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Author Topic: Aziz rudders  (Read 5181 times)

NFMike

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Aziz rudders
« on: August 22, 2012, 09:31:07 PM »

I'm building the Model Slipway Aziz and I think the instructions/diagram has the wrong centres for the rudders. It says 124mm, but the prop-shafts are 129mm centres.
Has anyone built this kit or heard of this 'problem'.

I did e-mail MS about it a couple of days ago but they've not come back at all - possibly they are on holiday.

Tug-Kenny

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Re: Aziz rudders
« Reply #1 on: August 22, 2012, 10:31:27 PM »


The rudders are offset to allow removal of a prop, should you need to, in the future.

Myself, I prefer then in line for better drive control, but that's just me.

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NFMike

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Re: Aziz rudders
« Reply #2 on: August 22, 2012, 11:59:22 PM »

The rudders are offset to allow removal of a prop, should you need to, in the future.

Myself, I prefer then in line for better drive control, but that's just me.


Ah. So its a kludge.
I'm not using their props (I have a pair of 4 Blade Kort/Kaplan props) so it might not be enough to get them in and out anyway.

As it happens I'm working towards making my rudders removable, as I don't like having moving things like that 'permanently' fixed. So that will solve the prop removal issue too if I put them on drive-centre.

Does it actually make a difference to control? As long as they are 'balanced' in having the same offset, and not stupidly far off centre, I'd have thought the effect would be very tiny.

While I'm here, what is the convention for handing of props on twin screw vessels?
I'd guess each prop would spin with the top blade travelling from ship centreline outboard when going ahead. (I'm avoiding using LH/RH as I gather there are two conventions around at present.)

Tug-Kenny

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Re: Aziz rudders
« Reply #3 on: August 23, 2012, 10:12:33 AM »


Yes, there conventions to this problem.  Myself, I like to thrust the water down between the centre line of the boat.  That way, the current of water meets the depths and rises again, whereas the other way causes the water to rise upwards against the least resistance away from the rudders and creates surf.      %)

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malcolmfrary

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Re: Aziz rudders
« Reply #4 on: August 23, 2012, 10:22:35 AM »

A kludge? No way.  Just a well thought out method using the components supplied to make servicing easier.  Changing the specification means that you have altered the design, and will need to write your own instructions.
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NFMike

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Re: Aziz rudders
« Reply #5 on: August 23, 2012, 12:32:31 PM »

Got a reply from Model Slipway this morning - they had been away.
"All measurements in the instructions are correct, there is no mention that the shafts should be central in the A frames.
Have a dry run - both assemblies together on the upturned hull; you will see that the A frames (with shafts) can be "rolled" in the mounting slots until perfect alignment is achieved.
"
If that means what I think then the shafts could end up not parallel to the boat centreline. They don't mention getting props in/out.

A kludge? No way.  Just a well thought out method using the components supplied to make servicing easier.  Changing the specification means that you have altered the design, and will need to write your own instructions.
Well, they have been doing this a bit longer than me, so I'm sure it would work, but it is still seems kludgy. I just feel that when the model is being viewed out of the water this is a place that will get looked at (especially with nice brass props) and that offset will be very obvious. I'd think increasing the Kort/rudder distance a bit instead would be less noticeable, but that obviously depends how much clearance would be needed.

Anyway, as I say, I am making my rudders removable, so will fit them and the shafts as near straight down the 129mm line as I can. From the MS instructions it seems there is quite a bit of wiggle available to get the alignments 'right', whichever way it's done.

NFMike

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Re: Aziz rudders
« Reply #6 on: August 23, 2012, 12:34:41 PM »

Yes, there conventions to this problem.  Myself, I like to thrust the water down between the centre line of the boat.  That way, the current of water meets the depths and rises again, whereas the other way causes the water to rise upwards against the least resistance away from the rudders and creates surf.      %)



Hmm. I thought the opposite as your convention might tend to pull more air from the surface in rough water. Though probably less of an issue with Korts round the props.

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Re: Aziz rudders
« Reply #7 on: August 23, 2012, 01:18:43 PM »

I read "kludge" as something which is inelegant, inefficient, clumsy or patched together. As the guy who drew the plans and wrote the instructions for Aziz - according to detailed directions from Lawrie White - I can't say I'm flattered by such a description of my work. If you think that the instructions are wrong (or "kludged") then by all means feel free to follow your own, but please don't use such derogatory expressions to describe something which you hadn't considered from all aspects.
Dave Milbourn
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malcolmfrary

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Re: Aziz rudders
« Reply #8 on: August 23, 2012, 01:42:15 PM »

If anybody could spot a 2.5mm symmetrical offset under the stern of a boat that size, good luck to them.  They would probably view it as a valid solution to making life easier down the line.  Forethought rather than panic.  Of course, changing the makers design to use Korts will involve a change to the geometry.  Did you actually tell them that you had changed the spec?  If not, they would be offering advice to result in a boat built to the original specification, not the home redesign.
Whether the shafts end up parallel to either the center line or each other is probably a function of the builder.  Do the instructions mention anywhere that the inside ends of the shafts should be 129mm apart?

