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Giving a centerboard a lift

Sep 27, 2011

My boat is a 1966 Allied Seabreeze yawl named Arcturus. The early boats (Arcturus is hull number 56) were referred to as the ‘bronze boats’ — in part because they featured a hefty 400-pound bronze centerboard. I eventually decided the centerboard lift mechanism needed to be modified to keep the bronze monster under control.

The centerboard lifting mechanism was solidly built but was too complex. A shackle attached a 7x19 wire to the board, about one third of its length aft from the hinge pin. The cable turned over a four-inch wire sheave in the keel, and continued inside a small bronze tube under the cabin sole. Aft, a second bronze sheavebox was positioned under the engine, whereby the cable turned upwards, continuing through another bronze pipe, until it exited in the portside cockpit locker and was wound around a bronze worm-gear winch, operated from the cockpit. This setup needed updating and I decided to simplify its design and create something more serviceable.

My modification was a big departure from original, and took five or six drawings before I was completely happy with it.

I envisioned a lifting arrangement that required no sheaves and that could be serviced at sea — simply a line going straight to the board through the bottom of the keel. I thought I could accomplish this by replacing the lid of the keel sheavebox with a stainless steel plate, onto which a stainless pipe would be welded. The pipe would span the cabin interior from the keel to the coachroof, and the cable would run inside it, exiting on deck level and led to a normal cockpit winch. A sailor, friend and world-renowned sculptor, Rodney Carroll, has a large workshop in an old warehouse in Baltimore and invited me up to use it. He could also help with the welds, with which I had no experience. Carroll and I spent some enlightening days in his studio drawing and re-drawing my ideas.

Choosing the pipe    
The pipe idea quickly gained steam. I ordered a length of 316 stainless steel pipe, 1.5-inch inside diameter (ID), schedule 40, which gave a wall thickness of about 3/16-inch. We sized the pipe on aesthetics — since it would run in the center of my cabin, it had to be a nice handhold and look proportional to the rest of the interior. It also serves as a mount for a centerline drop-leaf table. The 1.5-inch ID gives about 1.66-inch outside diameter, which suits just fine and feels solid in your hand.

From Carroll’s large supply of scrap metal, I found a 3/16-inch stainless plate that I could cut out for the new lid to the keel sheavebox (which had previously been fiberglass, about 6x8 inches). I used the old lid as a template and cut the new one with Carroll’s band saw.

Once inside the sheavebox, it was obvious that the original design had some serious flaws. The wire ran over a standard wire sheave, only just large enough for the wire diameter. This arrangement worked fine with constant tension on the wire — but release this tension, and the cable could easily jump off and jam between the sheave and the walls of the box. A light grounding with the board down could easily do this, and since the sheavebox is below the waterline, the only fix involved a haulout.

I soon realized that we’d need at least one sheave to make my idea work — as the board begins lowering from horizontal, the attachment point moves forward in an arc as the board swings down, so there would have to be something to deflect the line along its path and prevent it from touching the sides of the pipe. Using the old bronze bracket that the original wire sheave was attached to, I had a friend turn a new, custom, jump-proof sheave from a solid chunk of bronze. It resembles an anchor-roller sheave — narrow in the middle, to accept the cable (which is now Dyneema), and wide at the edges, with a deep vee shape. The sheave is nearly as wide as the bracket, and there is no way for the line to jump off. Furthermore, the sheave is only about one inch in diameter (versus the old one’s four inches), leaving space behind it to fish through a new cable, should it break.

Correct positioning
The next challenge was to position the pipe in the correct location on the steel plate for a fair lead. The cable would be turning forward now over the new sheave, and I needed to position the pipe exactly over the hole in the keel. This way, I hoped, if the cable were to break at sea, I could drop a weighted messenger line down through the pipe and it would travel right out through the bottom of the boat. All it would take is a quick swim to re-attach it to the board. I ended up using a clear piece of acrylic as a template lid and using only my eye, drew a small circle where the pipe would be welded. I transferred the circle onto the steel, cut it out on a band saw to a diameter just large enough to accept the pipe and we went from there.

The pipe’s design evolved as well. I decided against bringing the cable onto the deck and to a winch — the challenge of keeping this exit watertight was multiplied by the fact that the pipe would mount under the hatch slider turtle, making it nearly impossible to access. Instead, we fabricated a bracket in the top of the pipe, and I ordered a three-inch Edson wire sheave in bronze. Once installed, this sheave sits at the very top of the pipe, above the waterline, and is accessible, as it’s simply open. In bronze, it’s also quite attractive, and I designed the bracket to show this off. To do the heavy lifting, I removed the bronze worm-gear winch from the cockpit and made a simple bracket that we’d weld onto the pipe to then bolt the winch onto. Once complete, the winch will hide under the cabin table.

In theory, we now had a much simpler system — the cable would terminate on the board in its same location, turn around the new sheave in the keel and lead up through the pipe. It would exit the pipe inside the cabin around the new Edson sheave, whereby it would run along the outside and down to the winch.

Building and welding the pipe and its associated brackets in the shop was a cinch. I did the cutting (with either a band-saw or cutoff-wheel grinder), polishing and fitting while Carroll welded it all together. The biggest challenge was getting the angle between the pipe and the plate right so that the pipe would be vertical inside the cabin. We accomplished this by simply tack welding the pipe in place and dry-fitting it onto the keel, adjusting it before finishing the weld.

Installing the new system
The other big challenge was sizing the length of the pipe so we could install it. The whole thing is one piece now — the new stainless lid sits about three inches below the cabin sole. I needed to make the pipe as long as possible (it was going to be through-bolted through the cabin roof), but short enough to slide into place. I cut out several mahogany circles and laminated them together to use as a spacer between the top of the pipe and the cabin roof. Arcturus has a molded, fiberglass headliner, which I had to cut out so as to be able to bolt the top directly onto the deck. I used six-inch 1/4-20 fasteners (the bolts run through the pipe bracket and the mahogany spacers) and put cap nuts on the inside to finish it. We caulked and bolted down the stainless plate and followed up by bolting the top through the cabin roof, using a heavy aluminum backing plate (This was difficult, as the top of the pipe lined up with the hatch-slider turtle. To access the nuts, I had to tape a wrench to the end of a broomstick and carefully guide the nuts into place as my dad turned a wrench from below. The backing plate is hidden under the hatch turtle).

The big test would come when I attempted to drop a weighted line down through the pipe. With the boat in the slings, I fished a line through while my dad tensely watched from below. Out it came! With the line over the top sheave on the pipe, my dad grabbed the end under the keel and we ran it back and forth over both sheaves — the alignment was spot on. When we attached the board and the winch, it couldn’t have worked more smoothly.

This new system simplifies and strengthens the lifting mechanism on the centerboard to a nearly foolproof and serviceable system. The coming trans-Atlantic voyage, of course, will be the ultimate test.

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Andy Schell is a sailor, writer and rigger based in Annapolis, Md.

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