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[profesorul]

....The only sure way to find out the tank size required is to put it together, get yourself a test tank, trim the boat to neutral buoyancy, then use blocks of polystyrene foam fastened below the waterline (you can make a cradle to hold these) to raise the boat to the intended surfaced waterline. Take the blocks off, and measure them to find out the volume, add them all together, tack on 10%, and that is your ballast tank volume.

As an educated guess, I would think your LA will need between 500-700ml of ballast tank volume, assuming all the dive module is below the surfaced waterline.

I have a CILINDER with 96mm Inside Diameter and 300mm in Lenght witch can be used for the balast tank .

MARIUS
 
 

[Davy1]

Almost there Marius! (Sorry I'm answering your previous question.)
As David says, it is the DISPLACEMENT (i.e. volume NOT weight) of the superstructure that has to equal the ballast water. (David suggests adding a 10-15% safety factor.)

If you want the theory it is the Archimedes principle.

The implications for design of subs is that you need to minimise the displacement of the superstructure. (That is why you need to go for thin and strong materials.  I quite like tinplate - it is sheet steel after all!)

Superstructure weight is not important for ballast tank considerations but make it too heavy and your sub will roll over! There goes another design constraint!

David

[SwedishProjectBuilder]

[size=78%]So let's see If I understand correctly:[/size]
- in order to know how much water I need in Ballast Tank I have to CALCULATE the Volume of ALL is ABOVE the Water Line ? .
- how about hes weight as a Sub , I mean If weight is, let's say 7,5 KG and the Volume of everything is on above the water line is 0,8KG I need a ballast tank with 8,5KG with those 10-15% ?

1. Yes, you can roughly calculate the volume above water. And that will correspond to the volume your tank must be able to take in + some more maybe 10%.
2.
Ballast and ballast tank is two separate things.
You have your submarine. If it weighs in total 10KG (EVERYTHING), you need 10 Liter of volume below the surface to keep it afloat.
(If the submarine is 10 Liter and your sub only weighs 5KG, you will need 5KG of ballast, for example lead.)


If the volume above surface is 1 Liter (an air filled Tower for example), your ballast tank will need to take in 1 Liter of water before the whole submarine is submerged (neutral buoyancy).


If the 0,8KG above waterline equals 0,8 Liter, you will need 0,8 x 1,15 Liter in your ballast tank.
The weight of everything "above water line" is only interesting if you know what the exact density of the material is.
Extreme example:
If you have 0,8KG of styrofoam above water you will need 0,8 x 1,15 x 50 Liter of water in your ballast tank. Because styrofoam roughly is 0,02KG/Liter.

[profesorul]

THANK YOU SO MUCH to ALL . 
 
I'm gonna need some time to Practice and study all of these for better understanding . 
 
MARIUS
 

[Subculture]

I have a CILINDER with 96mm Inside Diameter and 300mm in Lenght witch can be used for the balast tank

The volume of that tank is over 1.7 litres. Whilst my previous estimate of 500-700ml was only a guess based on the size of the boat and scale waterline, I can say for definitely, that would be way too big for the model.

I take it you know how to calculate the volume of a cylindrical shape it's easy enough- pi*(radius squared)*length

Use centimetres rather than millimetres so in the case of your cylinder- 3.14*4.3^2*30= 1743 ml or 1.7 litres

[profesorul]

OK.  I have another cylinder :
 Inside Diameter = 0,90cm 
Height = 0.20cm
 - witch means he can take 1L of water inside .
Is perfect,at least for now.Wheel shall sea if is correct.
 
MARIUS

[Subculture]

Looking at your earlier pictures it looked to me like you are working with a ballast system based on a gear style water pump and a bag. The bag would be mounted inside the WTC and as the bag fills the air inside the cylinder is compressed. A pinch valve is necessary with this system to prevent water pushing out past the pump and ruining your trim.

This is very similar to the system used on the Thunder Tiger Neptune, although that boat uses a peristaltic pump, which is slower at pumping but self checking and thus doesn't require a pinch valve.

You can place the bag inside a smaller cylinder, this should be vented at the end caps to allow air to escape. the additional cylinder constricts the volume of the bag to the desired amount, also preventing it from chafing on internal fittings and keeps it in place.

