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Author Topic:   Erosion of Lower Unit from Stainless Accessories
Wet Foot posted 09-28-2003 04:09 PM ET (US)   Profile for Wet Foot   Send Email to Wet Foot  
Hi Guys,

Is it true that stainless steel accessories (props, hydrofoils...) attached to an outboard, causes erosion of your lower unit surface because of a chemical reaction between the dis-similar metals touching. A friend told me his lower unit has become badly pitted since he started using a stainless prop a few years ago. He spoke to Mercury and followed their recommendation to avoid this problem; but it continued. This issue is one I've never heard before. I postponed the purchase of my stainless steel Turbo-Lift until I learn more. Has anyone experienced a similar problem?

Sal DiMercurio posted 09-28-2003 04:36 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Web, the reason your friends lower unit is getting pitted is, he leaves the engine down & keeps his boat in the water & either him or a boat nearby is charging it's battery & is not properly grounded [ called electrolosis ].
Or he has no "anod" such as zinc.
By the way, your prop shaft is s/s, are you getting electrolosis from it ?
Sal
Clark Roberts posted 09-29-2003 05:26 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
I agree with Sal! With proper zincs and grounding connections between engine parts (lower unit to mid section to yoke to power head) there should be no metalic errosion problems. There can still be some amount of electrolysis (minor) if engine is left with foot in water (even some so-called fresh water) for extended periods./// Clark.. SCN
Bigshot posted 09-30-2003 03:32 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Here in FL we have a community called "The Inlets". They are not allowed to make new salt water canals so they make fresh water ones and have a travel hoist at the end of each canal to bring the boat from the fresh to the salt water....pretty cool. There are about 10 canals and ALL of them are having serious electrolosis issues. The out drives are literally being eaten away. My friend works on many of these boats and some are really serious(Volvo mainly). They have even had Mercury come down to assess the situation but no real luck yet. It is not really electrolosis more likely something acidic in the water. At fist the thought it was the local yahoo using a battery charger, etc but in alll 10 canals?
Wet Foot posted 09-30-2003 06:06 PM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
Thanks Guys,

Sal, that is true about the prop shaft...I thought it might be insulated from the aluminum and so not a factor. So would you guys feel good about attaching a large stainless hydrofoil to the lower unit of a new outboard?

Sal DiMercurio posted 09-30-2003 07:59 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Wetfoot,as long as you have zincs & don't leave the engine down sitting in the water you shouldn't have any problems.
Bigshot, could be that in salt water you are supposed to use zinc , zincs & in fresh water magnesioum in place of the zinc.
They should put both on if their running in both fresh & salt.
Sal
lhg posted 10-01-2003 01:37 PM ET (US)     Profile for lhg    
The problem wetfoot is referring to sounds like stray electic current coming off the engine, so something is definitely wrong with the electrical/battery system on the engine.

This past weekend, I witnessed something I have never seen before, on a like new Yamaha 150, sporting a brand new, highly polished Merc SS performance prop, left in water over a 4 day period. My Whaler, with similar props, was docked alongside of it, in crystal clear fresh water. By the 4th day, I was looking at his prop in the water, and it was dull looking, like brushed chrome, while my props still looked shiny, as usual. We tilted his motor up, and found the prop completely coated with a THICK calcium type coating, including some other areas on the lower unit where bare aluminum was exposed. We also noticed a ground wire on the engine was "burned" through, and loose. With the boat back on the trailer, it took successive applications of LimeAway to clean it back up, including newly rusted engine attachment bolts to hull! Touching the ground wire back to the place where it was supposed to be attached to the support bracket, resulted in a spark! The engine had recently been worked on, so the mechanic must have done something to the electrical system, allowing current to leak out of the engine electrical system, from the battery, into the water. The galvanic action, in just 4 days, was incredible.

Wet Foot posted 10-01-2003 02:32 PM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
I wonder if my friends issue might be that his sacrificial metal is zinc instead of magnesium as Sal mentioned. We boat in freshwater only. He tells me his electrical system has been checked thoroughly. Does zinc not work in freshwater?
Bigshot posted 10-01-2003 03:45 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
They are both softer than the potmetal outboards are made of so unless they were eaten off, either should work.
lhg posted 10-01-2003 04:51 PM ET (US)     Profile for lhg    
For about 10 years now, Mercury's sacrificial anodes have been a patented aluminum alloy, manufactured by Canada Metals for them. They are much more active than zinc, and protect better, in both salt and fresh water.

