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Helm Balance

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 08/31/2004 : 17:23:46

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Laux
 Weather helm is mostly a function of healing not rig balance. As the boat leans the CE moves toward the lee rail or even outboard of it and the boat tends to round up just as it would if you tried to tow it from the end of a wisker pole in normal operating position. <hr height="1" noshade id="quote"></blockquote id="quote">
Interesting point--I had attributed it partly to an asymetric hull shape under heel, but the leeward CE makes sense, too. I can imagine the effect of the genoa sheet pulling on the leeward winch, pulling the boat around to windward. Your theory suggest an additional lever arm affect. We'll have to try that theory on Arlyn Stewart...

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JimB517
Past Commodore

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Response Posted - 09/01/2004 : 13:27:20

My SR mast is raked very far aft. I have the balanced rudder. I usually am flying a 135 genoa.

No matter what the wind, I have a touch of weather helm. The boat will gently turn to windward if you let go of the tiller. This is a very handy property for single handed sailing. Tack through about 130 degrees, let go of the tiller, work the jib sheets, harden them up, grab the tiller, and the boat is right back on course like you did a 90 degree tack. Hands off helmsman.

As the wind picks up, the boat stays very balanced. Only light helm pressure is needed UNTIL heeling angle exceeds 40 degrees.

At that magic point, it is actually very hard to get the boat to heel any more, It starts to take a lot of force on the rudder, the boat wants to round up. Also everything falls over in the cabin, and if there are non sailing guests on board they get very nervous. Actually, if alone, I am having fun at this point! Boat speed up to 6.5! Spray flying! Boat charging through the seas! Time to reef the main? Maybe just tighten the outhaul and put the traveller down, sit on the rail, get out the tiller extender. Also this is a real good time to dramatically point up and scallop until the gust is over.

I agree that excessive weather helm leading to rounding up, is totally a function of heel angle. Reducing the heel angle by adjusting ballast (hiking out), traveller, sail shape, dumping the main, or reefing is the thing.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
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Response Posted - 09/01/2004 : 14:01:18

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Laux
 ...Weather helm is mostly a function of heeling not rig balance...<hr height="1" noshade id="quote"></blockquote id="quote">

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by JimB517
 ...I agree that excessive weather helm leading to rounding up, is totally a function of heel angle...<hr height="1" noshade id="quote"></blockquote id="quote">

Hmmmm?...Just last night I was out tooling around, winds were moderate and I was sailing along nicely with full main and 135 genoa. A change in wind direction resulted in rather excessive weather helm, to a point where I think I must have turned the rudder sideways a couple of times to compensate. Because of this new wind direction, I had to haul in the genoa sheet to trim (flatten) the headsail and once that was done, the tiller returned to two finger weather helm rather than the two-fisted weather helm experienced moments earlier. The difference in heel angle was less, but not considerable between the before and after trimming of the headsail.

So in my case last night, excessive weather helm was definitely caused by an imbalanced sail plan, which caused more heeling that was corrected once the headsail was trimmed properly.

Edited by - dlucier on 09/01/2004 14:04:11

Frank Hopper
Past Commodore

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Pitcairn Island
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Response Posted - 09/01/2004 : 14:45:28

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by JimB517
 Also this is a real good time to dramatically point up and scallop until the gust is over.
<hr height="1" noshade id="quote"></blockquote id="quote">
I pinch and feather

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Steve Milby
Past Commodore

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Response Posted - 09/02/2004 : 11:40:21

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Laux

...Weather helm is mostly a function of heeling not rig balance...
<hr height="1" noshade id="quote"></blockquote id="quote"><blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by JimB517

...I agree that excessive weather helm leading to rounding up, is totally a function of heel angle...<hr height="1" noshade id="quote"></blockquote id="quote">Actually, excessive weather helm has several causes. Heeling is one of the causes, and rig balance is another.

Weather helm occurs when the Center of Effort (CE) of the sail plan is not positioned directly above the Center of Lateral Resistance (CLR) of the hull and keel. When the CE is directly above the CLR, the helm will be balanced. For the purpose of this discussion, let's assume that our boat has a perfectly balanced helm.) If you tilt the boat in its longitudinal plane, so that it is sailing more bow-up or bow-down, it will cause the relationship between the CE and the CLR to change, and that will change the balance of the helm. If you tilt the boat in its latitudinal plane, so that it is heeling, it will cause the relationship between the CE and the CLR to change, and that will also change the balance of the helm.

