Maximum rudder angle before stall?

[bottle]

That would prevent the rudder hitting the prop but it wont do much else. As i already said, it wont prorect the rudder in a lock either.

 

Am I being thick, how is your rudder vunerable in a lock if it is at 90°, it is virtually under the boat and many boats actually fix the rudders at 90° to protect them when in a lock.

[RLWP]

 

Am I being thick, how is your rudder vunerable in a lock if it is at 90°, it is virtually under the boat and many boats actually fix the rudders at 90° to protect them when in a lock.

 

His is a broadbeam on a river, the cills on river locks are not always straight across the chamber

 

Richard

[bottle]

Compromise then set stops to not go past 60°

[Dalslandia]

Boating used to be a simple, enjoyable activity, learned by experience with a generous application of common sense, often aided by the more experienced. You got a feel for what worked with a particular boat and got on with it. I've never heard of rudder stops on canal boats, unless the " feet" left on the uxter plate by some builders count in that way. I'm saddened by the new wave of technological overkill that threatens to swamp the enjoyment of boating, at least to my naive yet experienced eyes. And no, I don't understand the science at all, it certainly wouldn't enhance the pleasure of being afloat. Sorry!

 

Dave

 

You or We, don't have to know the science to appreciate boating, but the science, experience put in the built of the boat, make it a better boat to handle and live onboard.

[blackrose]

I hadn't realised that there was a similar thread running already, (questionaire ....Kitchen rudders) I see it started in February while I was busy so I missed it. The consensus there seems to be " it might work but it's too complex/fragile/expensive for its advantages".

The only sophisticated design of rudder that seems to get a cautious thumbs up is the Schilling.

 

I know that I certainly wouldn't change the simple balanced plate rudder on my narrowbeam cruiser as it does everything that I have asked it to. I would love to fit something more efficient on the Humber barge but it only has an unbalanced rudder and I would be unwilling to do too many alterations to an eighty five year old boat.

 

 

edit for spelling

 

I don't think anybody's talking about changing the design of the rudder on this thread. If you look at my first post you'll see that my new rudder is a balanced rudder.

Does the angle of stall really matter in a canal boat?

 

When I raced Fireball sailing dinghys, yes the angle of stall mattered, going too far over with the tiller caused drag, hence a reduction of speed and lack of efficiency, not what you want in a racing dinghy.

Also an aerofoiled rudder and centerboard were essential in lowering drag.

 

To my knowledge the speed of a canal boat is not critical.

 

Perhaps it doesn't matter at the speeds we travel - I don't know. That was part of what I was asking in my original post.

 

Am I being thick, how is your rudder vunerable in a lock if it is at 90°, it is virtually under the boat and many boats actually fix the rudders at 90° to protect them when in a lock.

 

As I said in an earlier post - unless I restrained the tiller to keep the rudder at 90 degrees in a lock then it will just swing back out and so end of the rudder isn't under the boat.

Edited April 26, 2014 by blackrose

[RLWP]

Perhaps it doesn't matter at the speeds we travel - I don't know. That was part of what I was asking in my original post.

 

It's more complicated than the sailing boat. The water speed is what is coming off the propeller, not the boat speed. On top of that, the prop wash probably doesn't cover the whole rudder surface, and is rotating as well

 

None of that answers your question, just points out it's a tricky thing to work out

 

Richard

[bottle]

As I said in an earlier post - unless I restrained the tiller to keep the rudder at 90 degrees in a lock then it will just swing back out and so end of the rudder isn't under the boat.

 

So the angle for the stop does not matter, whether it is 35°, 60° or 90°, the stop will not protect the rudder when in a lock, fenders and buttons will do that and of course a watchful eye.

[blackrose]

 

You or We, don't have to know the science to appreciate boating, but the science, experience put in the built of the boat, make it a better boat to handle and live onboard.

 

Unlike Dave Moore, understanding how things work does actually enhance my appreciation and enjoyment of these things. We are only talking about how rudders work here, and that's real basic stuff - on the same sort of level as understanding the science behind how a heavy steel boat stays afloat in the water. There is no explanation other than a scientific one.

 

If Mr Moore isn't interested in how things work that's fine with me and I'm happy for him to carry on in blissful ignorance. However if understanding how a rudder works is a "new wave of technological overkill" it does make one wonder what on earth he makes of things like electricity! Why is he even using a computer?

As I said in an earlier post - unless I restrained the tiller to keep the rudder at 90 degrees in a lock then it will just swing back out and so end of the rudder isn't under the boat.

 

So the angle for the stop does not matter, whether it is 35°, 60° or 90°, the stop will not protect the rudder when in a lock, fenders and buttons will do that and of course a watchful eye.

