Twist

Stu Jackson · Nov 19, 2012

Don, I don't get it, and I think I know what a salute is (using all the fingers, not just the middle one!

).

I think an easier way is to visualize it is to keep your fingers straight first, then cup your hand.

Better yet, perhaps, on a broad or close reach, "play" with the vang and the mainsheet and see what happens.

Then read Don's Book and Guide.

Barnacle Bill · Nov 19, 2012

I assume you are talking about twist in a mainsail. If you are sailing close hauled (as close to the wind as you are able without luffing to a stop), then you will have your jib or genoa sheeted in all the way and the trailling edge of the genoa will have a straight leech. You will also trim in your main so that the boom is to the centerline of the boat (or nearly so) and then your mainsheet will be quite tight and the trailing edge of your mainsail will also be straight. Now there are different traveler positions you would use in various wind conditions, but that is another topic. With both sails fairly flat the leeches will be similar and so you will get that nice slot where the wind will flow undesturbed through that slot created by the two sails simularly trimmed. Now, if you eased the main sheet (and vang too, if that is in tight), you will see the boom rise a bit and the leech of the mainsail open up, or have more "twist" in the trailing edge or along the leech. Now you have a genoa leech and a mainsail leech that doesn't match very well, which disturbs that nice slot you once had. As you fall off, or sail closer or towards a beam reach (where the wind moves aft), and you ease the genoa to suit, you will see that the straight leech or trailing edge of the genoa or jib now is no longer straight, but has a great deal more twist. You always trim the jib or genoa first going to weather, and then you can trim the main second and ease the mainsheet and vang and open up the leech of the main, creating more twist and what you want to do is match the twist of the mainsail with the twist of the genoa so that you create that nice slot again. This is more easily seen if you were on a boat behind your boat, but you can still accomplish this on your boat looking at your sails from the back of the boat on the same side your sails are sheeted. I hope this helps.

All U Get · Nov 20, 2012

Hi Don,
Here's my way of thinking of it, (kinda early here). The trailing edge has a line sewn in it that controls how much air is in the sail. Pull it tight (down) and it holds more. Let it free (rise) and the air spills out. Then you can explain how you control the clew to do this. Hope this helps, happy Thanksgiving.
All U Get

Nodak7 · Nov 20, 2012

Don Guillette said:
I'm sure a lot of you have tried to describe some concept or other over the phone to a person who doesn't know what you're talking about. It ain't easy!!

I talk to a lot of sailors and I need a better way to describe TWIST. I tell them to form their right hand in a salute and then place their hand vertically in front of their face. What they are looking at is a "closed" main or jib. In other words, the sail is powerd up from top to bottom. I then tell them to turn their fingers only to the right. That is an "open" main or jib and they're spilling power out of the top of the sail. To power the sail back up they merely turn their fingers in slowly. That's what twist is all about.

Some get and some don't. Can any of you think of a better way to describe twist over the phone?

Don, I think I understand what you are asking for and have been trying to think of a simple way to describe it. I came up with one very basic example. Get a piece of printer paper. Hold it by the bottom corners with one hand on the right and the other on the left lower corners. Bend the paper in the middle and raise and lower the corners. It will "twist" the paper as the sail would twist.

If you raise the right corner a bit you will see the upper right corner of the paper "spill" out. Try it out and tell me what you think. Am I totally off the wall here?

Gudenuph · Nov 20, 2012

Perhaps just one explanation won't work for all people given their different backgrounds. So here are a couple more. Look up the back edge of the set sail, if it is straight---no twist, if it is curved---that is twist. The other is to hold a piece of letter sized paper on each end with one edge up and the other down, and sight along the top edge of the paper. Let one end tip to the side and the curve along the top edge is twist.
Don, the more I get into this, the more I see your dilemma. This is the third try at an explanation and I've darn near talked myself out of knowing what twist is--- Just kidding.
Geohan

Clark · Nov 20, 2012

How's this . . .

Twist is the difference in the sails angle of attack to the wind from the bottom to the top of the sail. No difference = no twist etc.

