Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: WCW on August 25, 2006, 01:57:41 pm

Title: Model narrowboat which won't steer
Post by: WCW 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? 
Title: Re: Model narrowboat which won't steer
Post by: Voyager 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.
Title: Re: Model narrowboat which won't steer
Post by: Doc 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
Title: Re: Model narrowboat which won't steer
Post by: johno 52-11 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
Title: Re: Model narrowboat which won't steer
Post by: WCW 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

[Too Large - attachment deleted by admin]
Title: Re: Model narrowboat which won't steer
Post by: Colin Bishop 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.
Title: Re: Model narrowboat which won't steer
Post by: WCW 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. 
Title: Re: Model narrowboat which won't steer
Post by: Daryl 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
Title: Re: Model narrowboat which won't steer
Post by: Colin Bishop 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!
Title: Re: Model narrowboat which won't steer
Post by: johno 52-11 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 (http://www.nb-president.org.uk/photo/largedrawing.htm)

John
Title: Re: Model narrowboat which won't steer
Post by: WCW 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. 
Title: Re: Model narrowboat which won't steer
Post by: Doc 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
Title: Re: Model narrowboat which won't steer
Post by: Tester 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
Title: Re: Model narrowboat which won't steer
Post by: malcolmfrary 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.
Title: Re: Model narrowboat which won't steer
Post by: WCW 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
Title: Re: Model narrowboat which won't steer
Post by: MikeK 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
Title: Re: Model narrowboat which won't steer
Post by: Doc 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
Title: Re: Model narrowboat which won't steer
Post by: MikeK 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
Title: Re: Model narrowboat which won't steer
Post by: Martin [Admin] 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.....

Title: Re: Model narrowboat which won't steer
Post by: CAD2 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?
Title: Re: Model narrowboat which won't steer
Post by: BobF 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
Title: Re: Model narrowboat which won't steer
Post by: WCW 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
Title: Re: Model narrowboat which won't steer
Post by: rata453 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.
Title: Re: Model narrowboat which won't steer
Post by: WCW 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
Title: Re: Model narrowboat which won't steer
Post by: George Turner Models 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
Title: Re: Model narrowboat which won't steer
Post by: WCW on October 13, 2006, 09:52:54 am
To counteract any effects of the extra weight from the internal strengthening, I have taken the lead-acid battery out (1300g) and replaced it with 2 7.2V nicad packs (800g).  This makes the boat weigh the same as your one without internal reinforcement.  When sailing it at the lake on a day with no wind or chop on the water, it still steered just as badly.  From this I don't think the weight is the problem.  The servo is fixed by a wire clip, it was attached to the servo when I posted the boat to you. 

I hope to get to the Warwick boat show, if I do I will bring the narrowboat and demonstrate the problem to you. 

Regards,

WCW
Title: Re: Model narrowboat which won't steer
Post by: George Turner Models on October 13, 2006, 11:46:06 am
Look forward to meeting you.

Sharon
Title: Re: Model narrowboat which won't steer
Post by: tigertiger on October 14, 2006, 03:24:43 am
Look forward to meeting you.

Sharon

Sharon, WCW,

Please let us know the outcome.
From this forim I can see that may people go the 'non-standard' route. There may be a useful lesson, even if it is a simple one.
Even if there is no clear resolution, I would be interested to hear.
Title: Re: Model narrowboat which won't steer
Post by: malcolmfrary on October 14, 2006, 10:41:43 pm
It might be a silly question after all this time, but I've just had another look at the picture at the start of the thread - how fast is it going?  In the picture the water looks very busy, and I would assume that a canal boat would proceed at a fairly leisurely pace. 
Title: Re: Model narrowboat which won't steer
Post by: WCW on October 15, 2006, 10:04:49 pm
The narrowboat is sailing quite fast in the photo, it was another club member sailing it while I took photos.  When I've sailed it it's mostly been at a slow speed, slightly faster than a scale 4mph. 

Regards,

WCW
Title: Re: Model narrowboat which won't steer
Post by: George Turner Models on October 17, 2006, 01:26:37 pm
In the circumstances George and I have decided to give WCW a full refund for the price of his kit as he is obviously not happy with the handling of his boat. I can only re-emphasise that this has been the only complaint with all the kits sold & we have done our utmost to rectify the situation.