 

I think you've misunderstood. I didn't really want to know where to put the stop on the rudder because I wanted to protect it - if you read back through the thread you'll see that RLWP brought up that issue. For me, it's about having a stop for the maximum effective steering angle of the rudder. My existing rudder has a fin which sticks up out of the water and stops the rudder against the stern at about 40 degrees. I thought I'd keep that design with my new rudder because it prevents me pushing the rudder too far over and I can feel when its at its maximum angle without looking. If on the other hand people are telling me that it's sometimes useful to have greater angles than 40 degrees for steering and the rudder doesn't stall then perhaps I'll put the stop further along the rudder to allow greater movement.

Edited April 26, 2014 by blackrose

[John V]

 

My current flat plate rudder moves about 40 degrees either side of centre and seems to steer fine at the stops, but I'm changing it for a this one below as it has a better profile. ?????????

 

 

 

I don't think anybody's talking about changing the design of the rudder on this thread. If you look at my first post you'll see that my new rudder is a balanced rudder. ?????????.

[Dalslandia]

I was intrigued by the bit about twisted leading edge rudders in Dalslandia's post and was doing a bit of looking up.(incidentally thank you for an extremely interesting post)

I am unsure if it is relevant to the low thrust and slow speeds of canal boats...I was also refreshing my memory about Schilling rudders, Kort nozzles and Kitchen rudders, all very interesting and excellent engineering but I wonder how easy they are to free up from the remains of an old mattress round a prop, while your head is down a weed hatch.

The Schilling looks more plausible for our shallow and often rubbish laden waterways but I wonder if it is worth the extra cost / complexity for a canal boat.

 

The schilling is a bit more complicated to make then a flat steel plate, but when don we don't need to think about it more then a rudder, a flap-rudder on the other hand have more moving parts, and can be more vulnerable. for those that can weld them self can easily improve there own rudder, look at Biggles rudder.

 

A twisted LE. rudder is one step up on the ladder in complexity and cost, but can be made with constant camber, just opposite over and below prop shaft, I am sure it will reduce power needed to go straight, and to shallow turns, maybe will pay off on a electric drive boat, It will have an airfoil look something like the airplane wing airfoil seen in page 1 on this thread.

 

but say we have an existing rudder we want to improve, use a pipe, or half pipe, diameter 10% of the rudder chord as leading edge, make the rudder max thickness 18-20% of chord at 20-30% of the chord, equal to both sides. but offset the leading edge radius 3% each way top and bottom of prop shaft, SO IT MEET THE PROP WASH. then fair the profile to 65-75% of the chord, and then finish with a fish tail or Flettner strip ( flat plate perpendicular to rudder) at the TE.

 

https://www.google.se/search?q=http://user.tninet.se/~trz012v/&source=lnms&tbm=isch&sa=X&ei=Mc1bU975JqGK4ASc8IF4&ved=0CAYQ_AUoAQ&biw=1366&bih=628#q=3-schilling+rudder&tbm=isch

 

https://www.google.se/search?q=http://user.tninet.se/~trz012v/&source=lnms&tbm=isch&sa=X&ei=Mc1bU975JqGK4ASc8IF4&ved=0CAYQ_AUoAQ&biw=1366&bih=628#q=twisted+schilling+rudder&tbm=isch

Edited April 26, 2014 by Dalslandia

[blackrose]

John V, I said the new rudder has a BETTER PROFILE, I didn't say it was a DIFFERENT DESIGN!!

 

It's still a basic balanced rudder! Surely anyone can see that from the picture?

 

balanced rudder

Web definitions

1. Balanced rudders are used by both ships and aircraft. Both may indicate a portion of the rudder surface ahead of the hinge, placed to lower the control loads needed to turn the rudder. ...
   http://en.wikipedia.org/wiki/Balanced_rudder

    

 

Edited April 26, 2014 by blackrose

[bottle]

Right, sorry to go off on a tangent.

[magnetman]

Mike why do you want to change your rudder?

I thought your boat handled perfectly well.

 

Or has your Bowthruster broken

[John V]

actually you don't state the design of your original rudder you just say that it is a flat plate rudder and that can be either balanced or unbalanced.

My Nichols's guide shows single plate rudders and double plate rudders both illustrations show unbalanced rudders

[blackrose]

actually you don't state the design of your original rudder you just say that it is a flat plate rudder and that can be either balanced or unbalanced.

My Nichols's guide shows single plate rudders and double plate rudders both illustrations show unbalanced rudders

 

I didn't need to state the design of my original rudder because that wasn't the point of the thread. You're the one who started talking about changing the design of the rudder so you've assumed something that wasn't the case. That's fine but you don't seem to like being told that the rudder design isn't changing. Perhaps you should have asked me for clarification instead of making an erroneous assumption based on your Nicholson's guide.

