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tpkas · 16-01-2020, 13:31

After some advice please.

The plan was to slip, possibly replace the saildrive hull seals and antifoul in about 5 months time however while removing some growth from the Volvo saildrives recently I realised that some of the antifouling was coming detached from the saildrive leaving some aluminium exposed. The zinc anodes are in excellent condition. The boat is exposed to fairly warm salt water. The props are s/steel and painted with prop speed.

I am trying to avoid slipping immediately (locally) and then again in only 5 months as I plan to have the saildrive hull seals done in a significantly larger boatyard with much better facilities several hundred miles away.

In your opinion are the exposed areas of saildrive likely to suffer from significant damage from corrosion in only 5 months?

Brian

**tkeithlu** · 16-01-2020, 13:41

Brian, a great tool is a silver electrode. You hang it over the side, connect your multimeter between it and the bonding, and if you've got 1.0 volts, your anodes are protecting everything below the waterline. They cost about $125, and are great peace of mind.

**tkeithlu** · 16-01-2020, 13:45

Here's one for $130. I think it's the one I use.

https://www.boatzincs.com/corrosion-...electrode.html

Dulcesuenos · 16-01-2020, 16:22

We sand our saildrive to bare aluminum and prop speed them,,, last round was eastern and then western Caribbean, no growth, a few bare spots, no corrosion.. I wouldn't worry,
And id use prop speed on the drives as well!

billknny · 16-01-2020, 16:37

Bottom paint will do very little or nothing to prevent corrosion on aluminum saildrives, and if the wrong paint is used, will accelerate it. Copper and Aluminum do NOT play well together in salt water. Is the bottom paint you used compatible with aluminum?

Also, saildrives are very susceptible to stray current corrosion. They can be totally destroyed in WEEKS not months if enough electrons are going the wrong way. The first symptom of this can be blowing off the paint.

boatbroke · 21-01-2020, 00:37

Hi Brian,

I think you are concerned about the bare aluminium exposed to the water and excess corrosion because of this?

Shouldn't be a problem, I'd say you'll have a nice friendly barnacle looking after that spot for you next time you go down!

If you were having paint blowing off previously then there may be an electrolysis issue, but paint on anything metal under the water never wants to stay there as well as glass/timber.

Often because sail drives are odd shapes they don t get the surface prep they should and hence paints wont stick as well as they should too.

If it is corroding, you will see black pitting. Next time to give it a rub, Scotch-brite the area and the aluminium will go shinny and if there is serious corrosion it will be obvious.

Highly doubt it will be an issue, especially if you've got an eye on it.

Good luck with it!

tpkas · 21-01-2020, 22:38

Thank you all for your replies.

Since I'm not in an area with high stray electrical current and I've never had corrosion issues before (when I had aluminium props) I think I'll rely on the "friendly barnacle" protection plan but will keep a close eye on it.

Regards to all,

Brian