Yes, I said lee helm!
Shanti has some serious lee helm. On the trip down from Florida I had the typical weather helm of a BCC which really isn’t all that much worse than many other boats I have sailed on.
So what is different? I had a new jib made. I changed the dimensions so the fair lead came down by the chain plates instead of back by the gate. I did this to give more overlap with the staysail to generate more power in the forward part of the sail plan…looks like it worked to well.
I think I still have more than usual weather helm on Adventure, flying a yankee, staysail and main.
I am planning to haul the boat and re-establish the waterline groove on the hull so that I can properly measure the mast rake, but had also wondered whether simply switching to a bigger jib would do something to help.
I figure in theory, the larger area of sail forward should naturally reduce weather helm.
You’ve obviously done so much that you’ve gone just over the point of balance.
I hope you’ll share with us the dimensional changes you made and what you manage to do now to bring the boat back into balance.
Michael,
I have a sail plan that shows the modifications I made. Presently my Internet access is down on my main computer. I will post when that is back up. Probably tomorrow.
There are two primary changes that were made. The fairlead point was moved considerably forward, up at the forward end of the main chains. And there was an increase of overlap between the Yankee and staysail. Sail area for the Yankee remains the same. No other changes were made.
So the sail area is the same, but the shape is different… and such that sail area is moved down and aft I assume, right? Your yankee is miter cut right? And you sheet is in-line (parallel) with the miter?
Is there any correlation between your jib outhaul set up and weather helm? Does the tack not get out as far on the sprit now?
Ben,
yes, sail area is the same or slightly less. I set her up for trade wind sailing. The new sail is cross cut, as the clew is much lower on her vs Yankee. Center of effort is a touch lower and bee’s nuts aft. The tack is about 3-4 inches aft from the fore stay now with jib outhaul system. But I had lee helm as soon as I put on the new sail, before I went to new system.
Ben,
yes, sail area is the same or slightly less. I set her up for trade wind sailing. The new sail is cross cut, as the clew is much lower on her vs Yankee. Center of effort is a touch lower and bee’s nuts aft. The tack is about 3-4 inches aft from the fore stay now with jib outhaul system. But I had lee helm as soon as I put on the new sail, before I went to new system.
If I’m right, he principal effort of the jib is transmitted to the boat via the forestay, and the fairlead point.
If the fairlead point is moved forward, the effort of the sail, and therefore the centre of effort of the boat is moved forward relative to the centre of lateral resistance of the boat, thus increasing lee helm tendency.
Perhaps playing with this will enable me to keep the yankee instead of going for a larger jib which would be more hassle to tack, but reducing my weather helm…?
Bingo! At least I think so. But everything I have read says that isn’t the case. Fairlead position shouldn’t make a difference. But that’s what I’m seeing.
Lets say you wanted to tow the boat. But for some insane reason you were going to do it by tying off on the bulwarks (I know it would probably bust the bulwarks). Now if you tie off forward of the lateral resistance of the keel, the boat would tow at an angle but with the bow facing somewhat forward. If you tied off on the bulwarks aft of the center of lateral resistance of the keel, the boat would turn around and tow stern first, but at an angle.
So the standard BCC yankee sheets aft of the center of lateral resistance of the BCC. My new jib sheets forward of the CLR.
Now as I fall more and more off the wind, the weather helm returns until it is about average for a BCC on a beam reach. Shes fairly neutral at about 65 degrees off the wind.
When I get into the office today I will look for the sail plan I drew up for the new jib and post it on here.
I’ll tell you one thing, enjoy your weather helm, because lee helm really sucks!
Hey Gary.
If you read the Pardey’s Storm tactics, they talk about the attachment points for the para anchor in much the same way, when they’re trying to get the correct angle if incidence of the wind/waves onto the boat.
If the para anchor is only deployed off the bow, the boat will point too much into the wind and not create the necessary slick, but having a bridle attached to the mainsheet winch, and then onto a block on the para anchor rode one can pull the boat into the 50 degree angle required.
It seems to me that perhaps your design for the jib took the clew a little too low, and consequently the fairlead a bit too far forward, whereas the standard one I think I have is a bit high.
Somewhere in between might result in a fairlead position a little forward from the current position & reduce my weather helm and balance a bit better?
I strongly doubt that Lyle Hess or Sam L.Morse got it wrong. I’ll need to check my sail measurements against his drawings.
Very interesting. Let us know what you find out about the fairlead placement. Drawings make it look like fairlead placement should be further aft anyway.
I’d maybe try using the same sail but send the fairlead aft, till the line of the sheet bisects the angle of the clew, and see what that does for the lee helm.
Perhaps the lee helm is cause by difference in the Coriolis effect between the US mainland the the US Virgin Islands.
Lee helm results when the center of effort of the sails is move too far forward in relationship to the center of lateral resistance. At what angle of heel does lee helm develop? I suspect the center of effort of the new sail is further forward than the standard jib top head sail. You may be able to counter the lee helm by raking the mast aft to move the center of effort of the sail plan aft. If lee helm is still present when the boat is heeled 15-20 degrees, raking the mast aft may not be enough to move the center of effort of the sail plan aft. In that case, the only solution is either to re-cut the head sail or have a new head sail made.