Edited April 26, 2014 by blackrose

[John V]

 

Well then you've assumed something that wasn't the case. Perhaps you should have asked me for clarification instead of making an erroneous assumption based on your Nicholson's guide.

 

Its Nicholls's Guide and viva voce....and incidentally according to that, your new rudder is a variation of a double plate design whereas your original was a single plate rudder

[David Mack]

Why does my existing rudder have a stop? Think about it... It's very difficult to tell where the stall point is without rudder stops so it's very easy to over-steer.

 

Why do I need to know the stall point? Rudder stops won't tell you that anyway - they will just tell you where the rudder stops have been fitted. You just learn by experience where is the best place to hold the rudder to achieve the turn you want, and not to oversteer.

 

The chances that the collective wisdom of this forum can tell you where the optimum point is for your particular boat are just about zero. If you fit stops beyond the optimum point then you can still learn to gauge the feel of the best position. But if you err the other way and fit stops too close to the ahead position then you have permanently lost some turning ability.

And another thing, without a rudder stop the rudder could go around 360 degrees and hit the prop. Not nice if you accidentally reversed into something (or some idiot steering wants to see what will happen...)

 

Does your rudder have stops or does it just swing freely? Do you think the boat builders just guessed or did they have some angle in mind? Where did that angle come from?

 

 

Fulbourne's rudder stops when the curvy raised bit on the top of the rudder blade at the back hits the uxter plate. That is at about the 90 degree position, and far beyond the range of normal steering.

 

I don't think Harland and Wolff designed this angle at all in the sense you are talking about. They just followed standard motor narrow boat practice first developed for the FMC steamers some 30-40 years earlier.

 

While the raised curvy bit functions as a stop (and keeps the rudder from turning round into the prop), its main purpose is as a lifting point for shipping and unshipping the rudder while the boat is afloat - that's why it has a hole in it.

 

And the 90 degree limit allows the tiller to be pushed to 90 degrees, ging space to enter the cabin or walk across the stern deck. It also allows the rudder to be pushed across clear of the cill in shorter locks - some on the Birmingham & Fazeley are a tight fit for a full length Big Woolwich. Rudder stops at significantly less than 90 degrees would be real nuisance and a potential hazard.

 

It may be easy for you, because you didn't design your boat, but you can be sure that someone had to think about the complexity of fluid dynamics, and angles of attack when they designed boats with rudders.

 

I very much doubt it! The rudder is just a flat plate which extends behind and in front of a shaft which is at a slight angle to the vertical, so that it is self centering (under gravity). And it works.

 

I suspect that the vast majority of clone craft narrow/wide boat builders give very little thought to such matters, yet most manage to produce boats which handle tolerably well in inexperienced hands.

 

Your post reminds me of people who fly in an aeroplane without giving a thought about how it's staying up there. It's simple isn't it?

Well as a regular business flyer across the Atlatic, I think that I and most of my fellow passengers are content to rely on those who design, operate and maintain the aircraft to do so in a way that keeps the plane in the air, without us needing to constantly think about angles of attack, flow separation and stalling!

[Dalslandia]

 

Its Nicholls's Guide and viva voce....and incidentally according to that, your new rudder is a variation of a double plate design whereas your original was a single plate rudder

 

So my new JC-illing rudder is a 3 plate rudder, the original flat plate is inside, with some lightening hole in it behind the stock

[blackrose]

Mike why do you want to change your rudder?

I thought your boat handled perfectly well.

 

Or has your Bowthruster broken

 

No the bowthruster is working fine. My boat does handle well, but several years ago Dhutch (Daniel) and a couple of other forumites had new rudders made by Yammanx and they looked pretty good, so I thought I'd ask him to make me one too. Unfortunately I never got around to fitting it. Last time I was in the drydock 4 years ago I didn't have time to fit it as I was prepping and blacking the boat by myself, but this time I should have slightly longer and as I'm twin-packing the boat I want to get the rudder off anyway so I can clean and paint the rudder tube. So it's a good opportunity to fit the new rudder.

 

The boat doesn't need it, but it's like a lot of other things I do. The boat worked fine without the big cleats and fairleads I put on and I've done loads of other things that didn't really "need" to be done. It's a hobby isn't it? I'm sure all the bits on your boat aren't purely utilitarian either.

Edited April 26, 2014 by blackrose

[blackrose]

Why do I need to know the stall point? Rudder stops won't tell you that anyway - they will just tell you where the rudder stops have been fitted. You just learn by experience where is the best place to hold the rudder to achieve the turn you want, and not to oversteer. I never said that rudder stops would tell me the stall point? But the rudders on most boats don't just spin 360 degrees - most stop somewhere.

