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Stainless Raw Water Pump

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  • Stainless Raw Water Pump

    I am replacing the old plastic & steel Mercruiser Pump with this one. The old one will be a spare on board. Will be easier to switch them out offshore, should the impeller fail.
    2001 246 WA
    Mercruiser 5.7 Horizon

  • #2
    Nice, where did you get it? I despise the mercruiser plastic pump on my boat.

    Comment


    • #3
      I got it off Amazon-free shipping. The vendor is Marine Power out of Louisiana. The impeller is OEM Mercruiser when time to replace. The price was reasonable, made in USA.
      2001 246 WA
      Mercruiser 5.7 Horizon

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      • #4
        Be certain you do not use bronze fittings on the water lines of the stainless steel pump.
        I can appreciate the Mercruiser pump, mine has lasted almost 20 seasons.

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        • #5
          Bonding and zinc's will allow bronze use. Without them any bronze would be toast with any metal harder in the system.
          Atlantic City, NJ
          1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

          Comment


          • #6
            Originally posted by Ship View Post
            Bonding and zinc's will allow bronze use. Without them any bronze would be toast with any metal harder in the system.
            The "hardness" of the metals in the system actually has little to do with the metal's potential susceptibility to galvanic corrosion. Without going into great detail, this should summarize it for our purposes.

            First when we talk about Bronze and Stainless Steel, they are both alloys.

            There are many types of corrosion in the marine environment, among them are: Stray current, Galvanic corrosion, Electrolytic corrosion, Poultice Corrosion, Crevice corrosion, Stress corrosion cracking, Erosion Corrosion and intergranular Corrosion.

            When we speak of corrosion between dissimilar metals in an electrolyte, Galvanic Corrosion (which is often incorrectly called Electrolysis) is the culprit. Another name for Galvanic corrosion is Bimetallic Corrosion. It is the enemy!

            For the purpose of corrosion studies all metals are "rated" on the Noble Scale (also known as the Electropotential Series or Galvanic Series) from least Noble to most Noble. The more Noble a metal, the more resistant to corrosion.

            Galvanic corrosion by definition is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in an electrolyte. Water in our case. The process is also how wet cell or flooded cell batteries produce electricity. Essentially, the less Noble metal (Anode) will corrode, giving ions to the more Noble Metal (Cathode). In some ways it can be a microscopic form of electroplating the more Noble metal with the less Noble metal.

            Bronze and Stainless Steel are relatively close on the Noble Scale, which is why they are used as underwater metals on boats. Generally, Bronze will not be sacrificed to Stainless Steel at any appreciable or great rate. Ninety something percent of all inboard powered boats are turning either Bronze or NiBrAl propellers on Stainless Steel shafts, with Bronze keys, Bronze nuts and stainless steel cotter pins... Of the literally thousands of vessels I've seen, I have never seen a bronze key fail from corrosion...

            Most raw water pumps are constructed with bronze bodies, stainless steel shafts, lip seals made of brass or sometimes Stainless Steel with a rubber seal and stainless steel spring, and impellers with brass female splines... All of which last years in contact with seawater. Freeze out plugs in engine blocks are also brass, and generally outlive the engine.

            The stainless steel replacement pump in Johnny's picture has stainless steel hose barbs which are part of the housing, so no bimetallic issues exist. The original Mercruiser pumps of that style were bronze, and were later replaced by the plastic ones due to manufacturing costs. The only potential downside I can see with the stainless steel pump is that the impeller might wear a bit more quickly. I would consider using a Nitrile impeller.

            Bonding....

            The purpose of a Bonding system is to protect underwater metals. It is done (simple description) by connecting all underwater metals together inside the boat to both the vessel ground and a large underwater anode. The theory is that when the metals are connected to each other electrically and to ground, that they all share the same electrical potential and do not sacrifice Ions between them. Bonding does virtually nothing to protect metals in the boat such as cooling system components, engines and such. A side note concerning Bonding systems... Due to hydraulic fluids, gear oils, Shaft Savers and such the quality of the electrical "connection" between most propeller shafts and the vessel ground can be nonexistent, or generally not optimal. Including a shaft brush in the bonding system is a worthy investment.

            Anodes....

            Traditionally, Zinc has been the anode of choice for inboard vessels. In recent years it has been proven that in saltwater, Aluminum anodes provide better protection to Bronze and Stainless Steel than Zinc.

            In fresh and brackish water Aluminum alloys and Aluminum/Magnesium alloys provide better protection.

            Additional benefits of the aluminum anodes are they cost and weigh less.

            Electrolysis....

