Anodes

My river boat is about ready to launch. I need to affix anodes and need guidance as to amount and placement. Please advise.

Ryland

 

You need to post more information. For example, size of the boat, material of the hull, shaft, propeller, drive, etc. materials.

 

Specs

She's a tri-hull pontoon, 60 feet long hulls, 60" diameter each, 3/8" thick steel, one Cat diesel long tail drive, calculated 9 knot top speed, 6 knot cruise at 2.5 gph, 85000 lbs empty, deck capacity 35000 lbs, 26" waterline loaded. Protected waters.

Ryland

 

http://www.performancemetals.com/anodes/AnodeFAQs.shtml
Some good info here. The missing information is the amount and size of the anodes.
A factor in your boat will be of course if it is painted to limit the area of exposed steel to the water.
Might be worth a call to these guys to get some sizing

 

360 ft of hull surface is quite a stretch. I would use aluminum strips, approx 20 sq.in. every 10 ft, mounted with stainless bolts.
Shaft and prop need extra protection, like a 2-part cylindrical electrode clamped on the shaft.

 

Anode Alloy

Is there a particular aluminum alloy that is best?

Ryland

 

If you looked at the Performance Metals link that I posted, they mention/suggest Navalloy, which has some other elements in it.
It would be worth the read.
An interesting point is that an anode can oxide over and limit the effectiveness of the anode. The Navalloy (which might be their proprietary alloy but other anode manufacturers might have their own equivalent) is supposed to be better than ordinary alloyed aluminum
On the other hand it might be just hype

 

Any alloy can be used, even the very cheap ones like "Zamac" that contain a large percentage of zinc, although the lifetime is shorter.
I would prefer a construction alloy, containing mainly Al, Mg and Cu. The surface must of course not be anodized or coated.