What now skipper - anode trouble

Im not the only one thinking along these lines /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif


""1) Has any metallic debris been left on the marina seabed underneath your boat. This can cause severe problems.""


/forums/images/graemlins/smirk.gif /forums/images/graemlins/smirk.gif
 
I've heard of boats that have suffered badly by being unlucky enough to be moored over lumps of iron and having major problems, which suddenly stopped when the boats were moved to other parts of the marina they were in.
Another thing I've seen is on a new sportsboat with outdrives was the bonding straps fitted incorrectly and so the first time the legs were lowered the thin bonding straps broke and their protection was lost. By pure chance it was spotted just before the boat was launched.
If I was lucky enough to have the sort of dough to own a boat like that I'd definitely have an isolating transformer on it.
 
Hugo

When I first located my boat a Swanwick marina I was horrified to find that my anodes where all gone in just three months, so I did some research..

Workout what kind of water your boat is sitting in, no I am serious! Sea water is 35 parts per thousand (ppt) salt, and the water at Swanwick marina is nearer 18 PPT. Pure fresh water is <0.5 PPT, and the definition of Brackish water is between 0.5 and 35 PPT use a Hydrometer to test this.

Now make the correct Anode selection, Magnesium for fresh, Aluminum for Brackish or Salt, and Zinc for Salt.

Many people do not think that Aluminum anodes can protect an aluminum outdrive but this is not the case, Aluminum anodes are not pure but an alloy made up of other metals including zinc and Indium, this composition means that they are able to protect the alloy of a stern drive as on the galvanic scale they are the most active, giving a voltage in salt water of -1.1v, compared with -1.05v for zinc and -0.9v for a alloy stern drive. These anodes have historically been used more on large commercial operations as they have a higher current capacity. The Consumption Rate is 3.4 Kg per Amp year for Aluminum compared with 11.11 Kg for Zinc.

A standard 100mm Zinc anode weights 1kg and the same size Aluminum one weights 0.4Kg, but taking into account the greater current capacity the Aluminum anode will last an extra 23%. Mercruser and the latest Volvo drives use Aluminum!

Now fit a Galvanic Isolator into your earth line to stop the other boats in the Marina using your Anodes, because without one you will all be connected. I would be great if you could do a full review on Zinc v Aluminum with some proper numbers, it is possible to work out the expected life of anodes given all the correct numbers, could you (the magazine) do this for say the Volvo DP290 drive, with stainless propellers. Maybe MG Duff or Performance Metals could help out?
 
What effect does the depth of water have on rogue metal sitting on the bottom. I have over 12 metres under my keel and as always boaters blame the marina for anode/prop problems. For all I know there maybe a submarine sitting on the bottom with its torpedo tubes open. /forums/images/graemlins/laugh.gif
 
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