Teaching Upwind Sail Trim

Teaching Upwind Sail Trim

We have a teaching philosophy that is unique. Most sailing schools will do a "ground school" for hours before the students get on a boat. The idea is to explain how it all works, so the  student is prepared intellectually for the experience. Our approach is to get them on the water right away and have them just do it - steer the boat, tack, and get the feel for it.

I believe that our approach is correct, up to a point. You need some practice before the sailing theory makes any sense. And my experience as an instructor is that a beginning student will do just fine steering beam reach, tacking, even steering close-hauled without any discussion of how it all works.

The turning point is when they try to control the tiller and the main sheet at the same time. Lots of confusion, including understanding wind direction. Tacking from beam reach to beam reach and seeming to lose the wind (because the sails are trimmed too tightly).

This is the point where they really need an understanding of how it all works. And that's hard to do on the water. You  need an image to show how it works. I believe it's all pretty simple (or at least
can be explained simply), with a visual from above.

The key concept is that upwind (beam reach and higher) the sail is a wing, it works just like the wing of an airplane. Now an airplane wing has to be at a certain angle to the wind, or it doesn't work. Same with a sail. So when you're trimming the sail going upwind, you're keeping the sail at the same angle to the wind all the time.

Let's see what this looks like from above on several points of sail - close hauled, close reach,  and beam reach (click on the diagram to start the animation):

 

b2ap3_thumbnail_Sail-Trim.gif

 

Note that the angle of the sails to the wind is the same on each point of sail, but the angle of the sails to the boat changes as the boat turns relative to the wind. Note how far "out" the sails are from the boat on beam reach to keep the same angle to the wind that you had on close hauled.

So when you're trimming the sails as you change course, you're keeping the sail angle to the wind the same. As you turn downwind, you have to let the sheet out to get more angle to the boat (to keep the same angle of the sails to the wind). Conversely, as you turn upwind, you have to pull the sheet  in to get less angle to the boat (to keep the same angle of the sails to the wind). You can play with a model sailboat, turning the boat up- and down-wind and keeping the sails at the same angle to the wind.

I have simplified the dynamics quite a bit, but this picture is what you need to understand sail trim upwind. For those interested, my biggest simplification is that you're keeping the sail at a constant angle to the apparent wind, not the true wind.

Also, this is not how you do it on the water. You're not thinkiing about getting the right angle of the sail to the wind (although that's what you're doing). But if you have this picture in your head as you trim the sails, you'll get there quicker and easier. And you shouldn't end up on a beam reach after a tack with the sails trimmed in tight.

 

My First Windsurfing Lesson
Demystifying Apparent Wind - Part 1

Related Posts

 

Comments 4

Michael Sherrell on Thursday, 19 November 2015 07:14

This animation is really cool, John. I just wish there was a way to summon it up at will while in the clubhouse during the pre-launch phase of the lesson. I have tried to explain the principle your animation demonstrates while on the water but students are almost always too distracted to get it.
What I think would help enormously would be a little model boat in the clubhouse with a flat bottom and a moveable boom, so you could demonstrate this and also things such as the S curve on the jibe.

This animation is really cool, John. I just wish there was a way to summon it up at will while in the clubhouse during the pre-launch phase of the lesson. I have tried to explain the principle your animation demonstrates while on the water but students are almost always too distracted to get it. What I think would help enormously would be a little model boat in the clubhouse with a flat bottom and a moveable boom, so you could demonstrate this and also things such as the S curve on the jibe.
John Bongiovanni on Thursday, 19 November 2015 16:36

I agree. In fact, I have just such a model (and a wind diagram) in my car. I used it today to explain slow-sailing on land.

I made the model myself, and it's not as sturdy as I'd like. I'll look into buying one, and if we can't I'll figure out how to make a better one.

I agree. In fact, I have just such a model (and a wind diagram) in my car. I used it today to explain slow-sailing on land. I made the model myself, and it's not as sturdy as I'd like. I'll look into buying one, and if we can't I'll figure out how to make a better one.
Michael Sherrell on Thursday, 19 November 2015 20:06

John, if you find some cheap enough at some toy store for example, please pick up one for me and maybe one for the clubhouse. We can probably get the club to reimburse us.

John, if you find some cheap enough at some toy store for example, please pick up one for me and maybe one for the clubhouse. We can probably get the club to reimburse us.
John Bongiovanni on Thursday, 19 November 2015 20:47

I'll look around. The problem is that the sailboat that exist that have moveable sails (so that you could actually demonstrate this) are realistic, and they have centerboards or keels. What we need (and I couldn't find a couple of years ago) ius one of these with a flat bottom, unrealistic, but just what you need to demonstrate this stuff on a wind diagram. So I built my own.

In any event (build or buy) the cost is pretty minimal.

I'll look around. The problem is that the sailboat that exist that have moveable sails (so that you could actually demonstrate this) are realistic, and they have centerboards or keels. What we need (and I couldn't find a couple of years ago) ius one of these with a flat bottom, unrealistic, but just what you need to demonstrate this stuff on a wind diagram. So I built my own. In any event (build or buy) the cost is pretty minimal.