene, o-aminostyrene, 2-amino-4-vinyltolueneJ alkyl-amino alkyl acrylates and methacrylates, e.g. diethylamino-ethyl acrylate, diethylaminoethyl methacrylatet dimethyl-aminoethyl acrylate, dimethylaminoethyl methacrylate~ t-butylaminoeth~l acrylate, t-butylaminoethyl methacrylate~
piperidinoethyl acrylate, piperidinoethyl methacrylate, mor-pholinoethyl acrylate, morpholinoethyl methacrylate, 2-vinylpyridine, 3-vinyl pyridine, 4-vinyl pyridine, 2-ethyl-5-vinyl-pyridine, dimethylamino propyl acrylate, dimethyl-amino propyl methacrylate, dipropylaminoethyl acrylate, di- ;~
propylaminoethyl methacrylate, di-n-butylaminoethyl acrylate, .

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di-n-butyl aminoethyl methacrylate, di-sec. butylaminoethyl acrylate, di-sec. butylaminoethyl methacrylate, dimethyl-aminoethyl vinyl ether, diethylaminoethyl vinyl sulfide, diethylaminoethyl vinyl ether, aminoethyl vinyl ether, aminoethyl vinyl sulfide, monomethylaminoethyl vinyl sulfide, monomethylaminoethyl vinyl ether, N-(gamma-monomethylamino) propyl acrylamide, ~-(beta-monomethylamino) ethyl acrylamide, ; -N-(beta-monomethylamino) ethyl methacrylamide, 10-aminodecyl vinyl ether, 8-aminooctyl vinyl ether, 5-aminopentyl vinyl ether, 3-aminopropyl vinyl ether, 4-aminobutyl vinyl ether,

2-aminobutyl vinyl ether, monoethylaminoethyl methacrylate, ~-(3,5,5-trimethylhexyl) aminoethyl vinyl ether, N-cyclohex-ylaminoethyl vinyl ether, 2-(1,1,3,3-tetramethylbutylamino) ethyl methacrylate, N-t-butylamino-ethyl vinyl ether, ~-methalimina-ethyl vinyl ether, N-2-ethylhexylamlnoethyl vinyl ether, N-t-butylaminoethyl vinyl ether, N-t-octyl-aminoethyl vinyl ether, 2-pyrrolidinoethyl acrylate, 2-pyr-rolidinoethyl methacrylate, 3-(dimethylaminoethyl)-2-hydroxy-propyl acrylate, 3-(dimethylaminoethyl) 2-hydroxypropyl methacrylate, 2-aminoethyl acrylate, 2-aminoethyl methacry-late. The presently preferred amino compounds are alkyl-aminoethyl acrylates and methacrylates, most preferably, t-butyl- aminoethyl methacrylate.
While linear polymers (including both homo and co-polymers) are preferred when the hydrophilic resins are used only to reduce the resistance on moving a coated watercraft surface through water there can also be employed cross-linked hydrophilic copolymers. Such cross-linked copolymers are frequently advantageously employed when antifouling agents are included in the composition to insure more permanent ad-herence to the underwater strUcture.

Preferably, the cross-linking agent is present in an amount of 0.1 to 2.5%, most preferably, not over 2.0~/
although ~rom 0.05 to 15%, or even 20~/c, of cross-linking agents can be used. Of course, care should be taken that cross-linking agents are not used in an amount which renders the product incapable of absorbing at least 2~/o Of water.
Typical examples of cross-linking agents include ethylene glycol diacrylate, ethylene glycol dimethacrylate, 7 .' 1,2-butylene dimethacrylate, 1,3-butylene dimethacrylate, 1,4-butylene dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, diethylene glycol dimeth-acrylate, dipropylene glycol dimethacrylate, diethylene gly-col diacrylate, dipropylene glycol diacrylate, divinyl ben-zene, divinyl toluene, diallyl tartrate, allyl pyruvate, allyl maleate, divinyl tartrate, triallyl melamine, N,N'-methylene bis acrylamide, glycerine trimethacrylate, di- -allyl maleate, divinyl ether, diallyl monoethylene glycol -citrate, ethylene glycol vinyl allyl citrate, allyl vinyl `-maleate, diallyl itaconate, ethylene glycol diester of ita-conic acid, divinyl sulfone, hexahydro-1,3,5-triacryltria-zine, triallyl phosphite, diallyl ester of benzene phosphonic acid, polyester of maleic anhydride with triethylene glycol, polyallyl glucose, e.g. triallyl glucose, polyallyl sucrose, e.g. pentaallyl sucrose, sucrose diacrylate, glucose dimetha-crylate, pentaerythritol tetraacrylate, sorbitol, dimetha-crylate, diallyl aconitate, divinyl citraconate diallyl fumarate.
There can be included ethylenically unsat~rated acids or salts thereof such as acrylic acid, cinnamic acid, carotonic acid, methacrylic acid, itaconic acid,aconitic acid, maleic acid, fumaric acid, mesaconic acid and citra-,' :

