Anodes

[XLD]

How affective are magnesium anodes when suspended from steel cables (bolted to the hull) into the water?

[hider]

54 minutes ago, XLD said:

How affective are magnesium anodes when suspended from steel cables (bolted to the hull) into the water?

If the cables are stainless steel, not very.  Stainless is a poorer conductor.

The effectiveness is also reduced because the cable and the terminations will have some resistance no matter what it is made of.

 

Why do you want to do this rather than attaching them directly?

[cuthound]

55 minutes ago, XLD said:

How affective are magnesium anodes when suspended from steel cables (bolted to the hull) into the water?

 

Probably not very. Anodes only protect a limited area around them. Something like 2 metres either side.

 

By cabling them to the hull the protective area will centre on the bolt securing the steel cable to the hull, not around the anode, so the protected are may well be above the water line.

[Alan de Enfield]

1 hour ago, hider said:

If the cables are stainless steel, not very.  Stainless is a poorer conductor.

The effectiveness is also reduced because the cable and the terminations will have some resistance no matter what it is made of.

 

Why do you want to do this rather than attaching them directly?

 

It is a very common way of doing it on Lumpy water boats (Alu or Zinc tho') and you can even buy them ready assembled.

 

Particularly used when at anchor or moored to pontoons.

 

Tecnoseal Zinc Hanging Anode 2.5 Kilo - 6mtr Cable - TCS Chandlery

 

Edited July 22, 2024 by Alan de Enfield

[XLD]

I've just had new anodes welded onto the hull during dry docking. The old ones still have a fair bit left so l thought l might as well hang them down the side of the boat as bin them.

[beerbeerbeerbeerbeer]

I had my old ones off the front welded to the swim a little distance from the others rather than bin them. 

[Tony Brooks]

2 hours ago, cuthound said:

Probably not very. Anodes only protect a limited area around them. Something like 2 metres either side.

 

By cabling them to the hull the protective area will centre on the bolt securing the steel cable to the hull, not around the anode, so the protected are may well be above the water line.

 

I don't think that is correct, assuming a low enough resistance in the cable. The electric cell is between the anode and the closest bit of steel, not the mounting bolt. The bolt and cable are only electrical conductors to complete the circuit. With the slope of the hull side on most boats, I suspect that the anode may well hang clear, so reducing the effectiveness of the cell and fail to protect as larger are as one fixed to the hull. It won't do any harm and might do a bit of good.

[blackrose]

4 hours ago, Tony Brooks said:

 

I don't think that is correct, assuming a low enough resistance in the cable. The electric cell is between the anode and the closest bit of steel, not the mounting bolt. The bolt and cable are only electrical conductors to complete the circuit. 

 

As odd as it sounds I think that's correct. As Alan says, it's common practice on saltwater boats. 

[hider]

Put them on the inside then they will last longer.    🤣

[matty40s]

Black them, they will last even longer

[XLD]

On 22/07/2024 at 23:04, matty40s said:

Black them, they will last even longer

Ha ha. I actually saw someone paint anodes with red oxide once 🙄

On 22/07/2024 at 16:13, Tony Brooks said:

 

I don't think that is correct, assuming a low enough resistance in the cable. The electric cell is between the anode and the closest bit of steel, not the mounting bolt. The bolt and cable are only electrical conductors to complete the circuit. With the slope of the hull side on most boats, I suspect that the anode may well hang clear, so reducing the effectiveness of the cell and fail to protect as larger are as one fixed to the hull. It won't do any harm and might do a bit of good.

Good point. Fortunately my barge has a fair amout of vertical hull just below thw waterline so thats where l ‘ll hang them