I have tried those after-market magnesium anodes for fresh water, and find they are not as good as the Mercury aluminum ones. But for engine brands other than Mercury, I suppose they would be better than OEM zinc in fresh water use.

DaveH posted 10-02-2003 05:00 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Bigshot: I think you mean the zinc anodes are a lower electropotential than the aluminum pot metal in outboards. Hardness has nothing to do with corrosion rates.

Larry: I would be intrested to see what aluminum-based alloy performs better that zinc in salt water. Almost all aluminum
grades that I have data for are a higher electropotential than both zinc and magnesium. The inclusion of aluminum only defeats the protection by raising the value away from anodic.

Also, your friend's S/S propeller wasn't coated with calcium; it was a combination zinc oxide and aluminum oxide. The source was from the engine's anode (assumed to be zinc) and any wetted bare aluminum spots. The current from the battery forced an overpotential in the aluminum engine and greatly increased the flow of electrons. The electrons flowed to the anode on the engine and anywhere else there were wetted dissimilar metals, creating a small circuit. The overpotential is similar to the commercial electroplating of metals.

Wetfoot: The sizing of the anodic protection of your aluminum engine (zincs) is based upon surface area (both the cathode and anode), electrolyte strength, connection method, and electropotential between the metals (how easily they give up electrons relative to each other). By adding a hunk of stainless steel to your engine, you are changinging this calculation. It may not be an issue if you are trailering your boat each time, but if you keep your boat in the water I would look to add an "anodic fish" and bond your engine to it at the dock. You can check the values with a simple multimeter and touching the probes to the anodeic zinc and you engine before and after. Then you can calculate the change in voltage and add enough protection to counteract the effects.

DaveH posted 10-02-2003 05:05 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Sorry about my poor spelling performance.

Wetfoot: I also forgot to mention that if you tilt your engine completely out of the water when not in use, you won't need any added protection, the standard zincs will suffice.

lhg posted 10-02-2003 05:53 PM ET (US)     Profile for lhg    
Dave - Thank for the information on the "coated prop". I know that Yamaha engine is going in for service to find the source of the problem.

As for Mercury's anodes, they advertise that they are a special sacrificial aluminum alloy, probably patented since they are only available under Mercury label, and for Mercury engines, and that they perform 50% better than zinc. I can personally confirm this is true, and they are much lighter weight than zinc. Check them out on an engine, or in a marine parts store. Mercury has not offered zinc anodes for ten years now.

jimh posted 10-02-2003 08:40 PM ET (US)     Profile for jimh  Send Email to jimh     
[I was thinking of changing TOPIC to "Corrosion" as this implies usually some chemical action, but "erosion" can also a result of chemical action-jimh]

There has been some highly publicized trouble with corrosion/erosion in certain lower units that contain large amounts of stainless steel. I believe that the Mercury Bravo III series, which has twin stainless steel propellers and internal stainless steel shafts and gears, has been mentioned as being prone to unusual corrosion. The BOAT-U.S. Organization has been leading a drive to get this problem into the open and get some compensation for owners who have had failures.

From this experience, I believe that having more stainless steel in the water does increase the risk of corrosion of the non-stainless material also immersed nearby. I don't have science behind that, but I just make that conclusion from these other cases.

Sal DiMercurio posted 10-02-2003 11:20 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Jim, it's always been that way with i/os because they can't be lifted out of the water.
All lower units have stainless gears & prop shafts & when left in saltwater, corrosion is inevitable.
Saltwater & aluminum just don't mix if the outdrive is submerged all the time.
Sal
DaveH posted 10-03-2003 10:32 AM ET (US)     Profile for DaveH  Send Email to DaveH     
Larry:

Some alloys can be used as anodes as you mention. They will have a mixture of a very anodic metal like magnesium and mix them with a metal that results in a stronger material. The reason for using these alloys is mainly for the strength of the resulting part. The use of the alloys in Mercury's case would be on mostly "hanging parts" like the "button" anodes of old that offer no structural value. They would screw on to a stud mounted low on the transom housing of sterndrives. The only structural part I recall is the sacrficial trim tab immediately downstream of the prop. I don't remember if they still use these though.

Anyway, a zinc alloy would undergo a dezincification, or rather, the loss of the anodic metal ions in the alloy during the corrosion process. Let me know if you can uncover any additional information from your Mercury sources. I have not kept up to date in the corrosion business and my background info is about 15 years old.

jimh: There's really not much science involved in measuring corrosion rates. I have the formulas and all you need is to learn how to use a multimeter, which I know you do. The challenge is to estimate the surface areas of the parts in question and to know what materials are involved. The rest is an easy formula used to estimate the amount of metal movement (plating layer thickness versus time).

