Schilling rudder project on narrowboat

[GUMPY]

I have been toying with the thoughts of a modified Schilling rudder for over 10 years since the days when I owned Parglena.  Since I sold Parglena I never got round to it as the cost of doing it is really not worth the small amount of improvement it might bring to the handling of Loddon.

 

[davidg]

On 05/10/2022 at 01:23, IanD said:

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

 

 

Hi Ian,

 

The Smiffs are obviously not keeping you busy enough.😊

A couple of questions I've been asking myself since you first put photos/drawings up of your rudder on this/other threads:

 

How do you drop the rudder out should the need arise? Normally there is enough play in the rudder tube to angle the rudder stock sideways so that the rudder can drop down one side of the skeg but with the wide flat plates top & bottom (& a wide skeg compared to a cast one) is this still possible?

 

And sort of related, should the rudder get knocked out of the bottom cup by the inevitable shopping trolley (or Vauxhall Astra bonnet in one memorable case I experienced - it was attached to the rest of the Astra) is it light enough so you can lift it back in? It looks as if there is a fair weight of steel involved in that fabrication compared to a flat plate.

 

The performance improvements look good and it will be intersting to hear how you find it; I wouldn't do it to my boat since it's one of god's own boats and handles like a dream but having steered other boats where it feels as if you are waving a bit of wet lettuce around in the water I can see the motivation.

 

David

[GUMPY]

1 minute ago, davidg said:

I wouldn't do it to my boat since it's one of god's own boats and handles like a dream but having steered other boats where it feels as if you are waving a bit of wet lettuce around in the water I can see the motivation.

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

[David Mack]

2 hours ago, Loddon said:

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

Even starting from 4mph 🤔

Tixall Wide! 

I do it every time I pass through, often a figure of eight. Did it once when towing a disabled boat on a long line, which rather confused the bloke who was steering it at the time.😁

[MtB]

2 hours ago, Loddon said:

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

Even starting from 4mph 🤔

 

Yes.

 

All the exhibitors attempting to turn like that in the pool outside the pub at is a fave event event at the summer historic boat rally there! 

 

 

Complete with p!ss-taking commentary on each boat's effort on the public address system.

 

[GUMPY]

3 minutes ago, MtB said:

All the exhibitors attempting to turn like that in the pool outside the pub at is a fave event event at the summer historic boat rally there

But not starting at 4mph

 

9 minutes ago, David Mack said:

Tixall Wide

Starting the turn at 4mph ? Bet you were popular with the natives

 

[David Mack]

9 minutes ago, Loddon said:

 

Starting the turn at 4mph ? Bet you were popular with the natives

 

Don't know about 4mph. None of the boats I have regularly steered have been capable of going that fast on the cut (at a reasonable engine speed).  But yes, I have looped the loop on Tixall Wide at my normal cruising speed setting, but the boat does slow down as you turn, so a forward speed of probably less than 2mph. There's plenty of width (and depth) so you don't ever need to be very close to any boats moored to the towpath.

Edited October 9, 2022 by David Mack

[PaulD]

7 minutes ago, Loddon said:

But not starting at 4mph

 

Starting the turn at 4mph ? Bet you were popular with the natives

 

No natives at Tixal. Only otherwise sensible narrowboaters doing figures of eight at full speed.

[Tacet]

11 minutes ago, PaulD said:

No natives at Tixal. Only otherwise sensible narrowboaters doing figures of eight at full speed.

Writing your name, as recorded on a tracking GPS, is a fun pastime for which sharp steering would be helpful.

[David Mack]

Just now, Tacet said:

Writing your name, as recorded on a tracking GPS, is a fun pastime for which sharp steering would be helpful.

It is said that James Brindley's assistant Samuel Simcock did the eighteenth century equivalent, immortalising his initials when setting out the original Birmingham Canal main line.

