Prop shroud

[fudd]

Morning.

Not wanting to nick Titan's thread, I would like to ask how many boats have a similar system to our boat Hunter. The prop sits it a tube about 16" long. This moves on an axis through the centre if the prop. We get no prop walk and she steers just as well in reverse as going forward. Once we had to reverse about 2-3 miles in reverse because we couldnt turn round. No probs at all. Must look a bit funny though. I imagine passers by thinking " hes got no idea how to drive a boat". I'm thinking there must be some disadvantage to this but can't think of any. We averaged 1 1/2 litres an hour going upstream on the Thames this summer so I don't think it's inefficient. Very little prop wash and can really move if we get on the straights! Any ideas?

Steve P

[Flyboy]

I've no doubt it's more efficient propelling the boat. The downside is what happens when the propeller is fouled by rope,plastic bags & all manner of debris? It would be difficult, if not impossible, to clear with the boat in the water. Probably why it never caught on.

What's it like steering backwards on a narrow canal in a crosswind?

Edited November 16, 2012 by Flyboy

[fudd]

I've no doubt it's more efficient propelling the boat. The downside is what happens when the propeller is fouled by rope,plastic bags & all manner of debris? It would be difficult, if not impossible, to clear with the boat in the water. Probably why it never caught on.

What's it like steering backwards on a narrow canal in a crosswind?

When we were in Oxford I got a twenty foot lump of 1 1/2" rope, and an anglers keep net and various other chutney around the prop. I just turned the shroud so it was facing the right direction and unwound it. I don't think it made it anymore difficult. In fact it may even stop stuff getting wrapped around it.

As for the wind, I don't know. Why should it make any difference? I've reversed on the Stort before and had no problems to speak of. I do remember struggling with a normal rudder system though. Anyway, if its a narrow canal I'm not going to go too far out of my way am I!?

[Bobbybass]

Morning.

Not wanting to nick Titan's thread, I would like to ask how many boats have a similar system to our boat Hunter. The prop sits it a tube about 16" long. This moves on an axis through the centre if the prop. We get no prop walk and she steers just as well in reverse as going forward. Once we had to reverse about 2-3 miles in reverse because we couldnt turn round. No probs at all. Must look a bit funny though. I imagine passers by thinking " hes got no idea how to drive a boat". I'm thinking there must be some disadvantage to this but can't think of any. We averaged 1 1/2 litres an hour going upstream on the Thames this summer so I don't think it's inefficient. Very little prop wash and can really move if we get on the straights! Any ideas?

Steve P

This sounds interesting..but I can't for the life of me figure how it clears the prop ?

Is it a huge diameter tube...or does the prop swing as well ?

 

Photo ?

[fudd]

This sounds interesting..but I can't for the life of me figure how it clears the prop ?

Is it a huge diameter tube...or does the prop swing as well ?

 

Photo ?

Can't do photos. Tried but without success. The tube turns. The prop stays still and the water is pushed out in the direction of the tube.

[Bobbybass]

Can't do photos. Tried but without success. The tube turns. The prop stays still and the water is pushed out in the direction of the tube.

 

Hmmm.....damn my lack of imagination....

So the tube...encloses the prop...front and back..but no danger of fouling the blades..?

[fudd]

Hmmm.....damn my lack of imagination....

So the tube...encloses the prop...front and back..but no danger of fouling the blades..?

Not front and back but along the line of the prop shaft.

[bottle]

Can't do photos. Tried but without success. The tube turns. The prop stays still and the water is pushed out in the direction of the tube.

 

Oh, Yes you can.

 

The photo needs to be hosted on the net, photobucket, or flickr for example.

[IanM]

 

[bowten]

 

We need that emoticon!!

[mike31]

http://myweb.tiscali.co.uk/alanann/bigber4.htm

 

heres a link to a pic, got one on my radio control tug.

[fudd]

http://myweb.tiscali.co.uk/alanann/bigber4.htm

 

heres a link to a pic, got one on my radio control tug.

That's it. Perfik.

[blackrose]

http://myweb.tiscali.co.uk/alanann/bigber4.htm

 

heres a link to a pic, got one on my radio control tug.

 

So the tube acts more as a rudder rather than an anti-cavitation shroud.

 

From the picture I can see that steering to starboard brings the port side of the tube into play (like any rudder), but in that position I'm not sure that the starboard side of the rudder-tube is doing anything at all?

 

It's interesting though and I've never seen anything like it before.

 

Edit: One downside though is that logs or baulks of wood which hit the prop could easily get jammed between the prop blade and rudder-tube, potentially damaging the prop or if you're unlucky even the gearbox. With a standard prop and rudder arrangement logs usually just get knocked away by the prop. That's probably why the rudder-tube isn't commonly seen on canal boats.

Edited November 16, 2012 by blackrose

[fudd]

Oh, Yes you can.

 

The photo needs to be hosted on the net, photobucket, or flickr for example.

I tried to put a pic of my Ducati on here. I did it through photo bucket. I couldn't get it to work. Someone else managed to do it. I'm a numpty

[fudd]

So the tube acts more as a rudder rather than an anti-cavitation shroud.

