Schilling rudder project on narrowboat

[Andy Br]

Hello,

Just posting this on here if anyone is interested. I tried doing some research and not a lot available RE narrowboats and high lift rudders and none (I could find) with any follow up on performance.

Background- I hired a few narrowboats before I bought my own. The hired ones varied in steering response when maneuvering- one in particular was excellent with very little forward movement and maximum turning effect at full helm and dead slow ahead. The others were okay. My own boat was pretty rubbish in comparison. Large angles of helm resulted in mainly forward movement and very little turning moment. I know the shape of the swim can affect handling but there is not much you can do about that once a boat is built! Mine has a fairly full swim. All the boats have a conventional narrowboat flat plate rudder and the only difference I can see is that my own boat is a bit bigger and has an Axiom prop (okay let's not start on that..).

Whilst not being experienced in narrowboats I have an extensive experience on sea boats, and a career manoeuvring ships. "High lift" rudders on ships increase the maneuverability immensely. For those who are not aware "high lift" rudders fall into two main categories- ones with a moveable flap that articulate through a mechanical linkage- known as 'flap rudders' (also known as Becker rudders- trade name- others are available- eg Barke, Hinze). The other type is the 'Schilling' type which is a solid rudder with no moving parts and features a trailing fish tail section. They tend to be well balanced with approx 40 percent area forward of the stock. From a pure ship handling point of view they are equally as good (in my humble opinion) so I opted for the 'no moving parts' experiment and armed with my welder and angle grinder decided to try to make a simple Schilling rudder and see if it made any difference. I didn't want to go mad and make something that weighed a ton so I decided to cherry pick the features of the Schilling that (I assumed) would make the most difference and I could quickly and easily replicate. Schilling rudders have an 'aerofoil section' which I decided not to bother with- I would retain the flat plate rudder as much as possible. They also have quite large plates top and bottom to help direct the flow- again I didn't want to add too much weight to something I was going to have to lift back on with a wetsuit! So I decided that increasing the area of the rudder forward of the stock to balance it as much as possible and adding a trailing wedge was going to be my limit.

I will attach photos of my simple mod which was simply grinding 3 inches off the back of the rudder and welding it on the front and replacing the 3 inches missing from the back with a piece of 4 inch angle iron. I had previously checked that there was loads of distance between the prop and the rudder.

 

The improvement in manoeuvring is absolutely immense and handles far better than any of the hired narrowboats. Hard over and dead slow ahead there is no forward movement, only turning moment- possibly even a tiny bit of sternway. Normal running on the canal is not adversely affected in any way, no vibration. The only thing is with the extra balance the steering is very light and won't automatically centre if I let go of the tiller. When I lift her out for blacking I may grind half an inch off the balance to try to improve on that.

 

just thought it might be of interest to someone.

Cheers,

Andy

 

[IanD]

You do have rather a lot of balance, normal recommendation for a rudder like this is 25% (pivot distance from nose, so 3x as much behind as in front) for tiller steering, so I'm not surprised the steering is very light and doesn't self-centre. For powered rudders (on ships, which is what most of the papers are targeted at) more balance is used (up to 35% or more) because self-centring doesn't matter, minimising the required steering gear force is more important -- in fact they tend to overbalance at large angles which would mean the tiller slamming right over.

 

Here's my Schilling rudder, and the profile used to build it...

 

Edited October 5, 2022 by IanD

[GUMPY]

Having looked at doing similar for many years but not got round to it my feeling is that it would improve matters by adding top and bottom plates as they will increase the effectiveness of the V at the back. Also agree with Ian that there is to much balance on the front if the rudder.

 

[Andy Br]

That is a lovely looking rudder Ian! Did you have a conventional rudder on the same boat previously to compare with? I wish now I had done some measurements with a strain gauge or something to quantify the lift. I also wish I had added the balance and wedge one by one to see how much effect each has. 

You are right about the balance for a tiller narrowboat. I will grind a bit off. I have a drawing of a real one on a ship I sailed on and it was about 40 percent balance but as you say 30 percent would probably be better. 

[Bee]

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. On our boat with a hydraulic ram providing the movement it took a while to get enough side to side swing to make the boat turn tightly enough. Eventually we have got about 40 degrees or maybe a bit more and that is OK for tricky turns. Interesting though, a bit of flat plate flapping around on the back of the boat has always seemed a bit crude.

[Andy Br]

28 minutes ago, 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. On our boat with a hydraulic ram providing the movement it took a while to get enough side to side swing to make the boat turn tightly enough. Eventually we have got about 40 degrees or maybe a bit more and that is OK for tricky turns. Interesting though, a bit of flat plate flapping around on the back of the boat has always seemed a bit crude.