Thus, you can adjust the amount of weather helm of a sailboat by changing the location of either the CE or the CLR.

If you move the CE forward of the CLR, the bow will tend to blow away from the wind, and the boat will have lee helm. If you move the CE aft of the CLR, the stern will tend to blow away from the wind, and the boat will have weather helm.

When the boat heels, the CE moves from its position directly above the CLR to one side of the CLR. If you enable the boat to sail more upright by hiking or by making adjustments in sail area or sail trim, the distance between the CE and the CLR will be reduced, and the amount of weather helm will decrease.

If you orient the bow of the boat up and the stern down (by moving crew weight aft), the CE will move aft in relation to the CLR, decreasing weather helm.

You can decrease weather helm by tilting the whole rig more forward when you tune the rig.

You can also decrease weather helm by adding more sail area forward, or by reducing sail area or sail effectiveness aft.

Finally, you can raise the swing keel partway, which moves the CLR aft in relation to the CE. (But not while racing, because it violates the racing rules.)

Edited by - on

Ed Montague
Captain

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USA
499 Posts

Response Posted - 09/02/2004 : 12:30:23

Steve, thanks for the concise explaination of how to change the sail balance to change helm preasure. I don't think I have ever seen it explained so simply and I have read many articles in sailing magazines on the subject. It makes sense now to reef the main before reducing head sail as the wind pipes up and weather helm increases.

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Dave Bristle
Master Marine Consultant

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Djibouti
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Response Posted - 09/02/2004 : 22:35:21

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 
If you orient the bow of the boat up and the stern down (by moving crew weight aft), the CE will move aft in relation to the CLR, decreasing weather helm.
<hr height="1" noshade id="quote"></blockquote id="quote">
Steve, I assume you meant to say "increasing".

One other point... Neutral helm is not actually the ideal. A moderate amount of weather helm is desirable for two reasons, one of which applies to everyone:

(1) The old adage in sailing is that if you let go of everything, the boat will stop. A variant is that if the helmsman lets go of the tiller, the boat will turn up and stop. That's with weather helm. With lee helm, the boat will turn downwind, and probably start a series of jibes--off into the sunset (or onto the beach). If an absolutely neutral helm were achievable (which it isn't), the boat will still sail away--not stop.

(2) Some very expert racers have told me that a small amount of weather helm increases "lift", thereby increasing speed. That seems a little counter-intuitive, since you might think that the rudder angle to correct for weather helm would increase drag. But apparently weather helm causes the angle of attack of the keel to lift the mast slightly more upright, getting more power from the sails.

So, rig adjustments, sail trim, sail shape, and weight placement all come into play, but the concensus among the authorities is that a small amount of weather helm, requring 3-5 degrees of helm to correct, is advantageous, and even a safety feature. If it causes rounding up, that's because you're heeling so much that your rudder is losing its purchase, and is turning into an aircraft-style elevator instead of a rudder. The key issue is, if you let go, what happens?

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 09/03/2004 : 09:49:10

This article titled [url="http://www.sailnet.com/collections/articles/index.cfm?articleid=colgat005"]"The Balance of Hull and Sails" by Steve Colgate[/url] explains helm balance (weather helm) quite nicely. The illustrations are worth a thousands words.

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Steve Milby
Past Commodore

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USA
5896 Posts

Response Posted - 09/03/2004 : 10:38:33

<blockquote id="quote">quote:<hr height="1" noshade id="quote">quote:
--------------------------------------------------------------------------------
Originally posted by Steve Milby

If you orient the bow of the boat up and the stern down (by moving crew weight aft), the CE will move aft in relation to the CLR, decreasing weather helm.

--------------------------------------------------------------------------------

Steve, I assume you meant to say "increasing".
<hr height="1" noshade id="quote"></blockquote id="quote"> No, but that statement does need to be corrected. I was correct in saying that tilting the bow up and stern down decreases weather helm, but I didn't correctly explain the reason. I should have said "If you orient the bow of the boat up and the stern down (by moving crew weight aft), the CLR will move aft in relation to the CE, decreasing weather helm." When you tilt the boat up or down in its longitudinal plane, you're really moving the CLR in relation to the CE, not the other way around.