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conic acid. Also, as previously indicated there can be used partial esters such as mono 2-hydroxypropyl itaconate, mono 2-hydroxyethyl itaconate, mono 2-hydroxyethyl citraconate, mono 2-hydroxypropyl aconitate, mono 2-hydroxyethyl maleate, mono 2-hydroxypropyl fumarate, monomethyl itaconate, mono-ethyl itaconate, mono Me~hyl Cellosolve* ester of itaconic acid (Methyl Cellosolve* is the monomethyl ether of diethy-lene glycol), Mono Methyl Cellosolve* ester of Maleic acid. -`
The polymers can be prepared for use as casting syrups, as aqueous dispersions, by aqueous suspension poly-merization or as solutions in organic solvents such as ethyl alcohol, methyl alcohol, propyl alcohol, isopropyl alcohol, -~
formamide, dimethyl sulfoxide or other appropriate solvent.
It has now been found that in addition to the polymers set forth in our Canadian Patent Application No.
076,719, there can also be used as polymers in the prac-tice of this invention polyvinyl alcohol, polyvinyl-N-pyrrol-idone, copolymers of vinyl pyrrolidone with other monomers, e.g. methyl methacrylate, cellulose ethers such as methyl ;
cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, partially hydrolyzed cellulose esters such as cellulose acetate having a degree of substitution of 1~ 3 to 2.3, cel- ~"
lulose acetate-propionate and cellulose acetate-butyrate of similar degree of substitution, carboxyl methyl cellulose, etc., vinyl acetate-vinyl alcohol copolymers, e.g. (20:80) `
polymethylvinyl ether, polyethylvinyl ether, polyurethanes formed by reaction of polyhydric alcohols such as glycerol, sorbitol, mannitol, pentaerythritol, trimethylolpropane, hexane 1,2,6-triol, mono or polysaccharides such as glucose, `~
sucrose, fructose and dextrin, tris dipropylene glycol phos-phonate, tris dipropylene glycol phosphate with an amount *trademark for 2-ethoxyethanol - ~ .
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of diisocyanate insufficient to react with all the hydroxyl functionality.
Such polyurethanes can have hydroxyl numbers of 100 to 500 and can be made from toluene diisocyanate, 4,4'-methylene bis (phenylisocyanate), oxydi (phenylisocyanate), 4-methoxy-1,3-phenylene diisocyanate or any other convention-al diisocyanate or higher polyisocyanates such as those men-tioned in U.S. patent 3,127,373. ~here can also be used polyurethanas formed by reaction of hydroxyl terminated polyesters with such polyisocyanates providing the hydroxyl ;
groups are in excess. Examples of such polyesters are poly-ethylene sebacates, the reduction product of an excess of ~ ~
l,4-butanediol with adipic acid and a small amount of tri- ~ ~-methylolpropane of molecular weight 3,000 to 12,000, ethy-lene glycol-propylene glycol adipate molecular weight l,900, glyceryl adipate-phthalate. Likewise there can be used poly-urethanes made by reacting such polylsocyanates with hydrox-yl terminated polyethers, e.g. diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol molecular weights of 200 to 3,000, polypropylene glycol molecular weight of 200 to 3,000, tetramethylene glycol molecular weight 200, l,000 or 4,000, glycerol-propylene oxide adducts ;
of molecular weight 265, 1,000 or 3,000, hexane 1,2,6-triol-propylene oxide adducts of molecular 500 to 4,000, oxypro-pylated sucrose. The hydroxyl numbers of such polyurethanes should be as indicated above.
Other suitable hydrophilic polymers include protein-aceous polymers such as casein and gelatin~ high molecular weight polyethylene oxide or polypropylene oxide, e.g. mol-ecular weight of 3,000 or above, preferably at least 5,000,polyethylene i~ine, and water soluble polyelectrolytes such : , :

, ,-as polyitaconic acid, polyacrylic acid, vinyl ether-maleic anhydride copolymers, e.g. where the vinyl ether is vinyl ethyl ether, vinyl methyl ether or vinyl butyl ether, ethy- -lene-maleic anhydride copolymers, styrene-maleic anhydride 5 copolymers (preferably containing at least 3~/a maleic an-hydride units), methyl methacrylate-maleic anhydride copoly-mers hydrolyzed ethylene-vinyl acetate copolymer containing at least 3~h vinyl alcohol units, phenoxy resins, e.g. the phenoxy resin of molecular weight 30~000~ see U.S. patent 10 3~305~526~ col. 9, line 60 et seq., polyvinyl acetals con-taining free hydroxyl groups, e.g. polyvinyl formal-poly-vinyl alcohol, polyvinyl butyral-polyvinyl alcohol.
Cross-linking of the applied coatings may be ac-complished by a variety of techniques~ Curing of polymers containing hydroxyl functionality may be done using ammoni-um, potassium or sodium chromate or dichromate or other strong oxidizing agents, e.g. in an amount 0.2 to 5% of the solids, Titanates, e.g. tetraisopropyl titanate, tetrabutyl titanate and tin compounds, e.g. stannous dodecanoate, stan-nous octoate can be used in like amounts. Polymers contain-ing other groups and vinyl unsaturation may be crosslinked by incorporation of free radical generators such as organic peroxides, e.g. any sodium peroxide, hydrogen peroxide, am-monium or potassium persulfate, organic hydroperoxides, per-acids, and peresters.
Examples of suitable per compounds include t-butyl peroctoate, benzoyl peroxide, isopropyl percarbonate, 2,4-dichlorobenzoyl peroxide, methyl ethyl ketone peroxide, cu-mene hydroperoxidè and dicumyl peroxide.
The inciusion of agents to create redox systems with the free radical generators aids in speeding the curing , ,: .

action as is well known in the art.
It is critical, as stated, to render the hydrophil-ic polymer water insoluble (if it is not already so) while `~
at the same time not destroying the hydrophilic prope~ties.
It is also critical that the hydrophilic polymer form a continuous film outer coating on the watercraft or other structurer i.e. it should not be masked or blocked by a hydrophobic film former for example.
The hydrophilic polymer coatings of the present invention can be coated over conventional antifoulants pro-vlding there is sufficient permeability that the bottoms of the watercraft are kept clean.
There also can be lncorporated with the hydrophil-ic polymers in the coating compositions of the lnventlon to provlde coatLngs to prevent fouling by marine organisms any of the conventional inorganic or organic anti-foulants ln-cluding cuprous oxide, copper powder, mercuric oxide, cup-rous oxide-mercuric oxide, e.g. 3sl mercurous chloride, organotin compounds including triphenyltin chloride, tri-20 phenyltin bromide, tri p-cresyltin chloride, triethyltin `
chloride, tributyltin chlorlde, phènyl dlethyltin fluorlde, tri (p-chlorophenyltin) chlorldé, tri (x-chlorophenyltin) chloride, dibutyl ethyltin bromide, dibutyloctyltin bromide, trlcyclohexyltln chloride, triethyltin stearate, tributyltln . . , j, . . . ~.,, 25 stearate, trlethyltln fluorlde, tributyltin fluoride, di- , phenyl ethyltin chloride, diphenyl ethyltin fluorldé, tri-phenyltin hydroxide, triphenyltin thiocyahate, triphenyltin trichloroacetate, tributyltin acetate, tributyltin neodecan-oate, trib~tyltin neopentanoate, trioctyltih neodecan~ate, tributyltin oxide, trioctyltin oxide, triphenyltin fluoride, tributyltin oleate, tripropyltin neodecanoate, tributyltin .", -10- ,'... .

