Centerboard, Construction, Part 4: Shaping the Board

Shaping the New Centerboard with a Rasp
Having removed the new centerboard from the mold, it was now time to start shaping it, so that it would be less boxy and more wing-like. The original centerboard was curvaceous, with a foil shape that, according to the original literature, provided lift and aided the boat when close-hauled and thus pointing toward the wind. If you've read the earlier parts of this article, you'll know that the plywood blueprint that I produced in the process of the destruction of the old centerboard was absolutely essential for the construction of the new board. This was no less true when it came to shaping the new board.
You might remember that after I constructed the mold, I transferred the shape and the measurements from the blueprint to the interior of the mold via a piece of white craft paper. I used this same piece of white craft paper to to transfer the measurements onto the new board.
The measurements to which I am referring are those that pertain to the grid system of sorts that I developed, wherein lines spaced every six inches provided reference points. More on this later. Below you can see the lines I drew on the new board with a black Sharpie marker.
Using a plumb bob, I extended these reference lines downward on the sides of the centerboard.
Below you can see all the reference lines - the ones on the top and the ones on the side.
Next, I laid out the foil-shaped cut-outs that I had made before I had destroyed the old board. These helped me to visualize curves that I would need to give to this flat board. I, of course, would not build up the board to achieve these curves. I would, instead, cut into it.
Therein lay the problem. How exactly would I cut into it? The only solution that I could come up with was this: sand it with an electrical random orbital sander until I had achieved the necessary curves. My biggest concern with this approach was that I was unsure how I would keep the board symmetrical. In other words, how could I sand it evenly on both sides? I couldn't imagine a way to achieve any level of consistency. Stumped, I put this project aside for a while, hoping that I could figure out a better approach.
That better approach came to be, quite serendipitously, not long afterwards, when my son got together with some of his buddies one Saturday afternoon to build a surfboard at a nearby workshop. The dad who owned the shop had spent much of his life in the maritime industry.

As a young man he had worked in various boatyards in Charleston and the Caribbean, and he had made many a surfboard in his day. Today, he still enjoys doing this on the side, so on this Saturday afternoon he thought he'd pass on some of his skills to the younger generation in the neighborhood. This particular lesson concerned epoxy work. Earlier in the day, before the boys arrived, he had cut and shaped the board on a fancy computerized cutting table in the back left corner of the shop. As he was explaining how this cutting table worked, I asked him about how he used to cut and shape those surf boards back when he was a youngster. In response, he said that back then he and everyone else did it by hand. It was then that I suddenly realized that maybe he could explain to me how I could properly shape my new centerboard. I explained to him my predicament, and he said that shaping my centerboard would present no problems whatsoever. He suggested that I return home and get the board and bring it back to him right then and there. He said he'd use it as a means of showing the boys how they used to do it back in the day. I was thrilled. Wasting no time, I returned home, and with the help of another dad, we transported the board from my house to this shop.
Before leaving home, I also grabbed a few other things: the plywood blueprint, the curved cut-outs, and also the piece of fiberglass from the old board.
As it turned out, it was the old piece of fiberglass that proved to be more helpful to him than anything else.

With a red Sharpie marker in hand, he quickly began drawing reference lines on the new board, using the old piece of fiberglass as a guide. The large red parallel lines indicate the point at which the board transitions from its plateau near the head to its steep slope on the trailing edge. The other red line that he is in the process of drawing indicates the point at which the leading edge of the board begins to curve.
The next thing I knew, my neighbor had grabbed an electric hand-held planer and started taking off thin layers of foam. He said that it was good that I had not started up this part of the project on my own, because if I had used the electric sander, as I had planed, I would have damaged the foam.
You'll notice that he started on the leading edge of the board - the part of the foil that would have the large curved edge (as opposed to the trailing edge that would have a knife-like edge). You'll also notice the red reference mark that he made for himself along the center of this leading edge. He drew this free-handed in about 20 seconds, just before he started up the electric planer.

He shaped this leading edge of the board in a very consistent pattern. He started at one end and made a complete non-stop pass all the way to the other end. This was the initial bevel. He then cut a second bevel just above that one. Finally, he cut a third bevel, this one below the initial bevel. All additional cuts that he made followed this bevel-upon bevel pattern. I can't remember how many passes that he made on this side, but it didn't take long for the foam on this side of the leading edge to begin to take on an attractive curved appearance.
At this point, he took a break and called all the boys back into the shop to lay down another layer of cloth on the surfboard. Note the special stand beneath the board. It was narrow enough to allow him to wrap the cloth over the edges of the board by about six inches without getting in the way. I would later mimic this stand, in a crude way, on my front porch when the time came to apply cloth and epoxy to the centerboard.
It was great to see the younger generation getting some experience with epoxy.

