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Author Topic: Model narrowboat which won't steer  (Read 15940 times)

WCW

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Model narrowboat which won't steer
« on: August 25, 2006, 01:57:41 PM »

I've built a George Turner Models narrowboat kit, it built well but when I put it in the water it won't go straight.  With the rudder central it turns to the right.  So I manage to get it going straight by steering it to the left.  It is just about steerable like this, but soon after it starts turning to the left with the rudder straight.  I got out of the water in a zig-zag fashion and had a good look at it.  The propeller shaft is straight, but from testing in the bath it went better with a deeper rudder.  So I went back to the lake, and no improvement, still wandering.  While reading a 30-year old Model Boats article on building an aircraft carrier, the builder said this wandered until he deepened the rudder and put a strip of 10mm square wood underneath as a keel.  I glued a keel on the back quarter of the boat (so it didn't foul the stand), went to the lake and it still was just as bad. 

Has anyone had this problem with a boat, and if so, how did you fix it?  Or even any ideas for what to do please? 
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Voyager

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Re: Model narrowboat which won't steer
« Reply #1 on: August 25, 2006, 02:36:34 PM »

Can you post some pic's of the rudder set-up of your boat, might be able to tell something by that.


Voyager.
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Doc

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Re: Model narrowboat which won't steer
« Reply #2 on: August 25, 2006, 03:00:43 PM »

WCW,
I've had boats with erratic steering before (ah, still do to some extent).  Part of it is in the design, part is just how 'scale' do you want it to be, cuz water doesn't scale down at all.  One 'biggy' is check for 'sloppiness' in the rudder linkage.  More 'free-play'/'sloppyness', more erraticness.  A rudder ought to be sort of close to the prop, in the direct flow of the water from the prop, and bigger is usually 'better', sort of.  Posting a picture of what is there now is a good idea.  Gives us more 'room' for guesses.
Good luck!
 - 'Doc
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johno 52-11

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Re: Model narrowboat which won't steer
« Reply #3 on: August 25, 2006, 04:20:43 PM »

WCW

Is your problem down to side paddle by the Prop. Narrow boats have quite large slow reving props if the prop on your model has been scaled down then you may be getting an effect off this. Dose your boat steer right until its upto speed then go straight. if you put it in reverse dose it steer left until its moving backwards. As with Real boats its easier to turn a boat round one way than the other.

John
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WCW

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Re: Model narrowboat which won't steer
« Reply #4 on: August 25, 2006, 05:06:36 PM »

Attached are 2 shots of the prop setup.  If they aren't clear enough I'll have another go. 

Doc: I understand that boats don't go dead straight, but this one turns 8 foot diameter circles with the rudder straight ahead.  And it will do this in either direction while going along.  There is a bit of slop in the rudder linkage, about 3 degrees of movement. 

John: The boat will steer either right or left up to speed, and when at speed it still does it, just the turns aren't quite as sharp.  I haven't tried it much in reverse but it doesn't go straight either.  It is easier to turn round one way than the other, but while on the water one minute after pulling right it will be pulling to the left. 

The bit I don't understand is why it will turn either way while going along.  If it turned one way I could set the rudder centre over to stop it, but I can't do this with it turning either way.  It does heel over when it is wandering noticeably. 

WCW

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Colin Bishop

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Re: Model narrowboat which won't steer
« Reply #5 on: August 25, 2006, 05:41:16 PM »

Some hulls are just directionally unstable, i.e. it doesnt take much for them to diverge from the straight line in either direction. One of my models of an early liner suffered from the same problem. If this is what is causing it then it might benefit from a small keel along the full length of the model, the aft section you have already fitted may not be enough. If you could fit a temporary keel using a couple of mounting points on the bottom of the hull you could experiment a bit.
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WCW

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Re: Model narrowboat which won't steer
« Reply #6 on: August 25, 2006, 08:24:22 PM »

A full-length keel sounds a good idea, I'll have to knock one up to try it.  Do you have any idea of the depth I'd need?  The boat's 24inch long and 5inch wide. 
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Daryl

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Re: Model narrowboat which won't steer
« Reply #7 on: August 25, 2006, 08:30:54 PM »

This is no help what so ever but a fellow club member has one of these and he sails it regularly at Yate. I can comfirm it does  go in a streight line. Alas i don't know if he has deviated from the kit, but changing the prop is likley.


