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Balance of an aircraft carrier

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wayne quigley07/01/2012 21:03:15
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Evening all
 
I have in the past tried and failed to make a basic stand of model of an air craft carrier,
 
hull was 33"long 9" wide and 10" deep with a overhang of about 2.5" to on side
 
now ballancing the think was to much for me I could ballace it stable but as soon as it tilted an amount it was unstopible all weight was at the bottom ect has any one got any tips as i was thinking of trying again
 
wayne
Colin Bishop, Website Editor08/01/2012 09:21:00
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Wayne,


With a hull of that size it will be very difficult indeed to get a stable model as the flight deck is proportionately very heavy even if you put ballast low in the hull.


A possible way to make the model stable would be to have an external keel underneath the hull with a weight attached to the bottom (a bit like a sailing yacht).

 

Most successful working aircraft carrier models tend to be quite a bit bigger that the dimensions you have described as this makes it easler to have a proportionately lighter deck, but even these are often quite 'tender' and can roll a lot.

 

Colin
Kimosubby Shipyards08/01/2012 10:59:40
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Wayne,
 
as Colin suggests, an external ballast below the keel is possibly the answer - I had to use the same on this ro-ro vessel to get weight very low because she is very top heavy, especially when the upper deck is populated with about thirty matchbox vehicles.
 
The ballast weighs about 3Kg and is a piece of heavy duty copper/brass bus bar from a mains electrical switching station. It is attached by two bolts up into recessed nuts sealed in the hull, so it can be easily removed when transporting the vessel. Oh, she's near 6 feet in length.
 
You can just see the attached bar, copper coloured, hanging below the hull in the attached image.
 
Kimosubby.
 

 
 

 
 
ashley needham08/01/2012 13:42:05
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I always make the hulls a bit deeper that strictly scale to overcome this sort of problem, however if you were building a more-better-than-wot-I-normally-make ship this may be more difficult and indeed the false keel would be the answer.. I suppose as you have already built the hull, it WILL have to be the answer!!
 
Just as an aside, the battlecruiser I made, with the 3/4" plank bottom and hardboard sides didnt want to stay upright on its ballasting trials, so I cut a square out of the plank and put a patch of hardboard to cover the hole underneath, and so the battery sits as low as poss. What a difference !! 
3/4 of an inch was the difference between stability and , er, non-stability. 
 
Kimo. Very nice and a whopper to boot, not a lot of hull below the waterline compared to whats on top, eh?.
I am sorry but your method of holding the superstructure on somewhat ruins the aesthetic for me... 
Ashley

Edited By ashley needham on 08/01/2012 13:47:24

Edited By ashley needham on 08/01/2012 13:48:52

wayne quigley08/01/2012 14:21:11
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thanks for the quick replies.
the models i do are luckly not fine scale or of certain vesals so i have a lot of scope.the false keel sound best as where I run the model of a battle ship the water is shallow.
 
 
ashley needham08/01/2012 18:02:45
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Wayne, the other thing to fit, especially on something like an aircraft carrier, is a bilge-keel, or stabiliser fins.
 
Make them much to big as scale ones are fairly useless. This damps down the wallowing quite dramatically. They could be easily detachable for sailing like Kimo`s keel,using nuts recessed into the hull, or perhaps having a coupe of short studs protruding out the bottom (using brass or stainkess steel) and painted black. no one will know they are there when the boat is in the water.
 
Ashley
Kimosubby Shipyards09/01/2012 08:44:17
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Yes Ashley,
 
you'd have thought I could have scrounged some white masking tape!!!!! BUT at least I'd removed the yellow elastic and ss hooks that also keep it all together for transport.
 
You can also see the stabiliser strips on the ro-ro vessel - these are about 3/8ths deep and not only greatly reduced roll, they form a flat base when the model is on the work top.
 
Kimosubby
ashley needham09/01/2012 10:16:24
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Kimo. 3/8 over the sort of length as per your ship is a reasonable size to have, or is it that your false keel is the damping force as it is in effect a large fin. mostly it seems that I see keels of inadequate size to have any decent damping properties.
 
OR.. i wonder if there is any sort of minimum size or area to have in order to provide good damping? One would have thought for instance a good and decent scale battleship of say 5 feet long would have fairly small scale bilge keeps and so be moderately useless?? or is that not the case.
 
 
Having a squareish hull also helps. I have never tried it, but a water filled damping tube is supposed to be fairly effective?
 
Ashley
Colin Bishop, Website Editor09/01/2012 11:00:39
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Ashley,


Experiments were carried out on late Victorian battleships in the Royal Navy. Fitting bilge keels had a dramatic effect in reducing rolling and thereby giving a more stable gun platform. The wider the keels, the greater the benefit up to a point as the keels also produced drag due to their surface area and slowed the ship down.



However, the parctical limitation was that the keels had to be fitted on the turn of the bilge so that they did not protrude either below the hull or stand proud of th e side of it as this would have caused difficulties in drydocking the ships.



Colin

Telstar09/01/2012 17:11:33
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Hi I read somewhere an article that said if the ballast is split, and half placed in the 'bilges' in either side of the hull it gave better stability than all the ballast placed down the center line of the hull. I didn't follow all the formulae 'proofing' this but it seemed impressive. Also it suggested heavy bilge keels helped to damp out 'Rolling'.
 
 
Don't know if this is relevent, but who knows
Tom

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