Having finished the wetting out of that second layer of cloth on the surfboard, my neighbor returned to the centerboard. and started working on the trailing edge - you know, the one that has that knife-like edge to it.
Unlike the leading edge, which he beveled several different times in a diamond-like pattern, on the trailing edge he made one large bevel by making multiple passes at the same angle. Notice that the old piece of fiberglass is still nearby. He used this as a reference.
Just as he did on the leading edge, on the trailing edge he made consistent, non-stop passes from beginning to end.
As he neared the point in the board where the tang (the piece of stainless steel) was located, he gradually lifted the planer up in order to create the slope that led upward to the plateau near the head of the board.

With a number of passes having been made, we turned the board around so that the trailing edge faced outward. This made it easier to plane.

After many passes of the planer on the trailing edge, my neighbor was satisfied with the shape of the board, and he, at this point, asked everyone to help him turn it over to the other side.I stopped him, however, and told to him that I wanted to check the shape of the board with the negatives of the curved cut-outs that I had made prior to the destruction of the old board. Lining up the cut-outs on the reference marks that were still visible on the leading edge of the board, I was amazed to see that my neighbor had exactly replicated the foil shape of the original board, simply by making visual reference to the old piece of fiberglass nearby while planing the new one. This work for him was really quite effortless, and it was for this reason that I, at that time, and still today, believe that the Ericson yard in Southern California in the 1970s employed some surfer dude, who was skilled in the shaping of surfboards in the traditional fashion, to make their centerboards. Can't you just see him there now? Sunglasses, Marlborough red hanging from his mouth, 8-track tape of Led Zeppelin playing in the background.

It was then time to flip the board over to its other side. At this point, my neighbor handed me the electric planer and told me it was my turn. I was hesitant to tackle this job, and I insisted that he would be the better man for the job. He, though, insisted that I needed to learn for myself. The other dads and the assembled boys agreed. Bowing to the pressure, I picked up the planer and starting cutting the bevels into the leading edge. Then, I started cutting the one large bevel in the trailing edge. The one thing I was worried about more than any other was removing too much material. After a number of passes, I asked my neighbor if he would do the finishing touches. He obliged.
He next wanted to show everyone the second step in shaping a surfboard, or in this case a centerboard. He, therefore, grabbed a rasp, and started making short, choppy passes from one end of the board to the next. He pushed the rasp away from him as he walked along the side of the board.
He said it was better to have a long rasp than a short one. The long one helps to keep the work area flat by helping you avoid the creation of valleys and divots.
He also made a few passes in the area between the leading edge and the trailing edge, just to remove the original slick surface from the cured pour-foam. It was slick, because the plastic within the mold had caused the surface of the pour-foam to cure with a mirror-like consistency. Recall as well that there was some waxy residue on this slick surface. All of this, of course, needed to be removed, so that the epoxy could bond to the foam.

During this part of the shaping process, I thought it would be good to check, from time to time, the shape of the board to make sure that the original foil shape was being maintained. It was, and that was good.

This picture, more than any other, illustrates the multiple bevels that he had cut in the leading edge of the board with the electric planer. Now, with the rasp, he is eliminating the edges of the bevel in order to make the leading edge more curved.
Satisfied with his progress, my neighbor moved to the third stage of the shaping process - the hand sanding of the board. In this, he emphasized once again that you should never use an electric sander on foam. He started by smoothing out the leading edge with a large piece of sandpaper. He said this paper was intended for a drum-roller sander, you know, the type of sander used to strip hardwood floors.
For the trailing edge, he used a large, flexible sanding block, the kind you can order online from automotive body-work websites. He said it was important that the sanding block be large, in order to avoid valleys and divots. He added that if a flexible block like this one is not easy to obtain, you can always make your own out of a 2x4 and some sandpaper that you've affixed to it with a staple gun.
He used the same technique with the sanding block that he had used with the rasp - short, choppy, yet consistent strokes, all of them pushed away from him as he walked. He never sanded back and forth.
You'll notice that it is considerably darker in this picture than it was in some of the earlier pictures. It was the middle of the summer, and an afternoon thunderstorm had been approaching us for some time. My neighbor continued working on the board until just before it started to hit us.
Unfortunately, therefore, I had to return home with a centerboard that was not yet fully shaped.
I was happy, though, that it was, at least, close to being fully shaped and that I had been so fortunate to discover that my neighbor could so easily apply his surfboard making skills and his former boatyard working skills to the shaping of this new centerboard. I figured I would wait a little while and then offer him some beer in exchange for coming over and finishing it off. Besides, I was right in the middle of another project on the boat at this point.
As it turned out, when I finally got around to calling my neighbor and offering him some beer to come over and finish up the board, he said he wasn't up for it. He said I'd be better off trying to do it myself than have him do it for me. This was a lesson he said he learned at the boatyard when he was younger. There was an old fellow there who was legendary for being able to shape things at sight. That old timer told him that you just had to feel it . . . you just had to sense it. That was the way to do it, and the only way to learn how to do it was to do it yourself. I knew of this now-deceased legendary old timer, because I knew his grandson (who lived down the street from me), so I knew that my sage-like, surfboard-making neighbor wasn't shooting me a line of bull. So, yes, I appreciated his words of wisdom (I guess), about his mentorship at the boatyard under the legendary old timer, but at this point I wasn't really ready to play the role of Grasshopper to the Master in Kung-Fu.  I would rather have gotten it all over, once and for all, with one easy beer-for-favor trade, so I covered up the centerboard and let it sit for sometime while I worked on other things.

