Can't Eliminate Lee Helm - Gremlins???

[svwalkabout]

Well...

Where to start... I can't eliminate the lee helm problem that I seemed to have built myself into. Here is what I have done / changes that have been made to the boat this year versus last year. I am wondering if I have too many things going on at once to be able to isolate the problem.

New standing rigging:
Standing rigging has been replaced and I know that the forestay was cut too short and as such, I have put the old one back on.

New rudder:
Changed the rudder profile a little bit but have gained control and responsiveness. I have also apparently decreased drag as the boat is faster upwind. The rudder is not underhung and does not wander when left unattended when under power with the outboard.

Sail modifications:
Changed the top 3 battens to be full battens instead of partial battens. I did this on an old sail to see if when I order a new sail next year if I will like full battens.

The problem presented itself this year when I was sailing in 12 - 15 knots of breeze and I let go of the tiller for a brief moment. The boat went from beam reaching to running really quickly (about 4 sec) instead of rounding up. I currently have 3-5 degrees of lee helm instead of 3-5 degrees of weather helm. Not good and not safe either...

I have been experimenting with forestay length and thus far have added length to the forestay (by way of an additional turnbuckle at the bottom for adjustability) and raked the tip of the mast back an additional 18" just to get a neutral helm. I am experimenting with the turnbuckle to determine how much length to add when ordering another new forestay.

From where I sit, this seems excessive and I am beginning to think that I have Gremlins on the boat.

So here are the questions that I have:
Can a new rudder shape change the balance of the boat?
Do full battens add Lee Helm?

Any one have any ideas on how to balance this boat and get a little weather helm?

Thanks in advance!

 

[Dan Johnson]

SVwalk...

If you have a lee helm, it means that the Center of Effort is forward of the Center of Lateral Resistance (pivot point) of the boat. That's the easy part.

You diidn't say what boat, what hull configuration (fin, centerboard, etc.) or type of rigging (full, fractional, B&R, etc).

Changing the rudder configuration probably has had no effect. Evidenthly there is no effort needed to stay in a straight line.

The full battens may be the culprit. By changing sail shape with them, you may have moved the main sail's center of effort further forward by their shaping the sail's contour. Try rigging them flat--no prebend for shape.

If you have a rolling furler, try rolling up the headsail a bit--that will take pressure off forward and reduce lee helm. Lastly, try moving the jib cars back a couple of notches to depower the jib (similar result but with full sail out).

Forestay length could also be a source. The further back a mast is tilted, the greater the weather helm. The converse is true (lee helm) of forward tilt. Put a weight on your main halyard. With the weighted end level with the boom it should hang less than a foot out aft from the mast. Putting some aft tilt into the mast so that the weighted main halyard hangs 6" to 12" back from the mast could solve your problem. The eighteen inch aft tilt seems excessive, in the realm of Skipjack aspirations.

Is there any pre-bend in the mast? Is it straight or bow'd? Adjust your lower shouds to set it up according to the manufacturer's specs.

Also, does the weight hang in line with the boom or is the masthead position causing it to hang to one side. If so, you need to adjust your uppers and lowers to center the masthead on the boat's center line.

Allen, other racers--ideas?

 

[Clark]

Brand/Model/Type of boat will be key in this discussion. I had a Sanibel 17 many years ago (at a time when I was much less experienced) that sailed pretty well balanced. She had a shoal keel with a centerboard.
One day in heavier winds, I could NOT get the boat to go upwind it had so much lee helm. After a few minutes of struggling and approaching a lee shore, I dropped sails and got the motor started before I ran aground. I later determined that my centerboard had not lowered completely and caused the center of resistance to move AFT; thereby creating the very bad lee helm.

 

[svwalkabout]

Boat Info

Sorry guys,

I forgot the most basic info. Thanks for the quick replies though.

The boat is a 1987 Hunter 26.5 with a shoal draft wing keel and fractional rig. The mast is centered on the boat and a weighted halyard hangs 18" aft of the mast.

I will try loosening the tension in the battens tonight to see if that allows the center of effort to move aft.

Thanks again guys, I'm pulling my hair out on this one!

 

[svwalkabout]

Also, I have tuned the rig per manufacturers instruction and there is approximately 6" of prebend in the mast. I have an adjustable backstay as well.

 

[Franklin]

wow...you gotta be doing some serious changes to make a fractional rig have lee helm.

If you actually improved the rudder so much that it is creating more lift, that would give you lee helm.

 

[Brian M H23]

Can you tell us a little bit about how you are triming your sails? Or, a little bit simpler - do you have this lee helm upwind...or only on a beam reach? You say you are fast upwind, and lee helm is generally not fast upwind, so that makes me think you have you need to trim the mainsail in more - with the new full battens, the sail doesn't luff where it used to, and you are probably not trimming it enough - but that is just my guess!

 

[svwalkabout]

Well...

Went sailing tonight and I think I have figured it out...

With regards to the previous post, my boat exhibits lee helm on all points of sail. And I mean all. Upwind, I trim the 135% mylar genoa so that the sail is 2-3 inches off the tips of the spreaders. I trim the main to the centerline and adjust the traveler up or down dependeing on the wind conditions. Prior to heading out tonight, I backed off the tension on the full battens as suggested above.

