Fitting Anodes to Steel Boat: Welded, Bolted, Amount, Material ?

[Atsai]

Hello there, sailers of the world!

My name is Jos and me and my girlfriend are refitting/ restoring a old Pine Island Clipper, designed by Denis Ganley from New Zealand....

We are almost done with all steelwork, replacing bad/ thin parts of plating and replacing steel with stainless in all parts where wood gets fitted onto the dek.

But i still have to fit some anodes... and have some questions about that!

- how many should i fit (and where)--> read somewhere that to many can give the opposite effect

- What material? (will be sailing fresh water for about 5 years, after that go out to sea/ travel the globe)

- Should i weld them to thehull (beter contact/ no paint behind them) or bolt them (maybe less contact/ possible to paint behind them)

Well, that's it for now. Hope I can read some wise words on this subject :-)

(I'm quite new at this sailing/ building boats)

Jos

[GordMay]

Greetings and welcome aboard the CF, Jos.

You’ll likely be interested in the information on this webpage:
Anode Weight Calculation
➥ http://www.boatzincs.com/anode_weight_calculation.html

[GordMay]

See Michael Kasten’s several excellent articles, on the subject:

* ➥ http://www.kastenmarine.com/_pdf/mbqCref.pdf

➥ Corrosion Prevention

➥ http://www.kastenmarine.com/_pdf/mbqMetRef.pdf

* Excerpted from “Corrosion, Zincs, and Bonding” (first link, above):

“ ... The best method for attaching zinc anodes to any underwater fitting is by welding. This is the only really positive way to insure continued electrical contact.
The zincs intended for welding onto underwater structures are cast around a steel bar. The ends of the steel bar are welded directly to the piece being protected.
If bolting is used, as is a more common practice on a non-metal boat, every effort should be made to assure electrical continuity. Zincs with a steel bar through them can be used here too by drilling the ends of the steel bar and bolting the bar to the fitting.
The heavy copper paste used by electricians for coating electrical connections will work fairly well to preserve the connection under the bolt head. Brazing or soldering the bolted
connection will also work well to assure a good electrical connection.
A good trick for attaching zincs that do not have a bar is to fuse a bolt or nut to the zinc anode by heating and melting the zinc locally with a torch until the fastener is effectively cast into the chunk of zinc...”

[lorenzo b]

LWL is 60'
Draft is 6'
Beam is 20'
I used 20 20lb zincs welded about every 10' in every direction
Traveled about 6000 knts in salt water in two years and zincs are about 50% depleted
Some have said I put on way to much zinc, but it's working for me.

[denverd0n]

I'm really surprised. Zincs have to be replaced periodically. I would not think you would want to weld on something that you know you are going to have to replace every year or so.

I guess you learn something new every day.

[Jim Cate]

FWIW,

The fin keel on our boat is a steel shell filled with lead and diesel fuel. The builder used welded anodes on it, and of course that worked well. However, we often slip the boat in places where welding isn't convenient, so I soon welded stainless steel studs onto the shell of the keel. We now drill holes in the steel bar that the zinc is cast around and use stainless nuts and lock washers to attach the anodes. Have had no problems with this method in the 6 years since doing the changeover.

Cheers,

Jim

[Atsai]

Thanks, everyone!

This is the great thing about the www.... sharing information which can help a lot!

Hope i can give some good advice in a couple of years!

[lorenzo b]

Originally Posted by denverd0n

I'm really surprised. Zincs have to be replaced periodically. I would not think you would want to weld on something that you know you are going to have to replace every year or so.

I guess you learn something new every day.

When you want to replace them you cut the tabs off with a small grinder leaving 2 inches and tack the new tabs to the old, takes a few minutes and a helper to hold them. If you have a steel boat you already have a welder. A lot easier and better then screwing around with bolts.
Go to a marine supply store that services a fishing fleet, I paid $40 per 20lb zinc a few years back. If you weld directly on your fuel tanks, make sure they are full to the water line.

[boden36]

Jos , welding is the only way to go with anodes on a steel boat, as you need a perfect connection.
An anode manufacturer should be able to advise on weight and placement, but remember that too many is as bad as too few.
I suggest you buy a silver chloride reference anode to test your anodic protection once you are back in the water. You use the anode with a multimeter and the resultant reading will measure the amount of anodic protection you have.
I bought one from Australia at a reasonable price. It came with great instructions and was easy to use. See rustseeker.com .
I have no connection with them, just a satisfied customer.

Regards,
Richard.

[Atsai]

Thanks!

Rustseeker seems a great little gadget.

(anyone else any experience with this product?)

[Boracay]

I'm not sure that using weight as the sole determinant is the way to go.

Certainly one needs to keep in mind with a steel boat that a single adverse event (faulty bilge switch in bilge water?) can remove anodes in a few months so they need to be big enough to provide.

However anodes are expensive and a drag. They are going to "vanish" slowly, even if there is no problem.

Other factors like frequency of slipping, condition of the bottom paint and amount of dissimilar metal below the waterline come into play.

My "solution" has been to mount a pair of the largest available from my chandler on either side of the keel , another pair of better streamlined ones half way up the underwater hull, two on the propeller shaft (check the shaft size and make sure they are a "good" fit), a pair on the skeg and another pair on the rudder.

Welding is probably better than bolting but making sure there is a good electrical connection with bolts may be more practical as welding is not available in some yards.

I use Primocon on any bare metal that I see below the waterline before antifouling.

I'm currently touching up any rust spots above the waterline with POR15/one pack enamel.

[Atsai]

Welding is most likely the best connection, but: behind the anodes it's not possible to put any coating on the hull....! Is that a problem????

[bangkaboat]

Originally Posted by Jim Cate

FWIW,

The fin keel on our boat is a steel shell filled with lead and diesel fuel. The builder used welded anodes on it, and of course that worked well. However, we often slip the boat in places where welding isn't convenient, so I soon welded stainless steel studs onto the shell of the keel. We now drill holes in the steel bar that the zinc is cast around and use stainless nuts and lock washers to attach the anodes. Have had no problems with this method in the 6 years since doing the changeover.

Cheers,

Jim

Good idea. If one shops around, one can find a specific anode with the strips pre-drilled. In shipyard/drydock work, I found that the barge zincs were always weld-on, but many of the tugs & fishboats, etc., had bolt-ons.

Atsai,
paint area behind zincs with red zinc oxide weld-thru primer before attaching zincs, if weld-ons. The arc will strike through the primer, unless too thick, in which case, give the area a couple of hits with your chipping hammer first.

[Jim Cate]

Another reason for bolting anodes: I have needed to replace anodes before a scheduled slipping. It is challenging to do this underwater with welded anodes, and not very hard at all with bolted ones.

May not matter for some folks, but we spend a fair amount of time in areas where a quick slipping is either not possible or too bloody dear. Nice to be able to do it myself.

Cheers,

Jim

[Atsai]

Hmmm... Jim's got a point. But we'll not be traveling abroad (overseas/ out of the Netherlands) in the next 5 or 6 years so welding can be done easily. Once we will set off for global travel, we will maybe have to change bolting (?)