Maximum rudder angle before stall?

[Dalslandia]

 

 

ok pax

 

Sure forums need developments, so we can see eyes, lips, and hear ton in voices, feel spits if someone in angry in his/her talk. ah maybe not. :-)

 

If what I remember about the cost of alcohol in Sweden is correct, that's probably as well....anyway whats wrong with aquavit.....cheers

 

 

edit to say sorry skol !

 

Skål!

 

yes it is expensive still more expencive in Norway, the Easter Saturday I was to the monopoly (yup still is) and bought a bottle, the store was filled with thirsty Norwegian

[Paul C]

Our rudder stop is the uxter plate. Before we bought the boat, the survey revealed a little wear in the area of the uxter plate where the rudder had repeatedly contacted. So, little plates of metal were welded there to make it thicker and more durable (after all, its the fuel tank here, and in any case you'd not want a hole in there even if it wasn't!) So the rudder stop potentially does two things - as well as protect the rudder, it protects whatever else it would contact.

 

The other useful addition I can make is that once I drove a dayboat which was horrendously set up - it had a throttle restricter to about 1/3 throttle, and a rudder stop so it swung about 45deg either side of centre, rather than a 'normal' narrowboats' swinging around 80deg each side of centre. It was a dog's breakfast to turn it in a confined space. So while rudder efficiency may drop off beyond the optimal point, I don't think its a sharp cutoff but a more gradual one, so 80 degrees of rudder is still somewhat effective and useful. Maybe the best angle (for one particular boat) is 65 degrees, or 60, or 70, or 72 etc but after a while driving the same boat you'd learn the mose effective point.

[ditchcrawler]

I don't understand the science but isn't a rudder on a turning boat a bit like a sailing boat and the apparent wind direction. so as you start to turn the flow has gone from straight ahead to some angle depending on how fast you are turning and how fast you are going forward. So the faster the boat is turning the more angle required on the rudder to keep the angle of attack the same.

[RLWP]

I doubt the speed of the boat makes a lot of difference. It will be the speed of the water coming off the prop that matters

 

Richard

[ditchcrawler]

Is there a general rule or does it vary from boat to boat and the type of boat? I've read some yacht forums and people are suggesting 25 - 35 degrees each way from centre, but would this be different on a bigger, heavier and slower boat? I imagine fluid separation on either side of the rudder (and drag) which leads to rudder stall is velocity-dependent? I'm just talking about a balanced rudder here, not Schilling, etc.

 

My current flat plate rudder moves about 40 degrees either side of centre and seems to steer fine at the stops, but I'm changing it for a this one below as it has a better profile. I need to weld a vertical piece on top to act as a rudder stop. Should I just put it in the same place as the existing rudder stop?

 

 

 

 

Why didn't you make a schilling rudder while you were going to all that effort?

[Dalslandia]

I don't understand the science but isn't a rudder on a turning boat a bit like a sailing boat and the apparent wind direction. so as you start to turn the flow has gone from straight ahead to some angle depending on how fast you are turning and how fast you are going forward. So the faster the boat is turning the more angle required on the rudder to keep the angle of attack the same.

Not sure what you mean, but at constant speed, a sharper turn require more rudder input, and probably a higher AoA at the rudder.

but turning with max rudder or best rudder, will reduce the forward speed, and the turning circle will be smaller and smaller, so the smallest turn is made at lowest speed, full or best rudder (if different) and a lot of propeller wash, nothing new there.

 

a rudder is making a side force at the stern, but boats can be a bit different depending on shape and trim, some will turn without a rudder, some don't like to turn, it means the rudder AoA will be different on those boat types at the same turn rate. (with the same rudder size and shape)

 

Edit, still sober. what a waste of a nice Saturday.

Edited April 26, 2014 by Dalslandia

[bottle]

I know I went off at a tangent but after all this discussion....

 

My thoughts set the stops at 90° and learn to control the rudder angle for best turn.

 

It is not an exact angle as it will vary depending on prop speed, boat speed and depth of water and probably a few other things....forgot gongoozlers.

Edited April 27, 2014 by bottle

[RLWP]

And cross winds. In a good blow, Tawny is travelling diagonally up the cut

 

Richard

[bizzard]

And cross winds. In a good blow, Tawny is travelling diagonally up the cut

 

Richard

Opening wide all the windows helps with that problem.

[RLWP]

Opening wide all the windows helps with that problem.

 

Who says it's a problem! It is one of my favourite bits of boat handling

 

Good argument for not having portholes though

 

Richard

[blackrose]

Why didn't you make a schilling rudder while you were going to all that effort?

 

It wasn't any effort for me - I didn't make it. It was made by another forum member as a favour. I know he made a Schilling rudder for Daniel but we talked about it and since my boat turns almost within its own length he decided I didn't really need a Schilling and thought that a plain tapered rudder would be best. I don't think Schilling rudders work well on every boat - they can increase resistance around the rudder which can lead to tiller shake as each blade of the prop passes over the rudder. I have a little bit of tiller shake anyway so I didn't want it to get any worse. Anyway after he'd finished making it he wouldn't take any money, so I wasn't going to turn around and complain!

Edited April 27, 2014 by blackrose

[blackrose]

I know I went off at a tangent but after all this discussion....

 

My thoughts set the stops at 90° and learn to control the rudder angle for best turn.

 

It is not an exact angle as it will vary depending on prop speed, boat speed and depth of water and probably a few other things....forgot gongoozlers.

