AluminumAlloyBoats.com

Can anyone tell me about anode tests?

With a multi meter and a silver half cell it reads 0.7/0.6v dc. I'm pretty sure that means the anodes are gone? How bad is that?

This an Aluminum Catamaran, 40 feet, salt water, tropics, 25 years old, last painted May 2017, last anode replacement Apr, 2016 (allegedly), not much growth on the hull but the props are very fouled.

She has been sitting in a marina for at least months now unattended (maybe longer). but not on shore power.

I looked around the hull for anodes but only found a clump of growth, if you paint anodes they don't work want about if they are dirty?

How can I tell if this thing is worth anything anymore?

cheers

Also if I snuck over and hung a pice of zinc on a wire off the rails or a cleat would that help?

Haul out is the only way to check the condition of the hull.

What am I looking for, could I see it on SCUBA?

If you can't see the anode then it/they cant see the water.
Looks like there are none on the props shafts either.
You are looking for pitting in the hull and if they just painted it they are either covering up a bad hull or don't know what they are doing.
Is the marina HOT [current in the water] where she is sitting?

Thanks welder, They definitely don't know what they are doing! The water is just hot here, I'm a few degrees form the equator, and still, no water movement but hard to say if there is stray current...

So I have seen pitting, and could recognize it. Usually paint won't even cover it up if it is bad. Where is the line between filling the pits with weld and replacing plates?

I am a fair welder, I could not do a good job re-plating 4mm aluminum with out a lot more more practice, but I could buy a cheep 200 amp mig and a spool gun, prep the pits with acid or abrasion or whatever is best and spend as much time as it takes to fill them all in. Buying an AC TIG is probably pushing the budget, if I could find a skilled welder here (unlikely) labor cost might take this past "economical recovery"

As long as my efforts would solve the problem, I'm will to put a ton of time in.

What some people do to hide pitting is to bondo or fill the pits then paint over, it would require soda blasting the paint off to clean aluminum to inspect properly.
And of course check the INSIDE of the hull too.

Garfield101, do you remember Kenny Roger's hit 'The Gambler" and the lyrics: "you've got to know when to walk away and when to Runnn~!"? Well, I'll advise you to be in a similar situation? Why?

if you're considering a 40'welded ANYthing that floats, and you don't have a competent metal qualified and dozen years of experience documented marine surveyor involved- already? Well to me your question indicates you should choose if you walk or run? Personally from the questions, I'd run if I were you.

For example, if the budget won't allow for an AC Tig power supply to do legitimate repairs, and you're seriously considering attempting pitting repair with MIG? Garfield101, you've already declared your budget may not be prepared to have 40' of welded aluminum junk! Just the cost to haul her, junk her according to local codes, and dispose of her (worst case of course) is going to be more than the few thousand to get TIG ready in AC!

So, while I don't have pictures of the boat's interior and bilges or her overall state of repair- both good reasons to be skeptical in my experience - and she's not on the hard where the true state of the boat can be assess/surveyed/understood..... I can just remark that unless the current owner is paying you to accept the boat- (5 figures min.) and he's posting a bond (bank held guarantee of performance - surety) for her seaworthiness for 2-3 years? (and I'll wager he's not) THEN you're back to deciding if you should walk or run from her. I still vote run.

Sorry to be sour grapes, maybe you have a good deal going? But...... I've seen to many welded aluminum boat deals in the last 50 years of building, repairing, surveying, designing these boats to be more than UBER cautious about buying something with my eyes as closed as yours are described in your posts! Garfield101, if you have to ask the question, and its a good one to ask if you don't know the answer: what does that indicate to you about your knowledge of judging this craft without a qualified marine surveyor?

Gar'101, good luck making good choices, wise choices, and with the state of the boat's preservation- hopefully she will be in good shape and last a long time once you start taking better care of her? But you might ask to split the survey costs and if the boat won't survey for the asking? the owner should agree- before the survey to pay the entire survey cost. If she has hidden issues and you can't assess them? I'd want to run to a marine surveyor not my banker.

Cheers,
Kevin Morin
Kenai, AK

Welding corrosion pits in hull plating is a fools errand. The corrosion runs through the core of the plate for considerable distance from each pit. The torch just blows out the degraded metal and the pits turn into holes that go right through into the bilge. Sandblast and fill the pits with epoxy to get a few more years out of it if you already own it otherwise, as Kevin says, "run".

For an aluminum boat, you want .90V

http://www.frankshospitalworkshop.com/e ... ystems.pdf

ok, i am totally unclear what a silver half cell is, and where i could source one. somehow i have dodged the corrosion bullet in my 25 years of saltwater/alum boat ownership. i would like to do some testing before my luck runs out.

boatzincs.com sells silver/silver chloride reference anodes (half cells)

i'll check 'em out. thanks