Centerboard, Construction, Part 1: Demolition of the Original Board

The Original Centerboard, during the Demolition Process

Soon after I purchased my Ericson 25, I decided to attempt to repair the original centerboard. You'll recall from my earlier two-part article, "Centerboard Extraction and Analysis," that the board, at the time of purchase, was damaged from what appeared to have been a grounding of the boat on the part of the prior owner. You'll also recall that I decided to repair the board. I began by grinding off the many layers of red bottom paint that had been applied by this prior owner over the thirty some odd years of his possession of the boat. Then, with the assistance of a friend with a die grinder, I ground out the cracked area of the board. I also ground the area around the pin hole at the opposite end of the board. In the course of my grinding I discovered what appeared to have been earlier repair work that had been attempted in these areas. It was very clear that salt water had made its way to the steel spine of the board and had created a lot of rust.
At the advice of a buddy at a local boatyard, I decided to put the board into hibernation, so to speak, within a temperature-controlled work space in my house. The thinking was that it would take many months for the board fully to dry out. I thus put the board down for a long nap, and I turned to other tasks. Distracted by a lengthy home-improvement project, various family concerns, and, of course, other projects on the boat, it would be a year-and-a-half before I turned my attention once again to the centerboard. When I did, I discovered the board was beyond repair. The rust within the board had caused it to split in the area around the pin hole.

The picture below, that I took at the beginning of the demolition process, should give you some idea of what I'm talking about. The crack in the board had expanded from being simply a small crack to one that was some half an inch in width. This had caused the fiberglass on the body of the board itself to split in a diagonal line from the leading edge to the trailing one. For some reason, I neglected to take pictures of this damage. Maybe it was too upsetting at the time.
Saddened by this discovery, I reluctantly came to the realization that I had no choice but to get a new centerboard from somewhere. I briefly considered paying Idasailor, a boatyard in Idaho, to build me a new one. They had constructed a new one for another Ericson 25 owner in that part of the country for around $1000, and he apparently had been pleased by their work, despite the fact that the new board was nowhere near the original weight of 150 lbs. If I remember correctly, it was somewhere in the neighborhood of 60-70 lbs. At any rate, Idasailor had recently constructed another centerboard for another Ericson 25 owner in Florida, and they had royally screwed-up. This centerboard, unlike the other one they made for the guy in Idaho, had no ballast in it whatsoever. Receiving it in the mail, and not knowing any better (because he had lost his original board while sailing the boat not long after purchasing it), he had his boat hauled out so that he could install it. He then had it splashed and decided to go sailing. Much to his chagrin, or I should say his unmitigated anger, that board would not deploy from the centerboard trunk. The reason? It was of such a lightweight construction that it floated. In short, it was little more than a surfboard. Idasailor did agree to correct the problem at their expense, but it was a major headache for the owner. Knowing this, and knowing that $1000 was far more than I wanted to spend on this component of my Ericson 25, I decided to consider other options. I should note, before moving on, that Idasailor is apparently no longer in business, so purchasing a centerboard from them is no longer even an option.
New Centerboard (in white) by Idasailor to replace the original (in blue) for the E25 owner in Idaho
Knowing that the purchase of a new centerboard was not a desirable option for me, I knew that I would need to build one for myself. I researched the various ways that others had built them, and I eventually concluded that the best approach would be to mimic what an Ericson owner named Gordon had done to construct a new board for his Ericson 23. Gordon had cut a new spine out of stainless steel and sandwiched the steel between UHMW plastic. He then shaped the plastic somewhat to give the board a foil shape, similar to the original board. Intrigued by this, I used as a basis for calculating just how much such a construction approach might cost me. I recall that it would have cost me a lot of money just for the stainless steel and the plastic materials, not to mention whatever other unexpected materials I might discover that I needed. I thought this was too steep a price to pay. I was also somewhat concerned that this type of board, although made out of stainless steel, might not weigh the 150 lbs that the original board had weighed. If you're thinking of taking this approach yourself, you might want to consider adding lead plates somewhere underneath the UHMW plastic. If you wish to read more about Gordon's approach, just check out the thread on the Ericson Yacht Owners forum. It is titled, "E-23 Stuck-up centerboard."
My overriding concern, as you should see, was to make the new centerboard as close as possible to the original board in terms of its shape and weight. The original specifications spoke of the importance of the foil shape (providing lift and assisting with pointing) and the 150 pound weight. Bruce King, the naval architect who designed the Ericson 25, obviously thought these qualities and quantities were important when he designed the boat, so I decided to stick with his original plan. The original Ericson literature on the centerboard addresses all of these matters, and you can read this information for yourself in the article, "Centerboard, Diagrams, Original." Here's the introductory material, though, in case your curious right here and now.

