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[offshore1987]

Hi peeps

I was just wondering if anyone has put water tanks ( like aircraft fuel tanks ) into there model boats? Of course this would be to weight the model down, but has anyone done this?

all the best  :)

[Bunkerbarge]

Here's mine, used as a feed tank for the boiler.  It is filled through one of the vent cowls fitted to the foc's'le.

[malcolmfrary]

Some large models use removable water bottles as ballast, but the problem with water as ballast is that it is the same density as the stuff you are floating in.  The advantage is that the model is easier to handle out of water.

[Big Ada]

I plan to use milk bottles filled with water in a barge.

Len   

[Manxman]

Hi,

Water for ballast is ok - with water weighing 1kilo per litre.  You could also use a flood chamber - a completely water tight chamber between bulkheads and a hole in the hull.  When the boat is lowered into the water it self ballasts, you will need a tube rising from the top of the chamber to above water level in order to vent the air from the chamber.  The method has been used many times with tow barges.

Cheers - Ken

[Red_Hamish]

Hello there Offshore, attached is a copy of my American pusher tug (towboat) based on the Model Boats Jenny Sue 2 plan. It is pushing an own design barge measuring 34" long with a beam of 14" As you can see it needs 4 x 2L water bottles to take it down to a realistic waterline. Hope this helps

cheers

Jim

p.s Thanks Doug from Lockerbie for the photos 

[offshore1987]

Thanks chaps this is all very usefull 

im going to give it a tinker and see what happens  :) if it fails il use some lead 

main reason is il have to carry this about 2/3 of a mile to the lank so everything little helps in the weight saving side of things the boat is ment to weigh around 18kg at full weight i think, lugin that along way would be apain  :angel:



all the best and thanks for the replys :)

[portside II]

hi offshore1987,
i use 4pt milk cartons for ballast in the bumb crane barge ,about 8 of them and it could do with some more .

and the RMS Paula N uses either 6x750cl water bottles or 6 x 12v 7ah batterys as ballast ,depends on what i have with me at the time.

daz

[offshore1987]

  looks stunning

iv worked out i need about just over 4kg which dosnt sound alot but thats 2x 6v 10amp batts, just think it would be a cool thing to have maybe, next plan is to find some tanks then get 4kg of lead and see what the size diffrence is  :) and see what would really work best

plus carryin it to the lake lol with the boat sand and batts and the other bits, would just make it a tad lighter, boat needs to weight around 18kg 

il try and keep this updated 

all the best

thanks for the info and pics

[Bryan Young]

Hi,

Water for ballast is ok - with water weighing 1kilo per litre.  You could also use a flood chamber - a completely water tight chamber between bulkheads and a hole in the hull.  When the boat is lowered into the water it self ballasts, you will need a tube rising from the top of the chamber to above water level in order to vent the air from the chamber.  The method has been used many times with tow barges.

Cheers - Ken

If you use this method you are not exactly ballasting the boat. As the volume is "free-flooding" all you are really doing is reducing the boats inbuilt buoyancy, hence lowering the safety margin. What you are advocating here is, in essence, chopping out a fair proportion of the boats hull thus making the boat smaller but with the same "top hamper". Not...definitely not...a method I would recommend. BY.

[banjo]

Make a trolley!!

Then you won't have to carry it!!

 

[Bunkerbarge]

Hi,

Water for ballast is ok - with water weighing 1kilo per litre.  You could also use a flood chamber - a completely water tight chamber between bulkheads and a hole in the hull.  When the boat is lowered into the water it self ballasts, you will need a tube rising from the top of the chamber to above water level in order to vent the air from the chamber.  The method has been used many times with tow barges.

Cheers - Ken

If you use this method you are not exactly ballasting the boat. As the volume is "free-flooding" all you are really doing is reducing the boats inbuilt buoyancy, hence lowering the safety margin. What you are advocating here is, in essence, chopping out a fair proportion of the boats hull thus making the boat smaller but with the same "top hamper". Not...definitely not...a method I would recommend. BY.

It's how real ships do it, allbeit with the assistance of a large pump

[offshore1987]

Make a trolley!!

Then you won't have to carry it!!

 

lol iv gota go about 2/3s of a mile along the beach front and it will be packed  dont wanna look a complete nerd pushin the thing as well  good option though 

[Bunkerbarge]

Make a trolley!!

Then you won't have to carry it!!

 

lol iv gota go about 2/3s of a mile along the beach front and it will be packed  dont wanna look a complete nerd pushin the thing as well  good option though 

If that's the case then I would seriously think about free flooding compartments for ballasting.  You need a compartment between bulkheads that has a lid below the normal water level.  This should then be made into a sealed tank, fitted with a line to outside the hull with a valve on it and a vent.  Put the boat in the water, open the valve and allow the tank to flood until it is completely filled then close the valve.  This should ensure the tank remains filled up to the top and you will not have any free surface effects to upset the stability.

