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Old 03-20-2017, 09:21 AM   #14
O C Diver
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City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 7,688
Quote:
Originally Posted by Steve DAntonio View Post
With one caveat, see below, there's little or no harm in having both a brush and anode on the shaft. In fact, unless you go with a high end slip ring type brush like the ElectroGuard Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships. the effectiveness of a standard brush is far from guaranteed. Having tested several different types, if you do go the economy route, the 'copper wand-style carbon brush' offers the best chance for low resistance continuity. The resistance threshold here is quite low, Standards state that the maximum allowable resistance between protected metals and anodes cannot exceed 1 ohm. That's often difficult to achieve with wired systems, much less between a contact and rotating shaft. While the shaft is spinning contact is often good, it's when it stops, and sits idle for days or weeks that resistance often changes.

Brushes can, however, be a double edged sword. If the hull anodes are depleted, the shaft anode will, via the brush, provide protection to all bonded hardware, until its depleted, which will happen quickly. Ultimately, Id recommend a brush, while ensuring all anodes are maintained.

This article explains a bit more about brushes and how they work with bonding systems Bonding Systems And Corrosion | | PassageMaker
Steve, thanks for the links. Some good information. Have you done any analysis on aluminum versus magnesium anodes in fresh water. Finding aluminium in all the sizes I needed was challenging enough, but magnesium is just not available in most of the uncommon sizes. While I will be in fresh water for 5 months this year, I will also be in brackish and the ocean. Assume aluminum is generally the best all around choice for me. Just isn't much information regarding how much of an improvement magnesium is over aluminum in fresh water.

Ted
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