A good rule of thumb is to ensure the ballast volume is about 10-15% of the internal volume of the WTC. This keeps the pressures raised inside the cylinder to fairly low pressures which relieves the strain on the shaft seals.

Clearly the WTC will need to be constructed to ensure that the end caps remain in place when pressurized. there are various ways of doing this, a very elegant way that Ron Perrott uses is to make the saddles in the sub hull overlap the endcaps slightly, so that the hull itself acts as a brace for the endcaps.

That's what I call elegant engineering- one item performing two tasks.

[profesorul]

Looking at your earlier pictures it looked to me like you are working with a ballast system based on a gear style water pump and a bag. The bag would be mounted inside the WTC and as the bag fills the air inside the cylinder is compressed. A pinch valve is necessary with this system to prevent water pushing out past the pump and ruining your trim.
Yes,my intention was to use that pump with those bag BUT is NOT 100% sure I stick to the plan  . I am thinking of using only pump to FILL/EMPTY a closed WTC ,that I mentioned earlier .

This is very similar to the system used on the Thunder Tiger Neptune, although that boat uses a peristaltic pump, which is slower at pumping but self checking and thus doesn't require a pinch valve.
Can You tell me please what is and what are the main types of " pinch valve"?.Some pictures/threads where to look for it.

You can place the bag inside a smaller cylinder, this should be vented at the end caps to allow air to escape. the additional cylinder constricts the volume of the bag to the desired amount, also preventing it from chafing on internal fittings and keeps it in place.
If I use a HOLE or another system to vent the WTC during the Filling operation WHEN I do the EMPTY operation the WATER is NOT GOING to be SUCKED inside the WTC,because is creating a vacuum ?

A good rule of thumb is to ensure the ballast volume is about 10-15% of the internal volume of the WTC. This keeps the pressures raised inside the cylinder to fairly low pressures which relieves the strain on the shaft seals.

Clearly the WTC will need to be constructed to ensure that the end caps remain in place when pressurized. there are various ways of doing this, a very elegant way that Ron Perrott uses is to make the saddles in the sub hull overlap the endcaps slightly, so that the hull itself acts as a brace for the endcaps.
I understand that and I can manage with securing the WTC caps.I am NOT familiar with RON PERROTT WORKS  .Do You have somesketchhdrawingss/pictures with his systems?

That's what I call elegant engineering- one item performing two tasks.

I did some small    progress on Tower Sail:
 




 
What do You think ?.That last Hole should be drilled?.

[Subculture]

So are you looking at pumping water into a sealed hard ballast tank now?

That's a slightly different system which involves higher pressures. You will also need to add baffles to the tank.

[profesorul]

Actually I don't think is going to be involved such pressure do the air is compressible  .
But I think is good to have a Safety Pressure System , a valve or something but NOT being decided eat what system I am going to use I am open to any possibility.
 
MARIUS

[Subculture]

You've lost me with that initial statement I'm afraid.

[profesorul]

 SORY . Wasn't my intention .
 
 What I mean to say is:
 I did not decide EAT what version to use ..... for now I study and try to understand what it would be easier and more appropriate for this project .... what advantages and disadvantages are of each type .
 
I have so many things to do mean time so I am not worry for that matter .
One of my problem is , I don't have ANY DRAWING/PICTURE about what holes have to drill as SIZE/SHAPE/nr of them/WHERE should be don BOTH on Upper Hull and Lower Hull  .
If some one can point me where to look or has some DRAWING wheel be great . 
 
MARIUS

[Subculture]

As you are now a fully paid up member of the sub committee and can access the full back catalogue of magazines online, i would suggest having a look at a series of articles titled 'The laboratory' featured in issues 29, 30, 31, 32 and 37.

I think you will find the information in those articles very informative.

Sorry, I can't help with drawings of the LA class, it's not a boat that has ever appealed to me so I have never carried out any research into it.

[profesorul]

HELLO ,
 
I have some questions :
- what methods are YOU use to properly align rudders and dive planes axes from hull , and 90 degrees to one another ?
- how to make perpendicular holes for those axis to the hull ?
Some Pictures with any system wheel be Much appreciated . 
 
MARIUS

[profesorul]

HI , 

Is me again !.
Where did buy when you need bronze bushings? ...... some individual/company/sites anywhere? ..... but to sell small quantities of 5-10 units and be reliable ...... meaning someone might purchased and received goods required!. 