When you have finished, remove the boat from the pond, put it on it's stand, and once again open the valve.  The tank will naturally empty it's contents all over your shoes to the amusement of all watching!!

You only have to carry a deballasted boat around then and, by using completely filled tanks, (called "pressed-up") you can judge with a degree of reliability where the boat will sit.  From your initial ballast calculations with the hull you should be able to determine reasonably accurately how much water is required to get the boat to it's marks and therefore the volume of the tank, or tanks, you need to construct in the hull.

[Bryan Young]

Evening Manxman and Bunkerbarge.
Perhaps we are talking at cross-purposes here. I have no problem whatsoever with free-flooding a sealed tank within a hull. As you say, that is how real ships do it. But that is a long way from drilling holes into a hull to let a compartment fill of its own accord. That's what would happen after a collision, and I've never heard of anyone calling collision damage as a form of ballasting. Real ships do,of course use water for ballasting purposes, but it is "on board" as an added weight and not what is euphamistically termed a "bilging" problem where no weight is actually added to the ship but only reduces the vessels inbuilt buoyancy. Sealed tanks within a hull...fine, free flooding from the sea into a compartment is a no-no. If it was OK then ships wouldn't sink and there would be no need to train in damage control exercises! I have no desire to go into the ins and outs of ship stability ( far too big a subject for this forum) but a lot of it can be summed up by "maintaining the hull integrity".

[Bryan Young]

Some large models use removable water bottles as ballast, but the problem with water as ballast is that it is the same density as the stuff you are floating in.  The advantage is that the model is easier to handle out of water.

I must have missed this one, but why do you think that the density of the water makes a difference? The only difference density of water makes is to the draught of the boat/ship when it is floating. The best example is of a ship loading in fresh water "to its marks" and then when it goes to sea in salt water it will rise bodily...quite a lot sometimes. This is what is known as "Fresh Water Allowance" and is marked on the Load Line as FWA. Not as simple as that, but that is the basic idea behind it.

[malcolmfrary]

The point was that if the extra (light) ballast is at the lowest point of the ship, the centre of gravity might well be compromised.  Ballasting a model does not quite follow full size rules.  As a rule, we don't carry variable cargo, a real ship does and so needs ballasting, and is designed with this in mind.  A model, on the other hand, is built to work at a given weight, and if we park our batteries (the best ballast) too high we can run into problems. 
Incautious building can create stability problems as well.  I recall a case of an article in a mag several years ago.  The guy had built a liner, very good-looking.  He was mystified as to why it exhibited loll.  The simple fact was that he had far too much weight in the superstructure - any more and he would have been re-enacting the Poseidon event.  I would hold that in a model, you need your structural centre of gravity as low as possible, therefore any added water ballast should be above any "solid" ballast, or at least sited so as not to raise the centre of gravity. 

[Big Ada]

Make a trolley!!

Then you won't have to carry it!!

 

lol iv gota go about 2/3s of a mile along the beach front and it will be packed  dont wanna look a complete nerd pushin the thing as well  good option though 

Put your boat in a pushchair and throw a blanket over it and you will look like a proud parent taking baby for a walk! 

[IainM]

Interesting discussion !!
As Malcolm says, getting weight distribution wrong can have rather unfortunate consequences.  One of our Club members has a 12 foot QE2 and got the ballast weight just right.  Unfortunately, to reduce the load on the thin ally hull, the weight was placed on a tray suspended from the upper deck level.  Yup ... you guessed it!  A tight turn into the wind and over she went!  (Some pikkies on the Edinburgh Model Boat Club site).  The Ballast weight tray was redesigned to sit on the reinforced bottom and allus now good.

I put together a wee 'how to' tutorial on Model Stability that you might find interesting, together with a drawing for a simple inclinometer.  Downloadable from http://www.sfmbc.net/stability_handbook_R5.pdf

On the subject of free flooding chambers, the Thunder Tiger RTR models have just such a thing, but the top of the chamber is below the load water line so to speak and is free vented to above the deck level.  This way there is no free surface in the chamber and so it does not cause rolling.
OK until you upgrade the battery packs thus increasing the weight!  Then its down to taping over the slots in the hull and reverting to normal ballast.

IainM

[Bunkerbarge]

On the subject of free flooding chambers, the Thunder Tiger RTR models have just such a thing, but the top of the chamber is below the load water line so to speak and is free vented to above the deck level.  This way there is no free surface in the chamber and so it does not cause rolling.
OK until you upgrade the battery packs thus increasing the weight!  Then its down to taping over the slots in the hull and reverting to normal ballast.

That is exactly what I described above.  It is important that the top of the tank is below the water line to ensure complete flooding.  This will also ensure the weight is as low in the boat as possible and will therefore not have any detrimental affect on the stability.