Rudder angle

[Shaneesprit]

Hi can I have your opinions on required rudder angle?
I will explain why later, as I don’t want to bias opinion, before having some basic answers

[Sailmonkey]

In my opinion you need some rudder angle to turn the boat. Or to keep the boat straight when there is lee helm or weather helm.

Without rudder angle you can’t turn.

Too much rudder angle turns the bot faster but with more drag.

[magicmoments]

I'm also interested in this and to add to the debate most tear drop shaped rudders need a few degrees on the tiller/wheel so that the windward side of the rudder is parallel with the hull. So my added question is is the rudder angle calculated from dead center OR the amount of angle after it is parallel with the upwind side of the hull? As an eample my rudder needs about 6* for the upwind surface to be parallel and usually an additional 3 to 6 degrees depending on wind strength and point of sail.

[Sailmonkey]

There’s a debate? There’s not even a question........what is the context?

[belizesailor]

Originally Posted by Sailmonkey

In my opinion you need some rudder angle to turn the boat. Or to keep the boat straight when there is lee helm or weather helm.

Without rudder angle you can’t turn.

Too much rudder angle turns the bot faster but with more drag.

Apparently your sarcasm was in vain. [emoji849]

[TrentePieds]

Quote: "Hi can I have your opinions on required rudder angle?"

Angle required to do what? Under what conditions? At what speed?

We'll be glad to help, but you have to help us help you :-)

TrentePieds

[Matt Johnson]

Based on your profile and the fact that this is in the Multihull portion of the site, I'm guessing you are asking about toeing in the rudders from parallel.... is that correct? Or are you asking about the Akermann steering geometry? Sorry, confused on the question.

Matt

[Sailmonkey]

Originally Posted by Matt Johnson

Based on your profile and the fact that this is in the Multihull portion of the site, I'm guessing you are asking about toeing in the rudders from parallel.... is that correct? Or are you asking about the Akermann steering geometry? Sorry, confused on the question.

Matt

Can Akermann geometry work effectively on something that also exhibits leeway?

[thinwater]

Originally Posted by Sailmonkey

Can Akermann geometry work effectively on something that also exhibits leeway?

If the optimum rudder angle is in debate, how do you know which rudder is wrong? And at a few degrees of helm, you'd be hard pressed to measure the difference in angle between two rudders; it only becomes significant much farther over, which is when it matters. It is not linear.


The thread starter is a trick question, because it very much depends on the boat. IMO the OP needs to refine the question a very great deal. (Stub keel, steep chop, and low speed, more. High aspect and deep keel, flat water, and high speed, less. How much are you pinching? Barn door or foil?)


I doubt anyone who has studied the topic would be biased by his thoughts.

[wingssail]

Originally Posted by Shaneesprit

Hi can I have your opinions on required rudder angle?
I will explain why later, as I don’t want to bias opinion, before having some basic answers

That is bit of a vague question.

Probably my answer is not what you are angling for (LOL) but it was a big topic for us the last three days racing in heavier breeze.

First off, our rudder can be turned as much as 90 degrees from centerline which is convenient for manuvering at slow speed.

And, when sailing or motoring whatever angle needed to maintain a heading or make a turn is used but usually: no angle.

Sailing upwind the rudder angle is more of interest to me.

We want about 3-6 degrees of weather helm rudder to ensure the rudder is contributing to the lift of the foils. I raked my mast back 11 inches at the tip to achieve this.

On windy days going upwind, when the boat is fully powered up, we have to work the sail trim (flatten main, traveller down, twist off the genoa, if set) to avoid excess rudder angle which becomes drag. Sometimes, like when racing in over 20 knots of wind, this is difficult; the mainsail is simply too powerful. Reefing would be an option.

In order to steer well, while steering for maximum speed and windward ability, you need to feel some pressure on the helm but not too much. Often if we don't have it right the crew yells at me about my steering but I am often distracted while trying to direct the trimmers to make changes which would improve the feel. It is a deleicate balance.

[thinwater]

FWIW, the rudder will be loaded with zero angle, since the boat is making leeway. I hear mention of "getting side of the rudder parallel with the boat," but remember that the boat is crabbing. Thus, rudder angle is in addition to the leeway angle. This is one reason why rudders have a different section than keels (greater angle of attack).

[sv_pelagia]

What a strange thread... no one has any idea what OP is asking. I certainly don't.

Perhaps he/she wants to know if a Rudder Angle Indicator is necessary (i.e., hydraulic steering)?

(Can't help it: spent 7 hrs yesterday installing a new rudder followup for new autopilot... nothing like being 6'3" and crammed into a stern locker.)

[Shaneesprit]

Hi sorry I was too vague and it took me a while to return.
My issue is with auto pilot and the amount of angle available with a tiller pilot. or lack there of.
So I was thinking only of the angle required to steer the boat correctly. and again this will have a much larger angle while tacking or manoeuvring, which I may have to exclude as I am not convinced there is enough movement in the tiller to tack,
my main thought is if the angle allowed by the tiller pilot is too small the pilot will forever be correcting it’s self.
I understand Ackerman principles and changing the rake angle of the tiller on my boat is not an option.
Rudders have a tear drop shape

[wingssail]

Originally Posted by Shaneesprit

Hi sorry I was too vague and it took me a while to return.
My issue is with auto pilot and the amount of angle available with a tiller pilot. or lack there of.
So I was thinking only of the angle required to steer the boat correctly. and again this will have a much larger angle while tacking or manoeuvring, which I may have to exclude as I am not convinced there is enough movement in the tiller to tack,
my main thought is if the angle allowed by the tiller pilot is too small the pilot will forever be correcting it’s self.
I understand Ackerman principles and changing the rake angle of the tiller on my boat is not an option.
Rudders have a tear drop shape

Shaneesprit, Your explanation helps us understand. I am not sure what kind of auto pilot you are using. My experience with tiller pilots are that when fully extended they provide more rudder angle than usually required to tack a boat. It may not be fast because it takes a second or two to fully extend either way. However, if the boat does not tack with that amount of rudder angle then the problem is probably not with the autopilot but with the boat itself.

One thing to check: how far from the rudder axis is the autopilot attachment.
The autopilot installation manual will specify that distance. Too far and the pilot will not apply sufficient angle. Too short and the pilot may not have enough power to move the tiller.

But generally tiller autopilots have sufficient power and travel to tack a boat. If not, you need to determine if the boat is slow to react or the pilot has insufficient power or travel.

[Shaneesprit]

Pilot is installed to manufacturers drawings, what surprises me is that gives me about 12’ of steering angle to port and 12’ to starboard, 23.6’ total.

See attached
225mm is the travel of the tiller ram
620mm is the distance tiller pivot to ram pivot.

I can’t see how this can be enough, having lost 60% of rudder, now I don’t particularly want the thing to turn for me, if it could steer in a roughly straight line towards a given heading that would be enough. it can hold a heading but it drives the tiller end to end and I know why it’s because there is not enough angle for the boat to react until it hits the stop.

So my thought is to gather some advice here and then reinstall the pilot to my own calculations. at say 580mm rather than 620mm thus increasing the angle available, but first I need to work out the angle required, or at least an educated guess.

My second idea would be to use the angle available from the same brand of pilots older model which this replaces ( which has more tiller angle available and used to work quite well but fail often )