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Author Topic: ballast in a boat hull  (Read 3310 times)

whizzo

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ballast in a boat hull
« on: November 02, 2012, 04:29:55 PM »

Hi again all , i am now working on a tid tug 1/24 scale - and am surprised at how much ballast is required to get the hull down to the right level in the water --  {:-{  now my main problem is that i am disabled - ( unable to lift much ,  age thing ??? ) so i was wondering if it was possible to make two watertight pods built into the hull  ether end of the battery which could fill through two small holes in the hull , battery would take it down to the right level - when finished for the day --remove battery lift model up  water would drain out through the said holes - a bit like a sub, then i would not have to use lead ballast O0 -please say if you think this will work or not - or any ideas please - many thanks for reading    regards Dave
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rmaddock

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Re: ballast in a boat hull
« Reply #1 on: November 02, 2012, 05:12:02 PM »

Dave,

I have a suspicion that chambers open to the water will not work as ballast..although I'm not sure I can explain why.

However, people do use bottles of water inside hulls for ballast on the same principal.
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RJR

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Re: ballast in a boat hull
« Reply #2 on: November 02, 2012, 05:12:31 PM »

Check out this thread here on Mayhem  Your thoughts taken to extremes, so yes it works


http://www.modelboatmayhem.co.uk/forum/index.php?topic=9014.0
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RJR

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Re: ballast in a boat hull
« Reply #3 on: November 02, 2012, 05:15:41 PM »

Dave,

I have a suspicion that chambers open to the water will not work as ballast..although I'm not sure I can explain why.

However, people do use bottles of water inside hulls for ballast on the same principal.


I think you are right a simple open chamber wont fill because there is nowhere for the air to get out. Its like when you submerge an upturned glass in the washing up bowl. The air stays in and water stays out. You would have to allow the air out of the top of the chamber.
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boatmadman

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Re: ballast in a boat hull
« Reply #4 on: November 02, 2012, 05:39:04 PM »

yes it will work - done it in the blue marlin build.

Just make absolutely sure your  tank is sealed properly from the inside of the hull, and, as Rob says, you need an air vent. Run a silicone tube from the top of the tank to some discrete point above deck level.

For each litre of water ballast you use, you can remove 1kg of lead.

For best results and minimum effect on stability, keep the tanks low and evenly positioned around the center line of the hull. Also, when building the tanks, put in some wash plates - dividing walls with holes in, this will reduce the free surface effect of the water and reduce roll induced by the ballast water. Remember to leave openings at the bottom of the wash plates for full drainage, and at the top for air venting.


Ian
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DickyD

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Re: ballast in a boat hull
« Reply #5 on: November 02, 2012, 05:39:43 PM »

You would need to vent above deck level. 


Just beat me to it Ian.
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Colin Bishop

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Re: ballast in a boat hull
« Reply #6 on: November 02, 2012, 05:40:24 PM »

If the water isn't physically confined within the hull then it will not exert any sort of righting moment when the hull is inclined such as rolling in rough water. Having a small entry hole may be sufficient as the water can't all get out at once but of course, as stated above, you will also need a hole at the top to let the air out.
Unless you also have 'dump' valves of some kind then when removing the boat from the pond you will need to either do it very slowly or have to lift most of the water out as well until it can drain away all over the bankside. You can see why many people prefer to have removable internal ballast although this entails taking some of the deck off while the boat is afloat to get it out.
There are clever options such as using onboard pumps to fill and empty the ballast chambers.
Water ballast can be made to work but you have to think it through.
Personally I just build small boats.  ok2
Colin
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Umi_Ryuzuki

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Re: ballast in a boat hull
« Reply #7 on: November 02, 2012, 05:47:41 PM »

We do it with simple barges.
A dedicated vent is created to allow air to escape.
It is the copper mushroom at one corner.

:)

boatmadman

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Re: ballast in a boat hull
« Reply #8 on: November 02, 2012, 06:10:14 PM »

Umi,

If that is your workshop, I an GREEN with jealousy!

Ian
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whizzo

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Re: ballast in a boat hull
« Reply #9 on: November 02, 2012, 06:18:41 PM »

Hi every one, many thanks for the replys - it would be easy to put a bleed tube for the air at the top of the tank and cover it with  some item  (tools etc) for the tug--  great help this site,,,  and a fantastic  group of guys - O0 regards Dave
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Stavros

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Re: ballast in a boat hull
« Reply #10 on: November 02, 2012, 09:59:49 PM »

Right then you modell is a 1/24th scale Tid Tug well let me put you right on a few things here you DO NOT need water ballast or any removable ballast in tug I should know as I used to have one.
 
1 you will need to put in around 2 lbs of lead in the stern and seal it in wiht some silicone mastic or whatever
 
2 You will not need anymore ballast....trust me on this one
 
3 Go out and buy 2 x 12v 12amp lead acid batts........Thats all you will need
 
I can assure you she will be on her waterline,yes I fully understand that you are dissabled But if you can manage the hull you will be able to carry the weight of batts,as you put the batts in the boat when she is in the water,wire the 2 12v batts together to give a longer running time,mind you if you use a Graupener 720 tourque motor with a 65mm prop you should get at least 8 hours running time.
 
Dave
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Bob K

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Re: ballast in a boat hull
« Reply #11 on: November 02, 2012, 10:27:59 PM »

As a pensioner with stiffening joints I can appreciate the problem.  Although I have seen fellow club members kneeling at the lake edge fitting and wiring batteries on the water this is not something I could manage.  The warship I am building now is quite a bit heavier than my others so I have opted for ballast chambers that can be flooded / blown from the transmitter.

Bending being a problem my other ships are launched with a couple of lifting straps straight off their carrying cradle near the water.  Car fan belts are ideal.  Yes, it is a lift, but only a foot or so with body posture fairly straight. 
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