laurate, tributyltin octanoate, tributyltin dimethyl carbo-mate, tributyltin resinate, tributyltin chromate, amyldi-ethyltin neodecanoate, tributyltin naphthanate, tributyltin isooctylmercaptoacetate, bis (tributyltin) oxalate, bis (tributyltin) malonate, bis (tributyltin) adipate, bis (tri-butyltin) carbonate, organo lead compounds, e.g. triphenyl lead acetate, triphenyl lead stearate, triphenyl lead neo-decanoate, triphenyl lead oleate, triphenyl lead chloride, triphenyl lead laurate, triethyl lead oleate, triethyl lead acetate, triethyl lead stearate, trimethyl lead stearate, triphenyl lead bromide, triphenyl lead fluoride, organic compounds including 10,10'-oxy-bisphenoxazine (SA-546~, 1, 2 ~ 3-trichloro-4,6-dinitrobenzene, hexachlorophene, dichloro- -diphenyl trichloroethane (DDT), phenol mercuric acetate, tetrachloroisophthalonitrile, bis (n-propylsulfonyl) ethyl-ene, etc. -The antifoulant is releasably entrapped in the ~`
hydrophilic polymer coating. The quantity of antifouling agent required in the coating, as would be expected, varies 20 with the particular agent used and the severity of fouling tendency encGuntered in thè particular service to which the coated vessel or static structure is to be used. In general, the amount of antifouling agent when employed will range from 2 to 20~/o of the resin by weight, although as littie as 0.1% of anti-foulant can be used based on the resin. The amount of anti-foulant should be insufficient to prevent the hydrophilic polymer from forming a continuous film~
Of course, there can be included in the formulation ~;~
conventional pigments and fih ers such as titanium dioxide, red lead, bone black, red iron oxide, talc, aluminum sili-cate, fullers earth, pumice, zinc oxide, calcium carbonate, etc.
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The coatlngs of the present invention can be ap-plled to the surfaces to be subjected to underwater condi-tions from solution in organic solvents or from a~ueous dis-persions. Suitable solvents include lower aliphatic alco-hols such as methanol, ethanol, propanol and isopropanol or ;~
mixtures of these solvents with higher boiling alcohols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, ethyl-ene glycol monoethyl ether, diacetone alcohol, n-butanol, 10 sec. butanol, isobutanol and mixtures of these solvents with water. In some cases aromatic and aliphatic hydrocarbons, e.g. benzene, toluene, xylene and hexane can be used. ~- -The coatings of the present invention generally exhibit adequate adhesion to marine surfaces protected by 15 corrosion resistant Einishes such as epoxy or vinyl based paints, to previously applied antifouling finishes and to polyester-fiberglass laminates. Typical of such finishes are those shown in Sparmann U.S. patent 2,970,923, Scott U.S. patent 3,214,279 and Robins U.S. patent 3,236,793. ;
The thickness of the coating applied will vary ;
with the particular formulation emplo~ed and the method of ;~
application. It can be from 0.1 mil. to 250 mils. or more in thickness. Usually it will be between 0.3 mil. and 5 a mils. The co atings can be applied to the marine surface, 25 e.g. boat bottom or hull or wharf piling by any conventional procedure such as brushing, dipping, spraying, roller coating, etc.
Coating applied at boat yards, marinas or similar locations will normally be placed in water soon after dry-30 ing. These coatings if made from linear, alcohol soluble polymers will remain alcohol soluble. However, as pointed .:

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out supra it is also possible to provide cured or cross-linked coatings which exhibit improved mechanical durabil-ity. There can be used the peroxide catalysts referred to supra alone, or as part of a 2-component catalyst system which is mix~d into the coating solution immediately prior to application~ Alternatively, the coating can be cured by incorporating a free radical initiator and heating the coat-ed surface aftér drying.
Two component catalyst systems for effecting cure at ambient conditions, e.g. 20 C., include peroxides of the type referred to upra together with such amine accelerators as ~,~-dimethy~aminoethyl acetate, N,N-dimethyl aniline, N, ~-dimethyl aminoethanol, N,~-dimethyl toluidine. The accel-erator can be used in an amount of 0.05 to 1 part per part of peroxide, e.g. a mixture of 8~/o benzoyl peroxide and 11%
dimethylaniline can be employed. ~
Tha invention will be understood best in connec- `
tion with the drawings wherein:
FIGURE 1 shows a boat having a coating accordlng to the invention, and FIGURE 2 is a sectional view along the line 2-2 ~-of Figure 1.
Referring more specifically to the drawingb, the boat 2 in water 4 has a coating 6 of hydroxyethyl methacryl-ate polymer (or hydroxypropyl cellulose) below the waterIine8. If desired, the entire boat can be coated with the poly-mer. The thickness of the coating 6 is greatly exaggerated for illustrative purposes.

