Mysterious centerboards.

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Tom Young
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Mysterious centerboards.

Post by Tom Young »

Does anyone have one? The Alden Challenger like many CCA designs from the era, has a long keel with a bronze centerboard. It's not unusual to hear owners say they can't really tell a difference between having the board raised or lowered. I can understand that as this is not the dramatic situation such as you'll find with a small boat and a daggerboard for instance.

Still, a nearly 300 pound slab of bronze sheet surely does something down there? I think it does but I'm a hopeful type so I've been doing some experimenting out there. I'm a general tweaker when sailing and pay as much attention to the telltales on my mizzen as the mainsail so of course I'll raise the board off the wind, totally if I sense leeway is eliminated deep off such as on a broad reach. Image At that point, telltales are flowing nicely with all three sails cracked off, the long keel and rudder giving what feels like a good cleaver to slice the water. Lift? Hmmm, maybe but modern boat design fans claim not much from these old foilless shapes. Still, we must get some, yes?

But it's when the wind is forward of the beam the board should come into play of course. So I've spent some time sailing alone (few would have the patience for this) trying to discern centerboard effect. My unscientific fun has been sailing with the board lowered and raised while "on" the wind. Mostly with full sails, the auto pilot steering an easy compass course (the boat will nearly sail itself in these conditions but the AP maintains the direction, or the orientation of the hull to wind). This gives me time to feel and watch. Image

While this shot is a little more off the wind, and in plenty of it, it still illustrates the first and simplest thing a centerboard should achieve. Cutting down on the boat slipping to leeward. I have a suspicion that some that have told me they can't tell the difference board up, board down, may not be aware that while the sails are trimmed and drawing nicely, they're slipping to leeward at a greater rate board up.

Afterall, the board is about 5/8" thick, 18" at the cord and reaches nearly 4 feet below the long keel. The upper area of the board is in the keel disturbed flow but at least, say half, 2 feet, is riding alone in clear flow.

I believe I'm able to see this illustrated in the readout from the GPS. Simply, sailing a course close hauled board up, sails trimmed, AP holding a compass course and observing actual GPS track. After a time, lowering the board shows a changing of GPS direction to windward, as you would expect. Little changes though in "feel" as the angle of the sails to wind stays much the same, as does the actual magnetic compass in the binnacle.

From there, the optimist in me could take over. As this fairly apparent direction improvement shows (I'll stab at about 10 degrees?), I can sense a change in speed. More that the boat "may" begin to feel more weatherly, and point a bit higher, This could result in needing to trim now slightly luffing sails, IF, this is so, it could only be the result of "some" lift from the board, despite the old foil less shape and angle.

Does anyone have any experience or data about keel centerboard boats, especially the older styles?
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Tim
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Re: Mysterious centerboards.

Post by Tim »

There is most definitely an improvement in overall lift with a board down on boats like yours. No, they are not fine hydrofoil shapes, but even a flat board in the water creates lift thanks to its angle of attack. This is what reduces your effective leeway. I hear this debate amongst Allied Seabreeze owners all the time (which boats feature a very similar hull configuration to your Alden). Lowering the board fully or partially may also have an effect on the overall center of effort of the boat, which in turn can have an effect on the boat's overall balance (i.e. weather helm).

While the boats sail effectively without using the board at all, all anecdotal evidence indicates a definite increase in lift (i.e. pointing ability and reduced leeway) with the boards down. Seabreezes were built with two different boards: the early boats featured heavy bronze boards (like your Alden), while the later boats had much lighter aluminum boards. I have heard no suggestion, real or imagined, that the material from which the board is built has any effect on the performance of the boat one way or the other. These types of centerboards do nothing for stability whether up or down, which is one reason many people don't sense much of a difference up or down, and a moderate increase in lift can be unnoticeable and unimportant to the casual sailor, leading to the endless debate on the issue. I say to each their own: there's a time and a place for using the board, and a time and a place to ignore it, probably. Tweakers will tend to play with the board a lot, while more laid-back sailors won't bother.

Rest assured that it almost certainly pays to lower the board when sailing upwind, but also that you'll still get there fine if you decide you're too lazy one day. Offwind, the reduction in drag by raising the board usually more than makes up for any perceived leeway that may be happening on those points of sail, at least from a beam reach onwards.
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Tom Young
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Re: Mysterious centerboards.

Post by Tom Young »

That's a good logical explanation Tim. The lift is also felt raising the board close hauled. It takes some muscle to get it moving as I suppose it's pinned against the slot. It takes no effort at all while anchored or motoring or headed off the wind.

I also put a new pin in this spring (went back to bronze as Alden spec'd, and it was available) mostly as I wanted to take up a little play. The board has bronze cheek pieces made to a fairly close tolerance inside the lead keel. But I found enough room to put a washer on each side of the board as I threaded the new bolt/pin into place. The original drawings show a spacer incorporated into the lead keel where the pin goes through. The space I found (between the original fixed spacers and the board)must be wear. I slipped the pin in partially and then tapped each washer up, after taping them with duct tape to the end of a framing square, till they appeared centered in the hole. It worked!

There's still a clunk if it's fully lowered and you're rolling at anchor but it's much less and of course not there at all when the board is working under sail. Image
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