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Sterndrives Galvanic Corrosion

Volvo Penta sterndrive units are equipped with zinc anodes to provide protection against galvanic corrosion. These zincs are sacrificial (in nature) and are designed to erode away, thus protecting the transom shield and drive units. In order for these zincs to be highly protective the following must be observed.

Never paint zincs.

When replacing zincs, make sure mounting surfaces are thoroughly cleaned. Tighten zincs ensuring a good contact to the drive and/or transom shield.

Zincs must be inspected every 14 days and replaced when 50% eroded.

Zincs on boats out of water for any period of time may develop a coating that makes it inactive. Sand zincs with coarse emery cloth or sandpaper to remove oxidation. Wire brush should not be used as metal residue will be left on the zinc.

Maintain the sterndrive and transom shield paint finish. Prime and paint all nicks and scratches. Use only genuine Volvo Penta sterndrive paint or equivalent. Copper base paint must not be used on sterndrive and transom shields. EPA certified anti-fouling coating, such as Classic Yacht Outdrive Anti-foulant are available for sterndrive use.

When copper base paint is used on the hull, there must be a 1" border between the paint and transom shield and any through hull fittings that are grounded. The 1 " strip should be painted with a non-metallic epoxy paint to prevent osmosis. This area should be cleaned manually.

Use only genuine Volvo Penta zincs. Some after market zincs may not meet mil-specs and are larger in size. Using larger prop zincs may cause a cavitation bubbles leading to propeller erosion. Numerous cases of non warrantable corrosion have resulted from using less expensive zincs that give inadequate protection.

When installing stainless steel props, make sure an extra bar zinc is added to the transom shield. See Service Bulletin 46-1, No. 12. (290 models only).

When replacing trim cylinder hoses on 290 transom shields, bonding kit (P/N 854625-1 ) must be installed.

For drives used only in fresh water a magnesium anode should be used. See Parts Bulletin 62-922. On SX and DP S use 3855610-6 for TSK and 3855412-7 for sterndrives.

To prevent reverse polarity from neighboring boats and when AC power is used, a ground isolator should be installed on the green ground wire as it first enters the boat. See diagram.

See Volvo Penta Publication P/N 7733534-7 Marine Electrical Systems for detailed information on electrochemical corrosion.
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