C30 Weather Helm Problem

[Don Guillette]

I get most of my material from talking to sailors. I feel if one mate has a questions others might also. This subject came from a C30 tall rig sailor on the Catalina site. He was complaining about excessive weather helm and how he had to crank on the rudder to keep going straight. The following is my opinion as to how he could solve his problem.

Here's what I said:

It is very difficult to determine the cause of a problem by reading 3 paragraphs but folks on this site and on the SAIL TRIM FORUM seem to do it all the time. If a mate, who understood sail trim, was on your boat he could probably determine the problem very quickly.

Since I don't know how your sail trim was set up let me explain the couple of things that cause weather helm.

The first cause is excessive heeling. The submerged part of the hull creates a force that wants to turn the boat to weather. Additionally, when you exert force on the rudder you're inducing drag and slowing the boat. Reduce heel and you reduce weather helm.

The second cause is mast RAKE (not to be confused with mast bend). The boat thinks you picked up the mast and moved it aft.

Why does this happen? In very simple, non scientific terms here's what the boat is reacting to. There are scientific names for the following stuff but let's keep it simple. The boat has a exact center point -- like a pivit point. Additionally, the mainsail has a exact center point and this is important especially with a mainsail the size you have on a tall rig. Both the center point of the boat and the mainsail have to be vertically in line. If the center point (DRAFT POSITION) of the main is aft of the center point of the boat, you get weather helm. Move the draft position forward and you reduce weather helm.

Sail trim is very simple to deal with once you understand DRAFT DEPTH, DRAFT POSITION, TWIST and ANGLE OF ATTACK. If a mate does not underatand those four elements, sail trim will never make any sense.

 

[Bill Roosa]

To put a little more rigor in the discussion:
All lifting surfaces, wings, keels, fins, rudders, and sails have an imaginary point called the center of lift. If you broke the surface down into little parts and imagine that the force on that part is an arrow, then sum all the little parts up with their forces you can imagine that all the force is acting at the center of lift and are the vector sum of all the little forces acting on the individual parts.
For a keel and rudder combination it is called the center of lateral resistance (CLR) for each sail it is called the center of effort (CE) and for all the sails in a sail plan it is called the the same thing, center of effort. Be careful that you locate the jib, mainsail and combined CEs
If you consider the CLE as the pivot around which all other forces act you will see that forces forward of the CLR turn the boat downwind and forces aft of the CLR turn the boat to windward.
When you have the sail plan balanced and with about 3 degrees of windward rudder the CLR is lined up with (fore aft wise) over the CE (total) and there is no tendency for the boat to turn either into or out of the wind.
So when you turn the rudder to make the boat turn into the wind all you are really doing is making the CLR move foreward. Ie less force is being made by the rudder as you went from a weather helm to a neutral and then leeward helm, and the vector sum of the keel and rudder forces is biased away (forward) the rudder because it is making less lateral force than when in a "balanced" configuration. In this configuration the CE (total) is aft of the CLR so the boat turns into the wind.
ANYTHING that moves the CLR or the CE (total) will turn the boat. Powering up the jib moves the CE forward, powering up the main moves it aft, adding more weather helm moves the CLR aft and lee helm moves it forward.
That is the reason you can steer the boat just by powering and de-powering the sails while leaving the rudder alone. And conversely why you can steer the boat with the rudder and leave the sails alone.
When you have excessive heel the CLR force is not acting "horizontally" and acts in a more vertical plain. That is why excessive heel can lead to lots of weather helm as you have to compensate for the lack of rudder contribution to the CLR by dialing in more rudder.

 

[Bill Roosa]

Most weather helm comes from underpowered jibs or over powered main.
I've seen this a lot as folks try and make their boat look like the pictures of boat beating to windward. the boom is amidships and it needs to be let out. the boat stands up, the weather helm disappears and the boat actually picks up speed.

 

[RichH]

I would forget about CLR, CE, sail area and location, mast rake, and most other 'technicalities' etc. etc. etc. as probably the prime cause of 'weather helm' on most boats is improperly raising the mainsail - correctly positioning the point of maximum draft via mainsail halyard tension. If that doesnt solve 99% of 'so-called' weather helm ... then you should 'futz' with normal sail trim, mast rake, etc.

The CLR to CE relationship is REALLY only for stable hove-to conditions, as its the 'dynamics' generated by the sails that ultimately 'balance' the boat ... you cant change the CLR; and unless the boat was designed poorly, mast rake isnt going to make all that big a difference or may only 'mask the symptoms' of whats causing adverse helm; BUT, one can 'easily' change/adjust the draft position in both the Main and the jib to get to 'precise' helm pressure, etc. 'while actually sailing' and very simply so by adjusting halyard tension in accordance of 'todays' wind and seastate conditions.