Barney posted 10-03-2003 02:48 PM ET (US)     Profile for Barney  Send Email to Barney     
This is a good article:
http://www.yachtsurvey.com/corrosion_in_marinas.htm Jim
Barney posted 10-03-2003 02:50 PM ET (US)     Profile for Barney  Send Email to Barney     
and this one http://www.yachtsurvey.com/corrosion.htm
DaveH posted 10-04-2003 01:27 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Barney:
I read all the information you posted off the Dave Pasoe site. It is well written and accurate.

One thing I would pay very close attention to is the inferior metal used in the Far Eastern manufactured boats (mostly trawlers). What you see isn't always what you get with regard to the metal as Pascoe briefly points out. There are so many grades of stainless steel, aluminum, and other common metals it would make your head spin. Whenever I have a friend looking buy a boat, ask my opinion on trawlers and why they are so inexpensive, I take them through one inch by inch showing them some of the signs that Pascoe mentions. It is usually enough to educate them and make them more discerning on the boat they look for. Yes, you do get what you pay for in this case.

The use, or rather, misuse of low grade metal has been a plague on us all here in the West due to integration of these products into our bridges, buildings and other critical areas. I sure many oldtimers recall the walkway platform in a Marriott Hotel that collapsed, killing many people about 15 years ago. The cause was traced back to improper markings on Far East manufactured bolts that were used in place of domestic bolts. The Far East bolts were not the grade they pretended to be (they were marked to appear as the stronger, more expensive bolts) and therefore failed-but bygosh, they did save a few dollars going with the lowest bidder.

My job selling industrial equipment sometimes requires certification of the origin of materials in critical cases. You would be hard pressed to find anyone in the USA still operating a foundry and being competitive. The majority of all castings are done in China where the labor is cheap and no one cares about the environment. I really do not feel comfortable with the quality of their workmanship nor do I trust their "Material Certs" to be accurate.

What can you do? Never buy anything labeled as just "stainless steel". If I buy hardware, I ensure that the grade is at least 304 S/S or better yet, 316 S/S. You can readily find it if you look in the right places. Never buy stainless packages (screws bolts, nuts) that are grouped together in a kit. That will ensure the worst grade for boating.

jimh posted 10-04-2003 10:02 PM ET (US)     Profile for jimh  Send Email to jimh     
As far as a remedy for this situation with the Whaler and new SS propeller, look for something awry with a ground connection in the motor. Somehow there is current that is seeking ground and is not getting there via its normal path. A ground return connection of some electrical device may be broken.

One thing that comes to mind is the tilt/trim electrical motor.

--jimh

Barney posted 10-04-2003 10:53 PM ET (US)     Profile for Barney  Send Email to Barney     
jimh, I think that is sum of it. DaveH make a good point also. I have seen "stainless" cabinets rust quickly in salt spray environments. The combination of materials and a small stray current can sneak up on us. Just as a note I emailed Mr. Pascoe a few years ago about a sterndrive problem that I had. He did respond and I appreciate that. Jim
Gene in NC posted 10-14-2003 08:36 PM ET (US)     Profile for Gene in NC  Send Email to Gene in NC     
Have AL corrosion, rust on PT motor, and SS prop on '87 OMC 90 on '87 Montauk, trailered but not religiouly fresh water rinsed or flushed. Probably infrequently washed down or flushed. Lives at my son's house in Wilmington, NC.

The question is, "Where to hookup the meter and what kinds of readings are we looking for?"

DaveH, what point on the engine? Are we looking for some voltage from B+ to the leg or anode?

Barney posted 10-14-2003 09:16 PM ET (US)     Profile for Barney  Send Email to Barney     
Gene, The only thing I can tell you is what Jimh said and the yacht survey info on DC stray current. Please look over the yacht survey info closely. It's hard to find a stray current that is constant and small. Check your wiring closely such as hot wire in a wet bilge. Old wiring and connectors that leak to ground on the engine or other component are suspect. In my case for instance, a boat I once had, not a Whaler, gave me notice that the factory wiring was messed up. When I plugged in a search light to find channel markers one night the plug melted down and the light went out. During the search light use the engine alarm went off. The engine alarm went off when the docking lights were turned on also. Hmmm. All the boat wiring at the console was undergrounded and was feeding back through other hot wires. Adding a ground to the console fixed it. It's unique to each boat. Good luck, Jim
doobee posted 10-14-2003 10:32 PM ET (US)     Profile for doobee  Send Email to doobee     
There is an aftermarket company that sells aluminum anodes now. I believe it is called Performance Metals. At this point they only make anodes for Mercs. There is a red ball molded into the anode. When the red ball is visible you know it's time for a new anode.
lhg posted 10-15-2003 02:37 PM ET (US)     Profile for lhg    
Since Mercury holds patents on their aluminum anode alloy, I would assume that this manufacturer is working under license from Mercury, hence only Mercury engine availability.

