The Four elements Of Sail Trim To take the mystery out of sail trim is to essentially understand that all the controls for the mainsail and jib only adjust four things and they are: Draft Depth (belly) Draft Position Twist Angle Of Attack Lets start with the first two elements. Why do we have to understand Draft Depth (belly) and Draft Position ? We have to understand them because they control three things - POWER, ACCERERATION and DRAG. Drag, is actually friction, which detracts from power and comes from the rudder, keel etc. A sail is like an airplane wing and if a plane flew sideways it would be called a sailboat. The plane's flaps, in the up or down position , produce a deep shape ( like a belly) and are used for takeoffs and landings. No flaps or a flat wing create less drag and are used for high speed and cruising. Where does the POWER to power a sailboat come from? It comes from three things and they are the SHAPE of the sail, which is either deep or flat. The power also comes from TWIST. Twist is the most important sail trim adjustment you can make. I'll go into the definition of twist in a later message. The final element of power is the ANGLE OF ATTACK and I'll go into the that definition later also. What is DRAFT DEPTH (belly)? It is " the % of sail width at a given point". To understand that definition we have to discuss DRAFT POSITION, which is " the point along the chord where the maximum depth falls". To find the chord you measure the foot of the sail and mark the halfway point on the boom. In other words, if the chord is 10' long then the 5' mark would equal 50%. The 4' mark would equal 40% and so on. So, if the belly of the sail was 1' deep then the draft depth would be 10%, which is a relatively flat sail. If the belly was 2' deep then the draft depth would be 20%. Now, you have to imagine a vertical line going up the middle of the belly of the sail. Where that imaginary line intersects the boom is called the draft position. Assume the skipper of the boat decided that the point of sail and wind condition he was sailing in would need a 20% draft depth and a 50% draft position to obtain 100% efficiency from his mainsail. You know what setting you have to obtain and that is a 2' belly with the imaginary line falling at the halfway point on the chord line. You may not know what controls to use or which way to trim them but we'll get into that later. It is very important that you understand draft depth and draft position before we go any further. Any questions on the above two items?
- Status
- Not open for further replies.
C
Claude Labrecque
Question on depth and position
Hello Don, We sail a Hunter 35.5 on Lake Champlain NY. As novice sailors, we are learning everyday and I find sail trimming very interesting. I understand both concepts of draft depth and draft position. Draft position is easy to calculate by measuring chord and by marking the boom as you explain. My question is the following: if the main sail is 44 feet tall (The “P” measurement: luff length of mainsail from tack to head), and there is some twist in the mainsail, at what level, vertical distance from the boom, should I look for maximum draft depth ? I hope my question is clear, my native language is French…
Hello Don, We sail a Hunter 35.5 on Lake Champlain NY. As novice sailors, we are learning everyday and I find sail trimming very interesting. I understand both concepts of draft depth and draft position. Draft position is easy to calculate by measuring chord and by marking the boom as you explain. My question is the following: if the main sail is 44 feet tall (The “P” measurement: luff length of mainsail from tack to head), and there is some twist in the mainsail, at what level, vertical distance from the boom, should I look for maximum draft depth ? I hope my question is clear, my native language is French…
D
Don Guillette
Question on depth and position
Claude: Excellent question.The belly starts on my mainsail about a foot above the boom and then starts to get to max depth about half way up. It is hard to get an exact measurement of depth so most guys rely on a guesstimate. If you have a draft stripe or seam, which I don't, it becomes a lot easier. Try this the next time your out sailing. The controls for adjusting mainsail draft depth (belly) are MAST BEND and the OUTHAUL. Increasing tension on those two controls REDUCES the belly and decreasing tension INCREASES the belly. When you think about it and visualize it in your mind, it makes sense. So, on your next sail, put zero pressure on the back stay and completely release the outhaul. That is your max belly for your sail. Next, apply max outhaul and backstay. That is your minimum belly for your sail. As you are apply or decreasing tension, watch the sail and see what is happening. I hope I've set yuo in the right direction.
Claude: Excellent question.The belly starts on my mainsail about a foot above the boom and then starts to get to max depth about half way up. It is hard to get an exact measurement of depth so most guys rely on a guesstimate. If you have a draft stripe or seam, which I don't, it becomes a lot easier. Try this the next time your out sailing. The controls for adjusting mainsail draft depth (belly) are MAST BEND and the OUTHAUL. Increasing tension on those two controls REDUCES the belly and decreasing tension INCREASES the belly. When you think about it and visualize it in your mind, it makes sense. So, on your next sail, put zero pressure on the back stay and completely release the outhaul. That is your max belly for your sail. Next, apply max outhaul and backstay. That is your minimum belly for your sail. As you are apply or decreasing tension, watch the sail and see what is happening. I hope I've set yuo in the right direction.