Most sailmakers are pretty smart with sail design and output performance ... its really quite a SHAME that the sailmakers dont include how to raise those (dacron) sails so that especially beginning sailors get the exact shape that 'should' be there so that the helm is slightly neutral.
Here it is again: http://forums.sbo.sailboatowners.com/showthread.php?t=120970

 

[Cayennita]

When I race and I am working the boat to the starting line and trying to create a nice big hole, I have 2 commands: rotate up or rotate down. To rotate up we ease the genoa and bring in the main. Gives you in a sense weather helm and the boat goes up without using much helm and the speed stays up. if I want to go down, then I say rotate down. Lee helm, again boats turns quickly with very little drag. Same as getting to the weather mark and you try to turn down. If the main is not eased and the genoa stays in, the boat wants to continue straight. Most sailors tend to over trim their mains. I leave mine with a hardly noticeable bubble in the luff. BTW make sure that the main leach is not so tight that it will hook to windward, it can also create weather helm. Same with boat gear. Move it aft as you would with people on the rail when racing.

 

[RichH]

"Most sailors tend to over trim their mains."

Boy oh boy do you hit that nail on the head ... and the same can often be said about over-winching in a jib/genoa.

Including overtrimming the main, most sailors also tend to overtighten the mainsheet .... which causes the leech to tighten and the leech responds by 'cupping up towards weather' ... and boy oh boy does that create 'weather helm' and unneeded excess heeling.

The solution is really look at the leech sections of the mainsail, especially at the battens. When pointing/beating on most cruising boats (with a properly raised well made mainsail), the second from the top batten should be close to parallel to the boats center line (if the sailmaker did a real good design job) and all the battens below this second batten should be flat straight at their aft ends ... overtension the mainsheet and all aft ends of the battens start pointing towards the windward side - and hello 'weather helm'.
If for some reason you HAVE to pull in tight, you must then apply more halyard/luff tension to compensate and return the sail back to its 'design' shape .... there are always 'two' adjustments when you adjust tension onto any 'edge' of a sail - primary adjustment and the compensation adjustment to get the shape back to normal.

This of course ignores when occasionally the gradient wind is different than expected and you have to add or remove twist, etc.

 

[Bill Roosa]

hey Rich
So you say you cannot change the CLR. Consider the following
The sum of all the underwater forces is the magnitude of the force that can be considered to be focused at the CLR The rudder and keel contribute to that sum. Since I can't change the angle of attack of the keel but can for the rudder I would assume that the keel contribution is pretty much fixed for any given sail trim. It may change in magnitude but the keel's CLR is a fixed spot. The same argument can be made for the rudder, changes in magnitude but not in the location of the CLR for the rudder.
SOOOO
As I recall from dynamics class
Fk*(x)+Fr*(y) = Ft*(z)
Where Fk is force acting through the keel CLR
Fr is the rudder force acting through the rudder CLR
Ft is the total force and Fr+Fk=Ft
x is the distanct from the datum (pick a convenient point) to the keel CLR
y is the distance from the datum (same one) to the rudder CLR
z is the distant from the datum to the total CLR for the underwater surfaces

Now if we pick the bow of the boat as the datum I think you will agree that x and y are fixed due to the boat not getting longer or shorter and the CLR location for the keel and rudder are fixed in space by their shape. I will admit the forces do not always act in the same plane though.
Fk is not much of a variable either for a given sail trim
Fr, Ft and z are the only variable left but we know Fr+Fk=Ft or Fr=Ft-Fk
dusting off the algebra book I get
Fk(x) + Fr(y) = Ft(z) ---> ck*cx + Fr(cy) = Ft(z) where the "c" prefix means it is a constant.
substituting
ck(cx) + (Ft-ck) = Ft(z) Hay looky!!!! only two variables!!

So if I move the rudder and change Ft how do YOU balance the equation???
I'm thinking that z is my only real option.
Perhaps physics in your sailing area is different.

I will note that the change in z is not what I'd call "dramatical" but the magnitude is pretty large and we are in water so "balanced" is a very fine line.

So while all you good folks though it was the sideways force at the rudder that moves the boat around it is really what that force does to the CLR that actually causes the boat to turn.

 

[Bill Roosa]

And also why an excessively heeled boat has weather helm

 

[RichH]

hey Rich
So you say you cannot change the CLR. Consider the following
<snip>
So while all you good folks though it was the sideways force at the rudder that moves the boat around it is really what that force does to the CLR that actually causes the boat to turn.

A boat 'sailing' will only have the rudder between 0° to about maybe 10° offset from the centerline .... between 5° - 10° or more, that's weather helm territory.

The following is a statics discussion to keep things simple ... just moment arms and projected areas. ......... A boat that has its rudder well beyond that ~10° is no longer sailing ... and for the sake of argument for the moment the boat is now in the realm of FUNCTIONAL OR OPERATIONAL FAILURE ... sumthin serious wrong wit dis boat, mon.
So when the rudder is well beyond, say, 10° as an extreme upper limit or normal operation ... were not talking 'sailing' anymore, agree.

at 5° offset that area projected against 'side foreces' is = area X cos 5° = area X .9962 .... we only lost less than 0.38 or 1% of the area holding back the CLR. At 10°, area X .985 ... we only lost 1.5% of area holding back the 'side forces' .....

