Basic question: propellers and stuffing boxes

[Guest]

You need to understand Archimedes

You need to understand Archimedes principle.

An items weight in air is very different to it's weight in water. A materials density is important when considering materials to build a submarine from.

Water weighs 1KG per litre in volume. Most plastics weigh about the same amount as water, but they're often filled with other materials which weigh more. PVC is one of the heavier plastics, it tends to be about 1.3 to 1.5 times the density of water, therefore, if you put the tube into the water it will sink. However a small amount of foam will enable it to float, as the PVC is only marginally heavier than the surrounding water it is displacing.

You don't have to use PVC tubing. ABS, Lexan, acrylic, preformed GRP tubing are all readily available in a range of sizes.

It's also worth pointing out that for a boat that is shaped like a cylinder, there is absolutely no need to use a WTC. You can build a dry hulled boat.

[modelnut]

I know Archimedes' principle. But

I know Archimedes' principle. But i do not know the precise volume of my finished model. I could make a rough guesstimate but I was hoping for an off-the-cuff opinion from experienced RC sub drivers.

Sorry, SubC. This is America. There are no ABS, Lexan, acrylic, or preformed GRP tubing available down at the local hardware store.
H@ll, I went all over town looking for plexiglass rods for my sub's lights and came up empty. Thought of clear plastic beads but what the craft stores had was too small.

Woke up this morning and "knew" that could make a cylinder sufficient for my needs. I will just bend and glue the ever-present FOR SALE sign into shape. I have a fiberglass kit so I could reinforce the thing from the inside.

I could just order a cylinder from someone online but I have the time to work right now. I don't want to wait a week or two.

Water weighs 1KG per litre in volume. Most plastics weigh about the same amount as water, but they're often filled with other materials which weigh more. PVC is one of the heavier plastics, it tends to be about 1.3 to 1.5 times the density of water, therefore, if you put the tube into the water it will sink. However a small amount of foam will enable it to float, as the PVC is only marginally heavier than the surrounding water it is displacing.

This I did not know. But that will be great for future reference.

Thank you for all your advice! But don't stop now. If you think of anything else don't hesitate. I am jumping into the deep end with this project so any lifeline would be great!

-Leelan

P.S. Now I just need to email D&E to see if there is an instruction manual for this WTC. As for a dry hull. There will enough piercings of the hull for control linkages etc that there will undoubtedly be leaks. I have the WTC to hand. Might as well use it.

[Guest]

But you do have Mcmaster-carr,

But you do have Mcmaster-carr, don't you. They sell all kinds of tubing. Then there is ebay.....

Regarding the dry hull, wet hull business, there are no more piercings in a dry hull than with a wet hull and WTC.

It's not possible to guesstimate the all up weight and/or displacement of your boat, you're asking the impossible.

Simplest answer to your question. Build you boat to fit the cylinder you have. Make it from plastic, if it's too heavy (unlikely), add foam below the waterline.

Andy

[modelnut]

It's not possible to guesstimate

It's not possible to guesstimate the all up weight and/or displacement of your boat, you're asking the impossible.

That's why it is called a guesstimate. It is not meant to be accurate. It can only ever be a probabilty --- a guess. I am sure other fellows have boats as large as mine will be and they know how much they weigh. Leaving aside the density issues, a "for instance" was all I was after.

As for fitting the WTC, I am trying to keep my boat as near 72nd scale as possible. I have the Revell GATO kit and a SKIPJACK hull in that scale. I also have a static Disney NAUTILUS in 69th. I want to keep my Vernian boat in this scale. I have some bits and bobs in hand for detailing.

Never thought of eBay. That might be a good idea.
Never heard of Mcmaster-carr. Might check him out as well.

The thing is that I am on vacation this week and wanted to make some real progress on this project. While, ultimately, time is not an issue. I only have five days left before I go back to work.

-Leelan

[modelnut]

Nothing on eBay. Mcmaster-carr has

Nothing on eBay. Mcmaster-carr has something that might do.

What can you tell me about a dry hull? I will do a search for info as soon as I post this. But direct experience from someone who knows would be a big help. Wouldn't all that trapped air be a problem? Wouldn't i have to add a lot of lead weights to make her sink?

Text fitted my WTC again. Even if I could get it to fit within the tube's diameter it looks like the WTC is too long. If I make her a dynamic diver then I could lop off the gas chamber . . .

Sorry. Building castles in air. A long way from that step.

-Leelan

[Guest]

How big is this boat?

How big is this boat?

[modelnut]

Main hull is basically SKIPJACK

Main hull is basically SKIPJACK shaped but sharper]my plan[/url].



Length of main hull 97.2 cm (38.27 inches)
Diameter 11.43 cm (4.5 inches)

-Leelan

[modelnut]

Found squat about dry hulls.

Found squat about dry hulls. I assume they involve sealed ballast tanks etc. Would have to drive the model too hard to be a dynamic diver I suppose.

Just guessing.

-Leelan

[Guest]

Nope, it would make a

Nope, it would make a very good dynamic diver, as the freeboard of the design is low and the control surfaces are fairly large.

Look at the designs on Norbert Bruggens page, they're all essentially dry hull. A dry hull can still have free flooding sections at the bow and stern, it's just the centre section which stays dry,as it's used as a pressure hull- no separate cylinder.

[modelnut]

Do you have a link

Do you have a link to Norbert Bruggens' page? OOPS. Found it. Modelluboot

Haven't started making the new cylinder yet. Would the weight of the PVC matter? Or would it be compensated by foam?

Have his book in the cart at Amazon. Just waiting for payday.

-Leelan

[modelnut]

From Modelluboot]The models in this

From Modelluboot]The models in this catalog are mainly 24 to 40 inch long and weight 8 to 12 pound. This makes handling easy.
[/quote]

Maybe I won't have to make a new cylinder after all! YAY!

-Leelan

[Guest]

I'm a bit confused- the

I'm a bit confused- the shape you've shown looks to me like an elongated teardrop shape. Therefore a cylinder won't look right, or are you modifying the profile somewhat?

[modelnut]

Sorry. http://www.subcommittee.com/forum/icon_smile.gif

This is my

Sorry.

This is my fourth try at building this boat. For my third I bought a Hawk Graf Zeppelin kit. It was way cheaper than any sub hull I could buy. Less work than carving a foam master. And it would be hollow.

With these advantages I gambled that the airship kit might make a good basis to bash my NAUTILUS instead of going from the ground up. With the length of the model given and stats of the real airship in hand I estimated that the diameter would be spot on or near enough.

It was! I only needed to add an inch or so in length to match Verne's measurements in 72nd scale.

But sadly the kit was not symetrical around its long axis. there was a definite bow. The ship sagged between the bow and stern. And it was not perfectly cylindrical either. It was squashed vertically. No circlular cross section.

So much for #3.

But when I saw Steve's build I had renewed hope. And I thought of a way to salvage build #3.

I chopped off either end of the Graf Zeppelin taking care to compensate for the bending. Then I glued the ends to the PVC center section. I slathered on some putty and sanded all evidence of the ridges away. And made it more circular at the same time. It worked!

That is why I needed the pipe.

-Leelan

[Guest]

Okay i understand now. I'd

Okay i understand now. I'd advise caution with a dry hull approach then. A dry hull has to act as a pressure vessel. If the hull is made up of bits and pieces, rather than a good quality laminate it could fail under pressure.

[modelnut]

Couldn't I just reinforce with

Couldn't I just reinforce with a layer of fiberglass on the inside?

-Leelan