Thoughts about heeling

[George Kornreich]

Hi, Don. I hope I'm not beating this topic to death, but I'm trying to get a good grasp on what causes heeling, because then I expect the other issues (helm, etc.) to fall into place. I understand pretty well the idea of centers (of effort and of lateral resistance), but whenever you look at vector diagrams they are essentially drawn in 2D, in the horizontal plane. They explain why the boat goes forward, why there is leeway, and some reasons for weather and lee helm (motion about the Yaw axis) but do not take into consideration the roll axis, which we airplane drivers are used to dealing with seperately. So, it was always my assumption that, regardless of other factors, wind blowing laterally against the sail would cause it to act as a lever and roll the boat into a heel. THAT'S why I always thought that the jib would cause the boat to head off (reduce weather helm) but at the same time act adversely to increase the rolling effect (adding to that of the main) and as a result increase heel and weather helm, and maybe cancel out some or all of it's beneficial effects on weather helm. Well, do I have this all screwed up in my mind? If the jib does not act as a lever (in the roll axis) then it all becomes clear, but if it does, it's clear as mud!Thanks again, Don. Hope you had a good Turkey Day!George

[Joe Boyette]

Sounds plausible to me. I tend to think of the sail as an airfoil similar to that of an airplane but tilted over to the vertical, (and past that when the boat heels) and I like to envision where the lift force is generating a force vector and in what direction. For example, when apparent wind builds, the sail generates more lift which pulls the boat over into a heel. As the heel increases, the pull is more and more out to the side of the boat and this generates weather helm as the rig trys to pull the boat along from off to one side of the hull as it travels thru the water. So we ease the main and the center of effort moves forward, taking pressure off the rudder. There are probably other very good analogies to what is happening...to my wife, the heel angle correlates directly to the fun factor so she never eases the main.

[Doug Rodrigues]

Hi George,As a fellow pilot (X-CFI / CFII and Ag Pilot), I also think of the sails as vertical wings and easily visualize the low pressure area over the sails sucking the boat forward. Of course, that is in addition to the ski effect at the bottom (windward side) of the sails too. Then there is the air deflection that follows the trailing edge of the sails resulting in a slight thrust effect. From what I read in these sailing pages, pure sailors think in a different philosophy but strive to achieve identical results. Interesting.........

[David Foster]

Weather helm results when the center of effort of your sails is behind the center of lateral resistance from your hull/keel (the underwater wing. Think yaw forces.Heeling results from the sideways component of the lift on the sail becoming higher than the lateral resistance and righting moment of the hull/keel. Think roll forces.Reefing reduces both weather helm and heel by moving the sail area forward (yaw) and down (roll).I think a joy of sailing is learning to tune, or shape the wings on our boats - a continuous wing design experiment!DavidLady LillieDavidLady Lillie

[Don Bodemann]

As another flyer and model aircraft designer, I was trying to decide how to word my two cents for this discussion, but I think Dave has broke it down nicely. Simply put, excessive heal (yes, my wife also says there is no such thing)and weather helm can be corrected by reducing canvas aft of the mast. This includes large head sails that extend beyond the mast.

[george kornreich]

just by looking. The pilot-sailor looks at the sail with his head bent way over to the side, so that he sees a "wing". But the wing analogy goes only so far. A sail is like the old slow flight wings of antique planes which were constantly shaped by wing-warping devices (no flaps or ailerons), and had no fixed metal (or canvas) across the bottom.But I still wonder what the jib does in this equation. While balancing the weather helm created by the main (further aft) by being foward of the center of effort and lateral resistance, does it at the same time increase the rolling forces? Picture it this way... you only have the main up and you have mucho weather helm. What do you get when you unfurl the jib (not a big genny which confuses the issue... more or less heel?

[Rick Webb]

The Jib is the Leading Edge Slat

[Sean Herron]

Hello,I have this book that I bought in France when I was a kid who had just taken to sailing because at that time I could not afford groundschool for my private pilot ticket...It is entitled 'Sailing Theory and Practice' by C.A. Marchaj...Surely you have already perused it's many two dimensional scribbles, but tell you what, I will mail it to you for a carton of Camels...Just kidding, also there is a 3D sailing dynamics engine out there somewhere, I forget the the link, just a curiousity I imagine from some bug eyed game programmer...You can also get some very interesting reading, need a whisky or two, from the link belowHave a nice day...SH.

[Doug Rodrigues]

Hey Rick, you're correct. That jib does function as the leading edge slat! I never thought about it that way, but that's exactly what it does! Now you've really got the sailors scratching their heads wondering what a SLAT is. LOL

[Dave]

Think of what is happening to the rudder when the boat is severely heeled and generating a lot of weather helm. If you wanted to turn the boat you would apply a force parallel to the surface of the water. When the boat is heeled the rudder is no longer vertical so the force generated is no longer parallel to the surface of the water, rather you are generating a significant vertical component of force, trying to push the stern of the boat deeper in the water and lift the bow out of the water. As the boat heels further this efficiency of the rudder is reduced until eventually all steerage is lost. This severe force on the rudder and hull is not good for it and should be considered when deciding to reef or not. That's why ocean racers now have dual rudders so when the boat is heeled they have a vertical rudder and maintain its' efficiency.Also as the boat heels instead of the wind flowing over the sail perpendicular to the mast it now has an angle of incidence to the sail and is flowing over it along some weird path that reduces the efficiency of the sail. Of course once you reach 90 degrees of heel the sail is pretty inefficient.Rule of thumb is 20 degrees of heel and then reef, beyond that the boat will not go faster and you will subject your rig and hull to forces for no logical reason. Happy heeling.C.d