Daryl
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Colin Bishop

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Re: Model narrowboat which won't steer
« Reply #8 on: August 25, 2006, 08:38:06 PM »

Quote
A full-length keel sounds a good idea, I'll have to knock one up to try it.  Do you have any idea of the depth I'd need?  The boat's 24inch long and 5inch wide. 

If it's going to work at all then half an inch should do it. Daryl has a point about the prop but I would have thought that if the prop is the problem the boat would always tend to go the same way. A smaller prop running faster would reduce the "propwalk" effect though. Another possibility could be the distribution of ballast in the hull. If the weights are at the ends the tendency to turn will be increased. If the weight is concentrated amidships or just aft of amidships then the model should be more responsive to the helm. Hydrodynamics can be a complicated business!
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johno 52-11

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Re: Model narrowboat which won't steer
« Reply #9 on: August 25, 2006, 09:04:32 PM »

Attached are 2 shots of the prop setup.  

 

WCW

I think part of your problem may be that the prop is in the wrong place. The prop should be in the swim under the counter and not going below the bottom of the boat. there should also be a lower bearing on a rail that runs under the prop. take a look at this diagram of President http://www.nb-president.org.uk/photo/largedrawing.htm

John
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WCW

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Re: Model narrowboat which won't steer
« Reply #10 on: August 25, 2006, 09:56:04 PM »

I've got a prop of the same diameter but a finer pitch, would this have the same effect as a smaller prop at the same pitch?  If the keel doesn't work then I'll get a smaller prop to try. 

The ballast is a 1.3kg lead-acid battery, in the hold just forward of amidships.  There's nothing much else heavy as the boat's designed so that the battery ballasts it down to the waterline.  So it can't be this at fault. 

I've looked at the narrowboat diagram, but from sketches I've seen of their hulls they taper underwater down to the propeller so that water can flow to the prop unhindered.  The hull of my model is flat across the stern where the propshaft comes out, if I put the prop up under the counter there wouldn't be any water flow around the forward side of the prop.  I can't move the rudder either as it is inaccessible under the counter stern. 
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Doc

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Re: Model narrowboat which won't steer
« Reply #11 on: August 26, 2006, 03:47:29 PM »

"same diameter but a finer pitch, would this have the same effect as a smaller prop at the same pitch?"
Yes, that's what it amounts to.  It'd also be slower than the original prop, but that just means higher motor speeds for the same resulting speed as the original. May, may not be a good idea, beats me.
I think the longer keel would be a pretty good idea.  Shouldn't hurt at any rate.  Tightening up the 'sloppiness' in the linkage is/can be a good idea too.  The 3 degrees wouldn't be that objectionable in a larger boat, but in a smaller one it certainly can be.  A 10 degree 'slop' in a full sized boat wouldn't make a lot of difference, but in a boat less than full sized it gets worse as the size in reduced.  (Does that mean angles get bigger as they get smaller?  Just a matter of degree?)
 - 'Doc
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Tester

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Re: Model narrowboat which won't steer
« Reply #12 on: August 26, 2006, 04:38:00 PM »

Why not speak to George Turner, he has allways seemed helpful to me.

By the way there was no mention of steering problems in the Model Boats review.

Richard
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malcolmfrary

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Re: Model narrowboat which won't steer
« Reply #13 on: August 26, 2006, 09:07:30 PM »

A mate who was given a narrowboat hull had great problems until he rebuilt the back end.  His steering and moving problems were caused by the underwater shape not allowing a proper flow of water over the prop, and cured by a very extensive re-shaping.  Looking at the pictures, it seems that there is a large flat vertical area in front of the top half of the prop, and this might well give some handling peculiarities.  Just an opinion as I have seen some of Goerges other products, and they do work really well.
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WCW

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Re: Model narrowboat which won't steer
« Reply #14 on: August 26, 2006, 09:37:24 PM »

I fitted a 15mm deep full length keel this morning and took it for a sail.  It still behaved just the same, turning in both directions.   I couldn't change the prop at the lake so it'll have to wait to next time. 

