Schilling rudder project on narrowboat

[IanD]

1 hour ago, Andy Br said:

Absolutely spot on. Plus builders have a load of bottom plate offcuts to use up on something.... 

My rudder that cost me a couple of angle grinder blades and a score of welding rods is a vast improvement so hopefully will encourage a few more to have a play. 

 

I don't know the exact cost of mine because it was bundled in with several other additional cost hull features, I suspect rather less than a grand -- there's a lot of cutting shaping and welding involved to build a "proper" Schilling like that, labour would be more than materials.

 

Adding on an angle-iron tail is much cheaper, but according to analysis and measurements also less effective -- though still better than  a flat plate. The bulbous nose of the Schilling stops the water flow detaching from the back of the rudder at high angles, which increases lift compared to a flat plate.

 

I must admit that I don't get the "flat plate works OK, no need for a better one" attitude, especially from people (lots on this forum...) who value their lovely hull shape -- why not have a cheapo brick-shaped hull instead, it'll do the same job just not quite as well? 😉

 

It's often been said that the canal world is famously resistant to trying anything new even if it might be better -- and a flat plate rudder certainly doesn't provide this kind of sideways thrust -- like a "free" stern thruster... 😉 -- especially at large rudder angles...

 

 

Edited October 5, 2022 by IanD

[harrybsmith]

Very pleased I came across this, I'll be knocking one up for my current build as it makes perfect sense 

[Bee]

Hmmm, There is probably science and tradition at work here. It could be that there is not a lot of science needed for a sailing boat or barge rudder, a flat plate is probably fine,, a slightly aerofoil section could offer a bit less resistance. Maybe when motors were first fitted to sailing boats nobody gave much thought to the shape of the rudder, a flat board would have worked as well as anything. Skip forward a few decades and most rudders are still flat plates. Ours is a hollow aerofoil and i have no complaints but I'm sure that there is much that could be improved in the design of rudders. I have a feeling that rudders with hinged sections or nozzles are perhaps the way forward but that's when it all gets a bit expensive Bow rudders anyone?

[Tony Brooks]

I got the impression that some of the Swiss lake steamers had a bow rudder that is used when they reverse out of a confined space. There is certainly a lot of chain clanking from down below until they go forward.

[blackrose]

On 05/10/2022 at 09:12, Bee said:

I'm surprised it makes much difference as narrowboats are not usually hampered by lack of rudder movement, 90 degrees either side of dead ahead is achievable even if that is not desirable. 

 

I recently changed my rudder and the problem is that most people who report improvements are reporting subjectively. When I took my boat out to test the new rudder I was very aware of the potential psychological phenomonon of positive bias - finding what you want or expect to find. I'm not trying to say that there are no real benefits, just that without objective data it's very difficult to be sure of their significance. My own subjective impression is that my new rudder has made very little difference to steering but might feel a bit smoother on the tiller with a bit less vibration. 

Edited October 7, 2022 by blackrose

[blackrose]

On 05/10/2022 at 10:22, Tam & Di said:

There is an enormous difference between a ship at sea and a narrow boat on a canal...

 

 

What is the difference exactly?

 

Ignoring tides, waves, etc, because we're just talking about vessel hydrodynamics, isn't it mainly a question of scale? I realise that some things don't necessarily scale up linearly or proportionally, but whether a ship at sea or narrowboat on a canal/river, the hydrodynamics are based on the same set of principles aren't they?

Edited October 7, 2022 by blackrose

[Tony Brooks]

1 hour ago, blackrose said:

but whether a ship at sea or narrowboat on a canal/river, the hydrodynamics are based on the same set of principles aren't they?

 

I don't think so. Even a boat hull on a canal is subject to the hydrodynamics produced by the restricted waterway. You only have to feel how narrow boats behave on deep, wide rivers compared with narrow, shallow canals. Inland boats are subject to this virtually all the time, ships only when in restricted shallow waters.

[IanD]

53 minutes ago, Tony Brooks said:

 

I don't think so. Even a boat hull on a canal is subject to the hydrodynamics produced by the restricted waterway. You only have to feel how narrow boats behave on deep, wide rivers compared with narrow, shallow canals. Inland boats are subject to this virtually all the time, ships only when in restricted shallow waters.

