Model ship stability

[Gehr]

Hi! I will be fortunate if I get help from the experts in this forum. I have a model ship designed by myself. Its tug type about 3 feet long and 7 inches wide. Single screw. Made up of composite material. It is Radio Controlled. Without power it moves straight. On power due to propeller walk effect it should drift to one side according to propeller rotation. It does. But soon adapts a ZIG ZAG course. I really need some practical tip to overcome this problem. Why it is happening?

 

[GregLocock]

Add strakes?

or post much more detail

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[Gehr]

Greg dear, thanks for the response. The model is flat belley. I grew a keel after much experimentation when it was not following propeller walk effect with zero rudder. Zig Zag phenomenon occured after introduction of keel. This is what you mean by strakes? I shall post the details very very soon to make things more clear and to get rid of the problem.
Zahid

 

[Strong]

I noticed the zig-zag effect in several small power boats (14 to 18-ft) when going slow. Either going slower (no fun) or speeding up would eliminate the problem. I suppose you could try various hull appendages to alter flow along hull and rudder, but the effect may be dominated by vessel length to speed hydrodynamics, and therefore not easily changed. At least your vessel is model-size and easy to experiment with!

Walt

 

[Gehr]

Thanks Strong. I have been doing the experimentation by myself now(previously my boys were involved in it) I noticed that without rudder (to see if it affects) when propulsion is applied at slow speed (wights re-distributed, I place small weights to achieve the draught) zig zag movement converts to a port side turn after a few feets straight movement. I tried hard with weight re-distribution but in vain. I placed small strakes as suggested by Greg, they increased the straight movement further a foot or so. Does it require re-location of propeller shaft? I would be obliged if someone could lead me directly to the nature of the problem?
sincerely,
Zahid

 

[MikeHalloran]

So, you've built a model scow, and you're trying to make it duplicate a particular bizarre behavior of a full-sized, full-hulled boat? Why?

You think we can figure out what you can't, without providing us even a photograph of the hull?

We're not _that_ good.



Mike Halloran
Pembroke Pines, FL, USA

 

[Gehr]

Mike dear, yes its a modelled scow, built for study purposes. I shall show the hull pictures. I know people in this forum are very good.
Zahid