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30 2-hydroxyethyl methacrylate (50 parts) and TiO
D (30 parts) are ground in a pebble mill to a fine powderO

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Additional 2-hydroxyethyl methacrylate (50 parts) is added along with ethylene glycol dimethylacrylate (0.2 part~, cobalt naphthenate, a conventional metallic paint dryer or catalyst ~0.1 part) and t-butyl peroctoate (0.4 part). The resulting viscous syrup is painted onto a wooden boat hull and cured at 20 to 35 C. The resulting protective marine coating is characterized by its ability `
to discourage barnacle and algae growth and corrosion on prolonged underwater exposure. Additionally it reduces the -10 drag on moving the coated hull through water. ;
EXAMPLE 2 ,~
The procedure of Example 1 is repeated with the modification that the coating syrup is cast onto a steel hull and cured at 100 C. in the absence of cobalt naphthen-15 ate. The drag on moving the coated hull through water was ~
reduced compared to an uncoated hull. ~ -The procedure of Example 1 is repeated employing an isomeric mixture of hydroxy isopropyl methacrylate isomer 0 in place of the hydroxyethyl methacrylate.

To a glass-lined reactor was charged 800 lbs. of ethanol, 200 lbs. of hydroxyethy~ methacrylate and 0.5 lb.
of t-butyl peroctoate. The reactor was flushed with nitroJ ~;
gen and heated to 80 C, over a period of 1 hour. The re-actor was stirred at 80 C. for 7 hours, wherein 9~h conver-sion of hydroxyethyl methacrylate to polymer was attained. ;
The resulting solution, containing 1~/~ polymer by weight was used for the formulation of coatings for sailboats and motorboats below the water line. The boats were made of `
wood, metal and fi~erglass (i.e. polyester impregnated fiber-glass). -Example 4 was repeated using 20 lbs. of methyl methacrylate and 180 lbs. of hydroxyethyl methacrylate as the monomer charge. A conversion of 95% was attained in 7 .'' ~', , .

hours. The resulting solution was used for the formulation of marine coatings in a similar fashion to example 4.
EXA~IPLE 6 Example 4 was repeated using 80 lbs. of methyl methacrylate and 120 lbs. of hydroxyethyl methacrylate as the monomer charge. A conversion of 90~/~ was attained in 6 '~ ;
hours. The resulting solution was used for the formulation of marine coatings in a similar fashion to Example 4.
E~YAMPLE 7 D 10 A 22 foot polyester fiberglass boat (Aqua Sport~ ;~
equipped wlth a 100 horsepower outboard engine was operated at two different throttle settings between two buoys approx-imately one mile apart. Average times required to travel between buoys going in both directions were determined at each throttle setting. The boat was then removed from the water, the bottom was washed with $resh water and dried.
The polymer solution of example 4 was applied with a roller to provide a dry coating thickness of 0.75 to 1.0 mil. "
The boat was replaced in the water and the speed at the same throttle s~ttings between the buoys was deter-mined. The following results were obtained.

Speed, knots Speed, knots Throttle Settinq Before Coating After_Coatlng low 10.5 12.0 medium 17.2 19.8 The results show a 13% reduction in drag resistance at a speed of about 10 knots and a 15% reduction at the high- -er speed.
EXAMPLE_8 The "apparent viscosity" of water at 23C. was measured using a Brookfield RVT Syncrolectric viscosimeter employing a ~1 spindle at 100 R.P.M. The value obtained was ;

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11.1 centipoises. The spindle was removed, dried, and was coated with the solution prepared in example 4 by dipping and allowing the spindle to drain and dry. The coating thickness was approximately 0.5 mil. The "apparent viscos~
ity" of water at 23C. was again measured at 100 R.P.M. us-ing the coated spindle. A value of 10.7 centipoises was obtained. The peripheral spleed of the #l spindle at 100 R.P.M. is approximately 0.6 mile per hour~ At this speed i~`.:' ' .
approximately 4% reduction in frictional resistance or drag -was obtained.

A 9 foot polyester-fiberglass dinghy was towed be-hind a motor launch with a rope attached to a spring scale having a capacity of ten kilograms. The dinghy was towed at 25 knots. An average force of 8 kilograms was noted on the scale~ The dinghy was then removed from the water, `
rinsed with fresh water and dried. The dinghy was then brush coated with the polymer solution of example 4 to pro-vide a 1.5 mil. coating, aftèr drying, the dinghy was again towed at 25 knots~ An average force of 6.5 kilograms was recorded on the scale. Thus, at 25 knots approximately 18%
-. . . ~ .
reduction in drag resistance was obtained.

Using a high-shear mixer, 200 grams of triphenyl lead acetate and 50 grams of titanium dioxide were disperséd in 8 kilograms of the polymer solution prepared in example -4. To the dispersion was added 2 kilograms of sec. butyl alcohol. A #l spindle of a Brookfield vlscosimeter was coated with the dispersion by dipping and allowing to dry.
An average coating thickness of 0.6 mil. was obtained. The "apparent viscosity"of water was measured as in example 3.

A value of 10.5 centipoises was obtained. The coating was removed from the spindle and the "apparent viscosity" was again determined. A value of 11.0 centipoises was obtained~
The coating composition prepared in example 10 was employed on sailing craft, both of the wood hUll type ; and polyester-fiberglass laminate type to provide a fouling resistant drag reducing coating.
EX~PLE_ll Example 4 was repeated using a monomer charge of 40 lbs. of hydroxypropyl acrylate and 160 lbs. of hydroxy-ethyl methacrylate. A conversion cf 85% was achieved after 7 hours. ~he procedure of example 8 was repeated using this solution. Similar results were obtained. The solution of example 11 was also coated on the bottom of a metal bottom-ed motor launch to provide a drag reducing coating.
EXAMP~E 12 The procedure of example 11 was repeated replacing the hydroxypropyl acrylate by 40 lbs. of acrylamide. Simi-lar results were obtained.

