Fishtail rudder

[KezzerN]

If fishtail rudders give better steering at slow speeds why aren't this style of rudder fitted to narrowboats?

[Gybe Ho]

1 minute ago, KezzerN said:

If fishtail rudders give better steering at slow speeds why aren't this style of rudder fitted to narrowboats?

 

Now you have done it, I fear an incoming essay length post from @IanD 

[KezzerN]

2 minutes ago, Gybe Ho said:

 

Now you have done it, I fear an incoming essay length post from @IanD 

 

 

It will be interesting reading for a newbie like me that is trying to learn as much as possible.

[David Mack]

5 minutes ago, KezzerN said:

If fishtail rudders give better steering at slow speeds why aren't this style of rudder fitted to narrowboats?

Because they cost more, a simple flat plate rudder is adequate most of the time, and because its always been done that way.

 

That said, a couple of years ago I found a 1935 drawing in the CRT archive of a fishtail rudder for GUCCCo boats, but I'm not aware they were ever fitted.

 

[KezzerN]

Just now, David Mack said:

Because they cost more, a simple flat plate rudder is adequate most of the time, and because its always been done that way.

 

That said, a couple of years ago I found a 1935 drawing in the CRT archive of a fishtail rudder for GUCCCo boats, but I'm not aware they were ever fitted.

 

 

 

Thanks for the link.  I shall have a read.

 

 

[Rod Stewart]

4 minutes ago, Gybe Ho said:

 

Now you have done it, I fear an incoming essay length post from @IanD 

I believe Ian hasn't got sole (see what I did there) rights to the schilling rudder on this forum. The site owner @DHutch made one and fitted it to his boat IIRC. He also contributed to the wiki page on the subject...

 

https://en.wikipedia.org/wiki/Schilling_rudder

 

 

I suspect the reason they are not generally fitted is one of cost.

[Gybe Ho]

1 minute ago, KezzerN said:

 

It will be interesting reading for a newbie like me that is trying to learn as much as possible.

 

 

He has a posh 3D rudder, quite rare. 

[Rod Stewart]

Just now, Gybe Ho said:

 

He has a posh 3D rudder, quite rare. 

Not really. Our 'flat' rudder is also 3 dimensional.

[KezzerN]

5 minutes ago, Rod Stewart said:

I believe Ian hasn't got sole (see what I did there) rights to the schilling rudder on this forum. The site owner @DHutch made one and fitted it to his boat IIRC. He also contributed to the wiki page on the subject...

 

https://en.wikipedia.org/wiki/Schilling_rudder

 

 

I suspect the reason they are not generally fitted is one of cost.

 

 

Thanks for the link.

 

 

[Gybe Ho]

Just now, Rod Stewart said:

Not really. Our 'flat' rudder is also 3 dimensional.

 

Oh a classic example of CWDF disputability compulsion syndrome, when does a flat plate rudder become 3 dimensional. 😛

 

Ignore me this morning, I am in a happy flippant mood because I am heading off to look at a narrowboat shell soon. 

[IanD]

11 minutes ago, Rod Stewart said:

I believe Ian hasn't got sole (see what I did there) rights to the schilling rudder on this forum. The site owner @DHutch made one and fitted it to his boat IIRC. He also contributed to the wiki page on the subject...

 

https://en.wikipedia.org/wiki/Schilling_rudder

 

I suspect the reason they are not generally fitted is one of cost.

 

I was very aware of the @DHutch rudder (and the fact he was pleased with how well it worked), it was one of the things that made me consider fitting one... 🙂 

 

I also think cost is the main reason they're not more widely used, they take a lot more time and effort to build than a simple flat plate rudder. I don't have an itemised number, only a total add-on for various mods/additions to the hull, but IIRC mine (made by Tim Tyler) cost getting on for a grand. Which sounds like a lot, but about 0.3% of the total boat cost in return for better steering (which it delivered as expected...) seemed like a good deal to me -- and several times cheaper (and much easier to fit in) than a (much-mocked...) stern thruster + tunnel which does very much the same thing.

 

 

Edited March 13 by IanD

[KezzerN]

On the subject of rudders, when I am turning the bow left it responds in an instant, but when turning the bow to the right it takes forever.  Is that to do with the rudder or the right hand propeller?

[IanD]

Just now, KezzerN said:

On the subject of rudders, when I am turning the bow left it responds in an instant, but when turning the bow to the right it takes forever.  Is that to do with the rudder or the right hand propeller?

The propeller, this is prop walk in action. It's made worse if the water flow into the prop is not too good, for example a short swim or a blunt end to it or the prop too close to it, all of which are common on narrowboats.

[ditchcrawler]

8 minutes ago, Gybe Ho said:

 

Oh a classic example of CWDF disputability compulsion syndrome, when does a flat plate rudder become 3 dimensional. 😛

If its not a drawing it must ne 3 dimensional even if its a flat plate 10mm thick

Ignore me this morning, I am in a happy flippant mood because I am heading off to look at a narrowboat shell soon. 

Good luck with that

 

[Rod Stewart]

7 minutes ago, IanD said:

 

I was very aware of the @DHutch rudder (and the fact he was pleased with how well it worked), it was one of the things that made me consider fitting one... 🙂 

 

I also think cost is the main reason they're not more widely used, they take a lot more time and effort to build than a simple flat plate rudder. I don't have an itemised number, only a total add-on for various mods/additions to the hull, but IIRC mine (made by Tim Tyler) cost getting on for a grand. Which sounds like a lot, but about 0.3% of the total boat cost in return for better steering (which it delivered as expected...) seemed like a good deal to me -- and several times cheaper (and much easier to fit in) than a (much-mocked...) stern thruster + tunnel which does very much the same thing.