With all of this in mind, I set out construct an entirely new board as close as possible to the original specifications. The first problem I ran into, of course, was that the original specifications said nothing about how exactly the original centerboards were constructed. From what I could surmise, Ericson Yachts had used a mold to produce these boards, so the first thing I needed to do was take precise measurements of the original board, so that I could figure how I should construct the mold. I also needed to take these precise measurements, because it was essential for me to destroy this old board, in order to figure out exactly how it had been constructed. In short, since there were no original blueprints or specifications for the construction of the board, I needed to reverse engineer the new board from the old one. From death comes new life, and it was necessary to destroy the old to create the new.

I began by laying out the old board on a scrap piece of finish-grade oak plywood. This piece of wood would contain many lines and numbers by the time I had completed this part of the project, so I wanted it to be as smooth as possible for the recording of this important data. After scribing the perimeter of the board on the plywood, I marked the board and the plywood at six-inch intervals. My plan was to use these six-inch intervals as reference marks for the many measurements I would make. You can see the pencil marks on the board in the picture below.
To replicate the foil shape of the board, I thought it would be a good idea to create a foil-shaped pattern on some separate piece of wood, since the two-dimensional piece of plywood underneath the centerboard would not allow for this. To get an accurate measurement of the shape of the foil, I used an angle gauge, a relatively simple tool with a row of narrow metal teeth that will conform to the shape of some object when pressed against it. To get consist measurements at each of the six-inch intervals, I held a spirit level on top of the housing of the angle gauge.
I then transferred these measurements from the angle gauge to the southern yellow pine, ensuring that the gauge was square with the pine board itself
It would have been nice to have had a longer angle gauge. That way I would have been able to measure the foil shape of the board all at one time. Since I didn't have such a gauge, I simply make two separate measurements - one at the leading edge of the board, the other at the trailing edge. The square, of course, helped me keep things true.
Below you can see how I have, at this point, drawn in pencil the complete foil shape based on the two adjacent measurements above.
I then took the southern yellow pine to the sawhorse and cut out the foil-shaped pattern with the jigsaw. My goal in this was to remove the foil-shaped pattern so that I would be left with a negative of sorts. The negative, of course, is the piece of wood to the right.
Confused? The picture below probably helps to clear things up. With a wooden negative of the foil in hand, I could gauge exactly how to shape the new board, in order to make it conform to the foil shape of the original one.
I created negatives for the entire length of the board, measured at the six-inch reference marks I had earlier made. Just to make sure that I could visualize the foil shape in a symmetrical fashion (as it should appear on either side of the centerboard) when viewing the board from the head or the foot, I used the negatives to scribe the foil shapes onto another piece of southern yellow pine. Below you see this piece of wood, with the many foil shapes corresponding to the six-inch intervals.

I then placed all the negatives on the board at one time to see if their top edges were all level with one another. This would provide me with some assurance that I had measured the foil-shape in a consist way from one end to the other.
Fortunately, these pieces of wood were level. On another note . . . in case you're wondering, I didn't make foil negatives for the last two reference lines near the foot of the centerboard, since the shape of the board changed considerable in this area as it neared its end.
I also measured the circumference of the centerboard at each of the six-inch reference lines. I wasn't going to leave anything to chance. I had to get every measurement I might possibly need before moving to the demolition stage of the project.
When the time came for the demolition, I called upon that same buddy of mine who had helped me clean up that board with his pneumatic die grinder over a year-and-a-half before that time.
He agreed with my assessment - this board was completely shot. He was more than pleased to help me tear it up. That's the fun part, right?
While analyzing it, he thought it was funny that the centerboard, when turned at this angle, looked like a smiling pig or some other creature.
His pneumatic chisel made short work of the crack that already existed in the board.
In no time, he had removed large chunks of material around the head of the board.
It was at this point that we made a very troubling discovery - troubling, that is, for all of you other Ericson 25 owners who still have the original board. In the area around the eyelet, there was no metal whatsoever. This is the eyelet, of course, through which the centerboard pin passes. The centerboard pin, of course, is what hold the centerboard inside the centerboard trunk. Without this pin, there is nothing that keeps the centerboard from sinking to the ocean floor. On this board, there was nothing but foam and fiberglass holding that pin in place. In other words, foam and fiberglass were the only things supporting the 150 pound board. More than one owner has lost a board due to the failure of the eyelet in the centerboard. Now you know why this happens. Water penetrates the pour foam within the eyelet over time. This water causes the metal to rust. Not only does the rust cause the board to split, but is also causes the metal in the area around the eyelet to disintegrate. If you purchase an Ericson 25 that still has its original centerboard (as many of them do), it would not be a bad idea to reinforce the head of your board with a metal plate in the fashion described in the article, "Centerboard Extraction and Analysis." It's much easier to maintain an old board than it is to build a new one, and if you must build a new one, it's much easier to do so with the old one as a reference.
My buddy then used a cutting wheel to open up the leading edge of the board.
He also cut into the body of the board to make it easier to extract large chunks of the fiberglass.
What the machine couldn't take care of, the hand tools could. Notice the circular cut-outs in the steel. These had apparently been put there by Ericson to allow the pour-foam to expand and envelop both sides of the centerboard within the mold.
We also noticed that the Ericson yard had welded a piece of steel on a diagonal atop the spine to reinforce the head of the board.
The cutting wheel and pneumatic chisel also worked wonders at the foot of the board.
As we removed one chunk of fiberglass after another, we eventually started to see what appeared to be lead plates on either side of the steel spine.