This would probably be similar to the situation with the Mercury interchangeable prop hub, now being offered by Michigan Wheel also.

Gene in NC posted 10-15-2003 07:31 PM ET (US)     Profile for Gene in NC  Send Email to Gene in NC     
Re stainless shafts, it is not the mass but the surface area exposed. Surface area of the prop is many times the exposed area of the shafts which changes that dynamic drastically. Additional consideration may be aftermarket props with SS alloys quite different from factory parts.
Gene in NC posted 10-18-2003 05:45 AM ET (US)     Profile for Gene in NC  Send Email to Gene in NC     
'87 OMC 90 w ss prop and excessive corrosion. Probable source of "stray current" found. Power head had been rebuilt. Wiring harness was rubbing on metal in port side head gasket. Unintenionally shifted harness woking on another section of it. Smoke! The abraded wire turned out to be B+. Assume minimal current current flow thru head gasket before my "assisted" dead short condition sent up smoke signal.
DaveH posted 10-20-2003 10:37 AM ET (US)     Profile for DaveH  Send Email to DaveH     
Gene:

Sorry I didn't see your post asking about how to look for problems with a multimeter. I have posted a link to a Boat US Tech area which details how to use the meter:

http://www.boatus.com/boattech/MarineCorrosion.htm

jimh posted 10-21-2003 08:15 AM ET (US)     Profile for jimh  Send Email to jimh     
On the boat the LHG mentions above (where a new stainless steel propeller was severely corroded after just a couple of days in fresh water), the cause was found to be electrical.

The 12-volt lead at a console cigarette lighter plug was in contact with the steering helm. Current was flowing back to the engine (apparently along the steering cables) and seeking a return to ground through the engine. The engine mount does have some metal-to-metal connections to the power head, but there are generally well lubricated with grease and may not be perfect electrical conductors.

The current flow was initially high enough that it burned off the small gauge wires which interconnect the engine mounting hardware to the main portion of the engine. (These wires are there precisely to maintain the engine's various parts at the same electrical potential in order to suppress corrosion.) This had the effect of isolating some of the engine assembly from good, direct contact with the battery negative.
(The battery negative is generally bonded with a large gauge wire directly to the power head near the starter motor.)

The net effect was to cause current to leak into the lower unit and seek a return via the water, causing the rapid corrosion of the propeller.

Fortunately, this unusual corrosion was promptly noticed, and the situation investigated before more significant damage could be done.

DaveH posted 10-21-2003 09:33 AM ET (US)     Profile for DaveH  Send Email to DaveH     
JimH:

Correction to your statement: The S/S propeller would never corrode when attached to aluminum, it was the cathode in this case. The action was actually plating or addition of a metal coating from either the sacrificial anode and/or the aluminum lower unit.

The action is always electrical. The question is whether it is from within (poor DC wiring or leaked A/C from shore power converter) or supplied from other surrounding boats or dockside shore power. See my post just below Larry's for more info.

BQUICK posted 10-21-2003 11:41 AM ET (US)     Profile for BQUICK  Send Email to BQUICK     
I get lots of white speckles on my lower unit when I have my stainless or bronze prop on but very little when the aluminum is on.

Bruce

DaveH posted 10-21-2003 01:00 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Bquick:
Hearing your description of your lower unit having white spots is probably caused by small pits or breaks in the paint of the lower unit. The unpainted spots are unprotected to increased corrosion rates since they provide a much smaller surface area compared to the protected (painted) lower unit areas. That means all to electrical current is flowing out of a very small area. (Think of high pressure water erosion through a very small hole in a dam as a visual example)

The white spots are actually caused by the creation of Aluminum oxide which are actually like a skeleton of the former alloy but larger. The oxides will seem like very fine grains of salt.