            The "Great Misnomer".... I'm always amazed by how some of the most knowledgeable marine professionals incorrectly refer to Galvanic Corrosion as Electrolysis. I hear and see it all the time, both in yards and even in some surveyors reports. One insurance company even listed "Damage to underwater metals caused by Electrolysis" as an exclusion/uncovered loss. We represented the owner after the claim was denied on the basis of "Electrolysis". After challenging the carrier and surveyor, the claim was paid.... and the language changed in their policies soon after.

            That said, Galvanic Corrosion is as described above. Electrolysis by definition is: The chemical degradation/decomposition of an electrolyte (in our case water) caused by passing an electric current through the electrolyte.... two very different processes!

            Electrolysis is best known for the removal of unwanted hair..... (Humor intended)
            Last edited by Surveyor; 02-21-2019, 12:49 PM.

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            • #7
              Gave simple answer to as you explained a complex problem. Having said that the solution is simple. Bonding and sacificial metals. Bonding can be just as complex depending on the conditions present.
              Atlantic City, NJ
              1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

              Comment


              • #8
                Originally posted by Ship View Post
                Gave simple answer to as you explained a complex problem. Having said that the solution is simple. Bonding and sacificial metals. Bonding can be just as complex depending on the conditions present.
                Ship,

                My comments were neither of a personal nature, nor directed at you personally. I was simply responding to what appeared to be misleading information as it related to the discussion of the stainless steel pump. I provided factual information on the subject which I thought would be helpful to readers, rather than misleading or alarming...

                I’ve been involved in this industry a long time and found that corrosion is one of the most misunderstood sciences or topics. Both among boaters and the professionals who service boats.

                I agree bonding can in some instances certainly be complicated.

                But in reading the thread which was about the stainless steel pump, ”Pequod” suggested that he “... not use bronze fittings on the water lines of the stainless pump”

                You wrote thst “Bonding and zinc’s will allow bronze use. Without them any bronze would be toast with any metal harder in the system”

                Perhaps I’m missing something in what you said... but neither of those comments make sense to me in the context of the Stainless Steel pump.

                What were you suggesting he bond and where were you suggesting he install zincs? What does the hardness of the metal have to do with the corrosion potential? I don’t understand.

                I would be be grateful if you would clarify this, as I don’t understand what you were suggesting he do to avoid as you put it, the bronze becoming toast.

                Thanks

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                • #9
                  Any bronze fitting subjected to salt water when there are dissimilar metals present and movement creates the conditions for current which in turn will cause the lower on the Noble scale to migrate to the higher metal. The term commonly referred to as electrolysis is more accurately similar to electro plating . The tin in the bronze with move in the absence of a sacrificial metal. Bonding allows directing the current and zincs provide the lower/softer metal to move. The standard fix for the use of dissimilar metals on boats. Or the more high tech version is a rig that neutralizes the current. I know your explaination is more complete but I like you have played with metal most of my life.
                  Last edited by Ship; 02-21-2019, 08:01 PM.
                  Atlantic City, NJ
                  1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

                  Comment


                  • #10
                    Now I'm really confused.
                    1988 26' cuddy
                    1975 20' open
                    31 Grand Slam
                    16' Sandpiper
                    14' Certified Fiberglass

                    Comment


                    • #11
                      Originally posted by Quik Fix View Post
                      Now I'm really confused.
                      Me too Jerry.... But I'm going to try to bring this back around and into perspective...

                      Comment


                      • #12
                        Originally posted by Ship View Post
                        Any bronze fitting subjected to salt water when there are dissimilar metals present and movement creates the conditions for current which in turn will cause the lower on the Noble scale to migrate to the higher metal. The term commonly referred to as electrolysis is more accurately similar to electro plating . The tin in the bronze with move in the absence of a sacrificial metal. Bonding allows directing the current and zincs provide the lower/softer metal to move. The standard fix for the use of dissimilar metals on boats. Or the more high tech version is a rig that neutralizes the current. I know your explaination is more complete but I like you have played with metal most of my life.
                        Ship,

                        I'm not looking to argue with you, pick on you or hurt your feelings... But you haven't answered the questions about the statements you made... and some of what you've said is incorrect...

                        Just to recap the thread a bit...

                        "JOHNNY" said he was going to replace the Mercruiser plastic pump with a Stainless Steel pump.

                        "PEQUOD" Suggested that he not use Bronze fittings on the water lines with the Stainless Steel pump.

                        YOU said, "Bonding and zinc's will allow Bronze use. Without them any Bronze would be toast with any metal harder in the system.

                        I gave a brief explanation of corrosion and some related information and asked you a few questions, trying to understand what you were saying.

