Sail Trim Basics

[Don Guillette]

Mates: The great golfer Bobby Jones said "There are any number of people who have devoted a lot of thought, time and effort to the game (sailing). They could have been reasonalby good if they had only started out with an accurate conception of what to do". Bobby's words apply to just about everything. There is a technique to hitting a golf ball, kicking a soccer ball, hitting a baseball or tennis ball and most importantly - sailing. What I am going to attempt to do is give the beginner to intermediate sailor the basics of sail trim together with a step by step approach that is easy to follow.How many times have you wondered what sail trim is needed for a particular wind condition or point of sail? Do any or all of the sail trim controls on your boat confuse you to such a point you don't use them? If you are anything like me, not too many years ago, the answer to both questions would be yes. Actually, I though I was the only sailing idiot on my dock and yacht club. Little did I know I was not alone.There are 4 things that you have to understand or sail trim will never make any sense to you. I call them "The 4 Elements Of Sail Trim" and they are DRAFT POSITION, DRAFT DEPTH (belly), TWIST and ANGLE OF ATTACK. If you do not have an understanding of those 4 elements, sail trim will never make any sense to you.Let's start with the easiest - angle of attack. Here's how sailing books will describe it. Angle of attack is defined as putting a sail at an angle to the wind so that the sail turns the wind so the high speed flow and the low pressure are on the leeward side and the low speed flow and high pressure are on the windward side thus causing the boat to move forward. If that doesn't turn off a begineer to intermediate, I don't know what would. Anyway, what that actually means, in simple English, is that the more a a sail (main or jib) is trimmed in the more power or lift it generates because you are forcing the to turn which creates a force. It's Newtons law - for every action there is a opposite and equal reaction. That force you are creating causes the boat to move forward.The angle of attack controls for the mainsail are the MAINSHEET and TRAVELER. Trim them in and the boat will go faster. Ease them out and the boat will go slower.The angle of attack control for the jib is the FAIRLEAD. Bring the fairlead inboard and the boat will go faster. Use the outboard track and the boat will go slower.Suppose you only have one set of tracks. If they are outboard then use a Barberhauler (which I'll explain later). If they are inboard then your already there. If you intend to race the boat, two tracks are preferrable. Next time your out sailing, try these adjustment and see what happens to the speed of your boat. Next session we'll discuss DRAFT DEPTH.Any questions on angle of attack?

 

[Dan Jonas]

Angle of attack

Don,The pilot in me had to respond to this one. I think it might be better described as the angle between the average cord of the sail and the relative wind. You can only increase the angle of attack until the sail stalls, so pulling it in may or may not make you go faster. I suppose at that point the relative wind might be pushing the sail rather than flying it. Also, you can only let it out until the lowering angle of attack reaches a point that lift is no longer created by the method you describe. Sailors call this luffing.I think your definition defines the "appropriate angle of attack" not angle of attack. Angle of attack is simply an angle, which may or may not produce the results you define. The idea is to recognize the optimum angle of attack for any given situation.OK, I'll be quiet now.Dan Jonas

 

[Don Guillette]

Angle Of Attack

Dan: Honestly, I don't make these terms up. Every book on sailing I've read calls it angle of attack. I understand what your saying but my purpose here is to keep it very simple so beginners can understand it. It is hard for them to grasp, as Dennis Conners describes it -"the angle of attack is the angle between the apparent wind direction and the sail's chord line". Most have no idea what a chord line even is and would probably have difficulty defining apparent wind and true wind. If I can get them to grasp that when going to windward, if they pull in on the sail or switch to an inborad track, they will go faster and conversely, if they do the opposite they will slow down then we are half way home. I'll work on the other points of sail later.

 

[Daniel Jonas]

Angles, Chords, Fat

Don,I'm sitting here trying to figure out how I managed to give a Dennis Conners definition for angle of attack. I was trying to make the point that the sails ability to "turn" the air is only valid within a certain range of "angle of attack". Just like an aircraft wing will only "fly" when the angle of attack is neither to large or to small.I know that your point was that as long as the air is being turned within that angle of attack, sheeting in increases power and sheeting out decreases it.When I was first learning to sail, I did not get the concept of the sail at all. I was operating under the impression that the wind pushed a sail (all the time). The instructor finally made a comment that it was much like an aircraft wing, just vertical. Having flown for many years, it was like the sun rose on the part of my brain that processed sailing. I told him that I now understood it, and in general terms I did. Things were much easier after that.I am looking forward to this series. While I know what angle of attack, chord, draft, and twist are, I'm not always sure what configuration is optimum at all times.By the way, you might think that twist would be a departure point between sailing and aircraft, but, the very first powered aircraft used wing twist to control the angle of bank. Those Wright brothers might have made good sailors.Thanks,Dan Jonas (S/V Feije II)

 

[Rick Webb]

Does This Help?

Sheeting in the main increases the speed of the wind across the sail creating more lift. Your jib also increases the air flow across the foil. Just like your leading edge slats.