Look forward to seeing you all at Blackpool, please don't spend all your money on John's stand but share it with us. ;D ;D

Sharon.
Title: Re: Model narrowboat which won't steer
Post by: Martin [Admin] on October 17, 2006, 05:56:29 pm
Just to prove the point, this is Georges model I tested at the Ellesmere show.....
http://www.modelboatmayhem.co.uk/wwwpics/PICT1396.MOV  (http://www.modelboatmayhem.co.uk/wwwpics/PICT1396.MOV)
( Quick time 10.2 Meg -  )

Martin
Title: Re: Model narrowboat which won't steer
Post by: WCW on October 18, 2006, 04:36:48 pm
Dear Sharon,

Thank you very much for the offer of a refund for my narrowboat kit.  Your help with the steering problem has been useful, many thanks.  The video Martin posted shows one steering a lot better than mine does. 

Regards,

WCW
Title: Re: Model narrowboat which won't steer
Post by: Stavros on October 18, 2006, 11:40:51 pm
WCW this might be a silly question but have you considered changing the rudder servo as I have had a similar probelm with a tug,it was nicknamed the drunken sailor by the lads at the club!!!!bloomin comedians.Try it as mine was allright on the bench,rudder was allways straight when it came back from sailing but would it go in a straight line no way it had a mind of it's own,try it,it could be the problem,if it is please throw it as far as you can or alternatively frame it and present it to Sharon with a bouquet of flower ;) :D
Title: Re: Model narrowboat which won't steer
Post by: WCW on October 30, 2006, 01:58:30 pm
Changing the servo had no effect unfortunately.  Thanks for the suggestion though. 

WCW
Title: Re: Model narrowboat which won't steer
Post by: Stavros on November 07, 2006, 11:34:16 pm
Paul good tip that one just set up yaucht with one set up changed at the lake due to other probs sent yaucht out could not understand for a second whyu it did not want to sail in st line,brought it back to see thta rudder throw was different wiht the new set,felt a right plonker(Welsh druid need not reply!!!!!!!!!!!!)
Title: Re: Model narrowboat which won't steer
Post by: tobyker on November 09, 2006, 11:59:36 pm
Strange. Have you checked the fore and aft trim of the boat? With a long flat bottom she won't steer if she is at all down by the bows, and this could cause her to swing either way. I'd even try a bit of ballast to get her down by the stern a bit, to see what effect that has.
Title: Re: Model narrowboat which won't steer
Post by: Daryl on November 10, 2006, 08:51:27 am
This is of no help but last weekend in the first round of our winter sereis steering competition one of our members had a GT Narrow boat and had nearly a clear round (10 obstacles). It steered very well, daft question but did you deveate from the instructions?
As with the above post my colleagues boat was trimmed level, I did mention to him about this post and he was mystified.

Daryl
Title: Re: Model narrowboat which won't steer
Post by: WCW on November 12, 2006, 10:05:13 am
Thanks for the fore-and-aft trim idea tobyker.  My boat floats level but digs the bows in when going along.  I'll trim it bow up and test it to see if it improves the steering.  It may be a while before I can test this though as the lake I sail on has been drained to be cleared out. 

psships, I'm afraid I can't afford a computer radio, I'm just using a Hitec 27MHz Ranger 2 set. 

Daryl, I added a plasticard framing to support the battery but otherwise it is as instructions.  The extra weight of the framing is compensated by using a smaller battery. 

Martin, I sadly won't be at the International Model Boat Show as it's a bit far to travel. 

WCW
Title: Re: Model narrowboat which won't steer
Post by: EXBoat on November 12, 2006, 10:24:44 am
It's all down to the torque of the motor, the boat will turn in the opposite direction to the rotation of the motor, you adjust the rudder on it's shaft until you get the boat running straight.
the trim control on the radio control system may be enough to cure the problem.

EXBoat
Title: Re: Model narrowboat which won't steer
Post by: tobyker on November 12, 2006, 11:59:57 pm
WCW, your description of the bows digging in confirms my view. Although I've not seen the prop shaft angle, I reckon this may be pushing the bows down, and making the boat unsteerable. Most long keel boats are designed with a bit of stern drag. I know that if i put my heavy bro-in-law in the bows of my canadian canoe I can't steer it at all - get him to sit a bit further back and she goes fine. You may have to opt for a more scale ie slower speed, involving less upwards thrust - but by all means try a bit of weight in the stern first. Good luck.
Title: Re: Model narrowboat which won't steer
Post by: Abuelo3 on November 13, 2006, 10:41:20 pm
Hello from Veracruz, México
Did you put some Resistances at the motor in order to not have "electric noise"  :oat the radio receiver, It is the diameter of the propeller larger than the length of the ruder.

best regards.
Title: Re: Model narrowboat which won't steer
Post by: wombat on November 15, 2006, 11:13:03 pm
Hi WCW,

Watching "Narrowboat Afloat" on Real-Time, all the narrowboats seem to be running stern down - the bows seem to be 6" to 9" higher than the stern

Tim the Wombat
Title: Re: Model narrowboat which won't steer
Post by: Malc Reade on November 15, 2006, 11:34:19 pm

Tim

Funny you should mention that..