Therefore beyond an extreme 10% rudder offset is functional failure of operation and below that 10° is 'trivial' ... and shouldnt be of concern to a 'newbie' or a 'cruiser'.

On a keel boat, (not a boat with centerboard or centerboard/keel) .... turning the rudder isnt going to affect the overall CLR significantly, as a loss of 1.5% projected rudder area at 10° is trivial when the boat is operated 'normally' .....; but, If you are holding that rudder much more than 10° your not 'sailing' per se, you are turning or you are hove-to .... or the worst case your rigging tension is really screwed up, your sails are beyond 'blown-out' etc., the pointy end is following you, the mast is waaaay wrongly raked ... and/or you didnt read Don's booklets!!!!!!!!

;-)))

 

[RichH]

And also why an excessively heeled boat has weather helm

Thats not entirely true.
A boat with a 'symmetric' hull form .... scow, double ender, flat sided catamaran, hard chined flat sided boats, etc. can be heeled over until the spreaders are in the water .... and little to zero weather helm increase.
Boats with radically curved sides, OK; but, not with sym-hull or flatish sided boats .....maybe thats why the new Bendytoes-50 has flat sides and hard chines aft?

a boat with too deep a 'forefoot' (section of the hull between the bow and the keel) is good for downwind in big waves, will be a helmsman's nightmare when going upwind ... and you cant fix the CLR when underway unless you have a centerboard (previous post).

;-)

 

[barefoot1985]

Years ago when we we first got our tall rig, shoal keel C30 I listened to the overpowered main underpowered jib discussion and found through on the water trials that it was not very effective in reducing weather helm. Rolling in the jib a little had immediate effect. Catalina says the boat sails best up on it's feet and I am a believer. Of course we don't race, just cruise.

 

[Don Guillette]

Barefoot1985: Induce about 20 degrees of heel and it will sail even better especially in about 8 to 10 knots of wind. 20 degrees is almost on it's feet. A perfectly flat boat will not sail well at all in 8 to 10 knots and it would be almost imposible to accomplish anyway.

On a masthead rig, which is what a C30 is, the engine is the jib. By rolling up the jib, it's like putting a restrictor plate in a stock car. If the boat is overpowered or underpowered you should first use your mainsail and jib sail trim controls to correct the situation before you start reefing. With well trimmed sails, weather helm is not much of a problem.

 

[sinnettc]

I had issues with weather helm the other day on my Capri 22 Tall Rig. Wind was blowing pretty hard, enough that I would have reefed if the Admiral was with me instead of my son, and I kept tugging on the backstay line with no effect. Finally figured out that the other side (it's rigged double ended so it can be tightened from either side) wasn't cleated. The lifesling was sitting on top of the cleat so I couldn't see it. D'Oh!

 

[kaptaindave]

There have been some interesting points brought up on this thread but there's a big one missing. Catalina came out with the tall rig 30, specifically the bow spirit to improve the "feel" of the helm. The Catalina 27 tall rig has a spirit while that C36, C34 and C28 just have taller masts. The C36 was introduced in 1982 which suggests by then, Catalina had refined the sailing characteristics of their boats to no longer need a 18" plank extending off the bow of the boat to get the forestay further forward.

Having said that, both the C27 and C30 had horribly shaped rudders by our current standards. Fortunately, most boats did from that pre-computer era so no one seemed to care... however Catalina did make an improvement to the shape of the C30 rudder around the time of the 1978 model year as seen here: http://i44.photobucket.com/albums/f17/kaptaindave/Rudder-C30/DSCN6799.jpg

With a deeper blade and a more vertical leading and trailing edge, the '78 rudder was a BIG improvement, so much so that the factory had a very successful recast program. For over 15 years, you could send them your old rudder and they'd recast you a new one on your old blade. Oh and poor Catalina 27 owners were stuck with the same rudder for the whole production run.

In Don's original post, there's no mentioning of the year of the boat but if it's the old old design, that sure it's helping any. And having said that, there's now a new even better design that brings current era rudder design theory's to classic fiberglass construction on a classic boat.

http://i44.photobucket.com/albums/f17/kaptaindave/Rudder-C30/DSCN6768.jpg


Here's a video on YouTube showing the new rudder design off and explaining the weaknesses of the old style in terms of design and construction: https://www.youtube.com/watch?v=sl8HL9o2lz0

Having said all this, I know what you're thinking. How can a rudder design effect the sailing characteristics of the boat that much? Well speaking as someone who has this rudder design on his personal Catalina 30, think of your rudder as your final word on what your boat does with all the hydro forces being thrown at your boat's under body. The rudder matters and matters alot more than you probably think.

The C30 has some specific design characteristics of which I'm keenly away. Weather helm starts at the usual places and can be largely overcome in the usual ways but the lack of a bow spirit and a barn door of a rudder (by today's standards) does it no favors. Just wanted to add my two cents to this discussion. Thanks for reading.