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Author Topic: DD Ripley  (Read 1906 times)

GG

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DD Ripley
« on: November 13, 2008, 08:28:17 PM »

Had an idea about improving the stability of slim models.  A destroyer seemed to be ideal and one based on USN vessels built in the 1930's was tempting (if only to prove that the US Navy in WW2 did not consist of just the Iowa class battleships and Fletcher class destroyers that modellers seem to favour).
A scale of 1/144 was used (as usuall!) to give a model length of 28 inches (71 cm) and a weight of just over 2 lb (1 kg).  A single 385 motor pushes it along at over 3 ft/sec (1 m/s), less than the dynamic scale speed but it looks good.  The camouflage scheme can be a little too effective at times.
I built this model expecting it to roll alarmingly and thus be ideal for testing my idea.  Alas, despite the modest beam (3 inches - 75 mm) it turned out to be quite stable.  If I forget about adding any top weight it gives me an excuse for building another (hopefully less stable) model.
GlynnG
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andrewh

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Re: DD Ripley
« Reply #1 on: November 14, 2008, 08:53:52 AM »

Glyn,

Thanks for the picture and information - do you seriously tell me there were other ships in the USN? :}

I'm sure that you will give us the info on your stability idea as it develops - my friends Blockade Runner is beautiful (and well made) but hideously tender - I am trying to get him to fit a simple drop keel just so that he can get some time on the water.

Please take this as a "Permanent invitation to inform and declaration of pre-approval of your Ideas" type of reply

I believe that weight is always one of the elements in narrow-ship stability - gel cells and nicd (Nimh) are fairly heavy, but lipos and li-ion cells are seriously light for their capacity.  I realise that publication requires pretty standard running gear, but its amazing how many peeps who build a GG design are ex-aeromodellers with flight gear and lipos. 
I'm running my Hellkitten on brushless and li-ion cells (ex laptop)  with reversing on a third channel - experiences will follow in a brushless thread
andrew
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Marks Model Bits

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Re: DD Ripley
« Reply #2 on: November 14, 2008, 09:18:27 AM »

I have always been impressed with your models they look good and are easy to build. It was you and Hal Harrison that inspired my daughter to build her first model boat when she was only 10 years old (HH's design won though :embarrassed: :embarrassed:) after seeing how easy they were to make.
http://www.modelboatmayhem.co.uk/forum/index.php?topic=3178.0

Mark.
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Martin [Admin]

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Re: DD Ripley
« Reply #3 on: November 14, 2008, 03:07:53 PM »

There was a very 'rolly' destroyer at Warwick, about halfway thorough this clip.



I remember back in the olden days, there was an article in one of the model boat magazines about
ship wobble, it was an idea to put a cylindrical tank transverse in the superstructure to counteract
the beam movement by using baffles or various viscosity liquids.....

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GG

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Re: DD Ripley
« Reply #4 on: November 14, 2008, 04:17:10 PM »

I see what you mean Martin.  It is the effect I wanted to duplicate but "Ripley" only heels, it doesn't wobble like that destroyer.
In fairness to the builder of that destroyer, the choppy water conditions probably made it appear to be less stable than it really is.
GlynnG
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Martin [Admin]

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Re: DD Ripley
« Reply #5 on: November 14, 2008, 04:33:13 PM »



....... no!   ok2
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GG

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Re: DD Ripley
« Reply #6 on: November 14, 2008, 08:23:12 PM »

Martin,
In which case the Destroyer must have too small a metacentric height.  Improvements could be made in two ways;
1) Rearrange the internal items to lower the CG of the model.  I once witnessed a most unstable model tug, usually the most stable of models.  The problem was apparent when the model was opened up.  The narrow sealed gel-cell was installed upright rather than laid flat in the bottom of the hull.
2) Reduce the weight of everything at or above deck level.  The only thing the decks, superstructure and fittings have to do on scale types of models is keep the water outside the model and look pretty.  They do not need to be strong enough for you to stand on the model, unless you prefer doing that to sailing the model?
GlynnG
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