What is head/lift indication in a digital compass on a sailboat?
A simple explanation would be great. I am reading a manual for digital compass and there is a paragraph with the following words:
The SpeedPuck automatically detects when a sailor is trimmed to a heading then provides the header/lift indication. When the device detects that the sailor is trimmed at a heading the trim angle is set. Then header/lift indication is given off of that trim angle. Once a tack or a jibe is detected the indicator resets and nothing is indicated until another trim angle is set. Each bar segment represents 3 degrees of wind shift.
I don't really understand what header/lift indication is. If only someone could explain plain simple words, that would be great!
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Let's start with the terms lift and header. Suppose I want to go that way, whichever direction that happens to be. If the wind is coming from that way, then I can't do it, at least not on wind power alone. What I can do is sail slightly to the left of that way for a while, then tack slightly to the right of that way and so on.
A change in the wind direction that makes it easier to go that way is called a lift (perhaps due to its effect on the crew's spirits, but that's just me editorializing). Conversely, a change in the wind direction that makes it harder to go that way is a header (probably a reference to the wind changing to be ahead of you, but that's a question for another SE.)
Now on to your compass. It is difficult to tell from your quote alone, and I have never used this sort of device myself. However, the idea I am getting is that somehow the programming inside the compass is able to determine if a lift or a header has occurred, and provide the helmsman some sort of signal as to that event, so as to allow him to adjust trim accordingly.
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When going upwind, a header is when there is a wind shift towards your bow, which would make you deviate further from your original heading provided you don't adjust trim. A lift is the opposite. Here's a nice illustration.
After checking out the product, I think I understand what it does:
When you've been on a certain heading for enough time, the instrument detects you're trimmed on a tack and if it detects a slight deviation from that heading, it will indicate this as a wind shift on the display.
If you tack or gybe, the instrument resets its wind shift indicator and waits to calculate your new heading on the next tack before starting to give you wind shift values again.
Bear in mind, this is all based off GPS data, so if you actually adjust your trim slightly, it might show it as a wind shift.
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