Bonding Basics - Steve D'Antonio Marine Consulting

1 BEST. PRACTICES. Bonding Basics The best corrosion protection for underwater metal fittings is a well-designed and -maintained Bonding system. by Steve D'Antonio D uring a recent boat inspection at a local yard, I noticed a marked disparity in the condition of two The Nature of the Beast Many seemingly inexplicable corro- sion problems are often chalked up, sacrificial anodes on the vessel's sometimes even by professionals, to transom. Commonly referred to as a bad ground. While the crews or zincs, although they can be cast from technicians making this dismissive other alloys, one had been consumed assessment are often accurate, they at a rate I thought consistent with the are also frequently at a loss to explain vessel's season afloat it was reduced just why this is so.

2 Indeed, while by roughly 50%. The other remained many understand that it's important in a near-virgin condition. I'd seen and valuable to have a Bonding sys- this phenomenon before and knew tem, far fewer truly understand what immediately something was amiss it is or how it works. Let's start with with the Bonding system. some Basics of grounding and When it comes to corrosion and Bonding systems. Above Cutless bearing shells are Bonding , boats can suffer the effects From a standards perspective the typically made from brass, and unless of a faulty electrical system in ways subject is complex, encompassing galvanically protected through a bond- that are not immediately obvious to guidelines from at least two American ing system, they will dezincify readily, as their owners.

3 It's up to vigilant yard Boat & Yacht Council (ABYC) stan- this one has. The good news is that crews to notice the sometimes subtle dards: E-2 Cathodic Protection and brass is less noble than most struts, indicators, track down and remedy E-11 AC and DC Electrical Systems, which means the bearing shell will be Bonding problems, and educate own- which focus on corrosion mitigation sacrificed before the more-expensive ers about this complex and often and electrocution/fire prevention, and difficult-to-replace strut. misunderstood subject. respectively. Although there are 18 Professional BoatBuilder The effects of stray-current corrosion on this propeller were dramatic, rapid, and unmistakable.

4 They could have been avoided with adequate Bonding . they rely on central Bonding buses. These are copper strips that run the length of the vessel, with various items connected by short lengths of wire. A. strip should be a minimum of 1 32". ( ) thick and no less than ". (12mm) wide. The connections to it are critically important. In no case should they be secured with self- tapping, sheet-metal, or wood screws. If machine screws are applied, the strip must be thick enough to be significant differences between a low-resistance connection to the tapped and must allow a minimum of grounding and Bonding systems, the Bonding system.

5 Four threads of engagement. In other terms Bonding and grounding are fre- Shaft brushes are specifically cases, through-bolts and nuts may be quently applied interchangeably. designed to maintain contact with a used to connect a wire's ring terminal Here, I'll focus on the goal of corro- rotating surface. They resemble the to the strip. sion mitigation and stick to the term brush in an electric motor's commu- Too often I see wiring ring termi- Bonding . In brief, a Bonding system tator and should be made from the nals connected to a Bonding strip electrically connects underwater metal same material: carbon. (Some use a with self-tapping screws that pass fittings such as through-hull fittings/ hunk of bronze or brass, both of through the strip and into fiberglass seacocks, rudders, and struts.)

6 Which are less effective.) To complete or wood, assuring a poor connection. Propeller shafts may be included in connections between these compo- Such connections are not ABYC com- the system; however, because they are nents for the purpose of Bonding , the pliant, and when I inspect vessels connected to the engine via an oil- conductors should be a minimum of whose Bonding systems are wired in filled medium the transmission and #8 AWG. If doing double duty as a this manner, I find loose connections because oil is an insulator, the con- lightning-protection system, they must almost every time. nection cannot be considered electri- be a minimum of #6 AWG.

7 If there's no Bonding strip, and cally sound. In order for propeller Rather than interconnecting each components are connected one to shafts and propellers to be included in item to the next in a daisy chain, the other via wires, avoid making the Bonding system, they must rely on Bonding systems are more reliable and connections through hardware. That a shaft brush, a device that completes present lower overall resistance when is to say, if two Bonding wires are Left Not all shaft brushes are created equal. Much like the brush contacting an electric motor's commutator, the business end that rides on the shaft should be made of carbon rather than simply a hunk of bronze pipe or rubrail.

8 Right A central Bonding strip or bus running the length of a boat allows for Bonding wires to be attached anywhere, which keeps those wire runs shorter and reduces resistance. If the strip runs along the inside of the hull well above the bilge, corrosion at connections is minimal. august/sePtemBer 2012 19. Above Daisy-chaining Bonding wires from fitting to fitting is common and often unavoidable. However, protected components should not serve as a path for current as they do here with ring terminals connecting on either side of the fitting. Instead, the terminals should be stacked one on top of the other (above right).

9 Fully 75% of the Bonding ring terminals I check are loose. They should be retained with machine screws, never self-tapping screws, regardless of the substrate. Right In the absence of a central Bonding strip, Bonding bus bars can be placed throughout a vessel to keep drops to individual components short and reduce to the number of connec- tions at each bonded component. connected to a single component, such twofold. First, Bonding provides a that anode will then afford protection as a seacock or strainer, install both low-current path to ground for stray to all metals that are interconnected ring terminals on the same fastener current.

10 Typically caused by a posi- and immersed in the same body of and stud rather than separately. This tive DC wire, often from a bilge water. (Typically, the same body prevents the Bonding system's low pump, which comes into contact with of water is limited to the water in voltage and current from relying on bilge water, stray-current corrosion is which these components are the comparatively high resistance especially destructive. In a matter of immersed, but the definition does not of the hardware component as a days, it can consume a propeller or include those connected through conductive medium. turn a shaft into a useless mass rid- water in hoses.)