Spinnaker Pole Height
Too many times have I been racing on a boat where someone says "The clews aren't even- raise the pole." Well, yes, this is true - the clews should be even - if you are using the right sail in the right conditions at the optimum wind angle, which is not always the case. When I ask a lot of people how the break looks, more often than not they are not, they are not so sure what I am talking about; the usual response is "fine". The correct response is "even". What that person is not aware of is that I am asking him if the pole height is right. Here are my tips for getting the pole position right when trimming the spinnaker.
Let's start out with a few truths and untruths.
1. The pole position largely affects sail shape - True.
2. The height of the pole is strictly determined by the height of the leeward clew - False.
3. The pole height controls the break of the leech, which helps induce the correct, designed sail shape when set right - True.
Now, lets establish a few important design aspects. Many of you have heard the term "a profile like a beetle's back" when describing spinnaker shape - starting round at the top and getting straight and vertical as you go down (see photo above). In order to achieve this modern shape, your spinnaker, when folded in half and laid on the loft floor, is cut with a distinct "S" curve along the luffs. Providing the correct pole height enables this curve to 'set' properly when being flown, thus giving us that desired shape.
Let's analyze some different pole height settings. With the pole too low, you'll be trying to pull that curve too straight. Instead of billowing away from the boat, the shoulders will curl over, causing the top of the spinnaker to break early, which causes the trimmer to tighten the sheet prematurely. The end result is an over-trimmed (and over-flattened) spinnaker, which is choking off flow of air around the main as well - all bad things.
As you raise the outboard end of the pole, you see the break change - instead of the breaking at the top, it moves down and evens out along the luff, as the top of the sail opens up. The break becomes even, indicating a properly shaped sail - at least in the front. The easy way to remember this is "move the pole to the break." If the sail breaks high, raise the pole.
If you have the pole too high, the opposite will happen. The shoulders will billow out too far- causing the bottom of the leech to break first- and the top to break late. This causes the trimmer to want to over-ease in order to get the top to break. The end result is an under-trimmed sail, with too much leech twist - allowing the air to escape over the leech instead of being directed to the foot, where you want it while sailing downwind.
What about the inboard end? Well, that's easy. One of the pole's jobs is to extend the sail as far away from the rig as possible. The inboard end is adjusted to match the outboard end, strictly to keep the pole perpendicular to the rig, therefore keeping it as extended as much as possible.
On the sheet end of things- the sail, remember, with the pole too high was inherently over-trimmed- so as the pole is raised, the sheet can generally be eased. And as the pole is lowered, the sheet generally will need to be trimmed, as the luff closes up top. An easy way to remember all this- " Down and in" or "up and out". Another consideration here is that the guy must be adjusted when raising or lowering the pole- if we are to raise the pole the guy must be eased, or the pole will oversquare. Again, "UP (on the pole) and OUT (on the guy and sheet). If we lower the pole, it will undersquare. Therefore, DOWN (on the pole and IN (on the sheet and guy). I often use the Phrase of "reigning in" the kite -The sail has gotten too far away from the boat -the guy was eased, so the pole end raised up a little- then the trimmer had to ease more because the luff wouldn't break- but when it does the whole thing is about to luff- so the guy gets eased again, and so on and so forth. Now the sail is truly ballooning, and needs to be "reigned in". AKA over-eased, under-squared and under-trimmed. This is a bad combination- a high center of effort, a low amount of pulling force due to decreased exposure to the breeze - bad and really bad. This is an occurrence I see way too often. If we pay attention to the subtle but important detail of the break, we will see that our clew heights often end up even- when the sail is being used in the proper range of conditions.
But what then, when we are not using it in the ideal conditions, such as a one design class where you are only allowed one sail, or when the breeze changes and you are not in a position to do a peel?
Lets look at the high wind side first. As the breeze increases, we sail deeper- squaring up more, and easing the sheet and consequently raising the pole to get the right break. Anytime a spinnaker sheet is eased - the clew goes out, but it also goes up. Now we have a sail that has a clew that is too high - as the sail we have up is designed to be trimmed with the clew lower. The end result is an asymmetric shape that allows the air to flow from luff to leech. The solution here is not to raise the pole further- that will only make it worse, since it will cause the trimmer to want to ease even more. This is where a twing on a spinnaker sheet becomes very valuable. In addition to keeping the clew lower, it will help increase the boats stability by controlling the oscillations of the sail. On lager boats, many times the solution is to trim it off what was the lazy guy instead of the sheet- until it is time to gybe, when you switch back to the sheet on a twing.
We said that if the clew is high, the air flows luff to leech- sound familiar? It should- especially if you use an asymmetric spinnaker or trim a headsail. As the breeze gets lighter, we sail higher angles. The guy gets eased out and the pole goes forward and consequently, wants to go up. The sheet gets trimmed in and the clew goes down. What often then happens is the clew ends up lower than the pole, wish is just plain 'ole bad. If we lover the pole enough to get it lower than the clew, now we have that asymmetric shape that we see screaming past us on the sprit boats- a low tack, with a high clew to induce that luff to leech flow, without choking off the newly established flow around the back of the main. Not the best way to use your kite- but remember, you were supposed to do a peel to a reaching sail five knots ago