- First scenario: you're sailing on a dead run when a gust hits. The force of the wind on the main will indeed cause the boat to want to round up a bit. However, since you're on a run, it won't cause much heeling, so you only have the first aforementioned factor to deal with.
- Second scenario: you're on a broad reach when a gust hits. Now you're in trouble -- you have both excessive weather helm coming from the force on the main, as well as weather helm caused by heeling. As you round up towards a beam reach, you can't depower the main, and you may end up capsizing.
- Third scenario: you're on a beam reach when the gust hits. Again, both factors will apply, but as the boat rounds up above a beam, the main will start to depower, reducing heeling and weather helm and saving your bacon.
Downwind sailing and the evils of rounding up
Great post, Nathan.
One thing that I can't figure out is sheeting in the main on a broad reach. I guess the apparent wind has to be enough forward that the sail has flow on both sides, so that when you let the sheet out you depower it. But if this is the case, you'd be luffing a bit with the sail too far out, no? And if the apparent wind is far enough behind you that you don't have flow on both sides, then power goes as exposed (cross-section) sail area, so letting the main out increases power on the sail, the opposite of what you want.
Am I reading this correctly, or (most likely) missing something?
Thanks! First of all, let's suppose that you've sheeted in the main "too far" so that the sail is stalling a bit. You are absolutely correct that easing the sheet will increase power on the sail. However, you will be decreasing the heeling force on the boat, which is the important thing to do to prevent rounding up.
Now, I frequently see sailors at CSC heat up from a run to a broad reach without touching the main sheet, and indeed in the right conditions, the main starts to luff a bit. This seems to be an especially frequent occurrence when the kite is up. So yes, it is in such situations that you certainly want to sheet in.
I might occasionally sheet the main in a little when heating up to a broad reach even if the main isn't luffing. This could partially stall the main a bit and kill boatspeed a smidgen, but by being able to play the sheet I feel I'm much better able to balance the boat. In any case, dumping the main in such a situation will also help avoiding rounding up, as mentioned above. Play around with this and see what you think!
To reinforce something you mentioned but didn't highlight.
I was out today with James C (great, wet experience), and he showed me a way to steer downwind, keeping the boat fairly flat. It's bascially what I had learned in the gennaker class last year (but James and I weren't flying the kite at that point) - if you're over-powered, go down, if you're under powered, go up. All with the tiller. It worked nicely (RS-500) without having to move a lot of weight around.