                        Based on what you've said, It seems that you think that Bonding and sacrificial anodes are the answer to what you described as "turning any bronze to toast."

                        So, based on your statements, in the context of the Stainless Steel pump, my questions remain, and are:

                        What were you suggesting JOHNNY bond?

                        Where were you suggesting he install zincs?

                        What does the hardness of the metal have to do with corrosion potential?

                        Concerning your last post... Your statement, "The term commonly referred to as electrolysis is more accurately similar to electro plating." You're almost on the right track concerning some similarities, but it is not "more accurately similar to electroplating." The only similarity between the two is that both processesuse electricity to split up a chemical solution. The main difference between electrolysis and electroplating is that electrolysis is the use of electrical current to drive a non-spontaneous chemical reaction whereas electroplating is the use of electrical current to plate one metal on another metal.

                        Bronze by definition is a Copper alloy. There are many types of bronze... Another common misconception relates to your comment, "The tin in the bronze with move in the absence of a sacrificial metal." This is incorrect, unless the Bronze you are referring to is "Cheap Chinese"/substandard alloy, which contains, as you noted some Tin. Without going into the various types of bronze, the three main types used in boats are Silicon Bronze (used primarily as fasteners), Manganese Bronze (used in propeller shafting and other parts, and 85-5-5-5 (known by several names including Red Brass). 85-5-5-5 and Manganese Bronze DO NOT contain any Tin.

                        Manganese Bronze is generally composed of 60.0- 68.0% Copper, 25.0% Zinc, 3.0-7.5% Aluminum and 2.5- 5.0% Manganese

                        85-5-5-5 Bronze is composed of 85% Copper, 5% Zinc, 5% Lead and 5% Silicon.

                        Due to the lower Zinc content, 85-5-5-5 is considered more resistant to Galvanic corrosion. Any "Bronze" with a Zinc content above 15% is not considered suitable for through hull fittings, seacocks & such.

                        Bronze through hull fittings, seacocks and such parts are by standard made of 85-5-5-5. The ones made by Perko and Groco are made of 85-5-5-5 Bronze.

                        When Bronze corrodes the process is known as Dezincification... In simple terms, the Zinc is leaving the alloy, or as you say, it is moving to a more Noble metal. Dezincification is generally visible when the bronze starts to take on a pinkish color. The process rapidly softens and weakens the Bronze.

                        Your comment that, "Bonding allows directing the current and zincs provide the lower/softer metal to move", is almost correct.... A bonding system actually provides an alternative path back to the power source that doesn’t travel through the water. The current travels through the bonding conductors in the vessel. The bonding anode sacrifices itself for the bonded metals. But, the softness or hardness of the bonding anode is not the factor... it's electrical potential, being low on the Noble Scale is the factor.

                        Putting Anodes on our shafts, rudders, trim tabs and such along with bonding is Anodic protection.

                        Although saltwater is more conductive than fresh, the Galvanic corrosion process is essentially the same.

                        The more high tech version you mentioned as "a rig that neutralizes the current" is a form of Cathodic protection, and is entirely different in how it works. It is commonly known as an Impressed Current system or ICCP (Impressed Current Corrosion Protection). They have been around for more than 50 years, the CAPAC systems being the original to my knowledge. They were used on the Marinette aluminum boats and on the Striker steel and aluminum hulls. Last I knew, the USCG was using systems made by Electroguard. These systems are generally used on metal hulled vessels, barges, oil rigs and ships but also on some large FRP & composite yachts to protect underwater metals. The Mercruiser MerCathode system used on many of their outdrive applications is a form of an ICCP system, but it is designed to only protect the aluminum outdrive and and transom assembly and not any other underwater metals.

                        In simple terms an impressed current system uses the vessel's DC power system to direct electrical current into the metals being protected (Cathodes)... the current flows into the water surrounding the vessel and flows through the water by Ionic conduction. It is then absorbed by the system's anodes and returned to the DC system. The system uses a Silver Silver chloride reference cell to monitor the hull potential and electronically control the output.

                        These systems work well, with one exception. Most do not function well in the presence of stray current.


                        I hope this clarifies things for anyone who has been following this thread.

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                        • #13
                          You are right. Sorry I put it in layman's terms.
                          Atlantic City, NJ
                          1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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                          • #14
                            Wow!.....Very informative and well written Surveyor. I am hoping there will not be a quiz on this in the future. If there is I want to be sitting next to Jerry.

                            regards Holty

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                            • #15
                              BTW. Your definition of electrolysis is only one of Webster's definitions. The transfer of anode or electrode through an electrolyte is another as is the removal of hair.
                              Atlantic City, NJ
                              1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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