When I was at last ready to embrace my inner board-shaper, I uncovered the board and assembled the necessary tools for the work that lay ahead of me. I made two different sanding boards, one out of 60 grit paper and the other out of 36 grit. I'll say right now that I never used the latter. It was just too gritty for that foam. I also purchased a longer rasp than the small one I already owned. You'll notice that the foam had become discolored over time, turning from a light yellow to a dingy yellow. This dingy color was only at the surface, It didn't take much sanding to get it back down to the lighter color.
As I sanded, I paused every now and then to make sure that the board was maintaining its foil shape.
I also took some measurements with the caliper. The board was 2-1/4 inches, just like it should have been, since I had constructed the mold to a depth of 2-1.4 inches. The only problem was this was the finished width of the old board. This new board was not yet finished, and I figured that by the time I had added all the cloth and epoxy that I needed to add, it would be at least 1/4 thicker. Keeping the width of the board under control was crucial, since the centerboard trunk was only 2-3/4 inches wide, and there needed to be some play within the trunk on either side of the board, and keeping the board to its original 2-1/4 inch thickness would allow for 1/4 inch play on either side.

At this point you might be asking yourself why I didn't just make the mold to a depth of 2 inches rather than 2-1/4 inches. The simple answer is that I just didn't think about it at the time that I constructed the mold. Knowing what I know now, however, I'm not sure that if I were to do it all over again, I would make the mold any less than 2-1/4 inches. For one thing, as I said in the second part of this article on the building of the mold, it would be difficult to construct it to a depth of 2 inches without running some of the material through a planer. In other words, the standard 3/4 inch thickness of one-inch stock makes the building of a 2-1/4 inch mold much easier than a 2 inch mold. If your not sure what I'm talking about, I explain it in greater detail in that part of the article. Secondly, it is actually helpful to have the extra quarter inch of foam on the centerboard when pouring the mold. There is very little room for error. In short, it's much easier to reduce the board by a quarter inch than to increase it by the same amount.
What this meant for me, though, was that I was going to have to pull out the electric hand-held planer and follow the same steps that my surfboard-making neighbor had followed - moving from the electric planer to the rasp to the sanding block. How did I know that I would need to take it down a quarter inch? I didn't know for sure, so I thought it would be smart to call another fellow I knew in the neighborhood - the same one I had called upon for some other projects in the past. He was a former cold-molded boat builder and MAS epoxy representative. Now he was boat surveyor and marine consultant. He told me that 1/4 inch was a good guess for the amount of build-up I could expect from the lay-up schedule he suggested (which I will discuss in the next part of this article). Receiving reassurance that I needed to take off a good bit of material from this board (1/8 inch on each side), I got to work with the hand-held planer.

I tried to use the rasp, but I had a knack for scoring the board and leaving divots here and there, so I put the rasp down and picked up the sanding board with the 60 grit paper stapled to it. This was the bomb. It did just what I needed it to do, and it removed the material in a consistent way.
My good buddy from out of town was visiting on this weekend. He's the same one who helped me pour the mold, so he was interested in seeing how this projected would turn out. Here he demonstrates the sanding method we used, which was almost identical to the one that I had learned from my surfboard-making neighbor, except that we used back-and-forth patterns on the large areas of the board.

This approach was good, but it was taking far too long, so I decided to grab the electric planer and take off more material than the sanding block could ever hope to do in the same amount of time.
My use of the electric planer was going very well, until I got down to the head of the board. I tried to bevel (slightly) the sharp edge of the head and ended up causing a chunk of foam to break off. I should never have attempted this on such a small edge. I should have used the sanding block for this. This is a spot that I would later have to patch with epoxy and colloidal silica.
My buddy and I then flipped the board over and started sanding down the other side.