To 500 grams of the coating dispersion of example 10 was added 2 grams of ethylene dimethacrylate (ethylene glycol dimethacrylate), 1 gram-of benzoyl peroxide and 0.4 -gram of ~,N-dimethyl aniline. The coating was immediately -applied to a polyester-fiberglass laminated boat hull sur-face. After drying and standing at 75F. ~about 24C.) for -two hours the coating merely swelled but did not dissolve in alcohol. The resulting coating was tougher when water swol-len than the coating of example 10. It was also effective as a fouling resistant drag reducing coating for the boat bottom.

A number of antifouling experiments were carried out using the hydrophilic polymers of the present invention.
After six months of testing on polyester resin panels the best results were obtained us,ing triphenyl lead acetate as the active antifouling ingredient. The results were also superior to using the antifouling agent in formulations which did not include the hydrophilic polymer.
Most antifouling compositions now used on ocean~
going vessels are based on the use of cuprous oxide pigmentl -0 h relatively inert material. A large proportion of the cup-rous oxide is not effectively used because it is encapsul-ated in the resin and is unavailable unless the resin it-self breaks down. A second disadvantage of cuprous oxide is that it can induce galvanic corrosion. In addition, because of its dark color, it is unsatisfactory as an antifouling ingredient or decorative finishes.
The United States ~avy is, of course, interested in antifouling finishes. It would like to have a 2-1/2 year `~
minimum, but finds that cuprous oxide coatings last from 12 18 months. Another market for effective systems is on tank-ers and large freighters. The operators are constantly seek-.
ing ways to decrease fouling because even a small amount of ' extra drag on the hull makes an appreciable difference to -the efficiency of the vessel, which has an important effect on the economics, particularly in tanker operations. In ad-dition, there is a need for periodic removal from service for bottom cleaning.
During the past decade a number of organometallic and organic pesticides have been found to exhibit high ac- ~ ;

tivity against a broad spectrum of marine fouling organisms.
Economic utilization of these chemical anti-foulants in shipbottom formulations has not been successfully accomplish - i - - : . . ~, : .. . - : , ~ ,., - .,, ~ .... . .

ed, however, primarily because of the encapsulation prob-lem. The new anti-foulants are all several times more potent than cuprous oxide, but their relatively high cost dictates that they be employed at a fraction o~ the normal concentratlon of the latter cuprous oxide. Continuous con-tact between toxicant particles in the paint fllm is not maintained at these relatively low concentrations, so that the toxicants are not even utilized as efficiently as cup-rous oxide, which in turn is also partially inactivated by encapsulation. Modification of the paints with inert ex-tender pigments or water-soluble resin constituents improves the efficiency of toxicant utilization, but degrades the physical integrity of the paint films to an intolerable de-gree, To date, the most successful compromise is represent-ed by blends or organometallic anti-foulants with cuprous oxide to obtain durability and high potency. However, such blends eliminate the two ma~or benefits offered by organlc and organometallic antifoulantsS freedom from the galvanic corrosion ha~ard of cuprous oxide, and flexibility of decor-atlve pigmentation.
The use of hydrophilic water insoluble polymers ofthe present invention reduces the problem of encapsulation of active~ anti-foulants in impermeable resin systems due to the water swellable nature of the hydrophilic film. ~n other acrylic resins and in other types of resin systems, solid organic and organometallic anti-foulants do not demon-strate any significant activity unless their concentration in the film exceeds a threshold of about 25% by weight of the resin. In the systems of the present invent~on activity at much lower concentrations is noticed indicating that the hydrophilic resin does not impermeably encapsulate the toxi-cant particlés.

In the following examples, 14 - 16, Hydron-S is hydroxyethyl methacrylate homopolymer. Hema ls an abbre-viation for hydroxyethyl methacrylate.

This series of experiments was designed as an at-tempt to determine whether ox not one of a variety of toxi-cants showed any activity against marine organisms when in-corporated into unmodified Hydron-S films. Accordingly, ethanol solutions of Hydron-S containing concentrations of 2 3~/O of the active ingredients were applied to panels and ~ -immersed at a Miami Beach test facility. Three toxicants of different chemical type were selected: Hex~chlorophene (Gll), tetrachloroisophthalonitrile (DAC-2787) and triphenyl lead acetate (TPLA~. These solutions, which contained 14%
Hydron, were applied by brush to panels of glass-reinforced polyester laminate which has been sanded to give a clean ;
surface. The details of the formulations are given in TabIe 1.
These panels were observed at monthly intervals.
After the first period, all three of the formulations showed ;
some activity against marine organisms. The resin itself was inactive, as demonstrated by the control sample which ~
rapidly became fouled. The Gll-containing series showed ;-good protection with the exception of the panel containing the 2% active ingredient (the lowest level). DAC-2787 was described as moderately active while TPLA exhibited a de-gree of control described as "startling". The films were completely free of slimes and silt, as well as macrofouling.
In all cases, the physical integrity of the film was good.
This was highly encouraging, since organolead compounds have not demonstrated useful levels of protection in coatings * trademarkS

,~.

even though they are known to have broad-spectrum activity in sea-water when leached out of porous blocks.
After five months' immersion, the Gll and DAC-2787 panels were removed because all had fouled extensively.
However, the TPLA series was still performing well, and af-ter six months the two films containing the most concentrat-ed quantity of active ingredient ( l~/o to 32%~ were still `
rated as 10~/o effec~ive at this time, the film containing 6% TPLA was rated 92%~ the 4% film 84%, and the 2% coating, 36%. ~omplete results are summarized in Table 2 -21~
'1' 4~
TABLE 1 ~l HYDRON-S FORMULATIONS, FIRST SERIES `

