sail trim

[Alan]

OK so you don't agree

Maybe it would be better if you hear it from Dave Dellenbaugh. I quote"Many boats use a technique called “vang sheeting” when sailing upwind in a breeze. If you don’t vang sheet, one problem you have is that when you ease your mainsheet in a puff, you allow the leech to twist and you make the mainsail fuller (because less leech tension means less mast bend). This is not good in a puff.You could prevent this by dropping the traveler to leeward instead of easing the mainsheet. However, on many boats the traveler is not easy to play or it doesn’t have enough range. This leads us to the vang. By using a tight vang (i.e. vang sheeting), you control mainsail twist and shape with the vang. The sheet then controls the lateral position of the boom, which is quicker and easier than using the traveler."

 

[Kevin3447]

Keep reading...

Keep reading, three more paragraphs down:"On a windy reach, assign on crewmember to play the vang (if possible). This person should keep the vang control line in her hands all the time. She should pull harder on the vang when you can use more power; she should ease the vang when you are getting overpowered and/or when the end of the boom is getting close to the water."Turtle was rounding up, so much that he auto-tacked. He should have dumped the sheet & vang to depower as much as possible. If you don't dump the vang, the main can't spill off as much, and you may still auto-tack.To add another reference, from Bill Gladstone:"To reduce power in heavy air:Flatten sails, lower the traveler, and if necessary, ease the sheet to add twist. Carry backwind in the main - as much as half the sail, rather than sail overpowered.""In heavy air we reduce power, first by flattening sails, then through twist, and finally by reducing angle of attack."So, yes, you're partially correct - first try to flatten the sails. If you're still overpowered, twist off the top (both jib & main - reduce heel & keep the rudder in the water). If you're in danger of auto-tacking/rounding up, dump the sheet & vang.Kevin

 

[Alan]

Kevin

We agree completely. Here are the actions to be taken as you posted:"In heavy air we reduce power, first by flattening sails, then through twist, and finally by reducing angle of attack." ...and reefing (my add-on)This is exactly what I have been apparently unsuccessfully trying to say. The point about adding twist is of particular note. When twist is being added after the earlier attempts to de-power, the amount of twist to be used must be large enough to completely luff the top of the main. If an insufficient amount is used the top of the sail will become even more powerful, increasing weather helm and heel. This appears to be the case that turtle described.

 

[Alan]

Though in thinking through...

...the procedure I use it is slightly different.First, flattening sails of course.Then I reduce angle of attack by lowering the traveler. This instantly de-powers the sail without the initial introduction of 'powering up' as it would if the sheet were being eased.Then, after the traveler is lowered and if more de-powering were needed would I increase twist by dumping both the vang and mainsheet. The benefit of this change would be to make trimming in puffs much faster and if the final step of increasing twist should be needed the angle of attack has already been decreased to minimize or prevent any powering up at the top of the main.I welcome your thoughts and suggestions with this.BTW, I think this is a great and valuable discussion. There should be more like this!