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 09/03/2004 : 13:08:44

Even ghosting downwind in very light air, if you let go of my helm my 78 fin SR boat will turn upwind. Charging upwind at 6+ knots, if let go of the helm the boat will turn upwind (in a hurry). Roller furling 135, balanced rudder, adjustable backstay, faired keel, very loose tuned rigging, mast raked way back (the boat is fast by Fleet 7 standards, especially in strong wind upwind where no one can stay with me - downwind Gary with his TR wing usually prevails). I have a lot of weight in the anchor locker with 50 feet of 1/4 chain and a 13 lb anchor. My OB is about 80 lbs. I keep the 16 gallon water tank mostly full because it corrects the well known "port list".

Mikes boat Mara (a 79 fin SR) has lee helm under most conditions. 110 hank on jib, stock boat in every way, standard rudder, heavy OB (new Honda 9.9). We raked the mast back as far as possible using the adjustments on the forestay and backstay and managed to get a slight weather helm.

Mast rake, rig tuning move the CE and distribution of weight inside the boat (moving the CR) make a huge difference.

By the way, rolling up the genny and leaving the main unreefed should move the CE AFT. You are creating much less drive with the genny yet leaving the main the same, the net effect is moving the driving force aft more towards the main. Also, a genny rolled up 1/4 loses a ton of efficency and is mostly just heeling the boat. Always reef the main first.

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 09/03/2004 : 15:27:03

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by JimB517
 ...rolling up the genny and leaving the main unreefed should move the CE AFT. You are creating much less drive with the genny yet leaving the main the same, the net effect is moving the driving force aft more towards the main. Also, a genny rolled up 1/4 loses a ton of efficency and is mostly just heeling the boat. Always reef the main first.
<hr height="1" noshade id="quote"></blockquote id="quote">
Agreed, Jim. If you're referring to my opening post (rolling up 1/4) that was with the main "reefed" to the max--"doused" is the better word. The C-25 sails much better on jib/genny alone than main alone--we were pulling about 5 knots, pointing pretty well and very upright, with the 3/4 genny alone.

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JimB517
Past Commodore

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USA
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Response Posted - 09/03/2004 : 17:21:03

Ah yes, the C25s third reef point (mainsail in bag).

The day I sailed my family from LA Harbor to Catalina we had a ton of wind. Main at first reef point, jib rolled to a 80% or less, traveller leeward, main ready to dump, me hiked out (225 lbs). Trying very hard to keep the heel less than 30 degrees for poor Spike. Boatspeed never under 6.5 knots. We were flying. The kids loved ducking the spray. I could have put in the 2nd reef but I thought it was better to get us there ASAP. I had to fall off a little and we eventually got right into the lee of the island about 50 feet off shore and then motored 5 miles back to windward.

I would like some suggestions how to get Mikes bone stock C25 (does not even have a pop top) a little more weather helm. Mikes the original owner since 1979. Its the absolute bare boat C25. The mast is raked as far aft aw we can get it. He has a very heavy outboard and we are both over 225 lbs (lots of weight in the stern). But it has lee helm even if I am not onboard.

Edited by - JimB517 on 09/03/2004 17:27:59

JimB517
Past Commodore

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USA
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Response Posted - 09/03/2004 : 17:31:18

Also when I've sailed under genoa alone, its very hard to point and the boat seems quite difficult to steer. Any little helm movement and the bow wants to blow downwind quickly and you cant bring it back. Lots of blown tacks the day I tried it (tacking out of our marina in a very big wind under genoa alone...didn't work).

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Derek Crawford
Master Marine Consultant

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USA
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Response Posted - 09/03/2004 : 18:58:05

Jim - I've had the same problem with "TSU". Going racing in 25+ knots we just put up the 110% - every time we tried to tack the bow just kept on falling to leeward. After tacking thru' 180 degrees a few times we started the motor and hoped they cancelled the racing! (They did!)
Derek

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Dave Bristle
Master Marine Consultant

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Djibouti
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Response Posted - 09/03/2004 : 19:44:06

Hmmm... Do you both backwind the sail as you're tacking, and then release after you're through the wind? That might be an anathema to a racer, but it seems to work for me in 20-somethings. I also try to time it so I don't smack a big wave just before I get through. That strategy, of course, won't be ideal rounding a race mark. How about a storm trisail?

