What does the centerboard do...?

Merlin Clark · Sep 19, 2012

With a keel centerboard, where the ballast is in the hull, the centerboard provides more lateral resistance (preventing side slip) and lift for beating (sailing upwind).
Downwind, haul it up to reduce drag and on a reach, the benefit from the entra lateral resistance may be offset by the drag depending on the boat. My impression anyway as I never clocked it.
With a swing keel, at least a good portion of the ballast in in the keel and this helps to stabilize the boat when it's down. With it up, the boat isn't very stable.

Indysailor · Sep 19, 2012

On my boat, I use the CB for beating against the wind; it helps the boat point better and keeps it from sliding to leeward. I raise it for the most part on other points of sail. It has practically no effect on heeling, as it only weighs 60 pounds.

Scott T-Bird · Sep 19, 2012

In that light breeze, it was to your benefit to sail with it up ... especially if you were sailing with the wind aft. You will skid sideways far more with a stronger wind and when the wind is forward. You will improve pointing in a strong breeze with the centerboard down. Since you do have a centerboard, it is very worthwhile to experiment on all points of sail in all conditions. Take notes, and you will eventually learn by experience how your boat performs best.

It sounds like you have already found out that there are many ways to sail a boat! The key is to learn what works best for you and yours.

capta · Sep 19, 2012

centerboards

We use our centerboard almost every day. Even at anchor it helps prevent the boat from rolling, considerably.
There are a lot of tricks to using a centerboard, but no rules other than don't leave it down in shallow water.
First you must realize that your board does not need to be all the way down to work. Being sort of pie slice shaped with the deepest point aft, even running dead down wind, if it is down only a few inches this puts a deeper point aft on the keel, allowing the bow to turn around a point more definitively than on the longer flat keel, giving more control in big waves and down more will lessen the rolling a monohull does down wind a lot. On a reach, with a big genoa and a reefed main for instance, your board can be used to move the center of lateral resistance aft or forward to help balance the boat. Even beating in relatively heavy weather (20 to 35 knots of wind) we do not often drop our board all the way. Ours is 24 turns of the winch up to down and we most often use only 14 turns. It does help significantly on leeway even in rougher conditions.
You are really going to have to constantly play with it to learn what works best for your boat, but I assure you that it is worth the time spent.
I originally suspected that the board cost us some speed when down, but after 3 US/Caribbean trips and a year of voyaging down here I do not now believe that. We even use it when motoring if we're rolling. But on a smaller boat, perhaps it does make a significant difference, but for my part, I'd rather be more comfortable going slower than rolling my guts out and going faster (a quarter knot?).
Hope this helps.

Victory · Sep 19, 2012

The centerboard's function is to discourage the boat from sideslipping.

If you had begun your sailing career on a dinghy you'd have learned that the center board, dagger board, lee board, or whatever.... is adjusted depending on your point of sail. These type of boats have no ballast, except for the crew, and the board is used to prevent sideslip. The further you turn downwind the less board you need.

On my dagger board boats (laser and Nacra) I ran with full extension when close hauling or close reaching, half way on beam and 1/4 down on broad reach or running.

You should experiment with your boat with different centerboard settings, marking the postions if needed. When motoring you won't need any...... and there's less drag with it up so you'll bet better mileage.

Ross · Sep 19, 2012

You can compare your compass heading with your gps heading and determine you leeway.

foolproof · Sep 19, 2012

We had a Catalina 25 that was a swing keel boat, which we sailed for pleasure. We kept the keel down most of the time because it seemed more stable that way. It was also much more stable in the slip with the keel down...we didn't have as much side to side roll as we would if it were up.

TomY · Sep 20, 2012

Ross said:
You can compare your compass heading with your gps heading and determine you leeway.

It's not unusual for someone to say they can't tell if their centerboard does anything. That's because it's effect is not what they are expecting.

Our compass heading may not change when we lower our centerboard going to windward, but if you watch the GPS heading, often we'll get another 5 to as much as 10 degrees increase to windward.

The boats compass heading, sail angles may all stay the same(I usually do this with the AP steering a compass course), as you watch the GPS course move to windward.

This is simply less leeway showing up on the actual course over the ground which is the result of the lift from the centerboard.

It is the centerboards actual lift increasing the boats windward ability, that lessens leeway.

Ross · Sep 20, 2012

I have been sailing at right angles to the ebb tide and heading east by magnetic compass and south east by GPS. That wasn't leeway that was set.

Todd Smith · Sep 21, 2012

Another way to measure leeway is to look at the wake off the stearn. You can then see the angle of your side slip throught the water.

GPS vs compass requires no current and well calibrated instruments to give good data.

anchorclanker · Sep 21, 2012

Try sailing with head sail only and you'll see how much that board does.

I took the boat out a while back and did just that. I wanted to sail with only the head sail just to practice. I got out there but absolutely could not turn up wind to any degree. Then it dawned on me I had forgot the keel up. Duh! I locked the rudder and started letting the keel down and immediately the boat came about and started heeling to windward.

The main would allow more windward sailing but your going to have more side slip the stronger the wind and the more you heel.

McZube · Sep 22, 2012

Interesting. I thought a centerboard was to let you know when to turn toward deeper water before running aground. Kinda like a curb feeler.

Joe · Sep 22, 2012

McZube said:
Interesting. I thought a centerboard was to let you know when to turn toward deeper water before running aground. Kinda like a curb feeler.

yeah, that too.... thanks for reminding us.

Joe · Sep 22, 2012

anchorclanker said:
Duh! I locked the rudder and started letting the keel down and immediately the boat came about and started heeling to windward.

Man....... that's a strong center board to make your boat heel to windward...

Ken13559 · Sep 22, 2012

Joe said:
Man....... that's a strong center board to make your boat heel to windward...

Must be a canting center board.

anchorclanker · Sep 22, 2012

Im not saying it was anything powerful, it was rather slow in fact, only a tick over 3 knots or so slightly close hauled. And it wasnt "heeled over" hard, but it was over close to 10 degrees. Im only pointing out that it wouldnt go anywhere but about straight downwind without the keel down. I was actually somewhat surprised it would have that much effect. I felt the boat turning before I let much more than a foot down.