Even though we had now removed all of the old, dingy, yellow layer of foam from the two sides, the stuff still remained on the edges of the board.
It took a lot of sanding to do the edges in the area around the head of the board. The crinkles in the plastic inside of the mold had cause there to be irregularities in the surface.
As we continued to sand, we began to see the outlines of some of the components of the steel and lead spine assembly. For example, one of the bent screws (that held the lead to the steel) came into view.

At this point, we stopped and measured the thickness of the board with the caliper.
We were pleased to discover that we had reduced the thickness of the board from 2-1/4 inches to 2 inches.
Now it was time to recheck the board with the wooden cutouts to see if we had maintained the foil shape. The port side was just right. The graceful wing-like curve was still there.
The starboard side, on the other hand, was a little off. It was a tad too flat in the mid-section between the leading edge and the trailing edge.
You can see what I mean in the close-up below. To remedy this, we worked this area some more with the sanding block. On this note, I should say that during this entire process of sanding down the board from a thickness of 2-1/4 inches to 2 inches, we sought to maintain consistency by giving the same about of sanding time to each side of the board. In other words, we would sand for about three minutes on one side, and then three on the other. Likewise, we would attempt to use the same types of sanding strokes. Nevertheless, we were thrown off of our game just a little bit by the consistency of the foam itself on this starboard side of the board. This had been the side of the board that had faced upwards inside of the mold at the time of the pour. Because of the pressure exerted by the foam during its expansion, it appeared that the foam on this side of the board was more dense (at least near the surface of the board) than it was on the other side, which had been facing downward inside of the mold. This is the only thing, as we saw it, that could have made the foam a different consistency. At any rate, because of the varying consistency of the foam on this starboard side, it required more sanding strokes than the other side. This is why we were slightly off when it came time to check the board for its foil-shape consistency on each side.
Eventually satisfied with the foil-shape on each side of the board, we began smoothing up the leading edge of the board with a large sheet of sandpaper. I had found this at the local hardware store, the same place where my surfboard-making neighbor hand bought his.
In the picture below, you can see the outline of one of the lead plates, just beneath the surface of the foam. This is all the more reason why the 2-1/4 inch deep mold was better than a 2 inch deep mold. There just isn't much room to spare.
We also cleaned up the area around the stainless steel pin shaft. The shaft was a good reference point during the sanding process. We knew that when 1/8 of an inch was showing on either side of the 2-1/4 inch pin, then we had reduced the thickness of the board by a total of 1/4 inch.
We also reduced the board by 1/8 inch on each end so that the total length would be 1/4 inch less. This was not something that we thought about or realized until the very end. When we had sanded the ends before this time, we were primarily interested in removing the old, dingy, yellow surface layer.

The last thing we did was to go back over the leading edge of the board with the hand-held piece of sandpaper. There were still some irregularities from the sanding block, and we wanted this leading edge to me as smooth and rounded as possible. This paper really did the trick.
This ends part four of my nine-part article on the construction of a new centerboard for me Ericson 25.


  1. Roscoe...I enjoyed your photos and commentary. I recently lost my centerboard (after it was fixed by a local marina repairman). The CB broke off the line block and fell deep into the channel, subsequently not retrievable. Would you consider fabricating another one (for a fee, of course)for my E25?
    Please respond as soon as possible.
    thank you

    1. Rara,

      Thanks for the compliments. I've heard of others losing boards in a fashion similar to what you you describe. Apparently, the freely dropping board causes the pin assembly to tear out of the hull. There's also been a case where the board itself broke off on account of internal rust. Maybe you've figured out which one of these it is already. Just thought I'd mention these scenarios. In terms of constructing a new board for a fee, when I first started constructing my own, I had it in my mind that I would do this very thing as a way to make a little extra money on the side. By the time I finished, I said I would never do this. There are just too many hours involved. Also keep in mind that to do what I did, you really need to have the original lead plates, which I believe are really important for keeping the board down in the water when the currents are pushing against it. If I were to start from scratch without and old board to work with, I would build one with a stainless steel spine sandwiched by synthetic material. There's a thread on the Ericson Forum where an E23 owner shows how he made one for this boat. It's on a thread that is titled something like "E23 and E25 Centerboard." The materials are expensive, but not overly expensive compared to what you'd need to spend to build one like I did. I would avoid IDA SAILOR, a boatyard up in Idaho. They charge about $1000 for what is essentially a surf board.