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Nov 12, 2012, 08:37 PM
Mmm, tugs...
patmat2350's Avatar
Discussion

Ballast Tanks


I've mentioned before how I like to make lidded compartments or removable ballast tanks to hold lead shot ballast. Here's my latest, in Sikuliaq. They'll be removable for easier filling and adjusting, and to make transport easier.

The tanks are faceted boxes of 1/8" plywood with plenty of gusseting inside. They nestle in between frames in fore and aft positions, and are built to hold enough shot to take the model to its waterline. A center divider will let me trim P&S sides.

BTW, solid lead weighs 6.5 oz per cubic inch. Round shot has about a 70% fill efficiency, which means a cubic inch of lead shot weighs 0.70 x 6.5 = 4.6 oz.

If I need 5 lbs = 80 oz of ballast, then that is 80 / 4.6 = 17.4 cu inch tank volume.

Since I designed the tanks in CAD, I was able to easily calculate the volume! Trial and error also works.
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Nov 12, 2012, 08:40 PM
Mmm, tugs...
patmat2350's Avatar
More examples:

Forward ballast tank in my 1:12 scale DUKW. More was installed behind the wheel arches aft.
Last edited by patmat2350; Nov 12, 2012 at 09:19 PM.
Nov 12, 2012, 08:53 PM
Mmm, tugs...
patmat2350's Avatar
My big 54" 45' ST tug used PVC pipes loaded with shot. They nestled into cradles for repeatable location.

Obviously, it's best to do this early in the construction!
Nov 12, 2012, 08:57 PM
P31
P31
Registered User
I like to use hefty bag's pre-measured at 1Lb and 1/2 Lb, then I can adjust them where I need them. I would have shot all over the place using that methode
Nov 12, 2012, 09:03 PM
P31
P31
Registered User
Looks very nice, and clean.
Nov 12, 2012, 09:04 PM
Mmm, tugs...
patmat2350's Avatar
I find it worthwhile to neatly store the ballast... "ship shape and Bristol fashion"... sort of like the difference between:

..
Last edited by patmat2350; Jul 24, 2016 at 07:28 AM.
Nov 12, 2012, 09:05 PM
Registered User
Gravman's Avatar
You always do such neat construction. Everything fits perfectly. The inside of your models are as well done as the outside. Everything has a place. Gives the rest of us mortals something to work towards. I like it.
Nov 12, 2012, 09:10 PM
P31
P31
Registered User
Ah, you close the hatch, and no one will know.
Nov 12, 2012, 11:55 PM
P31
P31
Registered User
Mr Pat, have you ever used water bladders that you could pump water in and out, I have heard of this being done but never seen it done.
Gary
Nov 13, 2012, 01:13 AM
Registered User
DDG 51's Avatar
In big tug boat I am using water tanks, instead of balast. They are free floded, there are holes on the bottom, air is going out via pipe over waterline. Once tug is in the water, tanks are floded, once tug is lifterd up, water is running out via holes in the bottom. Of course, there are two lead acit batteries, so some 4 LB of weight is there anyway. But better as 20 lb of shots. Water is always in the lake ;-) transportation is not required. Tanks alone are made of fiberglass, directly glued to the hull.
Nov 13, 2012, 01:30 AM
NeverAgainVolunteerYourse lf
nick_75au's Avatar
Water ballast does not work well for long narrow top-heavy hulls, the weight needs to be concentrated below the waterline.

Nice post Pat, Ive heard of lead shot placen into plastic bags and mixed with epoxy, then placed in the hull, this makes custom ballast that fully conforms to the available space but is still removable as the occasion may require

Cheers
Nick
Nov 13, 2012, 07:26 AM
Registered User
Jerome Morris's Avatar
Similar to fuel tanks aboard real vessels.


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