Swan Neck sheared off

[jelunga]

I'm not a theoretical mech eng, but I wonder whether the traditional shape will be stiffer, for a given size of bar, than a simple vertical shaft would be with a 90 degree bend at the top?

One reason for doing it the traditional way is that you can have a removable tiller which leaves a clear space that can extend behind the centre line of the rudder post.

 

Tim

I think the mechanical advantage is because if you had a straight vertical shaft with its axis of rotation in the same axis as rhe rudder, there would be too high a shearing/torque force where the straight vertical shaft met the top of the rudder stock.

The swan neck allows greater torsional rigidity oi the assembly whilst reducing shear/ torque forces af the point of attachment It also gives more space for the helms person fat arse.

[Timleech]

I think the mechanical advantage is because if you had a straight vertical shaft with its axis of rotation in the same axis as rhe rudder, there would be too high a shearing/torque force where the straight vertical shaft met the top of the rudder stock.

The swan neck allows greater torsional rigidity oi the assembly whilst reducing shear/ torque forces af the point of attachment It also gives more space for the helms person fat arse.

 

The shearing force will be exactly the same. I still think (without any theoretical foundation so perfectly willing to be shown to be wrong) that a straight vertical shaft will allow more movement under torsional load than will a traditional shaped Ram's Head made from the same section. The traditional shape will probably be a bit more flexible in other directions, though.

 

Tim

[Keeping Up]

... It also gives more space for the helms person fat arse.

 

That's the most logically scientific explanation that I've heard.

[RLWP]

The shearing force will be exactly the same. I still think (without any theoretical foundation so perfectly willing to be shown to be wrong) that a straight vertical shaft will allow more movement under torsional load than will a traditional shaped Ram's Head made from the same section. The traditional shape will probably be a bit more flexible in other directions, though.

 

Tim

 

If you make this into a thought experiment, what you are saying is that the longer the piece of material in the swan neck gets, the stiffer it is. That can't be right, otherwise a swans neck that projected sixty feet back and the forward to the tiller would be stiffer than the traditional one

 

Richard

[DaveP]

The lower part welded to the counter appears to be one piece (rather than two with a spacer) and not to have any bolts or screws set into it - as does the upper collar. The upper collar doesn't rotate with the tiller and the stock rotates freely within it; it's been greased regularly (albeit not frequently) by removing the nipple extender and jamming the grease gun into the hole in the last few years whilst I've had the boat [originally built in '79]. The hole doesn't appear to extend as far inwards as the rudder stock, so I assume there's a bearing somewhere below the upper collar.

 

The picture is a lot clearer than real life in showing different colours on the broken hub - I agree that it looks like it's cracked sometime in the past and failed under the stress of the walkway pressing down on it.

 

I'm now removing the paint with a chemical attack, so cleaned-up pictures should appear soonish...

 

Thanks for the suggestions so far (and the digression which does take the mind off the possible expenses and hassle of the repair!)

 

Cheers,

 

Dave

[Chris Pink]

No help but lots of sympathy because I loathe and detest walkways within locks.

 

They are completely stupid, thoughtless and dangerous designed by someone who has absolutely no idea of how a lock works or basic hydrodynamics.

 

Send the bill to BW

[the grinch]

It also gives more space for the helms person fat arse.

but that then opens up another can of worms as several old boatwomen steered the butty!!

[Guest]

That stud is actually a grease nipple on a tube extender, although judging by the paint over the nipple, and the dry rust where the rudder shaft comes through the collar, there has been no grease down there for a while.

I think the first step is to remove the paint completely, from all the circular bits, by sanding or chemical attack. Then you can see what other fixings might exist and proceed accordingly.

For instance, how is the the collar the nipple extension is screwed prevented from turning?

Is the bush welded to the deck a single tall bush, or a short bush with a spacer?

 

And what the hell is wrong with a bit of simple and obvious cleaning before posting pictures to ask questions?

Show some inclination to help yourself, don't just parasite on the back of others.

A bit harsh isn't it? Poor person has had an accident, and you make a statement like that?

 

I for one am sorry for the OP, hope you get it fixed soon, and most importantly hope nobody was hurt.

Edited May 6, 2012 by Guest

[MartinClark]

No help but lots of sympathy because I loathe and detest walkways within locks.

 

They are completely stupid, thoughtless and dangerous designed by someone who has absolutely no idea of how a lock works or basic hydrodynamics.

