Optimal rudder angle and weather helm for speed

[Jeffcrawford]

I own a 2006 Catalina 42 Mark 2 sloop. At a recent North U Sail shape course instructed by Bill Gladstone (the best Sail shape instructor I’ve ever sat under BTW), I asked the question about weather helm and should there always be a zero degree rudder angle. Bill responded that I check with the boat manufacturer and that in some cases as much as a 5 degree rudder angle may be recommended because of rudder design which in some cases can add lift to a sailboat and enhance speed. I’ve sent my question to Catalina directly and am waiting to hear back from their engineers. In the meantime is anyone aware of this answer?
Thank you!

[chrisr]

imho there is no simple answer - 'it depends'

will vary very much based on hull form & boat speed & AWA & TWS

but as a rule i'd say he's pretty much on the money...5 deg rudder angle would be abt the max i'd like to see. less is probably going to be better...depending...

cheers,

[s/v Jedi]

There are too many variables meaning you need to have a dynamic info display that adapts to conditions. For this you need a couple good sensors in the instruments network, then monitor the VMG.

Some advanced electronics can accept your polar diagram and are able to show you a percentage for optimized trim.

Now you tune trim for best performance and periodically check if you’re still at optimal trim.

[Jeffcrawford]

Yes, I agree with you that software upgrade will help in many respects to give VMG. In the plans for The future. Will help with many things such as this question and optimal AWA for optimal VMG under full sail and when motor sailing. I have Raymarine electronics and am planning to see the cost for upgrade. But have the feeling that upgrading everything including chart plotter will also require new radar, etc. so a significant cost upgrade. Hard to
Justify when considering everything presently works and we re only talking about optimizations yielding an increase of perhaps 0.1 ro 0.5 knots VMG for a recreational cruiser. Just part of the fun factor of sailing to consider.
But thank you men for both responses!

[Stu Jackson]

Jeff, I've sailed Catalinas since 1983. Even before I read your post, simply from the question, I said to myself 5 degrees. I've owned my C34 since 1998 and sailed SF Bay until 2016. 5 degrees was where the boat balanced wonderfully going upwind. Completely neutral helm got me going completely off course and into irons. I don't think this is related to Catalinas at all. Some weather helm was always what I was taught sailboats (should) do as part of their design.

[meirriba]

I would like a slight weather angle (slight being 3-5 deg) on any sailboat.
1. Gives better feeling on the helm.
2. Boat turns into wind when helm is not under command.

BUT, I will do it through sail trim.

[Bill O]

Originally Posted by Jeffcrawford

Yes, I agree with you that software upgrade will help in many respects to give VMG. In the plans for The future. Will help with many things such as this question and optimal AWA for optimal VMG under full sail and when motor sailing. I have Raymarine electronics and am planning to see the cost for upgrade. But have the feeling that upgrading everything including chart plotter will also require new radar, etc. so a significant cost upgrade. Hard to
Justify when considering everything presently works and we re only talking about optimizations yielding an increase of perhaps 0.1 ro 0.5 knots VMG for a recreational cruiser. Just part of the fun factor of sailing to consider.
But thank you men for both responses!

Jeff,
My first question would be, do you have a rudder angle indicator (RAI) now?

We use ours RAI all the time and find it is very good for setting the sails better/going faster.

You should price out the upgrade for the latest/greatest Raymarine package to make you gasp at the cost.

Once you recover from that experience, look at opencpn. Has all the bells and whistles of information (possibly more) provided by a top shelf electronic package at a fraction of the cost, then you could afford a new Halo radar to go with it!

We really like ours and have been using it for years.

[Stu Jackson]

Originally Posted by meirriba

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2. Boat turns into wind when helm is not under command.

BUT, I will do it through sail trim.

I believe that the sails need to be trimmed properly to begin with, and should (must?) be considered as a "given."


If we can all agree to that premise, then in addition to my earlier post, going upwind on a regular basis on SF Bay, or anywhere else for that matter, my boat would steer itself for long periods of time without the autopilot engaged with the wheel clocked about 5 degrees off center. It worked, consistently. I trim the sails and "find the groove." The boat sails itself. That just happens to be where the wheel is when (not if) it always works.


IIRC, I kinda found it by accident one day when I was sailing and steering by hand deliberately NOT using the autopilot. The goal was to minimize wandering and tweaking the wheel, which always adds drag.


I had a friend who sailed with me every single Friday for over six years, all year long. He was a great crew but he was a rotten helmsman. I finally got through to him when I said: "Dave, when you steer, only go spoke to spoke."



He finally understood and said, "Ah, now I see what you mean about finding the groove."