[David Foster]

increases roll force, and balances weather helm from the main. As Don said, the part of the jib beyond 100 percent of the distance from the forestay to the mast can increase weather helm. Furling the jib has also moves it down and forward, but decreases its total force balancing the main.DavidLady Lillie

[R.W.Landau]

The guys are right. Maybe this will help you a bit. Combine this info with what has already been stated.What the jib does: when any jib is used, the jib focuses air past the main and makes the main more efficient. When the main is working in this higher wind condition, it causes the main to over power the jib, thus causing the boat to round up. That is weather helm.I try to decrease sail area proportionally, fore and aft, to keep the helm balanced and the heel to less than 30 degrees in the gusts. George, I have never had enough wind with just the main up to create weather helm on my boat. All boat designs are different in how much sail, fore and aft, it takes to balance the helm.Heel: The forces on the sails can be broken down into two vectors. one fore and aft and one athwartship. When the force of the athwartship vector increases it increases the heel of the boat, To reduce the force, make the sails smaller so that the force is smaller. The reducing of the sails is reefing.r.w.landau

[Dave]

RW makes a good point. Let me just add to his comments a bit. Rather than a vector fore and aft and another one perpendicular to the direction of forward motion, think in 3 dimensions. In reality there are a host of forces acting on the vessel, many opposing one another. In the end they can all be summed into a vector along the direction of motion that has a magnitude. This vector can be broken down into component in the x,y, and z directions each with their own magnitude.The component in the forward direction makes the boat go forward, the component in the y direction makes the boat have leeway (assuming our grid is set up as x and y lie in the plane of the surface of the water, and the z component either tries to lift you boat out of the water or tries to sink it.Now consider the effect on the main. You have a center of effort where the vector acts through a point. Lets assume for discussion that the boat is perfectly vertical and the vector components are only in the x and y directions the x makes the boat move forward and the y makes the boat heel. As the boat heels the sail is no longer vertical so the vector through the center of effort is no longer in the x-y plane, you have now added a z component to the vector direction. So to sum up this is a complex force system in three dimensions, compounded by the effects of waves, currents, wind on the freeboard, drag from the rigging (much greater forces than you might think), rudder, keel, bouyancy, pitching causing shock loading, etc.If you want to test my comment about rigging drag force take a broomstick and stick it out the window of a car at say 25 or 30 miles an hour and hold it. Separation of the airstream caused by the shape of the stick causes a huge drag compared to a similar size stick with an airfoil shape which tries to maintain laminar flow. Now picture that broomstick say 45 feet long and there are 4 of them plus a couple more say 25 feet long.So even the rigging contributes to heeling the boat. Think about these boats in storms with zero canvas up and going hull speed under bare poles. The forces caused by drag on the rigging and mast are very large indeed.dave

[MArk]

And don't forget the fin effect. Sure the wind in the sail abeam causes a heeling force but to transfer that force to forward motion, you need a keel to work against. Without the keel to redirect that force forward, it would be like sailing a pie pan. You wouldn't heel much but you would only be able sail down wind.While the wind hitting from starboard wants to push the boat (especially the masthead) to port, the keel (and the rest of the hull to a lesser extent) resists the movement by exerting a "lift" or counter force back to starboard. The combination of the sail above and the keel below both contribute to the twisting force. Take away either and the boat won't heel. It is this play of wind against water that allows a boat to sail a direction other than down wind.Although some racers are designed to be sailed heeled to get around LWL rules by increasing the water line length (and therefore theoretical hull speed) when heeled, heeling in cruisers is to be avoided when possible. Not only is extreme heel uncomfortable, but also when heeled, you lose both sail and keel efficiency. That’s why you’ll usually go faster by lowering the sail area (reefing) rather than letting the boat heel more than 20 degrees.Related subject:There are a lot of books written about sail trim. Maybe it's time someone wrote a pamphlet on keel trim for all the people with centerboards. The Flying Scott Tuning Guide (related link) mentions centerboard trim only briefly.Happy sails _/),MArk

[Don Bodemann]

If this isn't all complicated enough, let's discuss the righting effects of a water balasted boat vs a keel boat....have at it guys

[Dave]

I can't see much use for it other than in long distance racing boats, the need to pump all that water from one side to the other is impractical for daysailors, or weekend cruisers. Of very serious concern is construction of the tanks. If the tanks don't have baffles and the liquid is free to slosh around you can have a very dangerous situation.All that mass constantly accelerating and decelerating changing directions etc. can have a very detrimental effect on the motion of the boat. If used I would only recommend totally filled tanks.dave

[David Foster]

I think it was a design breakthrough to get a real ballast on a 25 foot boat that is light enough to be easily trailed.DavidLady Lillie

[Rick D]

..and we used it on a demo day sail once. It was really easy to use and had a significant effect on heel. Rick D.

[Mike Whalen]

Yikes! I went to law school 'cause there was a low math requirement and now this. I guess if you race then this stuff is essential. I used to be a ratf guide. one of my fellow guides was a genious physics type. I'd mention that, "those clouds sure are wild looking." He'd go into an explanation of why they looked that way. "hey", I'd say, "I just want to admire 'em not understand 'em." Sorta like women, ya know. Everytime I see sail trim info I feel the same way. I get sucked into how this could be useful only to be completely lost in no time. I don't race and I like to think of sail as various acts of god. When the gods are unhappy they try to turn my boat over. If I loosen the main sheet or turn to windward, they stop. Do I know why these crazy gods are appeased in this way? No! I just know they are. So I appease them, sit back and let the sun hit my face and think, those clouds sure are wild looking!Later,Mike