[IanD]

2 hours ago, davidg said:

 

Hi Ian,

 

The Smiffs are obviously not keeping you busy enough.😊

A couple of questions I've been asking myself since you first put photos/drawings up of your rudder on this/other threads:

 

How do you drop the rudder out should the need arise? Normally there is enough play in the rudder tube to angle the rudder stock sideways so that the rudder can drop down one side of the skeg but with the wide flat plates top & bottom (& a wide skeg compared to a cast one) is this still possible?

 

And sort of related, should the rudder get knocked out of the bottom cup by the inevitable shopping trolley (or Vauxhall Astra bonnet in one memorable case I experienced - it was attached to the rest of the Astra) is it light enough so you can lift it back in? It looks as if there is a fair weight of steel involved in that fabrication compared to a flat plate.

 

The performance improvements look good and it will be intersting to hear how you find it; I wouldn't do it to my boat since it's one of god's own boats and handles like a dream but having steered other boats where it feels as if you are waving a bit of wet lettuce around in the water I can see the motivation.

 

David

 

I'm not at the boat at the moment so I don't know how the rudder is actually attached to the rudder tube, or how big diameter the tube through the hull is, or how the bottom bearing is done and attached, so I can't answer your first question 😞

 

It's certainly heavier than a normal rudder so would be harder to lift back in if it ever did come out of the cup, but getting *any* rudder back in can be a pig of a job anyway -- I've never had the misfortune of having this happen, if it does I'll just have to deal with it. It's certainly less likely to get bent than a normal rudder because the whole assembly is much more robust.

 

I plan to report back on how well it works, with thrust measurements if I get the chance -- even better would be a comparison with a flat plate rudder.

 

Better steering (especially at large rudder angles) wasn't the only reason for going this way, it also sticks out about 200mm less past the stern, and this helps if you want to get a 60' boat through a lock which is officially 57'6" long...

 

(yes I know boats with conventional rudders have done this, in the same way as some of them also steer very well -- but it's another advantage, it means I can use a short stern button so making it less likely that I'll have to lift it up)

[David Mack]

8 minutes ago, IanD said:

It's certainly heavier than a normal rudder

Is it much heavier? A simple plate rudder would normally be something like 12mm thick, but I assume the sides of the Schilling would be about 3mm thick, so they can be curved (and being curved will be much more robust than flat plate of the same thickness). That would give a weight reduction to compensate for the additional weight of the top and bottom plates.

[IanD]

1 minute ago, David Mack said:

Is it much heavier? A simple plate rudder would normally be something like 12mm thick, but I assume the sides of the Schilling would be about 3mm thick, so they can be curved (and being curved will be much more robust than flat plate of the same thickness). That would give a weight reduction to compensate for the additional weight of the top and bottom plates.

IIRC it's mostly 6mm plate, so may not be much heavier. The curved sections that form the nose (starting with a 30 degree angle between them) are actually cut from a large-diameter steel tube, then the bits behind them are angled flat plates with a small kink -- same for the tail.

 

The overall shape is very close to the drawing in the patent but a lot easier to make -- there are other drawings in the patent which also describe this kind of manufacture but which I didn't show to Tim, I just let him come up with what he thought was the best way of building it 😉

[ditchcrawler]

On 04/10/2022 at 22:54, Andy Br said:

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

 

 

 

 

 

 

I have seen this design used on ships lifeboats, probably in Norway

[Guest]

My own Shilling design and stern re-work for one day when the hull's out of the water... https://skfb.ly/6TqHH

 

Of course, the science holds up, but you'll never change the opinions of the bretheren because it highlights ignorance, and no one likes to be told that they're wrong 😂

 

At high deflection angles the profile stalls, as does a plate rudder at lower deflection angles. A shilling offers meaningful lift when plates are working as a prop-wash deflector only, with a huge induced drag penalty from the break-away turbulence. 

 

The NACA profile of a schilling depends on the application. As drag is a squared relationship to speed you'll find skinny ones on yachts and fatter ones on barges - the greater the camber the higher the lift but at a consequence of drag. The concave rear will prevent a high lift design from being too twitchy.

