Zinc Fish

[Lojanica]

Hi All,

Everyone is helpful so I'd thought I'd throw this out there.

My new dock space seems to be hot. Zincs on the prop and prop shaft are being taken much faster than before. The problem appears to be other docks which are wired and which I doubt I'll be able to sway their owners to fix said problem. Having said that I ordered a "zinc fish" so the collars on the prop and shaft will last longer. Any good way to attach to shaft. The current set-up is an alligator clip which isn't long enough to clamp to the shaft.

Thanks and any input is appreciated. "Boats---it's always something isn't it!!!"

[tkeithlu]

Assumedly your shaft is already part of your bonding that connects engine, rudder, DC ground and the like. Make a good connection to any part of that system, for example cutting off the alligator clip, crimping on a ring connector, and putting it under an engine bolt or battery ground. If your boat is not totally bonded together, then that's a problem in its own right. Check your bonding with some long test leads and your ohm meter to various components in the system, looking for near zero ohms.

[Jim Cate]

And when that fish has been eaten up, instead of buying another one, wander about in any boatyard and have a look for discarded anodes. Lots of folks replace them when they are less than half gone, and the big slab types from larger power boats contain a lot of zinc.

of course, these are not as clever looking as a fish...

Jim

[Lojanica]

Great tips Thanks

[tkeithlu]

I guess I'm the exception to Jim's rule. I take my 14 flat aluminum anode plates off each year and wire brush them. No point in throwing them away when there is bare aluminum surface still available. Not even bare metal on my steel boat rusts below the waterline.

[Jim Cate]

Originally Posted by tkeithlu

I guess I'm the exception to Jim's rule. I take my 14 flat aluminum anode plates off each year and wire brush them. No point in throwing them away when there is bare aluminum surface still available. Not even bare metal on my steel boat rusts below the waterline.

Not a rule at all, but having hung around in boat yards for decades, I've seen a lot of discarded anodes that had lots of zinc left in them. For folks with big, expensive boats, and who hire work done in the yard, the cost of preemptive replacement is a good value. For us dumpster divers, it is good, too!

I remember seeing an article in the Brit mag Practical Boat Owner advocating melting such scrap anodes down and recasting them to fit your own usage. that's a bit OOT for most of us, but for something to hang over the side on a wire, recycling makes good sense!

jim

[fstbttms]

Originally Posted by tkeithlu

I guess I'm the exception to Jim's rule. I take my 14 flat aluminum anode plates off each year and wire brush them. No point in throwing them away when there is bare aluminum surface still available. Not even bare metal on my steel boat rusts below the waterline.

Anodes do not prevent rust.

[captain58sailin]

You might take a look on your dock for wires touching the water.

[tkeithlu]

OK, time for me to learn something. What do anodes do? Why does my boat not rust under the waterline but does above?

[Scatterling]

Originally Posted by tkeithlu

OK, time for me to learn something. What do anodes do? Why does my boat not rust under the waterline but does above?

An anode has higher electropotential that the metal you're protecting (less noble). This causes the anode to corrode preferentially when the metals are in contact in an electrolyte and the electron flow is started.

Oxygen is the key component in corrosion (oxidation). If you can eliminate oxygen (done mechanically and chemically in boiler feedwater preparation), you minimize corrosion. There is less oxygen in water than at the water/air interface, so less corrosion below the waterline.

I hope this helps.

[fstbttms]

Sacrificial anodes help combat a variety of types of electrochemical corrosion; chief among them are galvanic and electrolytic corrosion (and don't call it "electrolysis," for God's sake.) An anode attached to an underwater metal part will corrode before the part to which it is attached does, by dint of being lower on the galvanic scale, thereby "sacrificing" itself to protect the more noble metal (typically bronze or stainless steel.)

Rust is not a form of electrochemical corrosion.

[captain58sailin]

Rust is a form of oxidization.

[tkeithlu]

I see the point, with some help from my chemist spouse. What I should say is that I'm not losing iron - nothing is dissolving under water, except for the anodes, which are pitting badly and need wire brushing each year. I maintain better than -1.0 volts between the test electrode and the hull.

Jim - "rule" was too strong a word - I completely agree with your advice.

[Lojanica]

So here's what I did. Bond a lead to the shaft engine and run to cockpit where a zinc can be hung. Will keep the underwater zincs closely monitored. Hoping the fish will spare the underwater zincs. Will start scavenging zincs at boatyards to add to the "fish pile."

Thanks.

[a64pilot]

It will make the other zincs last longer.
Primary use for my fish is of course I look at it everytime I use the boat, so if it starts getting eaten away I know I have a problem hopefully before I lose my $4,500 prop.

Many years ago I was a welder, and if I remember right zinc gives off a dangerous gas when welded, and maybe when melted?