But none of that is relevant to a rudder being used to steer, what matters is how much sideways thrust it can generate and up to what angle, and that has nothing to do with the depth of water, just flow from the propeller over the rudder.

 

A Schilling rudder produces more thrust at small angles and carries on working to much bigger angles than a flat plate, in fact at about 70 degrees deflection (see plot I posted) it can provide pure sideways thrust -- and a lot of it, more than a stern thruster.

 

If people are happy with their flat plate rudders then that's fine, but claiming that high-lift rudders like the Schilling don't make any difference contradicts the facts... 😉

[Tacet]

55 minutes ago, IanD said:

But none of that is relevant to a rudder being used to steer, what matters is how much sideways thrust it can generate and up to what angle, and that has nothing to do with the depth of water, just flow from the propeller over the rudder.

 

A Schilling rudder produces more thrust at small angles and carries on working to much bigger angles than a flat plate, in fact at about 70 degrees deflection (see plot I posted) it can provide pure sideways thrust -- and a lot of it, more than a stern thruster.

 

If people are happy with their flat plate rudders then that's fine, but claiming that high-lift rudders like the Schilling don't make any difference contradicts the facts... 😉

The diagram posted showed a maximum of about 75% sideways thrust.  Very impressive but not pure sideways.  Mind you, several on CWDF have plate rudders that allow the boat to turn in its own length so (ahem) that must be 100%.

I'm not sure that having the same sideways thrust at a lower angle is that useful.  More sideways when winding could be handy but that apart, mostly full lock is sufficient and typically precluded by the stern swinging in and the like.

Before the new and very  new Woolwich Ferries adopted their fancy Vorth Schneider propulsion, the proper paddle steamers had one engine per paddle.  They could turn in their own length.

[IanD]

24 minutes ago, Tacet said:

The diagram posted showed a maximum of about 75% sideways thrust.  Very impressive but not pure sideways.  Mind you, several on CWDF have plate rudders that allow the boat to turn in its own length so (ahem) that must be 100%.

I'm not sure that having the same sideways thrust at a lower angle is that useful.  More sideways when winding could be handy but that apart, mostly full lock is sufficient and typically precluded by the stern swinging in and the like.

Before the new and very  new Woolwich Ferries adopted their fancy Vorth Schneider propulsion, the proper paddle steamers had one engine per paddle.  They could turn in their own length.

I think you're misunderstanding the diagram. Starting at 100% bollard pull (about 100kg per 10hp), it shows thrust every 5 degrees. Maximum lateral thrust (60% + 60% pull) is at 45 degrees, by 65 degrees deflection the thrust is 10% ahead/40% lateral, it should cross the axis at 70 degrees deflection (side thrust only).

Edited October 7, 2022 by IanD

[Tacet]

24 minutes ago, IanD said:

I think you're misunderstanding the diagram. Starting at 100% bollard pull (about 100kg per 10hp), it shows thrust every 5 degrees. Maximum lateral thrust (60% + 60% pull) is at 45 degrees, by 65 degrees deflection the thrust is 10% ahead/40% lateral, it should cross the axis at 70 degrees deflection (side thrust only).

Well it might cross the axis at 70 degrees, and it might not; the diagram stops short of showing the point at which it crosses (if it does), and I think it is unsafe to extrapolate.  It is a bit odd to stop short of showing that interesting point.  What would be the reason?

 

What happens beyond 70 degrees?  Does the boat move backwards even though the propeller is turning forwards? Or does the flow across the rudder break away at some angle?  Me thinks that could be before 100% sideways thrust is developed.

 

 

[IanD]

14 hours ago, Tacet said:

Well it might cross the axis at 70 degrees, and it might not; the diagram stops short of showing the point at which it crosses (if it does), and I think it is unsafe to extrapolate.  It is a bit odd to stop short of showing that interesting point.  What would be the reason?

 

What happens beyond 70 degrees?  Does the boat move backwards even though the propeller is turning forwards? Or does the flow across the rudder break away at some angle?  Me thinks that could be before 100% sideways thrust is developed.

 

 

Maybe the plot stops at 65 degrees because that was the maximum possible rudder angle for that boat?