It really has made a huge difference.

Normal rudders (on ships at least) start to stall at angles much over 30 degrees and yet I have seen Schilling rudders go to 70 degrees and act just like stern thrusters. How much part the 'aerofoil' section plays in this I don't know, it certainly smooths the flow.

It just needs a few more people to tinker about with their rudders and report back! Im sure the standard narrowboat rudder can be much improved on with a few tweaks. It is very rare that you see modern ships (at least smaller ones designed for coastal use) built without some kind of high lift rudder these days and I notice the continental river barges have gone for at least 2 schilling rudders per propeller. My first experience of a Schilling rudder was watching a 55,000 tonne bulk carrier go perfectly sideways in conjunction with bowthruster. Awesome sight and thought then I would fit one if ever I got a boat. 

Be interested to hear if anyone else has had a tinker!

[matty40s]

2 other threads...

All I can say looking at your design is that I hope you dont have to reverse very often!!

 

[Andy Br]

1 minute ago, matty40s said:

2 other threads...

All I can say looking at your design is that I hope you dont have to reverse very often!!

 

Yeah I go astern a lot, especially if it's my nearest winding hole. I don't see its made any difference and anyway I cheat and steer with the bowthruster. 😉 

Interesting Matty, I will read those other posts tonight thanks.

[Guest]

Well done guys! Here's my plan in 3D. Top/bottom plates are important for performance. https://skfb.ly/6TqHH

4 minutes ago, Andy Br said:

Yeah I go astern a lot, especially if it's my nearest winding hole. I don't see its made any difference and anyway I cheat and steer with the bowthruster. 😉 

FFS don't mention that in conjunction with a bow thruster we can practically traverse ;)

[Guest]

For the trailing edge a Schilling profile should be concave, not convex. This increases the straight-line stability, otherwise she'll tend to wonder.

[Andy Br]

3 minutes ago, dpaws said:

For the trailing edge a Schilling profile should be concave, not convex. This increases the straight-line stability, otherwise she'll tend to wonder.

Unfortunately concave angle iron offcuts cannot be found in skips readily 😂. Yep definitely some tweaks I can make.

[Tam & Di]

Horses for courses, as they say. There is an enormous difference between a ship at sea and a narrow boat on a canal, and factors other than rudder size/style come into play. Having owned and worked craft from freight narrow boats to motor barges on the Thames and estuary, small coastal ships, and 24m-38m working craft on continental canals, I would suggest that hull design and engine:propellor relationship are probably more significant factors.

 

If you have no control over these, then changing the rudder on a craft that does not handle well could make a large difference, but it is not the be-all and end-all of boat design. The key phrase there is having "a boat that does not handle well" in the first place.

 

Tam

 

p.s. This is not meant as a put-down, and if you want to play with your rudder design, who am I to criticise. 🤷‍♂️

Edited October 5, 2022 by Tam & Di
add p.s.

[Guest]

Please ignore - found mi glasses...🧐

 

Edited October 5, 2022 by dpaws

[GUMPY]

Strangely if I put my tiller hard over the stern moves sideways and the boat does not go forward. Which means I can spin the boat in its own length without a bow thruster. What am I doing wrong 🤔

It's a flat plate rudder.

 

[Guest]

Just now, Tam & Di said:

If you have no control over these, then changing the rudder on a craft that does not handle well could make a large difference, but it is not the be-all and end-all of boat design. The key phrase there is having "a boat that does not handle well" in the first place.

 

So very true Tam. Unfortunately I can name on one hand the people on the cut who can both weld and understand hydrodynamics.... you know how it is!

[GUMPY]

5 minutes ago, Tam & Di said:

I would suggest that hull design and engine:propellor relationship are probably more significant factors.

 

^^^^^^^this^^^^^^^^

[Guest]

2 minutes ago, Loddon said:

Strangely if I put my tiller hard over the stern moves sideways and the boat does not go forward. Which means I can spin the boat in its own length without a bow thruster. What am I doing wrong 🤔

It's a flat plate rudder.

 

 

Now that looks like a proper boat to me... Going around in circles is easy, I'd like to see you traverse in a lock pound against a side-wind. Then you may start to impress me... 😆

[Andy Br]

5 minutes ago, Loddon said:

Strangely if I put my tiller hard over the stern moves sideways and the boat does not go forward. Which means I can spin the boat in its own length without a bow thruster. What am I doing wrong 🤔

It's a flat plate rudder.

 

That's a lovely looking swim! That is possibly why.

