Anodes

Philip Hodson · 28 January 2020, 09:18

Which are the best for salt water zinc or aluminium anodes
on a Bravo leg berthed in a marina ?

paintman · 28 January 2020, 10:23

Usual recommendation is:
Fresh water use magnesium
Salt water use zinc or aluminium
Brackish use aluminium

GuyC · 28 January 2020, 11:14

I'd suggest zinc. It's slightly more anodic than aluminium and you want the anode to protect the aluminium parts of your stern drive.

A quick Google and M G Duff suggest zinc as well.

https://mgduff.co.uk/find-your-anode...e-anode-search

beamishken · 28 January 2020, 11:20

Mercruiser used to use zinc but it was found to erode too quickly so switched to aluminium which lasts longer but still protects the drive.
Beware bravo anodes don't last long so keep an eye on them your lucky if they last a full season

Davie · 28 January 2020, 11:33

Have a look at mercruiser's own mercathode system.

mikehhogg · 28 January 2020, 16:41

There is a zinc alloy for the type of material used in the sterndrives\outboards etc when used in sea water. There is however a bigger problem and that's the Marina Wiring and the boat near you,badly wired boats with chargers and heaters and dehumidifiers etc can all cause problems. If you fit the correct anodes and find that they are being sacrificed quickly Move to another spot in the marina if possible. I just sold a Degroot all aluminium striker . Built in 1963 in the Netherlands there was a little sign in the galley that read "stay as far away from other boaters as is possible" All previous owners kept it on a swing mooring as it couldn't dry out due to unprotected props,As did I. The proof being no corrosion over fifty years later. There is a lot of conflicting information out there.

Philip Hodson · 02 February 2020, 09:24

Thanks guys,
it'll be zink then.

beamishken · 02 February 2020, 16:12

Quote:

Originally Posted by Philip Hodson

Thanks guys,
it'll be zink then.

Why would you pick zinc? mercruiser changed to aluminium several years ago because bravos were rotting away because zinc didnt last long enough

Philip Hodson · 02 February 2020, 16:59

Get you point Ken but the rib will be in the water for only 6 months

mikehhogg · 02 February 2020, 17:04

BEAMISHKEN . I hope I get this right. aluminium anodes are preferred by yachts and boats with ss steel \ bronze shafts or magnesium bronze props. they are also cheaper. aluminium being the better sarcrificer or more noble that the metals mentioned. A stern drive is ultimately made from aluminium so using aluminium anodes will ultimately result in some loss of material.Zinc is at the bottom of the nobility scale so zinc and its alloys are still a better bet than aluminium on a sterndrive. Graphite is at the top end of the scale so never use graphite grease in a marine environment. Zincs will oxidise in fresh or brackish water and will become useless until cleaned,another reason to use aluminium if moving from fresh to brackish to salt water. its a bit of a science, anodes are useless if not electrically connected to the material being protected,never paint them and so on. Going back to my original post anodes serve a function in protecting against galvanic corrosion but a sterndrive could loose a lot of its metal moored next to a boat connected to shore power that has poor wiring.

GuyC · 02 February 2020, 20:31

It's interesting as they do suggest aluminium anodes for stern drives which is counter intuitive to me. I think I'd accept greater loss of anode and go down the route of zinc.

mikehhogg · 02 February 2020, 20:39

GUYC . if they are suggesting aluminium then they may be aware of the true composition of the material in the stern drive or they think its a safer bet than a zinc being rendered useless by freshwater.

beamishken · 03 February 2020, 13:18

Quote:

Originally Posted by Philip Hodson

Get you point Ken but the rib will be in the water for only 6 months

My boat has been in a marina this year instead of on a mooring from July to January and all the aluminium anodes are totaly gone, you may struggle to get 6 months out of zinc. I've had them eroded totaly in 6 weeks before it depends on the location.
I'm sure mercruiser as the manufacturers of the drives know what they are doing by recommending aluminium. Presumably it is a less noble grade of aluminium than the drives are manufactured from.

mikehhogg · 03 February 2020, 15:46

Ken the problem may be the Marina.

beamishken · 03 February 2020, 15:57

Quote:

Originally Posted by mikehhogg

Ken the problem may be the Marina.

