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Rudder stop angle


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My rudder currently stops either side at about 50 deg and I'd always assumed that if it did turn any further it would stall, so it's very easy to take it to the stop for maximum turning.

 

When I install my new rudder I obviously want to ensure that the rudder turns no less than 50 deg, but if it ends up turning say 70 deg each way then will it be more difficult to use because if I turn it too far it will stall, so I'll need to judge max turning angle myself? 

 

I see narrowboats where the rudder turns nearly 90 deg each way before hitting the stop. How are they to use? Without stops at to limit the working arc of the rudder do you just get to know where your max turning angle is before the rudder stalls? 

Edited by blackrose
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There is no specific angle at which the rudder stalls. It depends in part on lateral motion of the stern, ie the relative direction of water travel at the stern. So when a turn is initiated, the stern is going straight ahead and the stalling angle is relatively low. As the turn gets established, ie the sideways momentum build up, more rudder can be used without stalling because of the changed angle of flow. So if you want the best rate of turn, there is no substitute for judgement.

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An advantage of 90 deg stops is that, in conjunction with lifted fenders,  it allows you to absolutely minimise the overall length of the boat if you have to.

 

Some  canal  boat rudders seem to have some effect when at  90 deg.  It is generally very limited but can help with a (very slow) turn.

 

N

 

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36 minutes ago, nicknorman said:

There is no specific angle at which the rudder stalls. It depends in part on lateral motion of the stern, ie the relative direction of water travel at the stern. So when a turn is initiated, the stern is going straight ahead and the stalling angle is relatively low. As the turn gets established, ie the sideways momentum build up, more rudder can be used without stalling because of the changed angle of flow. So if you want the best rate of turn, there is no substitute for judgement.

I agree and an occasional glance at the prop wash will tell you the angle at which the water flow splits which indicates the point at which the rudder stalls and where the turning effect starts to decrease. Find that point and reduce the rudder angle until the prop wash doesn't split and you have found the angle at which maximum turning effect occurs.

 

Howard

Edited by howardang
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We have 90 degree rudder angle (on a narrowboat) and make extensive use of it in tight locks. The only disadvantage is when reversing as you have to work quite hard to prevent the rudder going right to its end stops.

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9 minutes ago, blackrose said:

Ok that's interesting. I guess at very low speeds even extreme rudder angles can be effective. Are there any disadvantages to having wide open rudder stop angles? 

 

 I once observed Rocket Ron (Withey) reversing an ex working boat at Braunston. He had the rudder, hence tiller at 90 degrees (ish) to the boat. The boat went backwards in a straight line. When he was at the side of the wharf he hopped off and used the tiller to pull the boat backwards.

 

It's all about knowing your boat I suppose.

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22 minutes ago, blackrose said:

Ok that's interesting. I guess at very low speeds even extreme rudder angles can be effective. Are there any disadvantages to having wide open rudder stop angles? 

Only that you have to decide how far to move the rudder to get optimal effect, rather than any decision being taken out of your hands.

57 minutes ago, dmr said:

We have 90 degree rudder angle (on a narrowboat) and make extensive use of it in tight locks. The only disadvantage is when reversing as you have to work quite hard to prevent the rudder going right to its end stops.

I think it depends on where the pivot point is. On our boat, the pivot point is a bit forward of the aft-most part of the boat, so only about 70 degrees is required to make the rudder not the aft-most part of the boat. Some boats have rudders pivoting right at the back, in which case 90 deg would be necessary.

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17 minutes ago, Ray T said:

 

 I once observed Rocket Ron (Withey) reversing an ex working boat at Braunston. He had the rudder, hence tiller at 90 degrees (ish) to the boat. The boat went backwards in a straight line. When he was at the side of the wharf he hopped off and used the tiller to pull the boat backwards.

 

It's all about knowing your boat I suppose.

 

I quite often use that technique myself.

 

Putting the tiller all the way over in reverse means the rudder is partially blocking water flow to one side of the prop.  The effect of this is a weaker sideways force at the blocked side and a greater flow/force to the unblocked side of the boat.  This can be helpful to offset prop walk or indeed a breeze.

 

As you say, it depends on the boat, the size and speed of the prop and the shape of the rudder and the swim.

 

You do get some confused looks when reversing in a straight line in a breeze without touching the tiller though!