 

The chances that the collective wisdom of this forum can tell you where the optimum point is for your particular boat are just about zero. So you're saying I shouldn't be posting this question on the forum? I ask questions because I know that there are people on this forum who know a lot more than me. That doesn't necessarily mean I will take any advice as gospel. I will take advice and then draw my own conclusions. If you fit stops beyond the optimum point then you can still learn to gauge the feel of the best position. But if you err the other way and fit stops too close to the ahead position then you have permanently lost some turning ability. Which is exactly why I am asking the question.

 

 

Fulbourne's rudder stops when the curvy raised bit on the top of the rudder blade at the back hits the uxter plate. That is at about the 90 degree position, and far beyond the range of normal steering.

 

I don't think Harland and Wolff designed this angle at all in the sense you are talking about. They just followed standard motor narrow boat practice first developed for the FMC steamers some 30-40 years earlier.

 

While the raised curvy bit functions as a stop (and keeps the rudder from turning round into the prop), its main purpose is as a lifting point for shipping and unshipping the rudder while the boat is afloat - that's why it has a hole in it. There isn't a hole in it on my rudder. It functions purely as a stop.

 

And the 90 degree limit allows the tiller to be pushed to 90 degrees, ging space to enter the cabin or walk across the stern deck. It also allows the rudder to be pushed across clear of the cill in shorter locks - some on the Birmingham & Fazeley are a tight fit for a full length Big Woolwich. Rudder stops at significantly less than 90 degrees would be real nuisance and a potential hazard.

 

 

I very much doubt it! The rudder is just a flat plate which extends behind and in front of a shaft which is at a slight angle to the vertical, so that it is self centering (under gravity). And it works. And it works because naval architects knew the science and applied it over many decades.

 

I suspect that the vast majority of clone craft narrow/wide boat builders give very little thought to such matters, yet most manage to produce boats which handle tolerably well in inexperienced hands. I agree that most canal boat builders give very little thought to it these days, but those designs came from somewhere and were refined - they weren't just plucked out of thin air.

 

Well as a regular business flyer across the Atlatic, I think that I and most of my fellow passengers are content to rely on those who design, operate and maintain the aircraft to do so in a way that keeps the plane in the air, without us needing to constantly think about angles of attack, flow separation and stalling!

Who said anything about "constantly" thinking about those things? Personally I do think about them because they enhance my appreciation, but you're perfectly free to disregard them.

[John V]

 

So my new JC-illing rudder is a 3 plate rudder, the original flat plate is inside, with some lightening hole in it behind the stock

 

No...most of my comments were aimed at Blackrose for being sarcastic in his # 30 post ....The quotes are correct but they are from a book for people studying for their second mates, first mates or masters tickets and was written in 1905

[blackrose]

 

No...most of my comments were aimed at Blackrose for being sarcastic in his # 30 post ....The quotes are correct but they are from a book for people studying for their second mates, first mates or masters tickets and was written in 1905

 

In post 30 I said:

 

"I don't think anybody's talking about changing the design of the rudder on this thread. If you look at my first post you'll see that my new rudder is a balanced rudder."

 

It really wasn't meant to be a sarcastic comment and I fail to see how it can have been construed as such? However my apologies if that's the way it came across. As well as thinking about how we write replies in order to avoid offending others, I also think we need to be aware of how we read them.

Edited April 26, 2014 by blackrose

[John V]

 

In post 30 I said:

 

"I don't think anybody's talking about changing the design of the rudder on this thread. If you look at my first post you'll see that my new rudder is a balanced rudder."

 

It really wasn't meant to be a sarcastic comment and I fail to see how it can have been construed as such? However my apologies if that's the way it came across. As well as thinking about how we write replies in order to avoid offending others, I also think we need to be aware of how we read them.

 

 

ok pax

[Dalslandia]

 

No...most of my comments were aimed at Blackrose for being sarcastic in his # 30 post ....The quotes are correct but they are from a book for people studying for their second mates, first mates or masters tickets and was written in 1905

 

Okay, I have not read that one, I didn't write it either, but thinking about it, my rudder have 10 plates, that's irony, I am so funny, and have not even started on the whisky I don't have at home. and it is Saturday, to late for shoping

[John V]

 

Okay, I have not read that one, I didn't write it either, but thinking about it, my rudder have 10 plates, that's irony, I am so funny, and have not even started on the whisky I don't have at home. and it is Saturday, to late for shoping

 

If what I remember about the cost of alcohol in Sweden is correct, that's probably as well....anyway whats wrong with aquavit.....cheers

 

 

edit to say sorry skol !

Edited April 26, 2014 by John V