 

From the picture I can see that steering to starboard brings the port side of the tube into play (like any rudder), but in that position I'm not sure that the starboard side of the rudder-tube is doing anything at all?

 

It's interesting though and I've never seen anything like it before.

 

Edit: One downside though is that logs or baulks of wood which hit the prop could easily get jammed between the prop blade and rudder-tube, potentially damaging the prop or if you're unlucky even the gearbox. With a standard prop and rudder arrangement logs usually just get knocked away by the prop. That's probably why the rudder-tube isn't commonly seen on canal boats.

Funny enough Mike, that did happen once. It locked the shroud to port side. I couldn't move the tiller. Really though, it's something that can happen and 99% of the time it won't cause any real problems. When I had to clear the prop of rope I felt all around the edge of the prop blades. Sharp as a sharp thing. No burrs or anything. So it must afford some sort of protection. Swings and roundabouts I suppose.

By the way, what a lovely mooring you have. We went past a few weeks ago.

[blackrose]

Funny enough Mike, that did happen once. It locked the shroud to port side. I couldn't move the tiller. Really though, it's something that can happen and 99% of the time it won't cause any real problems. When I had to clear the prop of rope I felt all around the edge of the prop blades. Sharp as a sharp thing. No burrs or anything. So it must afford some sort of protection. Swings and roundabouts I suppose.

By the way, what a lovely mooring you have. We went past a few weeks ago.

 

Thanks - I haven't seen a boat go past me in what seems like a few weeks now. Mind you, it's been on red board a lot of the time.

[Teadaemon]

That sounds like a more primitive version of a Kitchen rudder - I've seen pictures of at least one narrowboat that had one installed, along with a custom tiller arrangement where the tiller could be tilted upwards to put the rudder into reverse.

[Grace and Favour]

That sounds like a more primitive version of a Kitchen rudder - I've seen pictures of at least one narrowboat that had one installed, along with a custom tiller arrangement where the tiller could be tilted upwards to put the rudder into reverse.

 

I thing that fellow member Biggles has something like one of these

[Radiomariner]

That sounds like a more primitive version of a Kitchen rudder - I've seen pictures of at least one narrowboat that had one installed, along with a custom tiller arrangement where the tiller could be tilted upwards to put the rudder into reverse.

 

 

Ah yes the "Kitchen Rudder" I recall seeing one on a tugboat in dry dock. Bit like reverse thruster on aircraft jets. Enabled vessel to go astern without changing direction of prop rotation. I recall that in this case the prop was in the middle of the vessel rather than the stern. Great manoeuvrability but talking to one of the crew, there was a risk of the tug capsizing if it tried to pull when the tow was more than 45^o to the line of the hull, and they had to keep reminding the captain of this!

 

The arrangement described by the OP is not nearly so complex. And is fairly common. Most modern ships lifeboats these days have this. Can;t remember the proper name. I think the main concern for the lifeboat is that that people in the water are less likely to foul the propeller! But it also made the boats (Max speed 6 or 7 knots) more manoeuvrable especially when trying, in a swell, to relalign it under the falls to lift it back out of the water.

[XAlan W]

http://myweb.tiscali.co.uk/alanann/bigber4.htm

 

heres a link to a pic, got one on my radio control tug.

 

I`m led to believe that the proper nautical term for that device is a KORT NOZZLE, but can stand being corrected

[bargemast]

I thing that fellow member Biggles has something like one of these

 

 

It wasn't Biggles, but Tim Swait, who you can find at the Build Blogs at : N.B.Trilby

 

My link

 

A very interesting blog where everything is explained, and shown with photographs.

 

Peter.

[Teadaemon]

I`m led to believe that the proper nautical term for that device is a KORT NOZZLE, but can stand being corrected

 

A Kort nozzle is similar, but different. It doesn't work like a rudder (and often has a more normal rudder immediately abaft it), but is there to make the prop more efficient (and provide a certain amount of protection), and is often employed with reversible pitch props that may be directly connected to the engine, with no gearbox at all.

[bargemast]

A Kort nozzle is similar, but different. It doesn't work like a rudder (and often has a more normal rudder immediately abaft it), but is there to make the prop more efficient (and provide a certain amount of protection), and is often employed with reversible pitch props that may be directly connected to the engine, with no gearbox at all.

 

 

There are also versions of Steering Kort Nozzles.

 

Peter.

[XAlan W]

When I worked as an engineer on a Smit deep sea salvage tug it had a device like the photo in post#11 & was always referred to by the crew as a Kort Nozzle

[howardang]

When I worked as an engineer on a Smit deep sea salvage tug it had a device like the photo in post#11 & was always referred to by the crew as a Kort Nozzle

The nozzle show in the photo is a Steerable Kort Nozzle and does away with the need for a rudder. A fixed nozzle is very common in Tugs and Anchor Handling Supply Vessels because of the increased thust that it produces, and is quite often used in combination with CP propellers. One down side with them is that it is sometimes possible to get objects - car tyres used as fenders, baulks of timber etc - fouled between the propeller blades and the nozzle.

 

Also many ships fitted with fixed nozzles also have twin rudders to increase manouverability.

 

For those who are interested here is a link to Kort's website

 

http://www.kortpropulsion.com/kort_nozzles_and_propellers.htm

 

Howard