Centerboard, Construction, Part 2: The Mold and the New Steel Spine

The mold, with the new steel spine within
In this the second part of a nine-part article on the construction of a new centerboard for my Ericson 25, I describe my approach to the building of a mold as preparatory work for the pouring of the urethane foam. This foam, once cured, would create the body of the new board. I also, in this second part of the my four-part article, describe how I, with a little help from a friend, created a new steel spine - one that would provide the new board with great rigidity.

You'll recall from the first part of this article, that I demolished the original centerboard and removed the original lead plates that had been secured to either side of the original spine. You'll also recall that the original spine was severely rusted in some places, particularly in the head and foot areas. For this reason, the original spine was obviously no good, at least in terms of using it for a new board. It was, though, very good at providing me with a pattern for the creation of a new steel spine. Likewise, it was very good at providing me with an understanding of where exactly the original spine was located relative to the external dimensions of the board.

You'll remember that prior to demolishing the original board, I traced it's perimeter on a piece of finish-grade plywood. I also made reference marks every six inches to provide myself with a grid system for taking measurements.
Now, with the original board having been demolished and with the original, rusty spine in hand, I was able to lay this piece of metal on top of the pattern and grid system that I had earlier drawn on the piece of plywood. It helped that I had marked the old spine with the same six-inch reference lines in the middle of the demolition process. With everything well-aligned, I traced the perimeter of the steel spine. I also scribed the circles within the spine. These, as I speculated in the first part of this article, were cut into the spine at the Ericson yard for the purpose of providing their pour-foam a means of spreading more readily throughout their mold.
Next, I laid one of the lead plates on top of the old spine so that I could trace it's perimeter on the plywood pattern. This plywood pattern would be my blueprint of sorts.

Satisfied with all of the measurements, I pulled out some white craft paper and taped it down on top of the plywood pattern.
This was how I created a paper pattern that I would later use for the cutting of the new steel spine.
While I waited for my metal-working buddy to find some time to give me a hand, I got to work on the construction of the mold. For some reason, I didn't take any pictures of the various steps I took to build this shallow box. I can say, though, that I built it to a depth of 2-1/4 inches, since this was the thickness of the original board, as I had determined from measurements of it prior to its demolition. If I knew then, what I knew by the end of the centerboard construction process, I might have made the mold to a depth of only 2 inches. I say this, because when it came time to apply epoxy and cloth to the new board, I realized that I would need to sand it down to about 2 inches in order to allow for the 1/4 inch build-up of the final layers. This sanding process was laborious and time-consuming. Nevertheless, if you happen to follow the steps that I have followed, you might be better off to build the mold to a depth of 2-1/4 inches rather than just 2 inches. You'll see in the third part of this article, that there is very little room for error when positioning the steel and lead within the mold prior to filling the space with pour-foam.

Below I illustrate how I installed pieces of 1 inch, i.e., 3/4 inch shelving board within the frame to bring the depth of the mold up to 2-1/4 inches.
In this photograph, the mold is half-way filled with the above-described pieces of shelving board. Since I didn't take pictures of this construction process, I don't remember exactly how I did it, but I must have constructed the frame of the mold out of 2x6s that I had ripped to the appropriate size. I would guess that I ripped these boards to 3 inches, since the 1 inch. i.e., 3/4 inch shelving board in the bottom of the mold would bring the depth of the mold up to 2-1/4 inches. I know that the bottom of the mold consisted of a piece of plywood, but it did not figure into any of these measurements, because it was external to the box, not internal.
Next, I laid out another piece of white craft paper on the plywood pattern so I could transfer the pattern to the mold.
This enabled me to trace the perimeter of the paper pattern within the mold.
There it is.
Then, I laid the paper pattern of the steel spine (that I had earlier made) on top of the outline of the centerboard, and I scribed all the appropriate lines. To keep things unambiguous, I did the outline of the centerboard in black and the outline of the steel in red.
The mold was, for the most part finished, and by this point my metal-working buddy had found the time to help me with the new spine. We started with a sheet (or a plate as many people call it) of 3/16 inch carbon steel. The original spine had been made out of 1/8 inch carbon steel, but I thought this was a tad too flimsy.
To make the initial cut, my metal-working buddy called on his own metal-working buddy down the street. This fellow had a plasma cutter, which made this task a relatively easy one. We started by laying out the white paper pattern on top of the steel and tracing the outline of it with a black Sharpie marker. Immediately afterward, the cutting began.