The mid-section of the board was still in excellent condition. It was a shame to have to demolish it, but the head and the foot had sealed this board's fate.
When we finally had removed one entire side of the board, we were able to get a good glimpse of things that formerly had been well-hidden. One thing that gave me pause was the discovery that the metal at the foot of the board still appeared to be wet.
An excellent view of the anatomy of the original centerboard.
Ever vigilant to record as much data as possible, I took the opportunity at this point to mark the metal, the lead, and the remaining half of the fiberglass was reference lines every six inches. These lines would prove to be very helpful in the project ahead.
You can see the black Sharpie reference lines on the fiberglass on this end of the board in the picture below.

The steel in this section of the board was in pretty bad shape. This made me feel a little bit better about completely trashing this board, although I could quite quash those pangs of remorse, no matter how I tried to reason them away.
The steel at the foot of the board was just as bad, if not worse. Yes, this destruction of the old was necessary for the birth of the new. That's what I had to keep telling myself.
Fortunately, I was able to remove the remaining half of the fiberglass in one piece. This would be of great help to me as I built the new board.
The next task was to remove the lead plates from the steel spine. This would take some wrestling. It wasn't easy, since the plates had been secured with stainless steel screws whose ends had been hammered over at a 90 degree angle after they had passed through both pieces of material.

You can see the heads of the screws below.

This picture allows you to see even more clearly just how bad the deterioration of the steel was in the head of the board, and yes those dark spots you see are areas that were still wet.

There you have it. One rusty and worthless old spine, and two lead plates that were ready to go back into service as soon as we could create a new spine for them.

After I got back home I laid out the old spine on some drop cloths so I could get a good picture of the foot. Just as was the case with the head, this part of the spine was still very wet. Hard to believe, but true.
This concludes the first part of my nine-part article on the construction of a new centerboard, according to the original specifications, for my Ericson 25. The next installment will concern the cutting of the new spine for the new board and the building of the mold that would house this spine (and the lead plates) during the pouring of the polyurethane foam.


  1. Hey, did you happen to digitize any of your work? I need to rebuild a board for my E23 and I'm wondering if this board, in any way, resembles a NACA profile. If it's a NACA profile I can skip the whole measuring process and just design new board with CAD and then have it waterjet cut.


    1. Thanks for visiting, Mike. No, I did not digitize any of this work. Did not have that as an option. Best of luck.

  2. I just purchased a 1975 e25 today. I have been reading your blog over the past year in anticipation of this day, and look forward to referring to it many times in the future. What an incredible resource. Thanks, Aaron

    1. Congrats on your purchase, Aaron. Glad that this website has provided you with inspiration. Best regards.

  3. Before ordering mine today I spoke with the gentleman at rudder-craft (Idaho sailor) and he assured me all the rumors of the rudder not being heavy enough are hot air. He also mentioned that his rudder is solid resin and has no metal other than the shot mixed into the resin to ballast it and that his rudder is a thinner more advanced NACA profile than the original.

  4. Hey Roscoe, I am having to do some serious repair on my board and found your post very helpful, as always. I did have the chance to see the original line drawings for the boat and it called out the centerboard was a NACA 0015 profile. Anyone rebuilding one can use that to generate a pattern for the foil shape. Thought others would find it helpful.

  5. Hey John, Thanks for getting in touch and thanks for the compliments. This is good information to know. A couple of years ago I looked on the Ericson forum and it indicated you no longer had any activity. I figured your had sold your E25. Glad to know you're still at it! Roscoe.