Edited December 1, 2022 by dpaws

[IanD]

8 minutes ago, dpaws said:

My own Shilling design and stern re-work for one day when the hull's out of the water... https://skfb.ly/6TqHH

 

Of course, the science holds up, but you'll never change the opinions of the brethren because it highlights ignorance, and no one likes to be told that they're wrong 😂

 

That looks pretty similar to mine. Will be "interesting" to fabricate with those smooth curves though, if you're making it out of steel plate... 😉

 

You might also want to lose the pointy bit on the endplates at the stern, they won't help the hydrodynamics and the unsupported sticky-out bit could be prone to damage -- and even worse, punching nasty little holes into wooden lock gates... 😞

 

Looking at the model you might also not have enough balance in front of the pivot which will give heavy steering -- I used 25% average (measured halfway up, I have a tilted shaft too) which is what Dalslandia (who really knew his stuff in this area, sadly with us no more...) recommended, along with other sources. The proof of the pudding will be in the water when it goes in sometime next spring... 😉

Edited December 1, 2022 by IanD

[Guest]

Some further info on Schillings for a narrowboat, from a real naval architect (with real qualifications from a university rather then a beaten up MIG welder...)

 

The tiller force is proportional to the resultant hydrodynamic force on the rudder, which is proportional to the square of the water speed at the rudder.

Since the rudder is placed behind the propeller, the water speed will be a function of applied power.

Now, I assume that the boat has come with one of those good old 30-40 HP diesels (more is usually unnecessary for slow-speed canal boats) and that the max. speed at which a rudder hardover can be required is 3-4 kts. I also assume that "rudder size 780 mm square" means 780x780 mm rudder size. With that engine power the water speed over the rudder can be estimated in 3.6 m/s (7.0 kt) and a hydro force of approxim. 300 kg will push on the blade.
 

The safe position of the pivot force, which will IMO keep you away from the centre of pressure overshoot, is 20-22% (C.P. will usually stay at more than 35% behind the leading edge of the rudder, but can advance to as much as 26-27% at some rudder angles). The torque on the rudder stock can be estimated in 150-160 Nm, and this will have to be countered by the push/pull on the tiller. I use to calculate the length of the tiller with a criterion of max allowed pulling force of 10-15 kg (approx. 100-150 N), but this is a matter of personal opinion.

[Guest]

11 minutes ago, IanD said:

 

That looks pretty similar to mine. Will be "interesting" to build with those smooth curves though... 😉

My own idea for a modified plate rudder was to machine the profiles either side from TIVAR Dryslide, and then bolt through the plate itself.

 

You can smooth out the curves quite easily, or increase the number of staggers, depending how patient you are

 

 

[Guest]

On 14/10/2022 at 13:10, ditchcrawler said:

I have seen this design used on ships lifeboats, probably in Norway

A flettner strip is a triangular strip applied at the trailing edge which increases the effectiveness of a rudder at small deflections. The Schilling fishtail rudder is just a variation on the Flettner profile so that the shape looks less like an afterthought. I would therefore expect that a width at the trailing edge something like 2% of chord might be about right.

26 minutes ago, IanD said:

 

That looks pretty similar to mine. Will be "interesting" to fabricate with those smooth curves though, if you're making it out of steel plate... 😉

 

You might also want to lose the pointy bit on the endplates at the stern, they won't help the hydrodynamics and the unsupported sticky-out bit could be prone to damage -- and even worse, punching nasty little holes into wooden lock gates... 😞

 

Looking at the model you might also not have enough balance in front of the pivot which will give heavy steering -- I used 25% average (measured halfway up, I have a tilted shaft too) which is what Dalslandia (who really knew his stuff in this area, sadly with us no more...) recommended, along with other sources. The proof of the pudding will be in the water when it goes in sometime next spring... 😉

Ahh dearest Jan, I do miss him. We discussed the subject at length (with some debate for ideal NACA profiles) but in general we agreed and enjoyed ourselves, often at the expense of others 😆

 

20-22% is what I have been recommended, see the post above for the reason why.