The reason that your propeller choice affects the growth of these spots is that the aluminum prop is of similar electropotential and would prevent any increased "spot" corrosion. The S/S and bronze are more noble (cathodic) to your aluminum lower unit and there for provide the electropotential (driving electrical force).

I would seriously look for problems with your set up. Some things to look for are:

* Is your sacrificial anode the right material for your area?
* Is the connection between the sacrificial anode clean and providing a good electrical contact?
* Have you ever serviced all your bond wires connections?
* Inspect all your wiring (as jimh explained, it can lead all the way to your dash accessories)

lhg posted 10-21-2003 03:05 PM ET (US)     Profile for lhg    
Regarding Dave's comment on the electrical short delivering 12 volts into the water, having seen the prop, I can say that it was indeed being COATED with a light gray zinc or other material. It took many applications of Lime-Away to disolve it off the surface. And I know Lime-Away will damage a galvanized (zinc) trailer frame.

Underneath this build-up, the shiny prop surface was still there. So the Electro-Depostion Process analysis makes some sense to me, with the zinc anodes of the engine providing the source, and protecting the aluminum engine parts.

But what Jim has said makes sense also, as the lower (in the water) engine bolt nuts and washers were all showing rust and beginning to corrode.

Dave, am I correct that by charging the SS prop positive by this current short, it was attracting particles from the sacrificial zinc, thereby coating the prop?

DaveH posted 10-22-2003 04:04 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Larry:

The S/S prop being more noble, acts to draw electrons from the less noble aluminum, unless there is a better source such as the sacrificial zinc.

Energy will always follow the path of least resistance. The energy between the metals is trying to come to a state of equilibrium (no exchange of electrons). The zinc offers up its electrons easier (least noble) than the aluminum and therefore will deteriorate (corrode) in place of the aluminum.

That is why good electrical contact and proper surface area are most important when sizing zincs. If you don't have good contact with the metal you are protecting, both metals (aluminum and zinc) will corrode, but at different rates.

The addition of an electrical short (impressed charge) on the aluminum only "turbo-charged" the reaction by increasing the rate of electron flow. When used in a metal plating factory, electricity is used to speed up the bath plating rate onto the parts immersed in the bath.

BQUICK posted 10-24-2003 03:12 PM ET (US)     Profile for BQUICK  Send Email to BQUICK     
Thanks Dave. Great explanation.

It's a manual start motor so no battery on board.
Even if I leave the motor down so the zinc in in the water it does it.

question: does the zinc only work if is submerged in the water or does it still provide some benefit?

Bruce

DaveH posted 10-25-2003 12:17 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Bruce:

Do your zincs work to protect the aluminum engine when not immersed in water? No, they do not. You need an electrolyte (salt water in this case) to allow the passage of electrons to ions in the water. The David Pascoe article referenced in the beginning of the thread is a well written and clear explanation of how this works.

Back to your problem, if there is no battery on your boat,then the corrosion can be accelerated by leaking charges from the dock power or other boats in the vicinity. Talk to a few people in your dock area and ask if they have problems with zincs that area completely gone by the end of the season or if they have polarity problems from their shore power. If so, alert the dockmaster and see if they can isolate this. To help protect your engine, I would repaint your lower unit according to the manufacturer's guidelines.

lhg posted 10-31-2003 02:47 PM ET (US)     Profile for lhg    
For those metalurgists that frequent this site, I just read that the sacrifical anodes used on all Mercury outboards and I/o's since 1994 are an alloy of indium and aluminum, and that they perform at least 20% better than zinc. I have noticed they are lighter in weight than zinc, also. Mercury claims to have a patent on this item.
DaveH posted 11-03-2003 09:00 AM ET (US)     Profile for DaveH  Send Email to DaveH     
Larry:

There must be something else in there since Indium is more cathodic than many alloys of aluminum:

http://corrosion-doctors.org/Aircraft/galvseri-table.htm

It doesn't make economic sense to me since zinc is so cheap and readily available. I'm sure you'll find out the mystery metal ;-).

BQUICK posted 11-03-2003 03:22 PM ET (US)     Profile for BQUICK  Send Email to BQUICK     
Dave, it's on a mooring nowhere near any other boats.
Gotta be electrolysis from disimilar metals alone (w/o battery) right?

Bruce

DaveH posted 11-03-2003 03:49 PM ET (US)     Profile for DaveH  Send Email to DaveH     
Bruce:

Based upon the information you provided, there does not seem to be any other driving factor other than dissimilar metals.

