Electrical, Grounding Bar, Copper, Part 1: Analysis

The original ship's ground
Every cruising sailboat should have a ship's ground. What is a ship's ground, you might ask? It is a common point to which not only the AC and DC electrical systems, but also the mast and the chainplates are grounded. For many a sailboat owner, a keel bolt serves as the ship's ground. For those, however, whose boats have encapsulated keels, or for those whose boats have a centerboard, a keel bolt is not an option. It must be, then, for this reason, that the Ericson 25 (which is primarily a centerboard boat) has, as it common ground point, a bronze bolt in the bilge adjacent to the centerboard trunk, near the lowest point in the boat. Is this single bronze bolt sufficient? That is the question that I asked myself in the refitting of Oystercatcher, my Ericson 25. The answer that I soon reached, after delving fully into the subject, was that it is not. In this posting, the first of a four-part series, I explain how I came to the conclusion that it was necessary for me to augment the grounding system of my boat by the installation of a copper grounding bar or strip.

Many a sailboat owner would debate me regarding my contention that the AC and DC electrical systems, as well as the mast and chainplates should be grounded to a common point. I'm not here to engage in that debate. I'll only say that this approach to things is in keeping with the standards and the positions of numerous authorities. For those who may be interested is this debate, see the now widely-read thread that I initiated some time ago on the Cruiser's Forum, "Grounding for AC and DC." http://www.cruisersforum.com/forums/f14/proper-grounding-for-ac-and-dc-72432.html
As I said in the introductory paragraph, the original grounding point was a single bronze bolt located in the bilge adjacent to the centerboard trunk. In the picture below, we see the centerboard trunk beneath the mast compression post. The area of the bilge to which I'm referring is to the left of the centerboard trunk, in the area between the hanging locker and the head.
When I purchased this boat, there was no AC electrical system and the DC electrical system was old, corroded, and minuscule. The grounding bolt, which we see pictured below, was used for only one purpose - the grounding of the rig in the event of a lightning strike. Even for this purpose, this grounding system was inadequate. For one thing, only the bow chainplate and the port and starboard chainplates amidships were grounded. Neither the mast itself nor the backstay chainplates were grounded. For this reason, we see not five cables in the picture below, but three. I should mention as well that by today's standards the gauge of these cables was insufficient.
These three cables were solid copper. The ends of each were wrapped around the bolt.
Ericson had sandwiched these three cables between two bronze washers.
Beneath the bottom washer there was a bronze nut, which secured the bolt to the hull.
I was able to remove the nut without having a helper on the other side of the hull.
The bolt was so securely fixed in place that it required several serious blows by the three pound hammer (pictured below) for it to break free.
Many coats of bottom paint had so completely covered the head of the bolt, that it had been impossible for me to see it until it broke free from its position.
Technically this fastener was a screw, but given its size and importance, I often simply refer to it as a bolt. What is its size? It's 1/2 inch in diameter.
Now that I had this 1/2 bolt out of the hull, it was time for me to figure out how I might install a properly-sized grounding bar or strip. What is a properly-sized grounding bar? To answer this, I had earlier referred to Nigel Calder, Boatowner's Mechanical and Electrical Manual (2005), pp. 219-35, and Don Casey, Complete Illustrated Sailboat Maintenance Manual (2006), pp. 569-81. Calder and Casey said many of the same things in terms of lightening protection in general. Likewise, both said that a copper bar is superior to a square plate. Studies suggest, they said, that lightning dissipates not from the surface of the copper, but from the edges. A long bar of copper is thus preferable to a small square plate due to the length of the edges of the bar. Casey in particular suggested that, for salt water boats, the copper bar should be at least 2 feet in length and that for fresh water boats it should be at least 12 feet in length. Knowing that my boat, Oystercatcher, would spend most of her time in saltwater, I was inclined to the smaller length. Knowing, however, that I might, at times, sail her in freshwater, I also wanted to consider how I might maximize the length of the copper bar for this boat.
I soon discovered that the maximum length of the new copper bar would be determined not by my own wants, but by the necessities imposed by the structure of the boat itself. The first thing I had to take into account were the 2,500 pounds of lead beneath the sole of the main salon. This lead sat on either side of the centerboard trunk, and it served as a dam of sorts between the forward and the aft ends of the bilge.
This meant that it would be impossible for me to run a twelve foot bar of copper underneath this part of the boat. Why? Because I would need to bolt this bar through the hull, and the lead would be an obstruction. This meant that I either needed to put the 12 foot bar to the port or starboard side of the lead (in the area of the settee lockers), or I needed to use a shorter bar and place it forward of the lead (in the area of bilge which extended toward the V-berth).
Lead on either side of the centerboard trunk with the two options indicated, port and forward
I did indeed carefully consider the first option - that of putting a 12 foot copper bar on the side of the hull and through-bolting it in the area of the port side settee lockers. If I had opted for this approach, the bar would have begun somewhere around the hanging locker, and it would have ended somewhere around the lazarette. The problem I had with this approach was that the bar would have been high on the hull - approximately as high as the paint roller you see pictured below. This meant that I would have needed to route many of the grounding cables not downward (to a low point in the bilge), but upward (to a point not far from the waterline). This was not acceptable. Therefore, I abandoned this idea and chose to mount a shorter grounding bar forward of the lead, in the area underneath the V-berth.
In the picture below, we see the grounding bar as it appeared after I had dry-fit it into place. The bar begins in the bilge, adjacent to the original grounding bolt, and extends forward by 4 feet into the bilge area beneath the V-berth. This picture also allows you to see further evidence for why the mounting of a 12 foot bar in the area of the settee lockers would not have been a good idea. According to my measurements, the copper bar would have been dangerously close to the bunk of the trailer (or even on top of the bunk of the trailer).
It would seem that my choice for the location of the smaller, 4 foot bar was a simple one, but it was not. Is anything in the refitting of a sailboat ever easy? I knew that I needed the bar to start in that area of the bilge between the hanging locker and the head. This, of course, was the same area where the original grounding bolt had been located.
Originally, I thought that I would use the original, 1/2 inch bolt as the starting point for the bar.
Soon, however, I realized that there was a problem. I had to take into account the cleats that I had installed in the large, aft locker of the V-berth for the mounting of the waste holding tank.
There were two sets of cleats. One set supported the shelf, which you see pictured below. The other set (visible at the top of the photograph), would support a storage shelf.
Taking measurements, I realized that a straight line (from the original grounding bolt into the V-berth locker) would hit several obstructions - namely the cleats that I had glassed to the hull. This meant that, if I wanted to use this original grounding bolt as the starting point of the copper grounding bar, I would need to put a bend in the bar. Specifically, I would need to angle it upward, away from the grounding bolt, so that it could then make a straight shot, forward into the port side of the V-berth locker.
 The red lines in the pictures above and below should make things clear.
With this plan in mind, I took the time to clean up the original bronze grounding bolt with a Dremel and a pocket knife.
In a short time I had removed over 35 years worth of gunk, and this piece of hardware was looking almost brand new.
With this original grounding bolt all cleaned up and with this overall plan of attack in mind, I moved forward with the ordering of the copper bar and the additional pieces of hardware that I would need for this project.

This ends this first posting on the analysis I made in preparation for the construction and installation of a grounding bar for Oystercatcher, my Ericson 25.

No comments:

Post a Comment