Definition of kludge - "An ill-assorted collection of poorly matching parts, forming a distressing whole."  Designing a layout to allow the simple removal of a pair of 4mm shafts by not having the rudders in line with those shafts is more an elegant solution than a distressing whole.  I say this as a long term bodgineer.  It could also be the case that this was a feature of the original.
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DickyD

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Re: Aziz rudders
« Reply #9 on: August 23, 2012, 02:13:58 PM »

I read "kludge" as something which is inelegant, inefficient, clumsy or patched together. As the guy who drew the plans and wrote the instructions for Aziz - according to detailed directions from Lawrie White - I can't say I'm flattered by such a description of my work. If you think that the instructions are wrong (or "kludged") then by all means feel free to follow your own, but please don't use such derogatory expressions to describe something which you hadn't considered from all aspects.
Dave Milbourn
I think anyone who rubbishes Model Slipway kits should really get their brain in gear before putting it in writing.

Model Slipway and Dave Milbourn have excellent reputations in the model boat industry and are second to none. Their kits are excellent along with their instructions.

Maybe Mike should try some of the other kits on the market, it might open his eyes a little.

Who is going to notice a 2mm difference between the centres of the prop shaft and the rudder [handy when wanting to remove prop shafts.] when under the model.

We assume Mike will be putting his build [complete with photos] on the forum so we can see how its done.
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ACTion

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Re: Aziz rudders
« Reply #10 on: August 23, 2012, 03:25:37 PM »

That's a very big welcome back to the 7th Cavalry! Now keep calm and breathe deeply, Richard - we don't want all that hospital stuff yet again.
Dave M
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Bryan Young

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Re: Aziz rudders
« Reply #11 on: August 23, 2012, 04:46:19 PM »

Hi. In "real" life it isn't unusual for the props to be slightly out of line with the rudders. Parially due to the transverse thrust effect of the prop wash on the rudders. Also, there are many ships ploughing the ocean with twin screws and only one rudder. So that clobbers the notion that a rudder has to be in line with the centre of the prop.
Apart from any purely mechanical aspects, having twin screws greatly increases the ships ability to manouever (I think I spleed that wrong) Some ships have inboard rotating props, but the most common is outward turning.
If a ship had both props turning in the same direction (lets assume clockwise when viewed from aft) then the ship would permantently want to swing its bows to port. Which in turn means that the ship would have to have a permanent rudder bias to starboard. Not a simple problem for the ship driver or helmsman.
As far as the rudders being "in line" with the props doesn't seem to matter all that much. On most modern ships the rudder(s) are only effective when the props are wafting water over them. No good when the engines are stopped. On older ships with a different hull form, a single prop and single rudder then the rudder would work reasonably effectively when the prop was stopped...down to a couple of knots headway.  OK? BY.
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NFMike

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Re: Aziz rudders
« Reply #12 on: August 23, 2012, 06:13:25 PM »

Well I do seem to have stuck my foot in the hornets' nest.
Firstly I apologise to those who have taken offence at my 'criticism' of the instructions, particularly Dave Milbourn. My use of the word kludge was clearly inappropriate and I should have checked the dictionary.
I also had absolutely no intention of rubbishing Model Slipway kits and I apologise for any implication in that direction. I am quite happy with the kit which I bought in the full knowledge that it might challenge me in places. I bought it partly on the recommendation of others that MS will provide support.

I do however dispute the implication that one cannot question something like this just because the company has a good reputation. I have in the past queried things that have been long established to be told by the relevant authority "Oh yes, no-one's noticed that mistake before", so if I think it may not be right I try to check.

If the original Aziz had offset rudders then that is fine. If not then I will know that the things are 2.5mm off and it will bug me, even if it isn't obvious. Sorry, that's just me.

And in answer to your last comment DickyD, it is already being documented on my website at http://www.sol.me.uk/, though there isn't a lot there yet as I haven't got far - obviously.