I'll ring George Turner next week to see what he advises.  The review in Model Boats said it sailed really well around a steering course, came 2nd in a national competition qualifier.  So there must be something wrong!!!  The shape of the stern does look strange but as the review boat steered fine it should work. 

WCW
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MikeK

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Re: Model narrowboat which won't steer
« Reply #15 on: August 27, 2006, 09:43:32 AM »

As Malcolm says, it looks like the top half of the prop is going to be stalling as it has a vertical surface so close to it and blocking the flow past.

MikeK
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Doc

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Re: Model narrowboat which won't steer
« Reply #16 on: August 27, 2006, 03:02:09 PM »

I wonder.  Just for 'grins' try reducing the length of the rudder (not depth, but length).  That would increase the boat's turn diameter too, though.  But, the 'floppiness' due to the linkage 'play' ought to have less affect.  On second thought, try reducing the depth of the rudder too, that way only the water flow caused by the prop would affect the directional control.  I'm to the guessing stage, so take it for what it's worth...  Maybe I'd better just be quiet.
 - 'Doc
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MikeK

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Re: Model narrowboat which won't steer
« Reply #17 on: August 27, 2006, 05:18:03 PM »

I wonder what would happen if you just gave it a good PUSH and see how it steers under its own momentum and maybe eliminate the prop from the possible causes.

MikeK
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Martin [Admin]

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Re: Model narrowboat which won't steer
« Reply #18 on: August 27, 2006, 09:16:18 PM »

I had a sail of George own model at the Ellesmere show today.
I couldn't believe it, it tuned within 1 1/2 lengths!!!
( The "anti swan "speed was also very impressive! )

Don't really know what to suggest.....

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CAD2

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Re: Model narrowboat which won't steer
« Reply #19 on: August 28, 2006, 02:52:07 PM »

There's no logical reason why a narrow-boat should heel when turning, so I wonder if that huge and deep rudder is being buffeted about by the turbulent flow from the prop. Your adding to its depth would only exacerbate such a problem. As Colin Bishop says, hydrodynamics can be a very complicated subject. I'd advise you to go back to the original rudder shape and recommended prop before you introduce any more unfathomables into the equation! If it works for the manufacturer then you've clearly done something "non-standard".
Another thought - some servos don't return to an absolute neutral i.e. the output disc will stop slightly short of dead centre, the side it stops depending upon which direction it is turning at the time. I had this problem with standard Futaba servos and only solved it by changing to HiTech gear. With a rudder that wide you wouldn't need much drift from centre to cause problems. Check this, then change your connections from tiller/pushrod and pushrod/servo to use ball-and-cup links. There's no slop in these whatsoever.
Finally, could it be that your initial problem might have been the position of the Rx aerial causing glitching when the boat is in the water? If this was the case then your experiments with the rudder etc might only have made it worse.
Good luck! CAD2
Last thought - the blindingly obvious one - are you sure that great big battery isn't moving from one side to the other?
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BobF

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Re: Model narrowboat which won't steer
« Reply #20 on: August 29, 2006, 08:56:04 AM »

Hi WCW,

As already stated, the prop shaft angle is unusual for a Narrow Boat, and would direct the water flow away from the rudder.

The type of rudder fitted is some times called a Barn Door Rudder. They can cause a problem, with water bleeding over the top and bottom of the blade, and reducing the blade effect. Quite often in full size shallow draft  craft, a plate is fitted along the top and bottom of the rudder to direct the flow towards the stern. When viewed from the back of the rudder, it looks like this   I

Bob
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WCW

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Re: Model narrowboat which won't steer
« Reply #21 on: August 30, 2006, 09:13:46 PM »

I rang George Turner, he offered to sort out the problem if I posted the narrowboat to him.  Very good service!  I'll get it off to him tomorrow, hopefully it won't be too long until it's working properly. Many thanks for your help.

