rva1945

I'm in the process of converting one of those to RC, with a homemade ballast system. It's important to know in advance how much water will it have to take to dive.

I'd appreciate any help.

Regards
Robert

stmjxxi

Volume of water ballast in litres = weight of the superstructure above the waterline.
Is this an exam question,Robert? You built a sub before.

Skip Asay

"Volume of water ballast in litres = weight of the superstructure above the waterline. "

Au contraire. Substitute "volume" for "weight".

Skip Asay

rva1945

Wrong, the amount of water you have to ut into your ballast tanks equals to the water displaced by the superstructure above the waterline, it's all about volumes, not weight.

When I build the SSN22 I knew from others' experience that the ballast water would be something between 80 and 120 cc, so I designed the WTC and hardware location accordingly. But it's not the case with the Revell 1/72 VIIC, right?

stmjxxi

Water weighs 1kg per litre round here

I should have said that I enjoyed your sub write-ups,Rob.

stmjxxi

I just measured the weight of the hull and made an estimate of the plastic weight above the waterline.I am sure of the physics.

rva1945

Thanks, are you talking about the Octobre 2009 MMI issue?

rva1945

The superstructure, I mean, everything that remains above the waterline when surfaced and that will displace water once underwater, could be made of styrene or depleted uraium, it doesn't change the amount of water you have to take to dive. It's just the volume.

Ok, the total fixed ballast and buoyancy reserve will not be the same, but to dive the sub, you need to take water to compensate for the additional water displacement, no matter how light or heavy is the body you submerge, its volume will displace water.

Have you ever heard about Archimedes?

stmjxxi

No I meant your internet ramblings about making the parts for your first static diving sub.I rarely enjoy articles of that nature.

I heard of Archimedes.That is the principle I am following.I dropped classical studies but took the school physics prize and got a qualification afterwards.And before anyone says anything,I mean net weight with the mass of the water displaced by the superstructure plastic accounted for.


Weight a minute.Are you looking for feedback? It stuck in my mind that I wished more internet articles on model subs should be just photos and diagrams and keep the text to little more than captions.More of the same please.

rva1945

Congratulations for your prize. Now do the following exeriment: fill a known volume (glass, cup, etc.) with water, get a plastic ping-pong, or table tennis, ball and put it to float, now somehow sink it applying a vertical force downwards, putting a lid to cover the cup until the ball is underwater, if the cup was filled to the border, as it should have been, water will leak t the sides. Now measure the remaining water inside the cup as accurate as possible.

Repeat the experiment but this time fill the ball with lead, AND SEAL IT if you drilled a hole in it (other wise water will leak inside the ball), it will sink to the bottom, of course, due to its weight, no ned to make it sink. Again, water will be displaced. Measure the remaining water and it will be the same. Why? Because the two bodies displace the same volume, no matter how much they weight.

It would be easier to do the experiment with two identical bodies with totally different weights, but I don't think they're easy to find, thus the exercise of adding weight to the ball for the second part.

We had that discussion with a naval engineer that was involved in the development of the TR1700, a diesel-electric sub designed for the Argentine Navy, and some of the guys present thought like you, later convinced of the mistake.

Maybe it works to consider weights in the case of this plastic kit, I'll be true to you: I did the same for the Seawolf, knowing the accuracy given the scale and materials involved, but that's not Archimedes, THAT'S NOT WHAT YOU SHOULD DO TO DESIGN A REAL SUB.

His principle states that a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid it displaces.

stmjxxi

Robert,I did the iceberg,the sluice gate and all manner of conundrums and was taught how to solve them by force diagrams.That is how exam properly couched questions are done.No debate over what the question was or what the reply was stating.

Skip Asay

stmjxxi - Since you say that you're already familiar with Archimede's principle, how about if you just admit that you misspoke and let it go at that. There's no need to point out how well you did in school or get all huffy. The responses you've gotten are all about trying to help, not put down.

Skip Asay

stmjxxi

Oh Crap,I said wrote plastic weight...damn.I should read my own posts more carefully.
Robert can suggest a better method other than tacking the three main sections together,ballast to waterline and add weights.They are the only akward bits.