Drive Corrosion
 

This past summer our Alpha 1 went from a few pitted spots to corroding in a few large places. The boat was in the water the whole summer, not taken to any other lakes, wasnt pulled for cleaning either. Does anyone know why a drive would suddenly start to corrode? Any things to prevent further corrosion?

Thanks,
Tommy

If you are going to leave it in the water again they sell anodes you can hang over the side to help with it. sail boaters use them.

One year I changed prop, from one stainless to another one, and forgot the continuity washer. That season the drive got more corroded than the previous ten years all together.

The Mercathode is an active electronic galvanic inhibitor. It only functions properly when the battery is connected to the system. Some people install a battery switch on their boats to prevent discharge by accessory loads and to prevent fire hazard. If you do this, be sure to connect the Mercathode to the battery on the HOT side of the switch so it stays "on".

Secondly, the Mercathode parts and the normal sacrificial anodes on the drive will need occasional maintenance. Inspection will reveal whether the anodes are corroded badly enough to replace them but inspection alone will not ensure that the galvanic bonding is intact on them (the "electrical connection to the drive"). They need removed, and the mounting point needs cleaned and the anode needs cleaned so it "bonds" properly to the aluminum.

Also, freshwater works best with magnesium anodes. Saltwater works best with aluminum anodes. The old Zinc ones are a balance between the two, but you need to use the correct ones for your water.

Chances are, your anodes have lost their bond to the drive and corrosion has been free to eat it up.

Another note: if you keep the boat at a dock or marina with 120volt service, then the grounding or polarity of the AC system of the dock could be faulty. Especially if there is a boat near yours that is "plugged in" to dock power.

We had a houseboat in 1967 that we sold to a guy who kept it at a marina. When we sold it, he pulled it out for inspection, and the outdrive (a Chrysler) looked fine. Two years later, he started the boat to pull out of his slip and it made horrible noises. He walked to the rear and the water was covered with a rainbow oil slick. The outdrive had fallen OFF the boat from galvanic corrosion (he had plugged into a reversed-polarity AC circuit with no ground for 2 years).

Do you have any ideas where these anodes are?

Torque tab (on the bottom of the cav plate)
2 dome shaped ones on the lower transom bracket bolts.
one clamped onto each trim cylinder ram.
One across the bottom of the gimbal plate.

They'll be the only intentionally unpainted parts that aren't stainless.

electroyalis(SPELLING?)
 

MCOLLINSTN, You are right ,you should see how this eats away on a stainless prop it unbeliavable how it just eats the prop away and on aluminum or brass it is in some cases impossible to weld .we have saw stainless props with holes completly thru the blade because of this.:( outdrives that stay in the water all the time should be pulled off and stripped to the raw material and fill the cavaities with aluminum putty or fiberglass resin and sanded smooth again, repainted using zinc chromate primer ,then primed again and painted to match, on a yearly basis or you will be buying a new out drive every couple of years or so. Darin

Check out this site ,under the link to "Bravo corrosion issue"http://www.sterndrives.com/supplies/mainsupplies.html

mcollinstn

Where is this box of wires in the mercathode thingey? is that the un painted box on the back of the transom/bottom of the drive?

Cuda and I both need new zincs for our Kaama drives. Anybody know where to get em?

Doc

Hyper, mine stays in all summer too. Every year I had to repaint my drives. Switched to Magnesium anodes last year and the drives came out looking like they went in. But, I also moved my boat to a different slip because I had a lot of older wooden and steel boats around me before and a boat near you with a bad ground system can damage your drives too. Switch to the magnesium anodes. Check your shorepower ground isolator if you stay on shorepower.

formula31 you switched to mag. zincs because you were using alum. in fresh water ?

was using zinc. didnt know any better, yea, fresh water. lake erie

tommy

the mercathode will have the "control unit" in a box clearly marked mercathode. It is usually mounted near but not on the motor. It goes to the piece bolted on the bottom of the transom bracket.

On some boats it was an option, not standard.