Replacing zincs on a saildrive

Volvo developed the saildrive more than 20 years ago. It’s a very versatile design insofar as it allows naval architects more freedom in engine placement because there aren’t any shaft considerations. It’s also aligned horizontally so the prop thrust is more efficient than an angled shaft that’s most common in contemporary designs. Some of the many marques that have saildrives are Swan, Baltic, Wauquiez, Dufour, and many multihull builders. One of the features of the saildrive is that it has, until recently, a one piece ring zinc anode that was installed with the drive shaft through the center of the zinc. This design necessitated the removal of the propeller to install the zinc. With a fixed or a simple folding prop, removal wasn’t a big consideration.

With the introduction of the Max-Prop, which had better reverse power than folding props, zinc servicing became a more involved operation. Divers, justifiably, charged large sums for changing zincs because the prop needed to be disassembled and reassembled carefully for it to work properly. This is a hard enough task on land, let alone underwater.

When I purchased a Max-Prop I was told to just cut the zinc in half and screw them into the saildrive. That was tried with little success. The engine vibration eventually loosened the screws and the zincs would fall off. Our boat Andiamo was in the northwest where one needed to be a hearty soul to dive. So, my wife Lisa and I would have a “haul and hang” in the boatyard which gave us about an hour to change the ring zinc. We became proficient at removing the Max-Prop, changing the zinc, and reinstalling the Max-Prop. This was about 25 percent less expensive than hiring a diver. About five years ago, we sailed south to the warmer climates of Mexico and changing the zinc myself became an attractive option.

I started experimenting with the zinc installation. My first attempt was to cross drill and tap the zinc on the horizontal centerline. Then I’d cut the zinc through the holes. The zinc was then installed and 5/16” set screws were inserted into the holes to stabilize the zincs. This was a very attractive solution, but vibration still won and the zincs fell out.

The next attempt was cutting and cross drilling the zinc and tying the two halves together with nylon wire ties. This secured the zincs, but didn’t hold them close and tight to the saildrive as required. Then I tied more nylon wire ties from the zinc around the saildrive through the water intake holes. That worked, but it was very messy looking.

Though all this experimentation, I keep looking at the flange on the saildrive wondering if I could utilize that somehow to secure the zinc neatly and simply. I finally found the courage to drill the saildrive flange to provide an anchor point for the zinc. I had noticed that the top half of the zinc eroded much more than the bottom half. I made a template for drilling both the saildrive flange and the ring zinc. This template was also used to cut the zinc. The zinc is cut so the two pieces are different sizes; the larger one is mounted on top and the smaller on the bottom. This allows enough room for the ring zinc to go around the drive shaft while providing a little more sacrificial mass where it seems to do the most good. The zinc pieces are both drilled with a couple of holes and the holes are painted with fingernail polish to prevent corrosion at the tie points. The pieces are installed with the wire tie locks hidden inside the ring for a clean, secure installation.

The zincs now are easily changed underwater with just a screw driver, pliers for tightening the wire ties and dykes (cutting pliers) for trimming them. I just put everything in a plastic bucket, fire up the hooka rig, and hang the bucket bail on the prop. That way, whatever I drop goes into the bucket!

By Ocean Navigator