 

Send the bill to BW

 

They are certainly potentially dangerous but BW has inherited them from the original design of the canal.

 

The position of the gate paddles (originally handspike-operated, and in many cases still so) means they can only be operated from the upstream side of the gate. The walkways do not go right across to the mitre but only as far as the paddle, which is usually in line with the stern of a narrowboat sharing the lock.

 

Of course,the locks weren't designed for narrowboats, but for short fat boats which would never have been able to get any part of them under these walkways.

[jelunga]

but that then opens up another can of worms as several old boatwomen steered the butty!!

But buttys didnt have swan necks just long tillers. Maybe there a clue in this?

[MartinClark]

But buttys didnt have swan necks just long tillers. Maybe there a clue in this?

 

...but the long tiller slots into the wooden rudder post or ram's head. That wouldn't snap off in the same way as a swan neck might, but could still be damaged if it came up under a walkway.

 

[the grinch]

But buttys didnt have swan necks just long tillers. Maybe there a clue in this?

 

i think you missed the joke!!

[jelunga]

i think you missed the joke!!

Probably. It was past my bed time!

[Guest]

I'd agree with that.

 

Quote "I just can't see why we can't have "straight" tillers."

 

The wide beam trip boat by me has a simple right angled tiller as opposed to the "Z" shaped swan neck on my NB. I have steered the trip boat and it feels little different to steering my NB. Based on this experience I am not convinced there is any great "mechanical" advantage to the swan neck. I seem to recall some other Leeds and Liverpool boats having simple right angled tillers.

[Neil2]

The wide beam trip boat by me has a simple right angled tiller as opposed to the "Z" shaped swan neck on my NB. I have steered the trip boat and it feels little different to steering my NB. Based on this experience I am not convinced there is any great "mechanical" advantage to the swan neck. I seem to recall some other Leeds and Liverpool boats having simple right angled tillers.

 

Yes they do - I'd forgotten about those short boats and if memory serves they just have an angled tiller bolted to the rudder shaft.

 

So is it just a NB thing and if so why?

[DaveP]

Couple more pictures

 

After cleaning the paint off the boss and collar -

 

 

The boss is the top of the rudder post hull sleeve and the collar just appears to be hammered into the top of it (note marks around the top). it's not going to shift easily!

 

From underwater, this is the best shot of the rudder -

 

 

The post appears to pass through the rudder being bolted onto it via some semi-cylindrical lugs. It terminates above the bottom of the rudder and then there's a protuberance that fits into the skeg. Feeling up the sleeve there doesn't seem to be any bearing or support within 6" of the uxter plate.

 

So I'm thinking that the rudder can be unbolted from the post and the post lifted up through the sleeve. Then a new post can be fitted to the rudder (drilled for the bolts), then the rudder and post reassembled with a new swan neck bolted to top of the post (rather than being welded as was). Still an out of water job though?

[casper ghost]

I had my swans neck shear in the same place as yours.

 

To fix mine I used a 9" grinder and cut off the part around the rudder bar at deck height. This left enough of the rudder bar sticking up so I could cut the top flat, fit a new bearing and weld the original swans neck back on.

 

No need to get the boat out of the water.

 

Casp'

Edited May 11, 2012 by casper ghost

[owen]

I had my swans neck shear in the same place as yours.

 

To fix mine I used a 9" grinder and cut off the part around the rudder bar at deck height. This left enough of the rudder bar sticking up so I could cut the top flat, fit a new bearing and weld the original swans neck back on.

 

No need to get the boat out of the water.

 

Casp'

agreed i posted a thread about swan neck let me know if i can help i dont do the welding but could put you in touch with someone who does

[MartinClark]

agreed i posted a thread about swan neck let me know if i can help i dont do the welding but could put you in touch with someone who does

 

I would have thought the nearby boatyard on the Dewsbury Arm (Calder Valley Marine) has had plenty of experience of re-attaching swan necks!

[DaveP]

After a summer in the S of France - it's all fixed now.

 

The rudder was attached only by two bolts through the stock - undone, this allowed the stock to be knocked up through the bearing. A new 10cm stub was welded on top after a bit of grinding round the circumference to provide a decent channel for the weld.

 

A new swan neck with split collar was then fabricated and fitted. The collar fits over the stub and is held on by a bolt through the stub and bolts though a flange to nip the collar tight onto the stub.

 

 

Before it went out into the cold and dark!