Yanmar Pleasure Boat Marine Engine Help

Inadequate Anode Maintenance

Once upon a time there was a very nice 45 footer called ' XXXX ' complete with a Bukh saildrive. The owner had hauled as there was water coming out of the saildrive gearbox vent, into the boat, and the whole caboodle was threatening to go under. A large hole in the side of the saildrive leg was the cause of the problem and the owner and various standersby where mouthing words like "useless heap of crap" "Warranty, this shouldnt have happened!" amongst other, less printable abuse. "Where is the anode?" said I. "Dont know, said the owner, was there 6 months ago." It was very difficult not to roll one's eyes! The rubber fairing had been flexing on the leg, as it is want to do, and bare aluminium was exposed to the ELECTROLYTE, aka seawater. As the sacrificial anode had long done its job and sacrificed itself the pesky little electrons decided to leave the ship via a new route.
After much looking around I called the electrolysis expert. After stalking the boat for a while he discovered the anchor locker, with 100% chain for anchoring. The owner showed us how he put out the chain, snubs it, and drops a couple of loops around the electric anchor winch before heading for the gin and tonic. Here was his problem. The poor little saildrive anode, designed to protect the leg only, was now asked to protect up to 150 feet of chain as well, depending what was in the water. No wonder it disappeared in a hurry!

Here is a picture of the circuit with 2 dis-similar metals in an electrolyte. Cost to fix the saildrive leg, $5000, cost of switch for the winch negative cable (shown), $10.

More problems
Q: Why are there little holes appearing in the boarding ladder where it goes under the water?
A: The FM radio aerial was connected to the life lines which were connected to the boarding ladder. If the ladder was down and the radio on, the electrons were deserting the ship. FIX? Install a proper aerial, put a switch in the negative cable to the engine or raise the boarding ladder when not in use.

Q: Why is my saildrive leg broken?
A: The boatbuilder, unbeknown to him, used a copper based anti-fouling paint on the leg.

Q: Again, why is my saildrive leg broken?

A: The zinc anode was a poor quality one.

Q: Why are there rusty cornflakes on my saildrive propeller?
A: There was no electrical contact between the hub and the blade holder ( a saildrive prop has a rubber bush ), the zinc was leaving the bronze, leaving a copper residue that looked like rusty cornflakes. FIX? Use a piece of stainless wire to bond the hub and the blade holder together.

Q: "Someone stole my outdrive anodes, I only put them on 4 months ago!"
A: Install a Mercathode ® or haul out when not in use.

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