Formulation _ No.Hydr_n-_ G 11 DAC-2787 TPLA E~OH
5 A (Control 13.8 - ~ ~ 86.2 lB 13.7 0.3 - - 86.0 -, -lC 13.7 0.6 - - 85.7 lD 13.6 1.2 - - 85.2 ,~
lE 13.4 2.6 - - 84.0 10 lF 13.0 6.1 - - 80.9 2B 13.7 - 0.3 - 86.0 2C 13.7 - 0.6 - 85.7 , ~
2D 13.6 - 1.2 - 85.2 , ;
2E 13.4 - 2.6 - 84.0 15 2F 13.0 - 6.1 - 80.9 ; -3B 13.7 - - 0.3 86.0 3C 13.7 - - 0.6 85.7 3D 13.6 _ _ 1.2 85.2 3E 13.4 - - 2.6 84.0 20 3F 13.0 - - 6.1 80.9 ,, TA,BLE 2 , S,UMMARY OF BEHAVIOR R~PORTS OF EXPERIMENTAL SURFACES -~
(Plates Immersed March 15 - Hydron-S Brush , ~oatings Containing Triphenyl Lead Acetate) 25 Anti- "
foulants Code _ ,Overall Ratin~, % _ May June July Au~st S~E~tember None A ~7 0 0 0 0 TPLA, ~h3B 10071 42 36 36 30 TPhA, 4%3C 10092 90 90 8 TPLA, 8%3D 10095 93 92 92 -~
TPLA, 16% 3E100 100 100 100 100 TPLA, 32% 3F100 100 100 94* 100 * Attributed to green algae which attached during prolific growth period but which did not persist. -`
Physical condition of all coatings was rated "good", without physical defects, at time of September report.
.
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Triphenyl lead acetate (TPLA) tests were also car-ried out at four concentrations from 2 to 16% by weight in Hydron-S and also in two copolymers (9~/0 Hema-10/O methyl methacrylate and 60~/o Hema-40~fi methyl methacrylate. The co-polymers have lower levels of sea-water permeability than Hydron-S. These coatings were applied by both brush and doctor-blade techniques. 8" x 10" aluminum alloy panels were employed in the testing of effectiveness against foul-ing. After one month the Hydron-S formulations performed better than the copolymers. Pigmentation of the Hydron-S
did not detract from its performance.

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% PAINT PANEL
POLYMER TPLA ##* ONE MD~TH
Physical % Rating Condition O.P.
Hydron-S 2 1l-l/c Good 95 1-l/b Good 100 1-2/c Good 100 1-2/b Good 100

4 22-1/c Good 100 2-1 ~ Good 100 2-2/c Good i00 2-2/b Good 100 158 33-1/c Good 100 3-1/b Good 100 3-2/c Good 100 3-2~b Good 100 16 44-1/c Good 100 4-1/b Go~d 100 4-2/c Good 100 4-2 ~ Go0~` 100 90/10 2 55-l~c Blistèring 98

5-1/b Good 100 5~c Good 100 5-2/b Blistering 80 4 66-1/c Blistering 95

6-l~b Blistering 70 6-2/c Good 100 6-2/b Blistering 65 8 77-1/c Good 100

7-1/b Blistering 40 7-2/c Blistering 90 7-2 ~ BliStering 20 16 88-1/c Blistering 70

8-1/b Blistering 35 8-2/c BlisteringO 50 8-2,~b Blisteringq 30 ..... - - ;.
60/40 2 99-1/c Blistering, Flaking 25 .l

9-1 ~ Blis~eFing 95 ;,`
9-2/c Bllstering t Flaking 35 9-2/b GQod 100 ;
1010-1/c Bl`istering, Flaking 70 ~ : :

10-1/b Good 100 ~` .
10-2/c ~ot Prepared 10-2/b Good 100 811 11-1/c Blis~:ing, Flaking ;~
(Corro~ion erUptions on portions ~f bare :
aluminum) 85 ~1-1 ~ Good 100 :
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TPLA # #* ONE MONTH
j . .
Physical % Rating - 5 Condition O.P.**

60/40 11-2/c Blistering, Flaking -;
(Corrosion eruptions on portions of bare aluminum) 25

11-2/b Good 100 16 12 12-1/c Not prepared

12-1/b Good 100 ;
12-2/c Not prepared 12-2/b Flaking 75 -* c c cast, b = brushed.
** O.P. = Overall Performance ~ EXAMPLE 16 In another series of experiments, aluminum panels were prepared from Hydron-S solutions containing the follow-ing antifoulants:

Test ,i~
Panel ~esig-na_ion _ Antifoulant _ _ _ 25 A. Bis(tri-n-butyltin) oxide, "TBTO"
B. Triphenyltin chloride, "TPTCI"
C. Tributyltin fluoride, "TBTF"
E. Triphenyllead chloride, "TPLC" - ~' F. Triphenyllead laurate, "TPLL" *
G. 1,2,3-Trichloro-4,6-dinitrobenzene, "Vanicide PB"
H. Saturated solution of Vancide PB in TBTO, "PBTO"
(ca 20.5% PB) *
I. 10,10'-Oxybisphenoxarsine; "SA-546" -J. Mercurous chloride, Powder 35 K. Cuprous oxide, Grade AA

The formulations containing these antifoulants are shown in Table 5, and the results after one month's immer-sion in Table 6. Again, these results are from tests in sea-water at Miami, Florida.
, Panels K4 and K16, each with cast and brushed films cbntaîning cuprous oxide on aluminum, were expected to show galvanic corrosion. Since cuprous oxide is of importance * trademark '1:2 - - . ~ - ., ., .. - . . .

for comparison, additional K4 and K16 films were applled to glass-reinforced polyester panels. K4 replicates were brushed, and K16 cast because only the latter panels were flat enough to permit accurate film draw-down.
A number of the formulations how considerable interest, not only because of the protection afforded, but also because of the sizeable content o pigments.

