Lateral Stability Problem

[Peter Webster]

Hi All,
        I have just finished testing my new paddler, a 1 1/2 times version of Glenn Guest's last model "The Phantom". The problem I am having is a disturbing tilt to starboard when I am turning in either direction, once I straighten up it tends to lessen in effect but the only thing which levels the model is to come to a complete stop. this leads me to think it may have something to do with the motor, a 12v geared MFA 1:87 ratio 540 size and mounted east/west in the hull. The motor side is on the starboard side and the gearbox side is therfore on the port side. Am I right in assuming the motor placement is the cause and if so how do I cure it or could it be something else. the paddleboxes are open to allow air to escape and I have fitted a small, 1inch, keel with a lead ballast fitted but the problem still exists.
       HELP!!!
Peter Webster

[derekwarner_decoy]

Hi PD’s – "my new PC antivirus/anti everything" would not allow me to log in to respond so …..Peter -  I am not familiar with GG’s "The Phantom"……is the installed drive as per specifications?........if the 12v geared MFA 1:87 ratio 540 size and mounted east/west in the hull…. the  rotation of the motor rotor should have no dynamic effects on the vessel in the [port to Stdb] motion, but will have a theoretical effect [fwd to aft]…all things being equal  
   
The simplest example to this is when we connect a low voltage DC motor to a [voltage+current supply], the motor elements convert the electrical energy to spin the motor body and also advance from the set position?  
   
Post some detail of the vessel……..was it very BUSY in Melbourne today? with 27,125,357 visitors @ the F1?.................I was bending bits of  5/32” brass tube ……Derek

[oldie]

Peter, I am not an expert in this sort of thing, but is the centre of gravity of the motor/gearbox positioned in the centre of the beam of the craft, as the motor end is heavier than the gearbox end.   Oldie

[malcolmbeak]

Peter

I'm not sure if it will be of any help, but if you go to Downloads/magazines/The Model Engineer you will find a series of articles written in 1944. This guy had tremendous trouble with instability, but seems to have sorted it out.

Malcolm

[Eddy Matthews]

Does the model sit level when it's first placed into the water Peter?

If it does, then I can only suggest that the superstructure is too heavy for the hull, or that the paddlewheels/paddleboxes are to heavy... What is the superstructure etc made from? It may need to be built from lighter materials.

A few photos may help if you could post some?

[Peter Webster]

Derek - No it wasn't busy as we are used to it now plus while at the model boat lake you forget the rest of the world, as you know.
Oldie - Yes, I had counterbalanced the motor side but to no avail.
Eddie - Yes, the model sits beautifully level and stable and the ballast is fastened to the keel as well as in the bottom of the boat. The internal ballast is lead shot and the keel is of sheet lead. The superstructure is 1/16 balsa and is basically a box sitting on the deck. The boat performs the same whether the superstructure is on or off it. The paddleboxes are of 1/8 balsa sides and 1/16 sheeting on the curved section. It does not happen if I cut the engine when turning and the tilting ceases straight away when the model has straightened up, if turned with power on. I have checked out the lateral balance by using my test tank, before the wife caught me, by pushing down on either paddlebox till it was submeged tp the deck level and releasing and it righted itself instantly so it has me totally baffled, to put it nicely.
Peter Webster
PS
 I am wondering if it's because of the direction our water goes down the plughole as opposed to yours.

[Eddy Matthews]

Yep a real puzzle Peter.... It sounds as if your topweight should be light enough to be handled okay.

Is the model sitting at its designed waterline? I can only suggest removing some of the ballast and fitting a small temporary bulb keel as used on yachts but much smaller.... With that attached to the bottom of the hull it will give a much greater righting moment which may cure the problem. If you attach it with a couple of bolts it can then be removed for static display.

[Peter Webster]

Eddy, I have already done so but it still tilts on turning when under power.
Peter Webster

[Eddy Matthews]

Without seeing the model and having a real idea of the weight of the various components I only have two other suggestions Peter. First increase the depth of the fin (maybe 4-5 inches or so), and second, try fitting bilge keels to help stop the boat from heeling in turns.

[Peter Webster]

Eddy
         I think the bilge keels may be the answer as I had an almost same problem with my 6 ft
Graf Zeppelin and a discreet  increase in the torpedo bulges fixed the problem so I will try the
bilge keels on this one.
Thanks,  I will let you know and post some photos within the fortnight.
Peter Webster

[mjt60a]

could the starbd paddle be deeper in the water or the floats slightly bigger or angled differently causing it to 'dig in' ? (though to be honest I doubt it, I can't see why it would only affect the boat during turns... :?  ) that is what seems to happen on my PBM model when reversing the motor to slow down/stop...

[steamboatmodel]

Hi Peter,
One of the Members of Metro Marine Modellers, had a similar problem with his Mt. Washington.  Whenever he turned the boat the inside paddlebox appeared to stick giving the model a list to that side even after the rudder was returned to neutral. He solved it by incorporating a counterweight on a servo controlled swing arm.
Regards,
Gerald

[Daryl]

I had a similar problem with my Bohemia. What I found out was by watching the paddles as she sailed by I noticed water coming out of the front of the paddleboxes as well as the back. When the boat turned the extra drag and weight caused the boat to lean to one side.

I solved this by remaking the paddle wheels, alowing a 2-3mm gap between the hud and each paddle float. This allows the water to flow through and not get carried around the paddlebox like a water wheel. The boat was a bit slower but far more stable. The same effect could be made by drilling holes in the paddle floats as near to the hub as possible.

Just a suggestion

Daryl

[Eddy Matthews]

It's not a solution I've heard of before Daryl, but certainly worth thinking about....

[Daryl]

Hi Eddy,
It had us baffled for sometime until the chairman of our boat club mentioned he had a similar problem on a paddler he built a while ago. He asked us to sail her parrellell to the bank and watch to see if any water was coming out of the front of the paddleboxes, we were surprised to find there was a resonable amount being carried around the paddlewheel.

So my son after some thinking downloaded a design he found on here and it worked. Now no water is seen coming out of the front of the paddleboxes and it no longer leans when turning.

Might be a solution, worth looking at to see if it helps. The model we have is the Pelikan kit Bohemia and my son used the paddles supplied in the kit which caused the problems. Now he scratchbuilt a pair from instructions on here. Not bad for a lad of 14. I understand someone else on here as a Bohemia kit did they use the kits paddles which to use look like two yogurt pots glued together of Blue Peter.
Daryl