After he finished cutting the first one, he picked it up laid it down on top of the steel and used it as a pattern for cutting a second one. We thought it would be smart to go ahead and make a second one just in case I screwed up the first. We accomplished all this work pretty quickly, but this was the middle of the work week and it was getting late, so we called it quits after we finished.
That weekend I returned to my metal working friend's house, and we did some of the detail work on the new steel spine. First, he took a piece of angle iron to the band saw in order to fabricate the reinforcement bars at the head of the board.

Note the plywood in the picture below. This is the plywood blueprint that had all the measurements of the original board. I used this as a constant reference during much of the construction process.

Having finished the reinforcement bars, he began to clean-up some of the rough areas left behind by the plasma cutter.

The new spine fit just right inside plywood blueprint.
We used this plywood blueprint to determine where the stainless steel centerboard pendent piece should be located.
This piece of stainless steel had been salvaged from the old spine. Despite its appearance, it was still in excellent condition. The black you see was not corrosion; it was  just left-over material from the old centerboard.
It was red hot by the time he finished welding it in place.

After he allowed it to cool, he cleaned up the weld with a grinder.

Back at my house, I thought of ways to improve the mold I had already constructed. I wanted to minimize the amount of sanding and shaping I would have to do after I had poured the foam into the mold. Therefore I decided to fashion some additions for the mold - additions that would provide it with angles and curves that more closely corresponded to the shape of the pattern drawn within the mold. To construct these additions, I used three layers of cheap, 1 inch shelving board, glued and screwed together. Nominally, shelving board is 1 inch, but of course, in reality, it's only 3/4 inches. 3/4 plus 3/4 plus 3/4 equals 2-1/4 inches. This, as said above, was the depth of the mold. I guess this is yet another reason why, if you happen to follow my steps, you might be well served to make the mold to a depth of 2-1/4 inches rather than 2 inches, even though that will mean you'll need to do a good bit of sanding to get the board down to two inches after you remove it from the mold.
I should note that I made the additions removable rather than permanent, thinking that this might be of help to me when the time came to remove the centerboard from the mold. When all was said and done, I don't think it really mattered. I could have permanently installed the additions and the board still would have come out of the mold.
I did install one portion of the additions permanently inside the mold. I was worried that the long, sharp end on the longest addition might break off, so I cut it off and glued it inside of the frame. Below you see that I've clamped it in place.

Here's the way the mold looked with all the additions in place. Constructing these additions was worth the additional work. It saved me a lot of time. I'm not sure that I could have shaped the board properly without them.
The next weekend I made one last trip to my metal-working buddy's house. Seeing for himself that the old centerboard had been compromised by water intrusion through the eyelet, he thought it would be good to install a stainless steel sleeve that would serve as a protective sheath.
First, he used a hole saw on the appropriate spot. I didn't take a picture of it, but the plywood blueprint told us exactly where to drill the hole.

He made sure that the stainless steel sleeve was perfectly square before doing the initial weld.
Then he did the final weld.

Back at home, I placed the new metal spine inside of the mold. Things were looking good at this point in the game. All I needed to do now was the pour the foam in the mold . . . or so I thought. Just as is often the case, it's just not that easy. There were many things I needed to think through before committing myself to that pour. All the issues that I had to address in advance of the pour and all of the issues I had to address during and after the pour are the subject of my next posting.
This ends the second part of a nine-part article on how I constructed a new centerboard for my Ericson 25.

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