ACTion

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Re: Aziz rudders
« Reply #13 on: August 23, 2012, 07:22:47 PM »

Mike
Your entitlement to question is not in dispute. What I objected to was the "kludge" word, which is demeaning and derogatory. I take a pride in my work and I find unjustified criticism hurts, especially when it's on such a public forum. Yes - nobody is perfect and mistakes are made, but Model Slipway take a lot of trouble to make sure their instructions are as free of mistakes as possible so that the relative beginner has the best chance of getting his model finished and on the water. That is why they have such a good reputation in the trade and with their customers. That said, having bought the kit you are free to interpret or ignore the instructions as you wish, but always bear in mind that the guy who wrote them has made at least one more Aziz than you have............and the guy who checked them has built another one.  8)

So, in answer to the only question you asked ("Has anybody built this kit or heard of this problem") I can say "Yes - I have built two models of Aziz and I can assure you that the instructions are correct and it is not a problem - or a kludge".
DM
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Stavros

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Re: Aziz rudders
« Reply #14 on: August 23, 2012, 07:26:46 PM »

And mwhy is it you have modifed the motors in your blog why not post your build up here so we can see how to build a model.I have built a couple of the MS kits and find them superb and the instructions second to none,clear and conscise and 100% Acurate with NO faults.


Dave
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malcolmfrary

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Re: Aziz rudders
« Reply #15 on: August 23, 2012, 08:22:25 PM »

Ahh, but, Dave and Dave, no instructions for a kit tell you  how to redesign it to use different hardware.  Anybody heading down that route has to do his own homework.  And converting from conventional rudders to Korts gives you a choice - move the props sternward to the pivot line of the Korts, or move the pivot line of the Korts to the vertical center of the props?
Was the real Aziz fitted with conventional rudders or Korts?  Is the move to Korts a deviation, or, as the great By Kapitan Bill Thomas would have said, "Well, these are not so much alterations as improvements!"?
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Stavros

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Re: Aziz rudders
« Reply #16 on: August 23, 2012, 08:37:02 PM »

Funny thing is Malc the Aziz allready has Korts and rudders fitted as std,so what improvement can be made to the running gear I really dont know.


Dave
,
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Colin Bishop

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Re: Aziz rudders
« Reply #17 on: August 23, 2012, 08:42:25 PM »

Just to stick a further oar in, so to speak; a lot of people don't fully understand how a rudder works. If it is in the propstream then of course the pressure of the thrust from the prop will bodily push the stern around but on sailing ships or paddle steamers this doesn't apply. Moving the rudder to one side alters the hydrodynamic configuration of the hull giving it what might be regarded as a 'banana' shape with the waterflow on each side of the hull at different speeds - not dissimilar to a aerofoil. This alters the balance of the hull in the water causing it to swing to one side or the other depending on the rudder position.

Model boats tend to rely on slinging water out to one side or the other to push the stern round by brute force which is not quite the way it happens with full size ships not fitted with thrusters.

Colin
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Bryan Young

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Re: Aziz rudders
« Reply #18 on: August 23, 2012, 09:27:20 PM »

Colin. Succinct as always.
Ages ago I made the point that if a real ship or a model is balanced correctly then the strin on the rudder would be negligible.
Shoving in strong servos etc. is not the answer. BY.
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irishcarguy

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Re: Aziz rudders
« Reply #19 on: August 24, 2012, 02:54:00 AM »

I am in the process of building Model Slipways Tamer lifeboat. I have already made some changes to the build not because I thought the design was wrong, it is not(I would not have purchased it in the first place) but because I had my own ideas on what might make it even better (probably not easy to do)That to me is part of the fun of the build. If I had a penny for everything I ever thought I could improve & didn't I would be retired now.Mike had a question & asked us if we could help, he also did approach MS but through circumstances beyond his control he did not connect with them. As Dave M said he had every right to ask, it was the tone that upset Dave,it felt like a put down. Mike has said sorry & I think he would like to move on, let us welcome our new member & make him feel we are really good guys which I believe we are. I am sure in due time when he feels more confident he will post his build for us to see & add another thread to the many that has made this forum in general a good place to belong to. Mick B.
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RJR

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Re: Aziz rudders
« Reply #20 on: August 25, 2012, 10:58:30 AM »

I find the Aziz handles perfectly As is !!! http://youtu.be/g4eOzmphcyY?t=2m17s
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Norseman

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Re: Aziz rudders
« Reply #21 on: August 26, 2012, 05:50:02 AM »

Mike has said sorry & I think he would like to move on, let us welcome our new member & make him feel we are really good guys which I believe we are. I am sure in due time when he feels more confident he will post his build for us to see & add another thread to the many that has made this forum in general a good place to belong to.

I think Mick put it really well. Also it's always easy to not quite get what you really mean across on a post especially with the odd word that has several connotations.

Dave
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