Hey Centerboarders!

[JMAC]

As I struck bottom more than I'd like to admit last summer, I'm wondering...Do you lose a lot or a little of the board's effect by keeping it up a bit instead of down all the way? Is there some sort of engineer's ratio or rule of thumb?

[preston]

Going upwind, you want it down.
But downwind, you could pull it all the way up.
Reaching, etc, put it somewhere in between.
Experiment!

Preston

[Thorne]

From my understanding, when you pull it back it puts the "resistance" or underwater foil effect further aft.

For some sailing rigs this is great, for others it may throw off the relatively delicate balance between the size / position of the sails and the resistance provided by hull/keel/centerboard/rudder. This can cause either lee or weather helm.

In other words, to put the centerboard further up most of the time will put that resistance further aft, possibly requiring a larger headsail to balance things out.

Experiment!

[Bruce Hooke]

It seems to me that a lot depends on the type of centerboard. With a centerboard that is pretty much a vertical foil when it is down, pulling it partway up is likely to mess significantly with the balance, as Thorne noted, without really reducing the draft that much until you have pulled the board up by quite a bit. On the other hand, with an older style centerboard that exposes a roughly triangular surface to the water, partially rasing the board should have a minimal impact on the balance. In addition, such a centerboard is not really a very efficient foil anyway, and pulling it up is not going to change the shape of the foil but that much either, so you won't loose much foil efficiency. What you will loose is the basic ability of the centerboard to keep the boat from sliding sideways when sailing upwind, and the amount you would loose is likely very roughly proportional to the amount the the board is withdrawn.

As Thorne noted, the best way to find out how things work on your boat is to run some tests.

I'm assuming that you are sailing a relatively small boat. In that case, unless you are sailing in waters where the depth changes very slowly, I do have to wonder how much good it is going to do for you to gain, say, an extra 6" of draft. Sure it may help you occassionally, but a lot of the time it seems like you will just hit bottom 15' further along on your course then you would otherwise have. Of course if you are trying to squeeze into really shallow water then that extra 6" may make a lot of difference...

[Thorne]

Here's a photo of the just-installed-today centerboard in my Chamberlain dory skiff.



Locked into a 45-degree angle with a position pin, the difference in height between fully down is not a whole lot - maybe 8" max? As Bruce mentioned, that's not gonna buy you a lot of room in thin water.

[ 12-03-2005, 08:40 PM: Message edited by: Thorne ]

[maa. melee]

Originally posted by Thorne:
Locked into a 45-degree angle with a position pin...

Are you sure you want to LOCK the board in that possition? Shouldn't it be balasted and lifted to a certain angle by a lanyard? If you hit bottom, you'll see what I mean.

[ 12-03-2005, 11:06 PM: Message edited by: maa. melee ]

[Todd Bradshaw]

You can generally just watch your track to see how much you're slipping sideways and adjust (lower) the board enough to minimize it. At the same time, you'll be able to feel whether or not you're having to use a lot of rudder to compensate for weather helm. If it seems like you're fighting the tiller or dragging the board through the water at a steep angle, lower the centerboard until the boat behaves better.

[Thorne]

Melee -

When you use the 'position pin' for a swing keel or centerboard, you just pull the pin when the water gets thin.

The pin helps you find the proper location, as it is hard to determine the angle o' de dangle by the pennon alone.

I can pin the centerboard all the way down, so that in a knockdown it stays extended for righting the boat. I can pin it at 45 degrees for downwind runs, and can pin it up for transport or rowing. Works fine!

[ 12-04-2005, 11:37 PM: Message edited by: Thorne ]

[ahp]

You may find that when you are sailing off the wind that you have a weather helm, and a catboat can be brutal. Of course you correct with the rudder to keep going in a straight line, BUT, that is like sailing with the brakes on. The rudder creates a drag as will as steering.

Try bringing the board part way up. If it is a swinging board the center of lateral resistance will move aft, and the weather helm, and the needed rudder correction will be less. You may be able to achieve a neutral helm on a small boat, which would have the least rudder drag of all.