Edited December 1, 2022 by dpaws

[IanD]

3 minutes ago, dpaws said:

A flettner strip is a triangular strip applied at the trailing edge which increases the effectiveness of a rudder at small deflections. The Schilling fishtail rudder is just a variation on the Flettner profile so that the shape looks less like an afterthought. I would therefore expect that a width at the trailing edge something like 2% of chord might be about right.

 

If you look at the profile of mine on the first page of this thread (lifted from Schilling's second-generation patent), the fishtail (30mm) is 30% of the maximum width (100mm) which in turn is 20% of the chord (500mm), so it's 6% of the chord wide.

[Guest]

1 minute ago, IanD said:

 

If you look at the profile of mine on the first page of this thread (lifted from Schilling's second-generation patent), the fishtail (30mm) is 30% of the maximum width (100mm) which in turn is 20% of the chord (500mm), so it's 6% of the chord wide.

 

The reason I liked the idea of profiled bolt-on plates was so that I could interchange the profiles and thus experiment. They'll all work better than a plate, that's a given, but I don't have the resources at present to model the parameters in order to refine further.

 

I look forward to hearing how your project goes.

 

For my hull the stern's a hydrodynamic mess and needs remodelling before I'll realise any benefits from profile variations. 

[magnetman]

I'd be worried about one of these rudders as it appears they are too cheap.

[IanD]

6 minutes ago, dpaws said:

 

The reason I liked the idea of profiled bolt-on plates was so that I could interchange the profiles and thus experiment. They'll all work better than a plate, that's a given, but I don't have the resources at present to model the parameters in order to refine further.

 

I look forward to hearing how your project goes.

 

For my hull the stern's a hydrodynamic mess and needs remodelling before I'll realise any benefits from profile variations. 

 

Bolt-on plates do indeed give you a lot more opportunity to play, just watch that you don't have possible corrosion issues with the steel plate underneath if water gets in behind them.

 

If you can I also suggest trying to get the prop rather further away from the deadwood (tip of swim) than is often done in narrowboats, this helps smooth the water entry into the prop and reduce prop walk -- and putting it closer to the rudder improves rudder response too. Can be difficult to do after the hull has been built though, you really need to extend the stern tube/bearing backwards -- or do what I'm doing and move the whole thing back a couple of inches so it sticks out less inside the hull and more outside.

[Guest]

2 hours ago, IanD said:

 

Bolt-on plates do indeed give you a lot more opportunity to play, just watch that you don't have possible corrosion issues with the steel plate underneath if water gets in behind them.

 

If you can I also suggest trying to get the prop rather further away from the deadwood (tip of swim) than is often done in narrowboats, this helps smooth the water entry into the prop and reduce prop walk -- and putting it closer to the rudder improves rudder response too. Can be difficult to do after the hull has been built though, you really need to extend the stern tube/bearing backwards -- or do what I'm doing and move the whole thing back a couple of inches so it sticks out less inside the hull and more outside.

 

 

The bolt on plates would be temporary, with the final choice fabricated from sheet.

 

Thank you for your thoughts, but no, the rear geometry has been calculated correctly and is optimised for that installation.

 

The hub does need to protrude further than is typical with modern day narrowboats, as they used to be on the originals.

 

 

 

One of many deliberate features that was originally stipulated by an architect and since misunderstood and ignored by the MIG monkeys.

Edited December 1, 2022 by dpaws

[ditchcrawler]

1 hour ago, dpaws said:

My own Shilling design and stern re-work for one day when the hull's out of the water... https://skfb.ly/6TqHH

 

Of course, the science holds up, but you'll never change the opinions of the bretheren because it highlights ignorance, and no one likes to be told that they're wrong 😂

 

At high deflection angles the profile stalls, as does a plate rudder at lower deflection angles. A shilling offers meaningful lift when plates are working as a prop-wash deflector only, with a huge induced drag penalty from the break-away turbulence. 

 

The NACA profile of a schilling depends on the application. As drag is a squared relationship to speed you'll find skinny ones on yachts and fatter ones on barges - the greater the camber the higher the lift but at a consequence of drag. The concave rear will prevent a high lift design from being too twitchy.

Have you actually made it, ready to fit?