The only other forces I can think of:
* Insulation on the engine wiring is bad.
* Zinc connection is poor.
* There's an electrical cable under the water nearby. (Is your mooring all steel chain or cable?).

Give me some more info if possible.

sr posted 07-10-2005 09:43 PM ET (US)     Profile for sr  Send Email to sr     
I read with interest on the interaction of ss with the electric charge.
I have noticed that a lot of times the ss bolts that hold on the sac. anode are white corroded and this is what causes broken bolts.
Is ss the best fastner?
Would a coating of dielectric grease assist with electron transfer and stave off corrosion?
seahorse posted 07-11-2005 07:27 AM ET (US)     Profile for seahorse  Send Email to seahorse     
Years ago Mercury came out with a toothed washer that completed the circuit between a stainless steel prop and the propshaft, which in turn is at the same potential as the gearcase.

They even had a bulletin on it since so many folks didn't use it or did not know about it.

where2 posted 07-11-2005 08:40 PM ET (US)     Profile for where2  Send Email to where2     
As for how to measure the electrical potential, once upon a time I recall seeing ShipShapeTV do an episode where they used a 5 gallon bucket full of "local" water in order to do an analysis of the need for a Zinc or a Magnesium anode. For measurement, they had test leads attached to a piece of material that they tossed into the bucket. They then proceeded to toss in some typical engine parts.

Anyone else remember that episode? I cannot seem to find a link on the ShipShapeTV website to ask a question.

sr posted 07-12-2005 10:30 PM ET (US)     Profile for sr  Send Email to sr     
I've got a couple more questions. On my 'zincs" I'm pretty sure one is zinc (bar) and one aluminum (tiller).
BOth are eroded and there is the classic white corrosion (aluminum casting?) there the bolt passes thru or is threaded into the housing.
Is there a problem with mizing zincs? Should /would dielectric grease stop the white formations?
This pertains to a 100hp merc on a montauk.
DaveH posted 07-13-2005 10:26 AM ET (US)     Profile for DaveH  Send Email to DaveH     
SR:
I'm not sure I understand your question properly but I'll try. I would not use dielectric grease on the zinc to engine contact. The white formation may indicate that your contact bonds are not clean or connected well. Wirebrush all anode connecting studs and properly paint all engine parts exposed to water. Do not paint the zinc anodes, contact area or studs that bond the zincs in place.

With regard to zinc anode size, larger surface area is definitely better than smaller however, the rate of corrosion, or loss of zinc, should give you an easy indicator of problems. A properly sized zinc shold last you a full season (4-5 months of constant immersion). If your loss rate exceeds that, you may have an electrical problem on your boat or in the water around your boat.

sr posted 07-14-2005 12:40 AM ET (US)     Profile for sr  Send Email to sr     
Sorry for the typos, I had too much sun yeaterday.
COntact bonds? As these the braided wire jumpers? I seem to get white powder in some, not all of where the ss bolts go into aluminum near splash areas. I thought iw was just salt water interaction? I thought of using dielectric grease on the threads of the ss bolts that go into the aluminum casting of the lower unit, and tilt/trim. Is this a good idea? All the engine parts *seem* to be painted priperly. I do not have white stuff seeping thrugh painted areas, only in the concealed thread areas.
My zincs are not eroded bad, and have just ordered all new aluminum ones. I believe all the zincs are original on this 91 (350 hours) trailered boat, never stored in water. Can/should a zinc or magnesium be installed alongside an aluminum anode (mix or match?).
I am really hoping I don't have an electric issue going on.
Batterys last, I catch fish, but it's the white powder in the threads that has me wondering. COuld it be from my salt water use? I always flush/rinse, but never r&r bolts and such.
DaveH posted 07-14-2005 03:19 PM ET (US)     Profile for DaveH  Send Email to DaveH     
SR:
Email me a few pictures detailing what you are asking. I do not want to give you bad information. Put "corrosion" in the subject line so I do not zap it.
d.han@earthlink.net

Remember, the sacrificial anodes only perform their function when immersed in water. They do not do anything when stored on a trailer. If you have wire contacts with white powder on the crimped ends or soldered joints, cut them out and replace them with clean connectors. You may use the same existing wire if the insulation is intact.

sr posted 07-16-2005 01:34 AM ET (US)     Profile for sr  Send Email to sr     
I am happy to report that DaveH looked over my pics and roported wth am I worried about.
It seems the white powder on the threads of the boltes is expected corrosion of the lower unit alloys. A brass brushing and reassembly is in order.
Now, has anyone used dielectric grease on the zinc threads?

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