I need some BUSHINGS for the Propeller shaft , at the aft and at the end of the shaft before the motor connection .
And If I find some reliable Place I'll take more for the further projects too .


MARIUS

[Subculture]

Norbert Bruggen will sell you bronze DU bushes in metric sizes from 3mm upwards. these are PTFE (telfon) and self lubricating dry and in water, really nice for sub use.

You can machine bushes from brass rod too, not as good as bronze perhaps, but good enough for model use provided you keep them greased/oiled.

[profesorul]

OK THANK YOU .
 
I found his Site but where are the Bushings ? .My GERMAN is limited to a couple words  . 
Can You post a link for ?
If is not allowed here , can You send me by PM?.
 
MARIUS

[Subculture]

http://modelluboot.de/Zubehoer/Dichtungen.html#WDR

Scroll down to bottom of page.

My German is pretty much non-existent too. I find online translators help a great deal.

[Subculture]

I've also got bearings off this chap.

http://www.ebay.co.uk/itm/LEAD-TEFLON-5mm-bushings-4-off-rc-model-boat-FSRV-/120681581242?pt=UK_ToysGames_RadioControlled_JN&hash=item1c192ecaba

[profesorul]

THANK YOU , 
 
I wheel look for it . 
 
MARIUS

[Davy1]

Hi Marius,

You can make your own bushes more cheaply by buying a length of PTFE rod , drilling it and cutting bits off. A brass or stainless steel shaft runs with very little friction.

The problem with PTFE is sticking it to the hull (it is hard to use adhesives. ) However  you can hold it with small self tapping screws or cut chunks out of the outside and mechanically trap it in the hole in the hull with adhesive (or resin in a fibreglass hull.)

Alignment etc. is tricky in the rounded hulls of submarines. But I know you are resourceful guy! You should find small spirit levels (little ones just a few mm long - available in DIY stores.) to be quite useful. You level up the whole hull and line up shafts with reference to that. I have also found a laser level (DIY stores sell them for leveling shelves) Avoid any of that nonsense and use them on submarines! Again start with the sub level and use the laser level like a very long ruler to line things up on the hull.

David

[profesorul]

THANK YOU DAVID
 
I wheel keep in mind Your recommendations .
 
MARIUS

[derekwarner]

Guys....the problem here is understanding the % of potential water adsorption in the synthetic material

Nylon11 will  adsorb 0.0002*^ of the initial SG * by diameter.....poly tetra fluoro ethylene has similar properties

So you drill & ream a 4.00 mm diameter hole in a nylon/PTFE bush........

1. immerse in water for 24 hours & the hole closes to 3.982 mm !!
2. remove it from the water for 24 hour's & the bore returns to 4.00 mm

Derek

[profesorul]

HI DEREK
 
So what are you tray to tell us is : DON'T USE IT , unless you have no ather option ?
Any way What sub stays in the water 24H ?!?!?! , maybe 2 or 3 times a Year for 20-30 min !.
 
MARIUS

[derekwarner]

Marius....here is an old posting from Paddle ducks.....................I would simply suggest you are cautious in the material selection.......
Subculture mentions ......"Norbert Bruggen will sell you bronze DU bushes in metric sizes from 3mm upwards. these are PTFE (telfon) and self lubricating dry and in water, really nice for sub use".
Bronze impregnated Teflon...either 40% or 60% [by weight] may be a better option......Why not contact Norbert & ask....

________________________________________________________

 Reply #1 on: June 15, 2005, 08:51:01 PM »

Hi Stuart

Today's PD postings have a selection of recommendations - "like I did this xx years ago but it didn't work" & here is another

I would also opt away from delryn, nylon or any of it's Du Pont cousins - they are all unstable ie., high expansion rates for little
temperature increase as compared to bronze etc (20 years ago I tried nylon for the prop shaft stern tube bushes - absolute waste of time

(motor current consumption doubled as the bushes grew & provided tighter diametrical clearance over the prop shaft) - I could get access to the external (rudder side) bush to replace it in sintered bronze, however the stern tube was 5/8" diameter copper tube about 2 1/2"long and epoxied into the hull - required a hacksaw and 4" mini grinder to get the tube out!


regards Derek