 

Could do... Does your rudder turn to 90 degrees?

 

What I've decided is to weld two 24mm stud connectors vertically onto the top of the rudder in different positions.

 

One of the stud connectors will be welded to approximately the current position of the stop (on the old rudder) and the second stud connector will be further back on the rudder. The length of the stud connectors is 72mm and they should just pass under the uxter plate (if not I'll cut them down a bit). Then I can screw a 24mm eyebolt into one or other of the stud connectors to see which one works best as a stop after the boat goes back into the water. Screwing the eyebolt into the stud connector which is further back on the prop will allow a greater range of movement and if I find that's no good I can change the position of the eyebolt to keep the stop as it currently is.

 

When I've decided which position is best I will put Marineflex over the threads of the eyebolt and screw it into the chosen stud connector. Marineflex can cure underwater and it will prevent the eyebolt rattling loose. I'm using an eyebolt so I can put a rope through it in case I ever need to get the rudder off in the water.

Edited April 27, 2014 by blackrose

[carlt]

 

I don't think Schilling rudders work well on every boat -

I've heard they can make some boats bob.

[bottle]

Hi Blackrose

 

Yes, my rudder does turn through 90°.

[blackrose]

Hi Blackrose

 

Yes, my rudder does turn through 90°.

 

I'll weld one of those stud connectors near the tip of the rudder then and that will give me almost 90 degrees.

[Ssscrudddy]

Well I dont know about all this sciencey stuff, but what I do know is this. My Sisters boat will turn much easier than my boat. Her rudder will turn 90 degrees in either direction, mine is much less than that. Her rudder will turn beyond it's steering ability (if that makes any sense), to get maximum turning effect I would need to leave it in a similar place to where my own rudder simply cannot turn any more.
Her boat easily spins around it's own centre point (almost), yet my own boat still gets a significant amount of forward motion causing me to put it into reverse to make a similar manoeuvre.

[Naughty Cal]

Blackrose I suppose you have thought about this already. But what will happen if this new rudder alters your boats handling for the worse?

 

Why mess with something if it already works well?

[blackrose]

Blackrose I suppose you have thought about this already. But what will happen if this new rudder alters your boats handling for the worse?

 

Why mess with something if it already works well?

By that logic nothing that humankind had ever conceived or invented would have been developed or improved.

 

However, if it does make the handling worse then I will simply go back into the dry dock for a day at a cost of £75 and change the rudder back for the old one.

 

I don't see why that would be the case. Daniel and others have fitted rudders made by Yammanx and as far as I know everyone was happy with the results.

[blackrose]

Double posting

Edited May 3, 2014 by blackrose

[Timleech]

By that logic nothing that humankind had ever conceived or invented would have been developed or improved.

 

However, if it does make the handling worse then I will simply go back into the dry dock for a day at a cost of £75 and change the rudder back for the old one.

 

I don't see why that would be the case. Daniel and others have fitted rudders made by Yammanx and as far as I know everyone was happy with the results.

 

1) That's incredibly cheap!

 

2) I predict that, chunky though it is, sooner or later your stud connector and eyebolt will get bent.

 

Tim

[Paul C]

Total cost £75 for a wide beam dry dock is INCREDIBLY cheap - what's the secret?

[blackrose]

 

1) That's incredibly cheap!

 

2) I predict that, chunky though it is, sooner or later your stud connector and eyebolt will get bent.

 

Tim

 

Well the only possibility I can see of that happening is if I reverse the rudder into a concrete bank or another boat hits my rudder from behind. That's never happened in the 9 years I've owned the boat otherwise the fin on the top of the existing rudder that currently acts as a rudder stop would have got bent. How do you explain why that hasn't happened? I don't generally see Liverpool boats with bent rudder fins. The stern fender protects the rudder so it would have to be a fairly extreme impact to knock the fender out the way, snap the side chains holding the fender on and bend the rudder stop.

Total cost £75 for a wide beam dry dock is INCREDIBLY cheap - what's the secret?

 

No secret. That's what they charge. http://harvingtonmilldrydock.co.uk/

 

However, there is no water and no electricity and if the river floods the drydock floods too!

 

Apparently it used to be about 30 or 40 quid a day until fairly recently. £75/day isn't cheap in my opinion but it's ok if you just need a dry dock for a day. If you need your boat out for a week it's bloody expensive for no facilities. Last time I put my boat into a dry dock 4 years ago at Winkwell in Hertfordshire it cost me £280 for the week.

Edited May 3, 2014 by blackrose

[Timleech]

If it's 75 quid for each and every day, including the first, then:-

 

It's incredibly cheap for one day

Reasonable for two

Expensive for three

Ridiculous for a week.

 

Tim

[John V]

all very cheap!!!! drydock on Medway up to 27 metres £300 in...£300 per week...£300 out......

[DandV]

Whio had stops at 45degrees either side and you could stall the rudder initiating the turn but left the distinct impression that once the turn had commenced the rudder stops were in the way. Now we have stops at 60 degrees and once the turn is underway the stops can still obstruct a non stalled rudder.

I watch the prop stream constantly whilst turning and frequently have to resweep the tiller to re-establish laminar flow. You can actually feel a change in tiller pressure at stall.. The actual stall angle? I think it depends on power setting,depth of water, phase of the turn and direction of the turn relative to prop rotation as well as boat specific factors.

 

Don.