I a surprised you got a reading with the Cathode painted? I would question the reading of .9

For alluminum max. is -1.05 MV

Readings will vary greatly depending on water quality and salinity. (More brakish water is a better conductor of current)

IMO I would replace with the recommended surface area. Clean cathode and see where your readings are from there.

If you find it does not fall within the target range you can add additional anodes to bring numbers up.

And yes, over protectionn can blister paint and worse can leach alloys from your alluminum hull welds...not a good thing.

One thought is if you keep the old anodes they probably have lost all or most of the contact with the hull, rudder, and tabs.
It does not take long for crude to destroy the contact.





safe boating,

dave

Jack

I believe I suggest S.S.wire brushing grinding may B over doing it

Norm,

Big s Live On

Thanks guys.

I'll put on just the recommended amount of anodes:

1 - 3' on each side of the keel
1 - 6" on each rudder
1 - 12" on each trim tab.

I used a sander to take the buildup of crud on the tabs, keel, and tabs down to bright metal. Will follow up with a SS brushing to remove any sanding particles.

Norm, great advice on getting the Capac sensor cleaned up.

If I need to add more anode, I can use the cleaned up old stuff. Back side (to the boat) is in really good shape. Water side was corroded pretty well but it cleaned up well. If I have to add, I should be able to do so fairly quickly with the boat pulled into shore. Just need to have the admiral pull me up if I seem to be stayin' down too long...

Bill

Bill,

I know this Gunna cause a bit of a stir on the site BUT if U need more than the recommended amount of anodes the vessel has a electrical leak some where or a ground to hull. Now I’m not saying it’s easy to find cause on my 74 I never found out why could never get it above .09 with all the chasing I did isolating all the normal things & some AB-Normal thingy’s. Now on the 89 F/B sedan when I bought it was on the low side of .09 than did all of the above $hit than hit a half sunk tire (another story) had to have a tranny rebuilt the guy told me about Shaft Savers invested in them fixed 2 problem a slight vibration & the Capac Meter jumped up to 1.0 til the marina waters warm up to the mid to high 70s & slim started to cover the senor but all I had to do is take the soft brush to her bottom & lightly clear it & around it, with in a few hours it’d be back up to par. So in my HUMBLE all this Magnesium loafs of bread etc are a short term fix. As I’ve said time & again the #3 biggest culprits R shaft isolation, bad wiring @ bilge pump ( take a hint from Diver Dennis’s way to seal bilge butt splices & others splices) & bad shore ground & stray $hit from other boater that’s when a Mag will help out on latter. Ok I’m open to chastising. AnyWho that’s my ½ pennies worth

Norm,

Big s Live On

PS : Dave I've heard of that oven cleaner trick never tried it it might B cheaper than PeelAway

Agreed!

One point if you start with new or clean anodes with great continuity to the hull, and you numbers are good then they slowly slip I have found that I the andoes are loosing continuity with the hull. Thats when the supplimental helps.

The bottom line is: If no corrosion is taking place things are fine in M land.


I also noticed that the new anodes I purchased might not be the same alloy composition as previous ones on the boat. They will also effect the potential.


dave

Bill, let us know how the shrink tube works, I was just thinking, what happened to your original insulater between the shaft and the tranny? JAM

Question?
This is my first aluminum hull boat. In my previous life I owned a steel hulled boat. The steel hull boat had welded studs to attach anodes to except the rudders, that was just holes drilled through. In reading this post and some of the others, I am right in assuming my beautiful Interlux 2000 and Pacifica Plus bottom job will now have to sacrifice "x" square inches down to the "shiny" for the entire size of the keel and pancake anodes? Please tell me I bumped my head and misunderstood. I thought I could attached with clean through-holes only for bonding contact. I have a call into the engineer from BoatZincs.com to ask but you guys probably already know the answer. Thanks, Capt. Paddwheel

I too agree with Norm on the origin of poor isolation. The prop shafts weren't that big of an issue to work out but I'm struggling with the rudder shafts.
Jim

Jack,

re: wha' happened to the plastic isolation tubes ...

Anybody's guess. Boat had been sitting in the water at least 3 years before we bought her last June.

I'm heading to the boat today to put on just the proper amount of anodes and do some measuring on the props (want to pull the current ones and put on a spare set). Somewhere I'd read it's possible to pull the props without dropping the rudders. There appeared to be plenty of room to slide the prop off the end of the shaft and clear the front edge of the rudder. My issue is what type of pulley puller I'll need (or what modifications I'll need to make to a standard one) to accomplish this. Won't use heat cuz that'd destroy the bearing in the strut. So it's some kind of shadetree modification that I'll need to use.

Bill

Afternoon, folks...

Update (multiple subjects, but they were part of this thread, so here goes...)
With the boat still out of the water:
1. Prop changeout - Starboard was "fall off the bone" easy. Once I took the cotter pin out, unscrewed the castle retaining nut, the prop pretty much slid off the shaft. Not wanting to complain, I changed that side out, tightened up the nut, new SS cotter pin and on to the Port side. Now there it was a bit more challenging. I'd purchased a 6" 3 jaw gear puller and was able to get it attached with the rudder turned full to one side**. Replaced the old prop and buttoned everything up.
** Note - if you want to / need to have the gear puller fit correctly, you could, either with a hacksaw or a cut off
wheel, lop the shaft down to about 3". Grind a square (about 1/2" long) at the newly cut off end. This
should allow for a crescent wrench to be used on the now easily squared to the prop shaft.

2. Anodes - attached the prescribed amount to the trim tabs, rudders. keel. ***

3. CAPAC sensor - as mentioned earlier, I found a small hole in the sensor. A check with a vendor resulted in knowing
no such hole should be there. Gobbed on some aquarium silicone (just enough to cover the hole to
keep out water). Sensor clean.

*** After boat's been in the water...
CAPAC reading at 6.4 . Realize that's not good. Think the doubling of the amount of anode used previously
may have masked a problem.

Believe that the cause may be that the bolts in the tranny / prop shaft aren't isolated and there's direct metal
to metal contact. Will be using 10mm bolts with shrink tubing over them (standard 7/16" bolts w/ shrink tubing
wouldn't fit.). Once all are done, will test.

Bill