Now explain how much twist is best and when

foolproof · Nov 20, 2012

In describing main sail twist, I like to think of the sail as the wing of an airplane. On most small airplanes the wing has a twist in it from the root to the tip, typically around 4 to 6 degrees from one end to the other. The reason for this is to keep the outer portion of the wing flying with a slightly lower angle of attack to retain roll control when the inboard portion of the wing is approaching the aerodynamic stall.

When a sail luffs it is very similar to a wing stalling. The big difference is that you can actually see what happens to the sail when it stalls. If you get too close to the wind, it actually starts pushing on the "wrong" side of the sail (the leeward side of the sail). This causes the sail to luff and thus, lose power. However, if there is considerable twist in the sail, the upper half of the sail is already stalled before you actually see it on the lower part of the sail. In a close hauled situation it is preferable to minimize the amount of twist to keep the entire sail "flying" correctly. The down side to this is that when the sail stalls, or luffs, the entire sail stalls together...that's when the boat stops heeling suddenly and the sail starts to really flog.

When this happens in an airplane, it immediately pitches nose down and will begin flying again when the airspeed picks back up...in a sailboat we turn to leeward to fill the sail again to make it "fly" correctly.

I hope this helps with your description of sail twist. I think I get it - I can point pretty close to the wind in my Catalina 30, but only if I minimize the amount of twist. I don't have a boom vang, so I have to haul the main sheet in really tight to pull the boom down to lessen the twist, then control angle of attack using the traveler.

foolproof · Nov 24, 2012

Great idea Don! Been wanting one since I started sailing this boat.

Jim11240 · Dec 21, 2012

How I explain Twist

Imagine your main sail.

It is attached to the mast at the front and, except at the bottom where the foot attaches to the boom, it is free to assume any shape it wants in response the wind, gravity, and the forces you put on it with the adjustments you make to the mainsheet, vang, etc.

Starting at the bottom of the main sail if you draw a line from the mast to the aft edge of the sail and project its shadow down on to the deck it will make an angle to the center line of the boat.

Now go up the sail about a third of the way and draw another straight line from the mast to the aft edge of the sail. A shadow of that line on the deck will have a slightly different angle with the center line of the boat.

Now go up the sail 2/3 of the way and draw the line from mast to aft end of the sail again and project it down to the deck. It will have a different angle to the boat centerline than the first two lines.

If these angles are increasing as you go up the sail, you have twisted your mainsail open at the top.

What adjustments could you make that might increase or decrease the difference between those lines and change the twist? What happens to twist if you have more or less wind? If you heel over?

Joe · Dec 22, 2012

Jim11240 said:
How I explain Twist

Imagine your main sail.

It is attached to the mast at the front and, except at the bottom where the foot attaches to the boom, it is free to assume any shape it wants in response the wind, gravity, and the forces you put on it with the adjustments you make to the mainsheet, vang, etc.

Starting at the bottom of the main sail if you draw a line from the mast to the aft edge of the sail and project its shadow down on to the deck it will make an angle to the center line of the boat.

Now go up the sail about a third of the way and draw another straight line from the mast to the aft edge of the sail. A shadow of that line on the deck will have a slightly different angle with the center line of the boat.

Now go up the sail 2/3 of the way and draw the line from mast to aft end of the sail again and project it down to the deck. It will have a different angle to the boat centerline than the first two lines.

If these angles are increasing as you go up the sail, you have twisted your mainsail open at the top.

What adjustments could you make that might increase or decrease the difference between those lines and change the twist? What happens to twist if you have more or less wind? If you heel over?

Uh.... okay.

bmorr · Jan 1, 2013

Joe said:
Uh.... okay.

Don, for me your salute illustration is simple and gives the basic idea.

Bazzer · Mar 10, 2013

With the boom on the centerline surely you are getting no drive from the lower part of the mainsail and are relying on the twist to get drive from the upper part of the mainsail. As a ex dinghy racer it is common to use the vang to Eliminate twist to get drive from the entire sail and often adjust the angle of attack just using the traveller, or slacken the vang to induce twist to depower the upper part of the mainsail when the wind strength increased and I needed to spill wind to reduce heeling. So why ever have the boom along the centerline?