 

 

Tis a thing of beauty. I have rudder envy. It also looks like it would make a convenient step up for getting back onboard (not that I've ever fallen in,noooo, not me).

[David Mack]

5 minutes ago, IanD said:

I don't have an itemised number, only a total add-on for various mods/additions to the hull, but IIRC mine (made by Tim Tyler) cost getting on for a grand.

That sounds a lot to me. Yours is a one-off, but if a boatbuilder did this on every build it could be a lot cheaper. There are specialist plate benders who could curve the two side plates to the appropriate profile, leaving the boatbuilder just to assemble the rudder. And a bulk order of bent plates would bring the cost down.

[Rod Stewart]

4 minutes ago, IanD said:

The propeller, this is prop walk in action. It's made worse if the water flow into the prop is not too good, for example a short swim or a blunt end to it or the prop too close to it, all of which are common on narrowboats.

Or the tiller and rudder aren't lined up.😂

[KezzerN]

4 minutes ago, IanD said:

The propeller, this is prop walk in action. It's made worse if the water flow into the prop is not too good, for example a short swim or a blunt end to it or the prop too close to it, all of which are common on narrowboats.

 

 

Thanks for the explanation. 

 

 

[ditchcrawler]

8 minutes ago, IanD said:

 

I was very aware of the @DHutch rudder (and the fact he was pleased with how well it worked), it was one of the things that made me consider fitting one... 🙂 

 

I also think cost is the main reason they're not more widely used, they take a lot more time and effort to build than a simple flat plate rudder. I don't have an itemised number, only a total add-on for various mods/additions to the hull, but IIRC mine (made by Tim Tyler) cost getting on for a grand. Which sounds like a lot, but about 0.3% of the total boat cost in return for better steering (which it delivered as expected...) seemed like a good deal to me -- and several times cheaper (and much easier to fit in) than a (much-mocked...) stern thruster + tunnel which does very much the same thing.

 

 

Looking at some photos of really big ones I see they are nicked about half way down the trailing edge, I wondered if that had anything to do with propwalk. I will try and find a photo

[IanD]

22 minutes ago, Rod Stewart said:

Tis a thing of beauty. I have rudder envy. It also looks like it would make a convenient step up for getting back onboard (not that I've ever fallen in,noooo, not me).

It is, much better than those useless tabs sometimes used -- see endless discussions on another recent CWDF thread... 😉 

 

21 minutes ago, David Mack said:

That sounds a lot to me. Yours is a one-off, but if a boatbuilder did this on every build it could be a lot cheaper. There are specialist plate benders who could curve the two side plates to the appropriate profile, leaving the boatbuilder just to assemble the rudder. And a bulk order of bent plates would bring the cost down.

 

I spoke to Tim, the cost was pretty much hours needed (including deciding how to make it and cutting the bits out) times hourly rate -- as I'm sure you know, anything non-standard and one-off always costs more than you'd expect... 😉 

 

All absolutely correct about cost reduction but it's chicken and egg, nobody's going to do this unless there's enough demand. Even with the bent side plates these would still have to be welded together and to the end plates, which also need cutting out and smoothing off, so it would still cost more than a flat plate.

 

And most boaters neither know nor care about any of this and are perfectly happy with their cheap standard flat plate, which works adequately... 😉 

Edited March 13 by IanD

[ditchcrawler]

8 minutes ago, ditchcrawler said:

Looking at some photos of really big ones I see they are nicked about half way down the trailing edge, I wondered if that had anything to do with propwalk. I will try and find a photo

 

9 minutes ago, ditchcrawler said:

Looking at some photos of really big ones I see they are nicked about half way down the trailing edge, I wondered if that had anything to do with propwalk. I will try and find a photo

[IanD]

9 minutes ago, Rod Stewart said:

Or the tiller and rudder aren't lined up.😂

Or the rudder is bent, more likely than the boat being built with them out of line... 😉 

[ditchcrawler]

How about this for a half way house. I did see this set up on a ferry lifeboat we were on 

[IanD]

9 minutes ago, ditchcrawler said:

 

 

That's to get different angles on the upper and lower halves instead of the "fishtail" being symmetrical, because the rotating prop means the water flow/pressure isn't quite the same -- one half can have a steeper fishtail angle than the other (the other side is the other way round). This gives slightly better rudder effectiveness but also slightly reduces rudder drag, which is important for ships travelling long distances and burning lots of fuel.

 

Which incidentally is one reason Schilling rudders are mainly used on slow-speed vessels like trawlers and tugs (and narrowboats!) where manoeuvrability is important and a small increase in drag matters less -- most ships use aerofoil rudder profiles like NACA which have less drag than a Schilling but don't work so well at high rudder angles, which of course are hardly ever used.

 

4 minutes ago, ditchcrawler said:

How about this for a half way house. I did see this set up on a ferry lifeboat we were on 

 

That's a bodge which better than a flat plate rudder (especially at high angles) but less effective than a Schilling (ditto) and with rather more drag -- but also much cheaper and can be added on to a flat plate.

 

As usual, you pays yer money and you takes yer choice... 😉 

Edited March 13 by IanD

[Gybe Ho]

22 minutes ago, KezzerN said:

On the subject of rudders, when I am turning the bow left it responds in an instant, but when turning the bow to the right it takes forever.  Is that to do with the rudder or the right hand propeller?

 

My old yacht used to do the same, basically the lower half of the propellor is pushing on firmer water than the top half and this produces a sideways push that is always present, you just notice it more when turning.

 

With my old yacht I could spin it in a tight clockwise circle that would throw crew off balance whereas the anticlockwise circle was much wider.