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HYDRO~-S SYSTEM CO~TAI~ING 4 & 16% OF VARIOUS
_ANTIP~ULA~TS IMMERSION TEST RESULTS _ :
ANTIFOULA~T PAI~T~ PA~EL ~* O~E MDNTH
Physieal % Rating Condition -.-F.
TBTO A/4A4.1/e Good 95 A4.1/b Good 95 A4.2/e Good 95 A4.2/b Good 95 A/16A16.1/e Soft 95 A16.1/b Soft 93 A16.2/e Soft 95 A16.2/b Soft 98 15 TPT CI B/4B4.1/e Good 100 B4.1/b Good 100 B4.2/e Good 100 B4.2/b Good 100 B/I6B16.1/e Soft 98 B16.1/b Soft 98 B16.2/e Soft 98 B16.2/b Soft 98 TBTF C/4C4.1/c Good 95 C4.1/b Good 95 C4.2/c Good 95 C4.2/b Good 95 C/16- C16.1/e Good 100 C16.1/b Good 100 C16.2/c Good 100 C16.2/b Good 100 TPL~ E/4E4.1/e Good 95 E4.1/b Good 95 E4.2/e Good 10Q
E4.2/b Good 100 E/16E16.1/e Soft 98 E16.1/b Soft 98 E16.2/e Good 100 E16.2/b Soft 98 40 TPLL F/4F4.1/e Good 95 F4.1/b Good 95 F4.2/c Good 95 F4.2/b Soft 95 F/16~F16.1/c Soft 98 F16.1/b Good 100 F16.2/c Soft 98 F16.2/b Good 100 Vanieide PB G/4 G4.1/e Good 91 G4.1/b Good 90 G4.2/c Good 89 G4.2/b Good 91 G/16 G16.1/c Good 95 G16.1/b Good 95 . . , .. ~ .. . . , ~, . , .
.

40~
TABLE 6 - Contld.
A~TI~OULANT PAI~T ~ PAMEL #* ONE MO~TH

Physical % Rating Condition O.P.**

5 Vanicide PB G/16 G16.2/c Good 95 G16.2/b Good 95 PBTO H/4H4.1/c Good 95 H4.1/b Good 95 ~4.2/c Good 100 H4.2/b Good 95 H/16 H16.1/c Good 100 H16.1/b Good 100 H16.2/c Good 100 `
H16.2/b Soft 95 `, 15 DOW SA-546 I/4I4.1/c Good 100 ';
I4.1/b Good 100 ~;
I4.2/c Good 100 I4.2/b Good 100 ;-~
I/16I16.1/c Good 100 I16.1/b Good 100 ~
I16.2/c Good 100 ~
I16.2/b Good 100 `

Mercurous J/4J4.1/c Good 100 `
Chloride J4.1/b Good 95 ~
J4.2/c Good 100 -J4.2~b Good 100 J/16J16.1/c Blisterlng 90 `
J16.1/b Blistering 99 J16.2/c Blistering 90 J16.2/b Blistering 99 - Cuprous K/4K4.1/c Corr. eruption 95 Oxide K4.1/b Good 95 K4.2/c Good 95 K4.2/b Good 95 ;,~
K/16K16.1/c Corr. eruption9~ `
K16.1/b Corr. eruption 99 K16.2/c Corr. eruption 99 K16.2/b Corr. eruption 99 * ~ ca~t, b = brushed.
**O.P. = Overall Performance.
In examples 14 through 16, the formulations con-taining pigments were prepared on a paint mill. All were applied (with the few exceptions indicatad) to 6061-T6 ano- `
dized aluminum alloy by doctor-blade coatlng or brushing.
In the following examples phr means parts per hundred of resin.
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Example 17 To a 10% aqueous solution of hydroxyethyl cellu-lose was added 1.18 phr. (based on polymer) of ammonium dichromate. A portion of the solution was coated on a pre-weighed glass slide and allowed to dry and cure at roomtemperature. The weight of the dried coating was then de-termined and it was placed in water over night. The coated y glass was blotted free of suxface moisture and weighed.
The coating had picked up 397% of its dry weight of water.
A separate portion of the solution was used to coat the streamlined dart as described below for determina- ~
tion of drag reduction. -Example 18 Example 17 was repeated using hydroxypropyl cellu-lose in place of hydroxyethyl cellulose with 1.12 phr. ofammonium dichromate. The dried, cured coating picked ~p 590% of its weight on immersion in water for 18 hours.
ExamPle 19 To a 10% solution of polyvinyl pyrrolidone in Ethanol was added 2 phr. of ammonium persulfate as a 10~
aqueous solution. The solution was coated on preweighed al~minum foil and allowed to dry at room temperature-. The film picked up 15 times its dry weight of water after 18 hours of immersion.
Example ~ff To a 10% aqueous solution of polyvinyl alcohol was added 2.36 phr. of ammonium dichromate. A dried film picked up 58.7% of its weight of~water on immersion for 23 hours-. ~;
- Example 2 A lO ft. vertical glass column, 6 inches in d`iam-eter was equipped with an axially located electromagnet at the top, an axially positioned guide line down the length of the column and photo-electric cells coupled with a timing device at the bottom of the column.
A streamlined aluminum dart having an axial hole through the center was positioned over the guide line. The column was filled with water. The dart was held at the top of the column by the electromagnet. A single switch, which turned off the current to the magnet releasing the dart, simultaneously turned on the timer. rhe interruption by the falling dart of the light beam ~ -between the photocells positioned at the bottom of the column turned off the timer.
The dart was timed without having coatings applied thereto, and ;
was then timed with various coatings applied to its surface. ;~
The average results (10 trials) obtained with the uncoated dart ,7''' ' ''' and the dart with the coatings of examples 17 - 20 are as follows:

Surface % H20 Drop Time Speed Coating Material in film ~Seconds)Increase %
None Aluminum 1.217 Ex. 17 Hydroxyethyl 403 1.183 2.8 Cellulose .