 

The trend line looks pretty smooth, there's no reason to think it wouldn't cross the axis at 70 degrees, and other reports of Schilling rudders confirm that they can provide pure lateral thrust at these large angles without the flow breaking away.

 

It's possible that at even higher angles the net thrust can be astern, this isn't just due to the direction of water flow but the high pressure in front of the rudder and the low pressure behind it due to the aerofoil shape which pulls the rudder (and the boat) astern.

 

If I can find two suitable strain/cable tension guages I will try and make similar measurements when my boat's in the water -- it might even be possible to do a direct comparison with a flat plate rudder if Finesse have a boat with one fitted at the same time... 😉

Edited October 8, 2022 by IanD

[PeterF]

This has got me thinking that perhaps one way to try this would be to make up two schilling rudder shaped half shells that have four recessed bolt holes in, drill four holes through your flat plate rudder and bolt the two half shells either side of your rudder. This saves dismantling your tiller, rudder stock and rudder and if it does not work then you can remove it. Probably still need it out of the water.

[IanD]

1 hour ago, PeterF said:

This has got me thinking that perhaps one way to try this would be to make up two schilling rudder shaped half shells that have four recessed bolt holes in, drill four holes through your flat plate rudder and bolt the two half shells either side of your rudder. This saves dismantling your tiller, rudder stock and rudder and if it does not work then you can remove it. Probably still need it out of the water.

That would certainly work -- don't forget that you really want the end plates too (see drawing and photo of mine), these increase thrust by making the water flow reverse direction (flow back away from the rudder) instead of just hitting the uxter plate or going down past the skeg.

 

The concerns I'd have about a multi-piece rudder like this on a narrowboat would be corrosion where the pieces join up, and also robustness if the rudder hits or catches on something -- especially the end plates, mine are 6mm steel. If you're worried about time/effort/cost a one-piece one would also be cheaper to manufacture than the two half-shells.

[Midnight]

Sightly variation but when in the dry dock in June a couple of 'mates' decided to weld horizontal top fins on my rudder. I wasn't convinced but thought I could grind it off next time so didn't protest too much. Coming out in July for our 3 month cruise I initially noticed a very slight vibration on the tiller bar so was very definitely sceptical. However I have to say there has been a noticable increase of speed especially at lower revs and we seem to have used less fuel. Not sure it's just my imagination but I'm hoping some of you engineering types will have a view.

[Alan de Enfield]

51 minutes ago, Midnight said:

Sightly variation but when in the dry dock in June a couple of 'mates' decided to weld horizontal top fins on my rudder. I wasn't convinced but thought I could grind it off next time so didn't protest too much. Coming out in July for our 3 month cruise I initially noticed a very slight vibration on the tiller bar so was very definitely sceptical. However I have to say there has been a noticable increase of speed especially at lower revs and we seem to have used less fuel. Not sure it's just my imagination but I'm hoping some of you engineering types will have a view.

 

Do you mean a version of these ?

 

         

 

 

These are called Dolphin fins (or Doel-Fins) and have been used on outboard and outdrive motors for pretty much as long as I have been boating (40+ years).

 

They bolt onto the cavitation plate and give extra lift, improve steering and reduce cavitation which all go to reduce fuel consumption.

[Jon57]

1 hour ago, Midnight said:

Sightly variation but when in the dry dock in June a couple of 'mates' decided to weld horizontal top fins on my rudder. I wasn't convinced but thought I could grind it off next time so didn't protest too much. Coming out in July for our 3 month cruise I initially noticed a very slight vibration on the tiller bar so was very definitely sceptical. However I have to say there has been a noticable increase of speed especially at lower revs and we seem to have used less fuel. Not sure it's just my imagination but I'm hoping some of you engineering types will have a view.

It’s called the Yorkshire udder. Milking it for all it’s worth.🤣get to bed now and get read for tomorrow 👍

[Tacet]

7 hours ago, IanD said:

Maybe the plot stops at 65 degrees because that was the maximum possible rudder angle for that boat

If the rudder can't reach beyond 65 degrees, the diagram can't show (and doesn't show) what happens at 70 degrees.  Which you said it did, and I say it doesn't.

[Andy Br]

1 hour ago, Tacet said:

If the rudder can't reach beyond 65 degrees, the diagram can't show (and doesn't show) what happens at 70 degrees.  Which you said it did, and I say it doesn't.