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37 minutes ago, TheBiscuits said:

As you say, it depends on the boat, the size and speed of the prop and the shape of the rudder and the swim.

Probably ought to add steerer's experience to that list. The more you practice, the luckier you seem to get at these things.

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2 minutes ago, Sea Dog said:

Probably ought to add steerer's experience to that list. The more you practice, the luckier you seem to get at these things.

 

It's a fair comment, but some boats it just won't work on no matter how experienced you are.

 

Even when there's not an audience! 🤣

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The architecture of a narrowboat semi-trad or trad stern means that if you did have a rudder stop at say 50 deg, the tiller would get in the way when getting on and off the boat. So, they are allowed to go much further so the tiller can be pushed out the way.

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4 hours ago, TheBiscuits said:

 

I quite often use that technique myself.

 

Putting the tiller all the way over in reverse means the rudder is partially blocking water flow to one side of the prop.  The effect of this is a weaker sideways force at the blocked side and a greater flow/force to the unblocked side of the boat.  This can be helpful to offset prop walk or indeed a breeze.

 

As you say, it depends on the boat, the size and speed of the prop and the shape of the rudder and the swim.

 

You do get some confused looks when reversing in a straight line in a breeze without touching the tiller though!

It’s a technique I discovered by chance, and can work surprisingly well at counteracting the effect of prop walking.

ETA The talk of stalling (not a usage I have seen before) has a lot to do with how much of the rudder is in front of the rudder stock.

Edited by Stilllearning
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Some boats CAN definitely steer in reverse. In my experience, its often in a particular rev range. Other boats can't do this (or if they are doing it, the effect is so small as to be unnoticeable). Also, some boats will strongly prop-walk while others don't particularly. Knowing your boat and its characteristics means that the elusive utopia of actually being able to control/steer backwards reasonably well, is a step closer....but often you need to accept that reversing will mean that there is a lack of certainty with the directional control (and plan around it). 

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There must be something wrong with my boat :)

 

The rudder goes to 90deg and will push the stern in the required direction when it is full over.

I can pull out of my mooring, turn it in its own length and go back in even when its windy.

It steers well both in reverse and forward.

 

Some of the many reasons it will be my last boat ;)

 

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On 02/07/2022 at 14:55, Paul C said:

Some boats CAN definitely steer in reverse. In my experience, its often in a particular rev range. Other boats can't do this (or if they are doing it, the effect is so small as to be unnoticeable). Also, some boats will strongly prop-walk while others don't particularly. Knowing your boat and its characteristics means that the elusive utopia of actually being able to control/steer backwards reasonably well, is a step closer....but often you need to accept that reversing will mean that there is a lack of certainty with the directional control (and plan around it). 

 

A bow thruster can also make steering in reverse much easier... 😉

 

(ducks and runs for cover...)

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I wonder to avoid the sweep of the tiller and someone getting knocked off of there couldn’t be a more limited range of motion and you release the stop device to allow a full range when you really need it, say in docking or shorter locks.  

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4 minutes ago, Paul C said:

If you avoid getting in the way of the tiller, you won't get knocked off by it. Its just a good habit to be into.

True, but given the number of boats out there with "suicide seats" of some description it's not a habit everyone subscribes to. Maybe they've all got rudder stops to prevent people being knocked off, but somehow I doubt it...

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1 hour ago, Alan de Enfield said:

 

And when you grow-up you can take them up 

 

I carry Epirbs, sat phones, life raft etc on my other boat.  
 

So what’s your point? 
 

any safety feature for the rare occurrence shouldn’t be discussed because it’s not manly?

 

Edited by Trawler
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Just now, Trawler said:


stabilizers make my trawler more bearable in certain seas too…

 

I even wore a life vest on a challenger for the Louis Vuitton cup. So what’s your point? 

 

 

His point (and others) is that *real* boaters don't have "girly buttons"...

 

Or onboard electricity, new-fangled modern rubbish, what's wrong with a paraffin lamp?

 

Or a water tank and shower, why do you need more than water cans on the roof and a cloth and bucket?

 

Or gas bottles -- you must be mad, real boaters cook on a solid fuel stove!

 

Or television, or a mobile phone, or access to the internet...

 

But at least they can do a John Cleese and look snobbishly down on all those horrible modern boaters who don't think anything less than 50 years old is automatically rubbish... 😉

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