[GUMPY]

8 minutes ago, Andy Br said:

That's a lovely looking swim! That is possibly why.

Indeed, that is one of the reasons I will never have another narrow boat.

It's 30 years old next year and I can honestly say I have never, in 50+ years, steered a better handling boat.

It was the second to last boat that Malcolm Pearson built https://www.malcolmpearson.co.uk/ and there is just so much that is right with it🤗

Edited October 5, 2022 by Loddon

[Andy Br]

12 minutes ago, Tam & Di said:

Horses for courses, as they say. There is an enormous difference between a ship at sea and a narrow boat on a canal, and factors other than rudder size/style come into play. Having owned and worked craft from freight narrow boats to motor barges on the Thames and estuary, small coastal ships, and 24m-38m working craft on continental canals, I would suggest that hull design and engine:propellor relationship are probably more significant factors.

 

If you have no control over these, then changing the rudder on a craft that does not handle well could make a large difference, but it is not the be-all and end-all of boat design. The key phrase there is having "a boat that does not handle well" in the first place.

 

Tam

 

p.s. This is not meant as a put-down, and if you want to play with your rudder design, who am I to criticise. 🤷‍♂️

Yes you are bang on but not much I can do to the boat design (which is pretty much perfect for us otherwise) and not much I want to do (costwise) in changing propellers and engines. The rudder however I can attack with welder and angle grinder in one day while the kids are at school!  

I'd love to try a different prop, it's currently an Axiom with hydraulic drive.

[GUMPY]

6 minutes ago, Andy Br said:

I'd love to try a different prop, it's currently an Axiom with hydraulic drive.

From what I have read that prop would be the first thing I would change. 

Who is the shell builder?

[Tam & Di]

Many modern builders (just a welder, really) make something like a rectangular steel box with a pointy bit at the front and a squarish or slightly semi-circular thing at the back - it's the cheapest option and requires minimal boat-building skill or knowledge. Buyers just basically want something to live on, and if it floats that's all they consider a boat needs. If it's ever moved then the front pushes up a little wave rather than cutting through the water, and a lack of proper swim means the flow cannot get properly to the prop or the rudder, but few people ever get to realise there could be anything amiss.

 

Tam

Edited October 5, 2022 by Tam & Di

[Andy Br]

13 minutes ago, Loddon said:

From what I have read that prop would be the first thing I would change. 

Who is the shell builder?

It's a Reeves so a decent boat, if a little full in the swim. Its trying to match a prop to the hydraulic drive that only runs at 500 rpm. Might have a look in the future although, with my rudder mod, I'm pretty happy with it now. One good thing is with the Axiom it stops so fast in astern. Great with kids and inexperienced wife helmsmen! 

[IanD]

4 hours ago, Andy Br said:

That is a lovely looking rudder Ian! Did you have a conventional rudder on the same boat previously to compare with? I wish now I had done some measurements with a strain gauge or something to quantify the lift. I also wish I had added the balance and wedge one by one to see how much effect each has. 

You are right about the balance for a tiller narrowboat. I will grind a bit off. I have a drawing of a real one on a ship I sailed on and it was about 40 percent balance but as you say 30 percent would probably be better. 

It's a new boat being fitted out now, will hit the water next spring.

 

If people want to take the view that 'my flat plate is just fine" or "the hull matters more" or "why bother on  a narrowboat" then that's OK, but they're ignoring the fact that there's lots of actual evidence that a Schilling rudder is better for low-speed manoeuvring -- including from a couple of knowledgeable people who've posted on this forum (Dalslandia, Dutch?).

 

I suspect the real reasons there aren't many on the canals is that most people don't care, and most of those that do aren't going to pay to get one made and fitted to replace what they've already got -- if you're having a new boat built then the cost is a small addition (a few tenths of a percent), but few people will shell out for a new rudder when they could buy an awful lot of beer instead... 😉

[Andy Br]

5 minutes ago, IanD said:

It's a new boat being fitted out now, will hit the water next spring.

 

If people want to take the view that 'my flat plate is just fine" or "the hull matters more" or "why bother on  a narrowboat" then that's OK, but they're ignoring the fact that there's lots of actual evidence that a Schilling rudder is better for low-speed manoeuvring -- including from a couple of knowledgeable people who've posted on this forum (Dalslandia, Dutch?).

 

I suspect the real reasons there aren't many on the canals is that most people don't care, and most of those that do aren't going to pay to get one made and fitted to replace what they've already got -- if you're having a new boat built then the cost is a small addition (a few tenths of a percent), but few people will shell out for a new rudder when they could buy an awful lot of beer instead... 😉

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.