I have to admit, however, that I might not have tried this when it's above 30. In these parts, that's a good time to keep your C-25 at the dock, unless you like green water coming over the coachroof. (Dog down that pop-top!)

Another thing--I generally don't harden the genoa too much when it's my only sail. I think that gives it a little more drive and moves the CE back--at least that's how it feels. It doesn't seem to matter if it's not quite filled at the luff, and a little twist doesn't hurt, either. But again, I'm often just sailing to nowhere and back.

Edited by - Dave Bristle on 09/03/2004 20:01:25

Steve Milby
Past Commodore

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Response Posted - 09/03/2004 : 20:21:24

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I would like some suggestions how to get Mikes bone stock C25 (does not even have a pop top) a little more weather helm.<hr height="1" noshade id="quote"></blockquote id="quote"> He should start by adjusting the rigging so that the mast is plumb. When the mast is plumb, the C25 should have some weather helm. After it is plumb, he should sail the boat and decide whether it has too much or too little weather helm, and fine-tune it accordingly. If he wants less weather helm, he should tilt the mast a little more forward. If he wants more weather helm, he should tilt the mast a little more aft.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Also when I've sailed under genoa alone, its very hard to point and the boat seems quite difficult to steer. Any little helm movement and the bow wants to blow downwind quickly and you cant bring it back. Lots of blown tacks the day I tried it (tacking out of our marina in a very big wind under genoa alone...didn't work).<hr height="1" noshade id="quote"></blockquote id="quote"> One of the key purposes of the mainsail is to help a sailboat point to windward. A sailboat pivots on its keel. When only the jib is flying, it pushes the bow of the boat to leeward. The only thing that resists that force is the rudder, at the opposite end of the boat, but, until the boat is moving through the water at a sufficient speed, the rudder doesn't generate enough lift to resist the force of the jib, pushing the bow to leeward. That's why the boat is hard to steer and it's also why it won't point very well at low speeds. As the boat's speed increases, the boat flying only a jib will point better, but even at its best, it will still not point as well as a boat sailing under jib and main.

When you are flying both a mainsail and a jib, the wind on the jib pushes the bow of the boat to leeward, and the wind on the mainsail pushes the stern of the boat to leeward. The keel is very narrow across the beam, but it is very broad and flat fore-and-aft. That broad, flat surface strongly resists the boat drifting sideways, but it provides very little resistance to forward motion of the boat. The keel changes the sideways pressure created by the mainsail and jib into forward drive, and that is what enables the boat to point to windward. By counter-balancing the forces on the jib, the mainsail is important to the pointing ability of the boat.

Whenever you tack, a boat loses speed quickly. Remember that, when you're sailing under jib alone, the wind is pushing the bow to leeward, but the rudder isn't generating enough lift to counter-balance the force exerted by the jib. That's why you were blowing tacks. You need the mainsail to push the stern downwind, which causes the bow to point more to windward.

A boat can sail with only a jib, but it isn't efficient, and it is easy to lose control at low speeds.

Edited by - on

Derek Crawford
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USA
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Response Posted - 09/03/2004 : 23:29:28

Dave - that point about backwinding the jib made me think. We do, routinely, allow the jib to backwind (it helps rotate the boat around the "barn door" of a fixed keel), but I wonder if, in a high wind, it causes too much rotation as we tack. Next time we are out in a stiff blow we'll try tacking without backwinding - I'll let you know the result!
Derek

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Dave Bristle
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Djibouti
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Response Posted - 09/04/2004 : 08:00:46

Derek: If your problem is too much rotation (tacking to 180 before you get back under way), then yes--try skipping the backwinding to see if you can maintain more speed through the tack. I haven't really analyzed what I've been doing--as I've said, I'm usually doing it while sailing to nowhere in no particular hurry. Week after next (subject to Ivan), I'll be sailing to somewhere, and will be more interested in long-term VMG.

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