While motoring out today, I was moving at a higher boatspeed than usual and I left the rudder unatended and Whamo! tiller went over and that's all she wrote.

Great evening of sailing though. Wind speed 12-15 with some short duration gusts at 18-20. The boat is fast as all get out and I was clocking 5kts upwind.

I'm pretty sure that the new rudder has too much material in front of the rudderpost.

Now where did I put that Skilsaw???

That's about the only thing that I could come up with.

 

[Franklin]

Well...
I'm pretty sure that the new rudder has too much material in front of the rudderpost.

Yeah, I'd put my money on that creating lift causing your lee helm.

 

[svwalkabout]

Franklin,

Thanks for the re-assurance. I thought I was going mad...

She goes to weather though! Fast and points higher than I ever have before.

Too bad it won't work for day to day sailing.

Thanks

 

[Dan Johnson]

Rudder material...

added to the front end of the rudder is usually intended to balance the effort needed to turn a boat. Sorta like power steering. If there is too much material on the leading edge, the rudder will snap over as soon as it's free to do so due to the force of the flow over it. That it is adding to the hydrodynamic lift of the rudder, enough to create a lee helm, is debateable.

All your trim actions seem to be the correct things done. Playing the traveler not the mainsheet is the key to fast upwind.

More telling is the mention of the Mylar headsail. Is that sail so much more efficient than the original sail that it is creating that much more drive due to the greater flow of air over it, enough to drive the bow off against the effort of the main? 18" of aft rake and still having a lee helm is most significant. What are your telltales telling you about your trim? Have you tried backing the jib cars off (aft a couple of notches)? Franklin pointed out how unusal a lee helm is for a fractional rigged boat. They are intended to be driven by a large mainsail (usually with a fuller roach at the top).

Also, having the winged shoal keel should contribute to weather helm and have more of a penchant to round up in heaver air. In heavier air this is a safety factor. Lee helm in heavy air can easily lead to a broach, lost rig, or worse.

Fire up the chainsaw!

 

[svwalkabout]

Dan,

I was wondering if the headsail could overpower the main as well, so I went sailing with just the main flying. Guess what... Lee Helm.

As far as trim goes, I did try backing the genoa cars off about 8" aft and no luck. The genoa teltales are all streaming aft and break evenly every time I tack. I have tried sailing with the genoa full out, partially furled, and rolled all the way in. Same thing, lee helm. Also, the teltales on the main are all streaming straight aft as well. Except for that pesky one on the top batten, but it flies aft most of the time as well. (Sometimes I just need to soften the mainsheet and bring the traveler up a bit to get it flying again.)

I have had the mylar headsail for several years now and have been able to tune the rig to have 3-5 degrees of weather helm in 12-15 knots of breeze. The main is pretty much blown out, but I am still able to shape it failry well and feel that I am getting plenty of power out of it. Also, the main has enough roach that it hits the backstay every time I tack and sometimes I have to force it through the tack. Just for reference, the main hits the backstay from the head all the way down to the second batten from the top.

 

[Dan Johnson]

Yep, that's a lot of roach...

in the main. Interesting--lee helm, main only. Center of effort is ahead of the center of lateral resistance even with a lot of mast rake. Depowering the jib by moving the cars back with no apparent improvement. Extreme rake had no effect.

The previous boat I raced on acquired a new 155 that was just too much sail for the boat. Best trim upwind in 10 to 15 knots was with the cars as far back as they would go (shame on the sail loft!). When the boat became over-powered in a gust, dumping the main had no effect on it at all--it would just flap and the boat would loose rudder from too much corrective helm and round up. The headsail's center of effort was too far behind the center of resistance because we couldn't add any twist at the top. The result was the opposite of the problem you have. Dumping the genny was the only answer--with an immediate loss of speed.

My suspicion returns to those full battens. They may have added more power higher up and closer in to the mast on a full roach main, even though the sail is "blown out". Trimming the main flatter with the outhaul, using a Cunningham, tightening the vang and halyard should only make it worse. Do they allow the mainsail's head to twist almost parallel to the wind when you drop the traveler? It's not uncommon for the roach to hang up in the backstay and I suspect a full batten would contribute to the problem.

See if it's possible to borrow a convential cut (triangular) main that would fit your boom and lift to see what the result on the helm might be. Full battens on that sail cut may make sense, give you the ease of dropping and bagging, and not be over powered up top. The jib could be put back to work at pointing. And, you could possibly shed the lee helm.

 

[Jim Kolstoe]

In reading the thread, along with your clarifications, it looks to me like the only explanation is that something you did has moved the center of lateral resistance significantly backwards. Otherwise you would not continue to have a lee helm running under mainsail alone with 18" of (I presume) aft mast rake. How hard would it be to make a temporary change to your rudder to experiment with this factor?
Jim Kolstoe, h23 Kara's Boo

 

[svwalkabout]

Just wanted to first of all thank everyone for their input regarding my dilemma.

I have figured out that the only thing that it can be is the rudder. Since my last post, I added an additional 6" of mast rake and still no luck.

So... After consultation with the rudder manufacturer, it appears that there may be too much material in front of the rudder post. The lee helm that I was apparently feeling was not lee helm after all and is simply an overbalanced / underhung rudder due to the position of the rudderpost.

We are in the process of modifying the rudder and once completed, I will post another update.

Thanks again for all the help

Clayton
S/V Walkabout