We saw a narrowboat on a low-loader in transit on the way down to the Warwick show last week, and it had certainly been floating aft-down by the amount that you mention in your post judging by the very obvious water line.

It might be a solution to this long running problem?

Regards, Malc


Title: Re: Model narrowboat which won't steer
Post by: andywright on November 16, 2006, 08:07:08 am
All boats steer better slightly bow up, bow down and they are like a round log. Water depth also has a bearing on this matter, though I don't think at model size we have to worry about it. Heavy weights ie batteries need to be as low as possible otherwise when turning the vessel will tend to heel to the outside of the turn, especially a displacement type craft, this does not apply to fast boats.
Title: Re: Model narrowboat which won't steer
Post by: Scottie on November 18, 2006, 07:59:36 pm
I had exactly the same problem with my ro/ro ferry although my set up was different. I have twin motors. props and rudders. At first I made rudders to 'scale' according to the plans and she wandered all over the lake just as WCW's narrowboat is doing.

So, I hear you all say, what was my solution?

BIGGER RUDDERS!!!!

I made two new rudders at twice the area of the originals - longer front to back and only slightly deeper than the first ones. She now sails in a straight line without any messing.

This may or may not cure your problem but it did for me.

Scottie
Title: Re: Model narrowboat which won't steer
Post by: wombat on December 12, 2006, 09:49:00 pm
Working on my narrowboat design, another though occurred to me.

If you have the weight concentrated at the stern and the bow, the whole thing is effectively a dumbell. With a long, narrow hull, this is more acute. The whole thing will be unstable and will tend to oscillate under steering

Tim the Wombat
Title: Re: Model narrowboat which won't steer
Post by: HS93 (RIP) on December 12, 2006, 10:05:53 pm
Has anybody seen the program on discovery home with Alan Herd ,his boat has a permanent list to one side ,once you notice it you cannot keep noticing it  Peter
Title: Re: Model narrowboat which won't steer
Post by: tobyker on December 12, 2006, 10:06:33 pm
I think the mass centralisation thing applies more to bikes and cars which rely on friction grip at the ends for roadholding. In boats which sit in rather than on their operating medium, the shape of the immersed portion, rocker and drag probably have more influence. If you were dealing with a very fast fin keel sailing boat, you might get a bit more speed in coming about if you kept the ends lighter, and this may also be desirable to reduce pitch in a fine ended craft. For narrow boat steering at scale speeds, I would venture that some keel drag and keeping the weight low are probably the essentials.
Title: Re: Model narrowboat which won't steer
Post by: Colin Bishop on December 12, 2006, 10:39:07 pm
A shallow lake and wheels would probably cure the problem....

Seriously, the distribution of ballast will affect the steering characteristics although, as has been pointed out, it is by no means the only, or even the most predominant influence, depending on the type of hull and the position of the power source. No keel means that a boat is likely to "skid" in the turn. A long keel boat will tend to steer a straight line ahead but be a pig to steer in reverse. A central keel will make the boat more sensitive, possibly excessively so, so you have to apply constant helm corrections. As far as weight is concerned it's best to either concentrate it amidships or more or less equally along the length of the hull. If it's at the ends, which would be pretty unusual, then it would adversely affect steering. A balanced or semi balanced rudder is usually better than the pintle hung variety and of course, if it is directly in the propwash then steering will be much more positive. My previous full size yacht had the outboard slung on the transom alongside the rudder which meant that you had no control until the boat was making appreciable headway either forward or astern which could make things difficult at times. My present boat has the outboard in a well just forward of the rudder which makes it much more responsive. You do however have to watch for the stern coming out as the boat turns as she pivots around two thirds of her length from the bow. It's all too easy to be watching what the front end is doing without realising that the stern is about to clout the boat in the adjacent berth!

All this presupposes a flat calm. Introduce the effect of windage and it all gets even more complicated!
Title: Re: Model narrowboat which won't steer
Post by: boatmadman on December 12, 2006, 10:51:11 pm
Working on my narrowboat design, another though occurred to me.

If you have the weight concentrated at the stern and the bow, the whole thing is effectively a dumbell. With a long, narrow hull, this is more acute. The whole thing will be unstable and will tend to oscillate under steering

Tim the Wombat

Wombat, what you describe is known as 'hogging' of the hull. probably not a problem in a model, but in real ships leads to fracture of the hull and often loss of the ship. Having said that, its always best from a stress point of view (mechanical not mental) to have weight evenly distributed along the boat.
http://www.worldwideflood.com/ark/hull_calcs/wave_bm1.htm

this is interesting!

Ian