There is no point discussing what a certain diagram shows or does not, Schilling rudders are proven technology and they do work very well. They can deflect the thrust 90 degrees to the propeller and yes I have experienced a couple of ships that have started creeping astern with hard over rudder and slow ahead engine. We also work with a minimum of 10% of the ships draught underkeel clearance- i.e. equivalent to the average narrowboat having 7.5 cm underneath. Therefore most marinas are not restricted water and there is no reason why a Schilling rudder should not work on the canal. (My own 'Heath Robinson' attempt definitely does).

The original point of my post was to see if anybody had any actual experience of them on a narrowboat. 

 

This diagram is just simply the turning circles of a ship in relation to the ships length. (L)

[Midnight]

12 hours ago, Alan de Enfield said:

 

Do you mean a version of these ?

 

 

Yes

 

[Tacet]

9 hours ago, Andy Br said:

There is no point discussing what a certain diagram shows or does not, Schilling rudders are proven technology and they do work very well. They can deflect the thrust 90 degrees to the propeller and yes I have experienced a couple of ships that have started creeping astern with hard over rudder and slow ahead engine. We also work with a minimum of 10% of the ships draught underkeel clearance- i.e. equivalent to the average narrowboat having 7.5 cm underneath. Therefore most marinas are not restricted water and there is no reason why a Schilling rudder should not work on the canal. (My own 'Heath Robinson' attempt definitely does).

The original point of my post was to see if anybody had any actual experience of them on a narrowboat. 

 

This diagram is just simply the turning circles of a ship in relation to the ships length. (L)

I have no doubt that a Schilling rudder is more effective than its plate counterpart.

But that diagram does not indicate that all the 

thrust is deflected at 90 degrees to the propeller. If it did, the ship would turn about its own centre of mass, that is about in its own length whereas the diagram shows three times its length is required even at IanD's 70 degrees.

 

[Andy Br]

12 minutes ago, Tacet said:

I have no doubt that a Schilling rudder is more effective than its plate counterpart.

But that diagram does not indicate that all the 

thrust is deflected at 90 degrees to the propeller. If it did, the ship would turn about its own centre of mass, that is about in its own length whereas the diagram shows three times its length is required even at IanD's 70 degrees.

 

The diagram above is a full speed ahead turning circle, not an indication of manouvring ability, i.e. the ship was doing probably 15 knots ahead before the turn. Look at the photo of the ship above you can clearly see the wash coming out approx 90 degrees to the ship. You can also read the text below, that was a scientific paper by a couple of Naval architects.

If you are interest in knowing more, there is plenty on the internet. 

 

 

[IanD]

3 hours ago, Andy Br said:

The diagram above is a full speed ahead turning circle, not an indication of manouvring ability, i.e. the ship was doing probably 15 knots ahead before the turn. Look at the photo of the ship above you can clearly see the wash coming out approx 90 degrees to the ship. You can also read the text below, that was a scientific paper by a couple of Naval architects.

If you are interest in knowing more, there is plenty on the internet. 

 

 

He doesn't want to know more, he just wants to argue that he's right by nit-picking -- and not for the first time... 😉

[GUMPY]

4 hours ago, Andy Br said:

The diagram above is a full speed ahead turning circle, not an indication of manouvring ability, i.e. the ship was doing probably 15 knots ahead before the turn. Look at the photo of the ship above you can clearly see the wash coming out approx 90 degrees to the ship. You can also read the text below, that was a scientific paper by a couple of Naval architects.

If you are interest in knowing more, there is plenty on the internet. 

 

 

When would it be possible to make a turn like that on a canal? 

Even starting from 4mph 🤔

Edited October 9, 2022 by Loddon

[Andy Br]

1 hour ago, IanD said:

He doesn't want to know more, he just wants to argue that he's right by nit-picking -- and not for the first time... 😉

Well I have just returned to my marina and done a tight 180 degree turn in 25 knots of beam wind in one go- something I could never have done without either bow thruster or going astern a few times before I modified my rudder. So I am very happy. 

Ian D I would be very interested to know how your rudder performs when you get your boat finished- please let me know- I may well go the whole hog and fabricate a proper Schilling. 

Everybody else can stick to their flat plate rudders!