 

[Dave]

A view from the couch

Don,While everyone is describing the bernoulli effect of air flowing across an airfoil and the lift created I don't see how you can not simultaneously discuss centers of effort and vector mechanics. In short the sum of the forces on the sale can be represented by a vector through the center of effort. This vestor has three dimension components of i,j,k with direction and magnitude. The component of the vector in the direction of the centerline of the boat is the one you want to maximize to make the boat go the fastest. Unfortunately there is also a component making the boat heel. As the boat heels the angle of attack is changed and the wind no longer flows across a the airfoil in the direction desired and you reduce your lift. Eventually as the heel angle approaches 90 degrees lift is no longer provided and you have other things to worry about. Of course if the inertia of the heeling is large you might continue well past the 90 degree point. You do a great job with simplifying an extremely complex and dynamic force balance system that will easily make non-engineers head for the power boat broker. Keep up the great work and I look forward to your discussion. You sail trim charts are great too!!Thanks,Dave

 

[David Droppa]

Two very basic questions

A few posts ago you said there is no dumb question, so here goes: I have two I have sailed for a few years without incident, but the last three years I have dumped my O'Day Javelin twice in high winds on a fairly small lake in New York State and would rather stay upright, especially with my outboard attached. First, I have never used my travelers; I just set them in the middle, and never knew what they were for. I learned that they are there for a reason in your posts, but that's it so far. To reduce heel, do I move them forward or backward? You said a flatter sail produces less heel, so I would guess moving them back reduces heel... is this right? Second... I see that reefing would be another opportunity to stay upright, but how the heck does one do that? If I roll the main up, the tackle connected to my main sheet disappears into the sail. Do I just drop some sail and it drops into the boat and I tie it up? I am going to try sailing with just a jib... I wouldn't have thought I'd have much control, but if I am sailing downwind, which is when I have dumped, then that wouldn't matter. I hope these questions are not too dumb, but I would sure appreciate some not-too-technical answers, Don! David

 

[Don Guillette]

David Droppa: I always try to keep the answers very simple. When I was learing to sail, most of the answers I got were so technical I did not know what they were talking about and I don't want to subject folks to that here on this forum. No sailor should have to go through what I went through in order to learn how to sail a silly sail boat!!Before I answer your first question, I have a question. I think you are referring to the jib fairleads instead of the traveler for the mainsail. I want to be sure before I go off on a tangent.On reefing the main - actually, you don't roll it up, you flake it. In other words, you drop the halyard slowly and make nice folds in the sail over the boom, first to one side and then the other and then you tie it up. The question becomes , when do you reef? The answer is, the first minute it crosses your mind that you think the conditions might demand less sail area. To sail down wind with just the jib alone is not a good idea. You'd be better off sailing with the reefed main alone. Reefing the main while sailing downwind is also not a good idea. You want to be head to wind when you reef the main.

 

[David Droppa]

Thanks, Don!!!

Don - I appreciate your response and your patience and clarity!! And you're right.. I was referring to the lines that control the jib (fairleads, eh?), that connect to cleats that are moveable forward or backward. Those are what I leave in the middle, since I don't know why one would move them either way. So then, what's a traveler? My main sheet goes through a block and tackle in the center of the boat, and it is in a fixed position. As for reefing... so when you tie up the folds, which sounds easy, then you have to leave a space so the cleat that's attached to the boom is free... otherwise the main sheet would be covered up, right? I can envision heading into the wind to drop the main some so I could reef it, but in the winds I was sailing in (solo) I think I would have had about 15 seconds to accomplishs this before I came about, and I figured that position was less stable than with the wind at my back... and experience now tells me it probably didn't make any difference... I would have gone over anyway! I guess the answer is to reef the sail before I leave port if the winds look that bad and I'm sailing solo? My previous boat was a Wildflower, and since the main didn't feed in a track, I could just uncleat the sail at the stern end and it would flap free, and I never had to worry about dumping, but with my Javelin, I can't do that. Thanks again for your response... I can't believe I am getting such useful advice here, and feeling smarter already!!!

 

[Don Guillette]

David: This may sound like a commercial but I can make your sailing experience so much easier and enjoyable for you. Space on this forum does not permit me to provide the level of infomation that I think you need. I mean we were all in your shoes at one time and a lot of sailors are still there, whether they want to admit it or not.It is very important to not only know the names of all the sail trim controls for your main and jib but also to know what they do. You can learn this a number of ways, one of which is to go out with another sailor or take lessons. The problem with that is they will use terms you may not understand and their explanations may be confusing. I suggest you invest $18.50 for my Sail Trim Users Guide plus $15 for my Sail Trim Chart. Everything you need to know about sail trim is contained in these two products. If you decide to take lessons, you'll be so much farther ahead because you'll know what they are talking about. In fact, if you totally digested the book, you could probably teach the class!!So Monday morning, do yourself a favor and call my friend Sara at Sailboatowners.com (tell her I said hello when you call)and order at least the book. Both products are sold with a money back guarantee. In other words, if you are not completely satisfied, I'll return your money and you can keep the book!! I'm really not worried about that as I've yet to have a book or chart returned.

 

[Ed6925]

Backwinding the main

Often while sailing my C310 upwind on a close reach in brisk winds (around 15-18K apparent), I will have the genoea trimmed in tight and the main trimed fairly flat. In this configuration, I tend to get a bulge in the front (luff) of the main, which I believe is being caused by the genoea backwinding the main. I can relieve this somewhat by moving the traveler to windward, however this tends to induce too much heel - if I drop the travel to leeward, the backwinding becomes more apparent.Some folks have told me this is normal and to forget it, because at this point the main is getting most of its drive off the back of the sail.What say you?thanksEd

 

[David Droppa]

OK

Don - OK... I'll do that. Thanks. David

 

[Don Guillette]

Sal Trim Basics

Ed: The bubble you describe in the main is backwinding from the jib and the only way to eliminate it by moving the traveler or easing the jib. I do not like to mess with the jib because the jib is the "engine" on a mast head rig. The jib is the first sail you trim on a masthead rig so when I'm working the main I just trim right past the bubble. I know a lot of guys that cruise and race with that bubble all the time but personally I don't like it even though I don't think it effects your speed to any great degree unless the bubble is massive. I'm a bit of a purist and when I visualize the sail as if it was in a wind tunnel with smoke blowing over it, I prefer to eliminate the bubble and get that perfect shape.