T
Tom
OK Don I understand (in theory) how to add draft
depth into the "belly" of the sail. Tighten the backstay or loosen the outhaul. But in "practice" how do I really accomplish this on my boat. I have a '99 C36MKII (split backstay) with no adjuster (and no real plans to add one). And from what I've read Catalina masts aren't *really* all that bendy nor are they designed to be. (yes I'm sure it can be done and I'm sure you have one on your C30 especially if you race). So that leaves me with an outhaul on my (fairly) big mainsail. I guess I have "moderate" tension on the outhaul, but its the one adjustment I rarely touch. For 2 reasons, a) its the only one that isn't led back to my cockpit and b) I did try and adjust it (light winds last weekend and I wanted to loosen it to get more belly) but with the friction from the foot of the mainsail in the boom it *barely* moved and I was pulling hard. It seemed like a huge hassle with no effect. Questions. 1) Do you really adjust (in and out) the outhaul that much when cruising/racing? 2) Do you have any tips to making this job work a little better? 3)How much am I *really* going to gain in sailing efficiencies by adjusting the mainsail belly in my type boat (which I'm told the Jib becomes so much more a critical adjustment)? 4) Would it really hurt to leave the outhaul, sort of in the "middle" position, and try to affect mainsail draft belly by using my rigid vang?
depth into the "belly" of the sail. Tighten the backstay or loosen the outhaul. But in "practice" how do I really accomplish this on my boat. I have a '99 C36MKII (split backstay) with no adjuster (and no real plans to add one). And from what I've read Catalina masts aren't *really* all that bendy nor are they designed to be. (yes I'm sure it can be done and I'm sure you have one on your C30 especially if you race). So that leaves me with an outhaul on my (fairly) big mainsail. I guess I have "moderate" tension on the outhaul, but its the one adjustment I rarely touch. For 2 reasons, a) its the only one that isn't led back to my cockpit and b) I did try and adjust it (light winds last weekend and I wanted to loosen it to get more belly) but with the friction from the foot of the mainsail in the boom it *barely* moved and I was pulling hard. It seemed like a huge hassle with no effect. Questions. 1) Do you really adjust (in and out) the outhaul that much when cruising/racing? 2) Do you have any tips to making this job work a little better? 3)How much am I *really* going to gain in sailing efficiencies by adjusting the mainsail belly in my type boat (which I'm told the Jib becomes so much more a critical adjustment)? 4) Would it really hurt to leave the outhaul, sort of in the "middle" position, and try to affect mainsail draft belly by using my rigid vang?
D
Don Guillette
OK Don I understand how to add draft
Tom: Sorry about the delay in answering as I missed your question. Your right, the Catalina masts are not very bendy but you can get some bend in them. I do have a backstay adjuster on my boat but I don't race it. I just cruise my boat as my wife has every creature comfort know to man on board and it would be a hassle to remove everything and she'd go nuts anyway. Also, it is too hard to maintain a steady crew, so I race on other boats. On the out haul - In answer to question 2, I assume you have the internal system as I do. The problem is the system is poorly designed. The difficulty is inside with the pulley system and to make it work properly you have to remove the boom and get inside and redo it. Another problem is the aluminum slug that that slides in the boltrope track. It has too much friction and it digs into the boom as you try to pull it back. In my case, I merely added 2 Harken triple blocks to the end of the boom and I could pull the cringle out of the clew if I wanted to. There are a couple of other ways to fix it also. If your interested , contact me off the forum at yankee3223@juno.com and I'll explain your options. Now as far as the importance of adjusting the outhaul - the outhaul controls the bottom 2/3 of the mainsail. You could leave it in the middle if you wanted to but you won't get the best results from your boat. It will sail OK but you could get more efficiency from it. You should really try to fix the outhaul as I think you will like the results. Also, you can't adjust the belly of the mainsail with the boom vang. The boom vang is used to adjust twist and draft position. On question 3 - the jib is the engine on a masthead rig but you can't ignore the mainsail. The mainsail is like the accelerator. Both have to work together to achieve 100% efficiency.
Tom: Sorry about the delay in answering as I missed your question. Your right, the Catalina masts are not very bendy but you can get some bend in them. I do have a backstay adjuster on my boat but I don't race it. I just cruise my boat as my wife has every creature comfort know to man on board and it would be a hassle to remove everything and she'd go nuts anyway. Also, it is too hard to maintain a steady crew, so I race on other boats. On the out haul - In answer to question 2, I assume you have the internal system as I do. The problem is the system is poorly designed. The difficulty is inside with the pulley system and to make it work properly you have to remove the boom and get inside and redo it. Another problem is the aluminum slug that that slides in the boltrope track. It has too much friction and it digs into the boom as you try to pull it back. In my case, I merely added 2 Harken triple blocks to the end of the boom and I could pull the cringle out of the clew if I wanted to. There are a couple of other ways to fix it also. If your interested , contact me off the forum at yankee3223@juno.com and I'll explain your options. Now as far as the importance of adjusting the outhaul - the outhaul controls the bottom 2/3 of the mainsail. You could leave it in the middle if you wanted to but you won't get the best results from your boat. It will sail OK but you could get more efficiency from it. You should really try to fix the outhaul as I think you will like the results. Also, you can't adjust the belly of the mainsail with the boom vang. The boom vang is used to adjust twist and draft position. On question 3 - the jib is the engine on a masthead rig but you can't ignore the mainsail. The mainsail is like the accelerator. Both have to work together to achieve 100% efficiency.
- Status
- Not open for further replies.