Ex. 18 Hydroxypropyl 593 1.179 3.1 Cellulose Ex. 19 Polyvinyl 1520 10180 3.0 ;
Pyrrolidone Ex. 20 Polyvinyl 57.8 1.176 3.4 Alcohol In place of the hydroxyethyl methacrylate polymer solution of example 4 to coat sailboats and motorboats there can be used the hydroxyethyl cellulose solution of example 17, the hydroxypropyl cellulose solution of example 18, the polyvinyl pyrrolidone solution of example 199 or the poly-vinyl alcohol solution of example 20. "~

Similarly, in place of the Hydron-S and the copolymers employed in examples 14, 15 and 16 there can be used the same weights of the polymers of examples 17, 18, 19, 20 or 21.
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Claims (41)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A marine structure which is a watercraft having an adherent con-tinuous exposed coating consisting essentially of a water insoluble hydro-philic polymer which is swellable to an extent of at least 10% in water wherein the hydrophilic polymer is selected from the group consisting of hydrophilic cellulose esters, hydrophilic cellulose ethers, hydrophilic polyurethanes, hydrophilic vinyl lower alkyl ethers, vinyl alcohol group containing polymer, polyvinyl pyrrolidone, partially hydrolyzed polyacryloni-trile, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, proteins, high-molecular weight polyalkylene oxides, and phenoxy resins wherein the coating is sufficient to reduce the drag-of the watercraft when in water.

2. A marine structure according to claim 1 wherein the hydrophilic polymer is normally water soluble but has been cross-linked sufficiently to render it water insoluble.

3. A marine structure according to claim 1 wherein the hydrophilic polymer is a water insoluble cellulose ether.

4. A marine structure according to claim 3 wherein the cellulose ether is a hydroxy lower alkyl ether.

5. A marine structure according to claim 4 wherein the cellulose ether is a hydroxymethyl cellulose.

6. A marine structure according to claim 4 wherein the cellulose ether is a hydroxypropyl cellulose.

7. A marine structure according to claim 3 wherein the cellulose ether is a carboxymethyl cellulose.

8. A marine structure according to claim 1 wherein the hydrophilic polymer is a partially hydrolyzed cellulose ester of a lower alkanoic acid.

9. A marine structure according to claim 8 wherein the cellulose ester is a cellulose acetate.

10. A marine structure according to claim 1 wherein the hydrophilic polymer is a water insoluble hydroxyl containing polyurethane.

11. A marine structure according to claim 1 wherein the hydrophilic polymer is a water insoluble vinyl lower alkyl ether.

12. A marine structure according to claim 1 wherein the hydrophilic polymer contains vinyl alcohol groups and is water insoluble.

13. A marine structure according to claim 12 wherein the vinyl alcohol group containing polymer is a water insoluble polyvinyl alcohol.

14. A marine structure according to claim 12 wherein the vinyl alcohol group containing polymer is a hydrolyzed ethylene-vinyl acetate copolymer.

15. A marine structure according to claim 12 wherein the vinyl alcohol group containing polymer is a polyvinyl acetal.

16. A marine structure according to claim 1 wherein the hydrophilic polymer contains vinyl pyrrolidone units.

17. A marine structure according to claim 16 wherein the polymer is water insolubilized polyvinyl pyrrolidone.

18. A marine structure according to claim 1 wherein the polymer is partially hydrolyzed polyacrylonitrile.

19. A marine structure according to claim 1 wherein the polymer is an ethylene-maleic anhydride copolymer.

20. A marine structure according to claim 1 wherein the polymer is a styrene-maleic anhydride copolymer.

21. A marine structure according to claim 1 wherein the polymer is a vinyl alkyl ether-maleic anhydride copolymer.

22. A marine structure according to claim 1 wherein the polymer is a protein.

23. A marine structure according to claim 1 wherein the polymer is a high molecular weight poly lower alkylene oxide.

24. A marine structure according to claim 1 wherein the polymer is a phenoxy resin.

25. A marine structure according to claim 1 wherein the coating has en-capsulated therein an anti-fouling agent.

26. A marine structure according to claim 25 wherein the coating is a film having a thickness of 0.3 to 5 mils.

27. A marine structure according to claim 25 wherein the hydrophilic polymer is normally water soluble, but has been cross-linked sufficiently to render it water insoluble.

28. A marine structure according to claim 25 wherein the hydrophilic polymer is a water insoluble cellulose ether.

29. A marine structure according to claim 28 wherein the cellulose ether is a hydroxy lower alkyl ether.

30. A marine structure according to claim 28 wherein the cellulose ether is a carboxymethyl cellulose.

31. A marine structure according to claim 25 wherein the hydrophilic polymer is a partially hydrolyzed cellulose ester of a lower alkanoic acid.

32. A marine structure according to claim 25 wherein the hydrophilic polymer is a water insoluble hydroxyl containing polyurethane.

33. A marine structure according to claim 25 wherein the hydrophilic polymer is a water insoluble vinyl lower alkyl ether.

34. A marine structure according to claim 25 wherein the hydrophilic polymer contains vinyl alcohol groups and is water insoluble.

35. A marine structure according to claim 34 wherein the vinyl alcohol group containing polymer is a water insoluble polyvinyl alcohol.

36. A marine structure according to claim 34 wherein the vinyl alcohol group containing polymer is a hydrolyzed ethylene-vinyl acetate copolymer.

37. A marine structure according to claim 25 wherein the polymer is water insolubilized polyvinyl pyrrolidone.

38. A marine structure according to claim 25 wherein the polymer is a high molecular weight poly lower alkylene oxide.

39. A marine structure according to claim 25 wherein the polymer is a phenoxy resin.

40. A marine structure according to claim 1 wherein the hydrophilic polymer is swellable to an extent of 20 to 120% in water.

41. A marine structure according to claim 1 wherein underneath said exposed coating is an inner coating comprising an anti-foulant, said hydro-philic coating being sufficiently water absorbable that water reaches said anti-foulant and the anti-foulant is gradually leached out while the water-craft is in the water.