Find a nice windy day, head upwind, closehauled, disengage the autopilot and play around with your wheel until you find little to no resistance with your jib telltales doing the proper thing.



Find your groove. It's there. Don't let your instruments get in the way. Good luck, have fun.

[wingssail]

Originally Posted by Jeffcrawford

I own a 2006 Catalina 42 Mark 2 sloop. At a recent North U Sail shape course instructed by Bill Gladstone (the best Sail shape instructor I’ve ever sat under BTW), I asked the question about weather helm and should there always be a zero degree rudder angle. Bill responded that I check with the boat manufacturer and that in some cases as much as a 5 degree rudder angle may be recommended because of rudder design which in some cases can add lift to a sailboat and enhance speed. I’ve sent my question to Catalina directly and am waiting to hear back from their engineers. In the meantime is anyone aware of this answer?
Thank you!

It is valuable to understand why a bit of weather helm improves windward performance.

Weather helm is the rudder angle needed to compensate for a boat's inclination to turn into the wind. It is cause mainly by the center of effort on the sails being aft of the center of lateral resistance (the keel). Sail shape, windspeed, keel shape, and angle of heel affect it, as does the rudder shape and efficiency.

Most keels are more effective at generating lift when they have an angle of attack, meaning that they are not pointed directly into the flow of water but somewhat turned towards the windward side. More lift from the keel makes your boat move to windward (or prevents slippage to leeward).

When there is weather helm it means that the sails and hull are turning the boat to windward.

The best result comes when you use the rudder to stop that turn but still maintaining a slight angle of attack. At that point you are developing lift from the keel and lift from the rudder itself. Too much weather helm means that you are dragging the rudder around trying to overcome the tendency of the boat to turn. In that case the drag offsets any benefit from the lift of the foils.

You control the amount of angle of attack and weather helm required by sail trim (keeping center of effort from going too far back), by flattening the main and big headsails, easing the leeches, and reducing heeling.

Some very sophisticated instrumentation might give you indications of how much weather helm is best. Looking for a set number of degrees of weather helm may not be perfect for all boats and conditions. VMG is a good indicator but you have to be cautious using VMG. It is easy to overshoot.

My feeling is that over reliance on the instruments is detrimental (and I am an instrument junky!). It is best when you can develop a feel for your boat and begin to tell when the pressure on the helm is about right. You will feel "in the groove" and the boat is climbing to windward nicely.

Another indication is found by looking at the wash from the rudder off the back of the boat. It should not look like an oar stroke with whirlpools. Also noise from the rudder, it should not sound like a waterfall.

Finally, you can get a handle on how much is right with tips from successful helmpersons who steer similar boats.

[BillKny]

Originally Posted by wingssail

Most keels are more effective at generating lift when they have an angle of attack, meaning that they are not pointed directly into the flow of water but somewhat turned towards the windward side.

Actually, ALL keels REQUIRE an angle of attack to generate lift. A keel moving straight through the water would generate no lift at all. The angle of attack of the keel is result of the leeway made by the boat.

It's all interrelated and connected in sometimes mind-bending ways...

[Dockhead]

Originally Posted by wingssail

It is valuable to understand why a bit of weather helm improves windward performance.

Weather helm is the rudder angle needed to compensate for a boat's inclination to turn into the wind. It is cause mainly by the center of effort on the sails being aft of the center of lateral resistance (the keel). Sail shape, windspeed, keel shape, and angle of heel affect it, as does the rudder shape and efficiency.

Most keels are more effective at generating lift when they have an angle of attack, meaning that they are not pointed directly into the flow of water but somewhat turned towards the windward side. More lift from the keel makes your boat move to windward (or prevents slippage to leeward).

When there is weather helm it means that the sails and hull are turning the boat to windward.

The best result comes when you use the rudder to stop that turn but still maintaining a slight angle of attack. At that point you are developing lift from the keel and lift from the rudder itself. Too much weather helm means that you are dragging the rudder around trying to overcome the tendency of the boat to turn. In that case the drag offsets any benefit from the lift of the foils.

You control the amount of angle of attack and weather helm required by sail trim (keeping center of effort from going too far back), by flattening the main and big headsails, easing the leeches, and reducing heeling.

Some very sophisticated instrumentation might give you indications of how much weather helm is best. Looking for a set number of degrees of weather helm may not be perfect for all boats and conditions. VMG is a good indicator but you have to be cautious using VMG. It is easy to overshoot.

My feeling is that over reliance on the instruments is detrimental (and I am an instrument junky!). It is best when you can develop a feel for your boat and begin to tell when the pressure on the helm is about right. You will feel "in the groove" and the boat is climbing to windward nicely.