I absolutely agree with Rod. Besides the backstay, if your forestay is too loose, this allows a “bagging” in the foresail forward of the center of lateral resistance.
Also, a new foresail with a tired main will place most of the effort forward of the mast, producing a lee helm.
The fairlead placement, although important, is not a significant factor in this, assuming it is placed to match the design of the sail.
Interesting thread which continued while I thought about it overnight so I will share my experiences. Looking at Gary’s sail plan, the jib sheet block does seem well forward (based on a theoretical line going through the clew from a point at 90 degrees to the luff) but in practice, mine is also further forward than ‘theoretical’. I have a similar 8 oz yankee that hanks on to a dyneema running jibstay. The clew of this sail is lower than the standard sail due to a shorter foot (14 ft 10 in?) and longer leech with resulting sail area slightly more (less than 10% increase?) than the standard yankee given in the BCC sail plan. My moveable jib block is placed about where the aft portlight is but I usually have to make a small adjustment to avoid an over-riding turn on the jib winch and attach a second (snatch) block (slides along the bulwarks on a webbing strap) between the gate in the lifelines and the aft chainplate to get the sail to set nicely so this means my true attachment point is well forward. My mast has no rake and I no longer have the weather helm problem that plagued me earlier. My running jibstay does mean that the luff falls off slightly and I also try to sail at moderate angles of heel as well as there seems to be no benefit in sailing the old girl on her ear! My main is also quite old, so all of the points raised so far on this thread seem to fit the observed facts!
Jib trim -
When I sailed Shanti down from Florida a couple of years ago we had a new standard BCC yankee built by Skip Elliot to use. For some reason Shanti had an extra one stowed away. This sail of course trimed back by the gate. So we were sailing with a new jib and old main as John mentioned. Our headstay was not tight enough and we had (although I didn’t realize it at the time) to much sag in the forestay. The result was we could not point well. We were tacking through 110-115 degrees. We had the typical weather helm the BCC has always enjoyed.
I can’t remeber when, but at some point when I had the new sail and was going to the new jib outhaul system, that my headstay was to slack. So started a campaign to make sure the new system set the tension properly to conform to the design specs of the new jib. Which was 6 inches of sag. This required some where in the niehborhood of 1500lbs of tension on the headstay. The sail now sets with proper shape.
Jib trim -
When I sailed Shanti down from Florida a couple of years ago we had a new BCC yankee by Skip Elliot to use. For some reason Shanti had a new one stored away. This one of course sheeted back by the gate. So we were sailing with a new jib and very old main as John mentioned. I did not realize we had not set up our headstay tight enough and could only tack through 110-115 degrees. We also enjoyed the usual weather helm of a BCC.
The next year I had a new jib built by Doyle because I thought the problem was a poor cut on the yankee. When I started designing the new flying jib system, I become aware of the headstay tension problem. So I designed the system so I could achieve 1500lbs tension on the luff, so the sail would fly to its designed shape. Doyle told me they cut the sail for 6 inches of sag. This has been achieved and I now sail well to weather with the new system. I tack between 90-95 degrees.
The fairlead position I am using is confirmed by 3 different methods.
First, the angle of the sheet to the fairlead point is determined by drawing a line from the midpoint of the luff through the clew. This method is confirmed by Doyle. Doyle places a trim stripe at the clew so one can line up the angle of the sheet for proper fairlead placement. See attached photo. Notice the stripe at the clew.
Second, in practice this works correctly as the telltales I have along the luff of the sail break at the same time when the sail starts to stall or luff.
Third, the sail shape looks correct. Draft is where it should be from top to bottom.
So this is not a trim problem. The fairlead is where it is designed to be.
Now the old main with the new jib is an interesting observation. But I had that same situation on the trip down, and I had weather helm then.
Healing angle is interesting. We all have observed an increase in weather helm the more we heal over. Well, the more I heal over the worse the lee helm gets. Now this brings up an interesting point. I and many of you have always been told that this is due to the shape of the hull changing as the boat heels over. And I’m sure this has something to do with it. But I am starting to wonder if a part of it is due to the stronger pull from the attachment points of the sail to the boat, as in fairlead position.
So to summarize. All factors are fairly much the same between the yankee and the new jib. Trimming the sail is not a factor, as that is correct. The only thing that has changed between the yankee and the new sail is the tack at the end of the sprit is about 3-4 inches aft. I find it hard to believe that this small change alone can cause me to go from heavy weather helm to heavy lee helm.The only really significant change is the fairlead position. And I now have lee helm.
I’m going to get the previous yankee I had and put it on for a sail. My curiosity about all this is killing me. This way I will have a side by side comparison so to speak.
Of course it will be a few weeks before I can as I have to haul out and complete repairs to the cutlass/shaft log/engine mounts.
