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Ballast tank questions

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Ballast tank questions

Postby Oddwired » Sun Jun 09, 2013 2:24 pm

Hello all, I’m working towards building the wtc and ballast tank module for a type 212 submarine.

At the moment I’m focusing on making a working ballast tank, it will work on the high pressure pump plan, IE filling up a tank using a high pressure water pump and emptying it by opening a valve, the built up air pressure should then force the water out.

I’ve got pvc pipe that can take the pressure and have started producing lexan endcaps and the threaded rods to hold them in place but I would appreciate some advice before I move onto the next step.

Image
Image

First of all I’m a little worried about the seal size.

As you can see above and below the wall of the pipe is kinda thin (about 3 mm), the pipe can take the pressure but it gives very little surface area for the rubber between the lexan cap and the pipe to hold an airtight seal.

Image

I’m going to try the method drawn below but would appreciate advice on whether I’m about to spend a lot of time on something that won’t work.

Image


Any sugestions before I push ahead would be much appreciated
Thanks and over to you
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Re: Ballast tank questions

Postby Sub culture » Sun Jun 09, 2013 4:40 pm

I trust that isn't going to be the length of your tank?

Since your using PVC pipe, why not keep it all PVC, and use that material for the endcaps too? Then you could solvent weld the end caps in. You could add a mastic sealant (e.g. sikaflex) around the outside for belt and braces.

You will need to baffle the tank to prevent sloshing, and make sure the water pick-up inside the tank is in the middle and at the bottom of the tank, that reduces the risk of the pressurized air escaping under extreme manoeuvres.

Keep the tank as short and fat as possible, as even with baffles the water can move about, and long slim tank will be far worse than short fat one.
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Re: Ballast tank questions

Postby Oddwired » Sun Jun 09, 2013 7:32 pm

Ah thank you yes.
First yup definitely cutting the tank down to at most 30cm and perhaps as far as 20cm leaving me with a 2 or 3 litre tank (i know that some of that space will be filled with pressurized air) but pretty confident that that aught to be enough to sink it when properly trimmed.

i will certainly have a go at gluing the caps in however I was wondering if a better approach would be instead of a whole cap just a larger internal ring to expand the surface area as pictured below.

Image

This way i can stick with the orignal idea of holding the lexan caps on with rubber seals, the surface area of the seals will be large enough to hold the pressure and I can still get inside the tank for maintenance etc.

Will be going shopping for parts tomorrow!

Thanks again for the reply very much appreciated.
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Re: Ballast tank questions

Postby JWLaRue » Sun Jun 09, 2013 9:48 pm

I like this approach a bit better as it would provide a better seal.

However, let me ask a question. This is just to be a ballast tank, correct? Then why not just glue the end caps to the cylinder?

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Re: Ballast tank questions

Postby Scott T » Sun Jun 09, 2013 10:49 pm

How about getting a cap and slicing a quarter inch ring off the open edge. Then put both endcap and ring on the end of the tube.
Glue the ring to the outside of the tube. Now you have a shelf on the tube to place the gakset that is the same width as the end
cap. Maybe a sketch later.

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Re: Ballast tank questions

Postby Sub culture » Mon Jun 10, 2013 5:14 am

This must be a very large 212 requiring 1.5 to 2 litres of ballast. What scale is it?

Generally you can fill a tank to about half to two thirds full with the pressurized system, when using a geared pump of reasonable ability/quality. A Kavan pump would be a good choice here, as they pump at reasonable volume, although you can expect dive times of at least a minute for the size of tank you have in mind. You can fit two pumps to improve diving times, assuming you have the space, and budget allows.

I don't like the seal you have gone for, because it won't allow any 'squish'. Rubber doesn't compress as it is squeezed, it extrudes. If you must have a removable cap, then I would advise going for an o-ring of reasonable cross section. What is the internal diameter of the tubing?
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Re: Ballast tank questions

Postby Oddwired » Mon Jun 10, 2013 7:12 pm

The pipe diameter is 4 inches so roughly 10 cm or so.
I had a feeling the tank might be a bit large but wanted to play it safe as I would like to make a slightly large version so I have room for adding extra features once I’ve got the model working, say 1/35 scale was the plan putting the model at roughly 1.6 meters long.
The pump I’ve been advised to use is the windscreen washer pump off an old ford, apparently the people at sheerline model submarines seem quite keen on this method so it seemed like a sensible idea to follow their path.
The tank design was actually stolen from this websites design for a wtc.
http://www.rc-submarines.net/how-do-you ... r-out.html
However if people feel this is too potentially risky I’ll probably just go the route of welding complete endcaps onto the pvc pipe.
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Re: Ballast tank questions

Postby Sub culture » Tue Jun 11, 2013 4:28 am

Okay, i can tell by your last post that you are very new to this game.

For a start a 1/35th scale 212- are you sure?

That is going to be a very large and cumbersome model to lug about, why do want a boat as big as that?

Think about halving the scale, and certainly no larger than 1/48th scale.

Second point- a windscreen washer pump is going to be too small for that size of tank- you will be there all day waiting for it to fill.

Third point, don't make ballast tanks bigger than they need to be.

