Hello everyone,

I finally decided to take the plunge and introduce myself on this forum. I do not speak a word of German, so I'll try to introduce myself in English.

I am a French 19-year resident in Brittany (region of western France). For 5 years, I am interested in this hobby. I have undertaken several projects that have failed, so I plan to take back some points to concentrate me on a new model.

This is a model of Collins, which I have begun modeling in Solidworks :



I am currently in graduate studies so I take advantage of a summer vacation to do some work on this project !

Greetings,
Simon

Hi Simon,

nice to have you here. Your drawing looks interessting. Can you tell us the scale?

Regards

Andy

First Idea on Your drawing:

Please take the trimming tanks at point with the same distance from the tower/fin to forward and aft tank.

When You trim the boat with those piston tanks, only the tower is on the surface. To hold the boat on an even keel, the tower needs to be in the CG of the trimming tanks.

Lothar

Thanks for your messages !

Andy > The scale is about 1:45. I will use a 160 diameter pipe.

Lothar > If I understand you well, you propose to place the trimming tanks precisely at the same distance from the tower ?
Actually, I fail to understand why. To my mind, the trimming tanks must be placed at the same distance from the Centre of Buoyancy of the submarine in diving, like for the ballast tank.

I'm looking forward to your reply !

EDIT : the more I think the more I doubt ! I will probably see more clear tomorrow, sleep on it...

Hi Simon,

You understood right, I try to explain it:

while diving, first the main ballast tank is filled. Now the boat should "hang" in the water with the tower on the surface. Now You want to make a perfect trim, so You move both trimtanks. If they are not in the same distance to the tower, one makes more, zhe other one less movement. This would be not the best way to trim.

To go deeper than leaving the surface, You need just 5 or 10 gramms of ballast. If You put them on the bow or on the stern, makes no big difference in practice (maybe in theory).

In most of my boats I tried to arrange as I decribed before and was successfull.

I hope I could help a little bit.

Regards

Lothar

btw: nice CAD-work.

Hi Lothar,

I took the time to reflect on what you said. In fact, I had not factored into my calculations that the center of buoyancy of the submarine changes during a process of diving ... but now, it seems to me quite obvious !

Well, I fully understand the position of the trimming tanks around the tower. And if I understood well, the main ballast should be located approximately in the middle of the deck (and even a little further forward).

However, there is something that disturbs me, I'll try to explain it with simple words. I hope my English is understandable enough !

When you want to trim the submarine at the beginning of a navigation, you first fill the main ballast tank. Once the ballast full, only a portion of the tower is above the water. The main ballast corresponds to the lower part of the superstructure. Then you work on the pistons.

Once the perfect balance achieved, you empty the main ballast tank. And at that moment, I think, the submarine should sink at the front, since the pistons no longer act on the top of the superstructure, but on their lower part ! As the tower is not at the center of the submarine, the balance can not be achieved in that order.

Do you follow me ?
Is there a difference to be made between theory and practice, or have I misunderstood something ?

If I was not clear enough, I can make a diagram. This may help to understand my question...

I have no doubt that the provision of your ballasts on your submarines is successful, but I try to understand the system in all its forms

Thank you,
Simon

Hi Simon,

there is no difference between pratice and theorie. You are right, the Bow should be lower, if the boat comes to the surface without pistons. But that's the trick: The difference is only a millimeter or so, because the difference is only some gramms between a piston in the stern or near the tower. Or in other words; the center of boyancy is moving only a little bit.

Very interesting effekt besides: If You "hang at the periscope and want to go deeper by flooding both pistons the same "little bit", You will see, that the boat takes down the bow some degrees.

If a boat isn't exactly symmetrical in the lateralplan, There is no "perfect position" for the pistons.

Hope my english as good enaugh....

Regards

Lothar

Hi Lothar,

Thanks for your informations, it's more clear now for me !

I worked on my CAD modelling :



The pistons are now around the tower. Not exactly at the same distance, but I tried to do my best to place those tanks. If I place it exactly at the same distance from the tower, I'll have to reduce its length to do it and I fear to have too small pistons.

Currently, my pistons are 210mL each (the inner diameter of the tube used is 50mm). The sub is about 1700mm in length and my main ballast is 2,5L : I wonder if I should not make it larger.

What's your feeling about this layout ? Do you think I'm on the right track ?


Regards
Simon

In my opinion, the piston tanks are on the right place. But I can't say if 2.5 liters main ballast will be enough. You should make a rough calculation about the volume above the waterline. Remember! It's the volume what counts, not the weight at all.

A very nice drawing, but it's hard to say if everything is fine. What kind of CAD are you using?

For a Sub of 1700 mm length at a Diameter of about 180 mm (I believe) Those pistons are big enaugh for sure.

Great drawing.

Lothar

Thanks for your messages, I appreciate your help.

Andy > I have in mind that it's the volume what counts, but how do you manage to make a rough calculation ? I mean, do you only use your CAD or do you wait to dispose of your hull for some tests in the water ?

Currently, this is just a simulation. I can't build the hull for the moment (a friend is about to make me the wooden form) so the construction is almost stopped. I am working only on the pistons and on some portions that are independent of the hull or ballast.

I use Solidworks 2009.

Lothar > The sub is 160mm in diameter.
Actually it's a small pressluft compared to your models

Hi Simon, I see you're in good hands!

Bye
Alexandre