Another indication is found by looking at the wash from the rudder off the back of the boat. It should not look like an oar stroke with whirlpools. Also noise from the rudder, it should not sound like a waterfall.

Finally, you can get a handle on how much is right with tips from successful helmpersons who steer similar boats.

This is a great post; maybe the definitive post on the subject


A bit counterintuitive, but you need a bit of leeway for the keel and rudder to perform. The keel is not cambered (unlike airplane wing) so need angle of attack to generate lift. That angle of attack is exactly leeway.


Like Fred, I'm an instrument and measurement junkie, but like Fred, I would emphasize the role of feel here. You just feel it when you catch the groove upwind. The instruments will tell you about it only later. So there's nothing to replace feel. I always steer by hand when trying to get into the groove -- I want to feel it.

[DougM]

The previous posts nailed the fundamentals of the problem.

However I have a question (just academic really) - would it be fundamentally necessary to have rudder angle (turning leeward) in order for the rudder to be lifting along with the keel?

Thinking geometrically, t seems to me that with a zero rudder angle, the rudder has an angle of attack that is exactly equal to the leeway angle, which is by definition identical to the angle of attack of the keel?

To get a rudder to be neutral, would it not have to have an angle, in the 'turning to windward' direction, equal to the angle of leeway?

I think think that is true with respect to simple geometry ?? But maybe it is not true with respect to lift generation as the rudder is in the wake of the keel?

Or maybe I'm totally off base ... ?

[wingssail]

Originally Posted by DougM

The previous posts nailed the fundamentals of the problem.

However I have a question (just academic really) - would it be fundamentally necessary to have rudder angle (turning leeward) in order for the rudder to be lifting along with the keel?

Thinking geometrically, t seems to me that with a zero rudder angle, the rudder has an angle of attack that is exactly equal to the leeway angle, which is by definition identical to the angle of attack of the keel?

To get a rudder to be neutral, would it not have to have an angle, in the 'turning to windward' direction, equal to the angle of leeway?

I think think that is true with respect to simple geometry ?? But maybe it is not true with respect to lift generation as the rudder is in the wake of the keel?

Or maybe I'm totally off base ... ?

I don't think you are off base. However I know from experience that I need a bit of weather helm to achieve good windward performance; the rudder must be angled a little bit, and I will feel that on the helm. So, no we don't really want a neutral helm with no pressure. If there is no pressure on the rudder I feel like I just can't steer and I complain to the trimmers. In that case they trim on the main or pull up the traveler. We primarily play these controls to achieve the amount of weather helm that "feels" right.

And think about this: if the sailboat has 5 degrees of leeway then possibly we have an angle of attack of the keel of 5 degrees. To have a neutral rudder, meaning aimed right exactly into the flow, it would have to be turned for 5 degrees of lee helm. Very counter intuitive and counter productive.

Another thought: You would have zero leeway if it wasn't for the pressure of the wind on the sails, but it could be possible to create an "angle of attack" while motoring by turning the boat slightly towards either one side or the other, and holding it there with the rudder. The boat would begin to "crab" sideways. That is what we want to use to oppose the leeway. An aircraft creates angle of attack with the horizontal stabilizer. Airplanes don't have leeway but they have a "sink rate", which is equivalent. But by creating an angle of attack (and with the asymmetrical shape of an airplane's wing) they can climb at a greater rate than they are sinking towards the earth. This is what we'd like to achieve with a boat: to climb to windward at a greater rate than our leeway.

[Quebramar]

I recall having read somewhere that a slight angle working «*against*» where they boat wants to go (into the wind) helps lift the hull and therefore reduce the slowdown effect of the water.
Would this also explain the benefit a weather helm?

[MicHughV]

I think what is key here is whether the rudder is a skeg hung rudder..or a spade rudder.

A skeg hung rudder has the leading edge of rudder, parallel to the hull centerline, so when the rudder is turned...say...5 degrees...the skeg and rudder combined give a nice " foil" shape...such as it were...

My first boat had this setup, and for the boat to track straight and true while going to weather, under sail..it required a slight turn on the wheel.....I kinda liked this, as it required a modicum of pressure on the steering wheel.

My last boat has a deep spade rudder...it likes to be parallel to the hull centerline, for optimum performance.
The leading edge of the rudder is somewhat ahead of the rudder post, but when turned....say 5 degrees, I can tell that it is trying to stall, hence it is happier straight ahead.

Having said all that, sailing to weather is a different animal from sailing downwind, and if sail trim is not correct, it too will affect rudder performance.