Forth point, the page you linked to is for a WTC not a ballast tank. The system you are proposing is going to run at pressures of about 40-60psi, if you add that up over the surface area of the endcaps (which are the weak link in the chain) you don't have to be a rocket scientist to figure that the tanks need to be very strong. Bear in mind that some of Sheerline's tanks are made from brazed up stainless steel (Type VII and Type II).
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Re: Ballast tank questions

Postby Oddwired » Tue Jun 11, 2013 7:39 am

Ah yes I am a bit of a novice when it comes to model boats, I have flown aircraft for a bit but this is indeed new ground for me.
In view of peoples suggestions I will probably go down the solvent welding route instead of the openable tank; will just standard pluming solvent for connecting drain pipes work?

To be honest the main reason I want to keep it larger is so there is room for any extra equipment I might want to add at a later date, I know perhaps not a good thing to think about for a beginner but once I've got it going I’d like to have room for fittings such as periscopes etc but I can certainly drop the size a bit.

Also I will knock the tank down a size or two as well, are there any rough sizes of tank vs size of model guides out there? And as for pumps I’ll investigate caravan pumps, I was considering perhaps dividing the tank up into multiple smaller ones with a windscreen pump for each as I've got quite a few of those pumps to hand and it would make leveling the boat a lot easier.


Thanks again for everyone's patience with me the fng :D

All the best and should be out to cut out some of the endcaps over the next few days so will have some more photos soon.
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Re: Ballast tank questions

Postby Sub culture » Tue Jun 11, 2013 9:10 am

Firstly, I think you are being too ambitious in your choice of subject for a first boat.

Secondly, auxiliary items like working periscopes can be added to the smallest of boats these days- radio equipment and batteries are small these days. Years ago it was far more difficult. Regardless of that, forget about them for your first or even second boat.

Third, do not make multiple ballast tanks- recipe for disaster. The only time that works out is twin piston tanks positioned either end of the C.G. A single tank is a must, don't copy fullsize boats with multiple tanks, because it will prove impossible to trim your boat accurately.

If you want to start off with something, grab yourself a plastic kit like Trumpeter Seawolf, or the revell Type VII or the new Revell/Moebius Skipjack. To convert the latter with your own built WTC will cost under a £100, including the cost of the kit, cut your teeth on that, then move on to the big scracthbuild.

Before you do that, grab a hold of a copy of Norbert Bruggen's Model Submarine Technology, as it covers all the theoretical bases for pressure hulls and ballast systems. Ignore the advice in that book at your peril.

Last but not least, don't be cheap, sign up for membership which gives you access to every issue of the SCR back to the year dot.
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Re: Ballast tank questions

Postby Chuck Chesney » Tue Jun 11, 2013 10:54 am

Oddwired, I couldn't agree more with Andy (Sub Culture). Many, many, fellows let their wants far outreach their knowledge and abilities in regard to their first model submarines. A model sub is at least as technically complex as most basic R/C aircraft, resulting in a large number of model submarines ending as monuments to frustration, lost time, and wasted money.
Go with a simple, easy to build, transport, and operate model. I promise that it will be far more challenging than you think. For a first model, thinking that "bigger is better" isn't the smart way to go in most cases, and fully operating bells and whistles won't lead the way to success....just frustration.
Chuck

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Re: Ballast tank questions

Postby salmon » Tue Jun 11, 2013 11:36 am

And I jump in on the bandwagon. Crawl, walk, run. Get the basics down first. Get one sub, at least under your belt, before bells and whistles get added. That was the advice given to me and the mantra I used while I was building. Get her working first. This is the most frustrating hobby I have ever been in, but the most rewarding. I cannot think of any of my R/C history adventures that come close to the love I have for R/C submarines, but it could have been very different if I did not follow the advice given. We want to see you succeed.
If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.
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Re: Ballast tank questions

Postby JWLaRue » Tue Jun 11, 2013 12:29 pm

Sub culture wrote:Before you do that, grab a hold of a copy of Norbert Bruggen's Model Submarine Technology, as it covers all the theoretical bases for pressure hulls and ballast systems. Ignore the advice in that book at your peril.

A better suggestion for a beginner's book would be Steve Neill's "R/C Submarines for Dumba$$es". It's a free download that can be found here:

http://www.subcommittee.com/phpBB3/viewtopic.php?f=21&t=11183

Norbert's book does contain loads of useful information, but it's not the easiest book to read. Plus a number of the circuit diagrams have been said to be either out-of-date or incorrect.

I strongly agree with Andy's recommendation to joni the SubCommittee and pull down the back issues...and suggest that you read Skip Asay's series of columns titled "How it Works". Skip is one of the godfathers of this hobby and is very good at explaining the various facets of r/c subs.

As to the size of the subject chosen....my opinion is that this is a very personal choice and whether it's right for you depends heavily on your existing modeling skills.

-hope this helps,

Jeff
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Postby Giovanni » Tue Jun 11, 2013 12:34 pm

Delete
Last edited by Giovanni on Tue Jun 11, 2013 3:12 pm, edited 1 time in total.
Kind regards,
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Re: Ballast tank questions

Postby JWLaRue » Tue Jun 11, 2013 1:00 pm

I have. Very nice hull, builds into a very nice running boat.

Do you have any specific questions that I might be able to help you with?

-Jeff
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