zinc versus aluminum galvanic protection

[River Cruiser]

Boatpoker I have a friend with aluminum hull houseboat. Like me he’s a freshwater boater on the currently flooding upper Mississippi. He had aluminum alloy anodes put on when he launched it in 2013, I’ve tried telling him to haul and check his hull and anodes but he is the type of guy who will only haul if he was to ding a prop. What is your opinion of his choice of anodes and his haul out schedule?

[Sailmonkey]

Originally Posted by River Cruiser

Boatpoker I have a friend with aluminum hull houseboat. Like me he’s a freshwater boater on the currently flooding upper Mississippi. He had aluminum alloy anodes put on when he launched it in 2013, I’ve tried telling him to haul and check his hull and anodes but he is the type of guy who will only haul if he was to ding a prop. What is your opinion of his choice of anodes and his haul out schedule?

I'm not boatpoker, but if I was an aluminium boat owner I'd have one of these without question to keep an eye on this sort of thing

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

Our boat isn't metal, but the expensive prop is. so I check it at least monthly.

[boatpoker]

Originally Posted by River Cruiser

Boatpoker I have a friend with aluminum hull houseboat. Like me he’s a freshwater boater on the currently flooding upper Mississippi. He had aluminum alloy anodes put on when he launched it in 2013, I’ve tried telling him to haul and check his hull and anodes but he is the type of guy who will only haul if he was to ding a prop. What is your opinion of his choice of anodes and his haul out schedule?

Aluminum anodes are the only material suitable for all waters and while they will last longer I'd be checking monthly until I got a handle on how long they'll last in any particular harbour. Aluminum is a great hull material but galvanic and stray current protection is CRITICAL.

[Les Noble]

Old thread, but feedback welcome. Real world results of aluminum conversion with questions. I have an 1986 aluminum 42' sailboat and after 6 year refit on the hard, splashed last August. Decided to switch to DIY aluminum anodes as a friend has his own mill, CNC and lathe. Bought 2 AL plate for the raw material.
https://www.rotometals.com/apn-8-alu...te-1-x-6-x-12/
For the 2 hull anodes, cut on table saw and drill press.
For saildrive; the CNC was tabletop and the AL was very gummy, so more difficult. There was also a void in the plate so had to start over in a different section.
The pencil anode on the engine was cut on lathe. The original zinc was half gone after 5 years. Beta 38 was installed new in 2017 and has an isolated ground. The old anode brass housing was drilled out and AL was pressed in.
The boat as two swing keels, fore and aft. The aft hub that the keel attaches to had serious corrosion and a new one was machined. I added smaller anodes to the hub and keel as there weren't any before.
First cruise: Starting and ending in Norfolk, VA and reaching Halifax, NS, September to Thanksgiving. Lots of motor sailing unfortunately.
Pulled the pencil anode last week and it was gone down to 1/4" left in the brass housing. I winterized the engine after Thanksgiving and used RV antifreeze (No poison in bay). Since then, at the exhaust gooseneck, the antifreeze was pasty/gelled where the anode was. The antifreeze at that end of the heat exchanger had drained down the hose or evaporated. I soaked the gooseneck in vinegar to knock off the hard deposits near the anode location. All the brass was pristine.
The swing keels are in keel boxes with removable plexyglass lid. Removed the aft lid and scrubbed the anode on the hub/keel and they looked good from a foot in the water. Barnacles are colonizing on them and will knock them off when in warmer waters.
I have a reference electrode and have done 3 readings all -1.08ish, Hampton, Norfolk and Bristol, RI.
Questions: Now I am trying to figure out if I have an issue or not. There are other threads about Beta Marine engines eating engine (zinc) anodes and that is a whole other thing. I will make many replacement slugs.
I am researching antifreeze to see if there is a reaction issue. Thoughts on this?
I am second guessing my choice of metal suppliers. Its not outright milspec and I bought a plate of zinc also to switch back if negative results.
Any input appreciated.

[boatpoker]

A proper aluminum anode is an alloy with other metals including indium.
A chunk of aluminum of unknown alloy composition is unlikely to work.