Yes marinas often are the problem or even a neighbouring boat. However as mercruiser recommends aluminium which lasts longer but still protects, aluminium would be the sensible choice
I'm sure mercruiser are the experts in this.

mikehhogg · 03 February 2020, 16:13

Science aside I have a mate who hates parting with money. He goes around the marinas gathering old anodes, he has no idea what their composition is ,he melts the lot and casts a block around a stainless steel wire . attaches that to the sterndrive and throws it over the side. Never had a problem with corrosion but forgot to take it back into the boat a few times. what is it they say "whatever floats your ship" or sinks your boat lol

GuyC · 03 February 2020, 16:59

Quote:

Originally Posted by beamishken

Yes marinas often are the problem or even a neighbouring boat. However as mercruiser recommends aluminium which lasts longer but still protects, aluminium would be the sensible choice
I'm sure mercruiser are the experts in this.

They also sell replacement sterndrives!

I'm not suggesting that I'm more of an expert than Mercruiser but when the OP originally asked, my immediate thought was zinc and this was backed up by the info on the M G Duff website.

https://mgduff.co.uk/yachts-and-powe...c/cmbravo3kitz

M G Duff are anode experts and maybe they are hedging their bets by recommending zinc safe in the knowledge it will protect the sterndrive at the expense of a few more anodes, which obviously they sell and make money from.

beamishken · 03 February 2020, 18:28

Quote:

Originally Posted by GuyC

They also sell replacement sterndrives!

I'm not suggesting that I'm more of an expert than Mercruiser but when the OP originally asked, my immediate thought was zinc and this was backed up by the info on the M G Duff website.

https://mgduff.co.uk/yachts-and-powe...c/cmbravo3kitz

M G Duff are anode experts and maybe they are hedging their bets by recommending zinc safe in the knowledge it will protect the sterndrive at the expense of a few more anodes, which obviously they sell and make money from.

Several years ago mercruiser were faced in the us with a class action lawsuit regarding corrosion on bravo drives, it was after that they switched to aluminium anodes.
If you search mgduff international online http://mgduff.co.uk/find-your-anode/...e-anode-search
They dont make an aluminium anode for the bravo range and only a very limited range of zincs & only list the bravo3 2003 onwards.
Whilst mgduff are a respected anode supplier personally I'd rather go with what the manufacturers recommend. My experience is that aluminium anodes protect my drives & last longer than zinc. But I do know once either anodes are totally depleted that the drives aren't long in starting to fizz away themselves particularly bravo 3s with the big stainless props. If stainless wasn't the only props available I'd actually prefer ally props

Poly · 04 February 2020, 06:54

Quote:

Originally Posted by mikehhogg

...I hope I get this right... ... aluminium being the better sarcrificer or more noble that the metals mentioned. ...A stern drive is ultimately made from aluminium so using aluminium anodes will ultimately result in some loss of material...
...Graphite is at the top end of the scale so never use graphite grease in a marine environment. ...its a bit of a science, anodes are useless if not electrically connected to the material being protected,... sterndrive could loose a lot of its metal moored next to a boat connected to shore power that has poor wiring.

Mmm.

It can’t be both more noble and a better “sacrificer”!

The drive is not made from pure Aluminum (and potentially neither are the anodes!); pure Al is a very soft metal and pretty much useless for engineering.

There are speciality marine greases around that do contain graphite... I think to understand why that is less of an issue than you imagine you would need to look into the detail rather than just the scale - but using gold on boats is also not intrinsically bad!

The risks from neighbouring shore power issues are often overstated for classic rib use - because most of us don’t leave our boat connected to shore power so don’t have the electrical connection for the other half of the circuit.

MY ADVICE would be if you have a mercuriser system, then there is a highly respected marine outboard/outdrive engineer in this thread who provided a one line suggestion. He’s probably seen more mercuriser corrosion than everyone else on this forum combined - so I’d look at his suggestion!

beamishken · 04 February 2020, 14:52

Even running mercathodes as Davie suggested once the anodes are eroded the corrosion starts on the drive