Saturday, February 16, 2013

@SamuelBBlouin Neutralizing Your Helm





Question: How do I fine-tune my settings or technique to achieve a neutral helm when following a 420 tuning guide?

No matter the boat, whether it is a 420, FJ, Optimist, or something else, the key to neutralizing the helm is aligning the center of effort with the center of resistance.  The center of effort, or draft, is the deepest part of your sail at a given time. The center of resistance is the centerboard, dagger board, keel, etc. 

To understand this visually, think of your 420 fully rigged and upright with the centerboard straight down.  If you were to draw an imaginary vertical line through the boat, the deepest part of the sail should line up with the centerboard to obtain a neutral helm.  As the center of effort falls aft of the center of resistance you will start to experience weather helm, as if someone is trying to pull the tiller away from you. Conversely, as the center of effort moves forward of the center of resistance, you will experience leeward helm. This will feel like the tiller is getting pushed toward you.

In most boats, balancing the helm is a function of Cunningham (In an Opti, this is your Sprit Halyard) and Mast Rake, assuming your other basic settings are set appropriately for the wind conditions.  As the wind’s velocity increases, the draft will move aft, and you will see horizontal wrinkles form across your sail.  In windier conditions, this is a signal that your draft has moved aft of the center of effort.  The easiest solution is to put on more Cunningham, which moves the draft forward to offset the draft’s movement in higher wind speeds. 

Conversely, if you have too much Cunningham on in lighter winds, you will see vertical wrinkles along the luff of your sail. This indicates that the draft is likely too far forward of the center of effort, giving you leeward helm.  A looser Cunningham setting in these conditions will allow the draft to move aft to line up with the center of effort.

In addition, the mast rake may complicate achieving a neutral helm in a boat like a 420 or FJ.  Using a forward rake in light air will give you more power.  Keep in mind, moving the rake too far forward will keep the draft forward of the center of effort, even at the Cunningham’s loosest setting. Raking forward will narrow your slot and give you a more favorable jib lead angle, both favorable in light air. However, the only way to obtain a neutral helm, if you move your rake too far forward, is to angle your centerboard forward; this is not possible in most classes.  Thus, moving your rake further forward than 20’6” on a C420 can actually hurt more than help in lighter air.

As conditions get windy and out of control, raking backward is essential to getting twist at the top of your sail and widening your slot.  The twist will help you spill the top part of the leech of your sail to depower. The extra room in the slot will enable you to ease the main to a greater extent in the puffs, helping you depower or plane without interfering with the sail flow over the jib.  However, as the rake gets more and more extreme, you will not be able to pull on enough Cunningham to neutralize the weather helm.  In the most extreme conditions where you are raking way back (In the C420, this is when your rake is less than 20’), you need to raise your centerboard an inch or two to tilt the center of resistance aft toward the center of effort, neutralizing the helm.

Your settings will vary a great deal depending on crew weight and the wind conditions. Understanding the theory behind how your controls work will let you find out what settings will neutralize the helm on any boat with any crew. I always recommend going out and putting marks all over your mast (see the previous Zim Coach post), so that you know exactly where your personal helmneutralizing settings are in all conditions.

See you on the water,

Zim Coach

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