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Subject: Re: [worldcruising] Zinc Anode protection for Steel Boats
From: Bob Young (polaris9@XXX.XXX)
Date: Tue Sep 25 2001 - 13:16:00 EDT
The following formula can be used to calculate the correct total weight of
zinc for optimal protection. I used it for an aluminum boat I used to
own, and after applying the 30 lbs of zinc derived from the formula I used
a corrosion meter and it reported slight over-protection, so I think the
results are in the ballpark.
W = kL (B + 2d) / 15.6
where -
W = total weight of zinc in lbs.
L = waterline length in feet
B = waterline breadth (max) in feet
d = draft in feet
k = 0.165 for fiberglass
= 1.0 for steel
= 0.625 for aluminum
I also used to own a steel boat, and did not encounter any problem with
rusting at the attachment points. Welding is clearly advisable here, to
ensure electrical continuity. You need anodes both sides of the rudder
and the keel, and on the hull distributed such that no point is more than
about 6 feet from an anode. The zinc will be depleted over time, so I
would start with slight overprotection, which is far less critical with a
steel hull than with aluminum. I would in any case always prefer too much
zinc to too little.
Bob Young
On Tue, 25 Sep 2001 15:55:06 -0000
steelboat2000@XXX.XXX wrote:
> Can anyone help! We are going to be launching our 14 ton 44 foot
> steel cutter this spring, and have not been able to come up with any
> information on where and how many zinc anodes to put on our boat. We
> already have shaft zincs and one on the propeller. ......
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