After thinking about this for a few minutes after I sent it I think I need to correct myself. If I understand this correctly, a death roll caused by a puff is not due the apparent wind shifting forward. An increase velocity only would cause the apparent wind to shift aft and an increase in hull speed would shift the apparent wind more forward, right? Instead a death roll in a puff is caused by a shift in the wind which is many times is accompanied by an increase in wind velocity. If the shift changes the apparent to a more forward angle and the top of the sail is out beyond 90 degrees then the top of the sail will be more likely to sail upwind. Another cause of the death roll is a wave that pushes the stern to leeward resulting in the relative apparent wind shifting forward. Sorry for my confusion. Please correct me if I'm still confused.
Rob Hodson
My understanding for what it is worth; when the top part of the sail is trimmed out too far, the wind angle at the top of the sail makes the top of the sail suck upwind leading to the death roll. If you think about the wind angles, the apparent wind is somewhere around 150 degrees aft of the bow. The reciprocal angle is 30 degrees. With the top of the sail trimmed at 90 the top will be stalled. As you ease the top of the sail further forward, say 60 degrees from the bow, it becomes unstalled and starts to "sail". This happens easily in a puff when the apparent wind moves forward for a moment until your hull speed increases and then move aft again. If the top of sail is trimmed at 90 degrees and a puff momentarily shifts the apparent wind forward from 150 to 120, the top is gonna start sucking up wind. It doesn't take a lot of force at the top of the mast to tip the boat over. The mast is a big lever. Hope this is helpful. The way to avoid this phenomenon and not stall the top of the sail is to sail by-the-lee. The way to stop a death roll if you can, is to stall the top by trimming in or steer down hard and fast by-the-lee or do both simultaneously. Rob Hodson
Wayne,
Wayne Wager asks: what is the significance of having the top batten at 90 degrees? Is this always the proper trim?
Here is my theory: Assumming the force vector from the sail is square to the top batten when going downwind, especially in big breeze, it is best to have this vector (drive from the sail) pointing in the direction you want the boat to travel. When the top batten goes beyond 90, the force vector points in a direction that forces you into a deathroll. The affect of a big gust is to stretch everything (sail, mainsheet, vang, ...) and twist the sail so the batten goes beyond 90 and BAM, you are swimming. This may or may not be true, however it seems to make sense to me.
The part of the equation that is difficult to master is how much vang and mainsheet to have in any given wind and wave condition You can reef on the vang and let the boom out to 90 because the vang will hold the leech stable and keep the batten parallel to the boom. Obviously it is slow to have too much vang going downwind, so we slack the vang at the weather mark. As you slack the vang, you must pull the boom in less than 90 to keep the top batten at 90. The "twist" along the leech is affected by a combination of mainsheet position and vang tension. Getting these two settings correct is a part of the equation and is different for every wind condition.
Come on Dan, Andy, and Dennis. Clue us in on what you've learned in the Gorge.
MJ
In a message dated 5/4/04 1:36:51 PM Pacific Daylight Time, Wayne@evpartners.com writes: Received on Tue May 4 21:03:16 2004