WCW
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rata453

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Re: Model narrowboat which won't steer
« Reply #22 on: October 04, 2006, 04:00:17 PM »

WCW,
         
           I used to build full size narrowboats for a living and had I built one to the design of your model it would not have moved through the water. It definitely wouldn't steer backwards either! I suggest that the only way to cure this would be to put a proper swim on the hull. On a full length working boat of 72ft long, the swim can be up to about 16 ft long, finishing with as sharp an edge as possible. On my model steam tug I fitted two long parallel keels two thirds of the length of the hull(about 10mm deep) just to help stabilise it.  regards, John.
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WCW

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Re: Model narrowboat which won't steer
« Reply #23 on: October 10, 2006, 10:05:29 PM »

I got my narrowboat back from George Turner, with a refund of the postage.  He said there was nothing wrong with it at all, it sailed just the same as his ones.  I put it in the lake and it still wouldn't steer straight consistently.  I took a video of how it sailed and sent it to GT, haven't had a reply from him.  He did comment that my boat was heavier than his, I'll try fitting a smaller battery so it floats higher.   At the moment the narrowboat's sitting around with nothing doing, I've left it to finish off a Customs launch from Model Boats plans. 

rata453, what you're suggesting sounds like my only option unless the lightened boat works.  I'll have to pluck up courage to cut up the hull to taper the stern underwater to the prop.  Would the taper section curve in or be straight? 

Regards,

WCW
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George Turner Models

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Re: Model narrowboat which won't steer
« Reply #24 on: October 11, 2006, 01:40:37 PM »

Unfortunately at present we have been inundated with orders so have not had the time to watch or reply personally to 'WCW'. May I firstly state that of the hundreds of this model we have sold he has been the first person with any problem.

Obviously we have tried to help, but when people deviate from the instructions which we know to work then they are entering uncharted territory. George's boat without battery & with all figures and resins weighs 610 gms, the boat in question without battery & only 1 figure 1100gms - 80% heavier.

Further as everyone who knows George will attest -  George would not sell a kit which did not work to his extremely high standards. Please also refer back to posts 7, 12, 18. We will be attending the Blackpool & Warwick shows this year & the only thing further I can suggest is that WCW attend a show so we can help him out on a face to face basis with him steering the boat on the water. Further our kit will be available for all those interested to have a go.

From George's test the prop was not the problem or the prop shaft angle, the shape of the stern is fine as with all our other narrow boat kits which we have sold. A further point which may help solve the problem is that a rudder extension has been attached to one side of the rudder supplied in the kit, this is not according to build iinstructions.

I will attach part of our response to the person in question which may deal with a few of the mentioned points and be of further help.

On receiving your n. boat the first thing that struck me was the high class of modelmaking & attention to detail. On looking inside again a first class job but perhaps very over engineered with layers of plastic stuck to the sides and bottom making it very strong but heavy. This is somewhat unnecessary - I have thrown a narrow boat (without battery) 30 feet down the garden, don't ask why! Apart from a figure and resin part coming off the only damage was to paintwork. Also the prop shaft comes out low & the rudder is lower than on my boat, with an extension fitted to 1 side.

The 1st test was in the bath, I fitted the recommended 6v 7ah jell cell into the battery compartment, once again very well made but unneccessarily over-engineered, switched on, checked trim, placed onto water, went fine. 2nd test took boat to local park, switched on put boat on water, with a little trim adjustment off she went, seemed to steer strangely - found servo sliding out of box, pushed in firmly tried again - no real problems.

These boats being long & flat bottomed are prone to cross winds & currents but this can be sorted with trimming. With this sort of craft you will have to change trim to suit wind direction.

My conclusions are that I canot find any major problems, you do have to adjust trim as you sail but no more than on my boat, advice re checking servo, trim, range check on radio. Plus mention of weight difference - 80%.

It should once again be stressed that a heavy boat will not steer as well as a boat built to the recommended instructions.


Many thanks to all those who have offered advice on this topic and apologies for such a long post.

Sharon
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