## New member with question: About calculating divetank

Place for general submarine conversation

### New member with question: About calculating divetank

Hi friends, this is my first post as an new member to the Committee.
My name is Mats Wergeland and a live just outside Stockholm in Sweden.
I have hust started to draw an submarine. This is a Project that i have been thinking about for a long time.
I have built RC-planes since i was i kid (i´m now 45) but now its finally time for a sub since they have always been facinating to me.
So: Now to the question:

The volume of the WCT is totally 2,77/Gallons/ 1,8 L.
The volyme needed to sink fr "max" surface-level down to just below surface is 0,32 Gallons/ 1,2 L. Hov much Moore water will i need to pump in to dive down to aprox
2 m/ 6,6 feet?
I estimate that it will be my maximum depth.
As i have made the sketch the tank now has 0,13 Gallon/ 0,5 L left for the dive from surface down to the max depth (6,6 fet).
Will this be enought??
The boat will be run in ½-salt water (the Baltic-see).
I hope that you understand my question?
I really need to find this out befoore i can go on with my drawing but i have´t been able to find the answer anywhere on the net.
Hope you can help?

Rgs

Mats W
Mwd
SubCommittee Member

Posts: 8
Joined: Mon Nov 11, 2013 12:23 pm
Location: Stockholm, Sweden

### Re: New member with question: About calculating divetank

Hi Mats,

Welcome to the SubCommittee! You've come to the right place for all kinds of good information on r/c submarines.

If the 1/2 liter is enough additional ballast (volume) to bring the sub to just below the surface, then you can expect the sub to keep on sinking to the very bottom. This assuumes that you mean that there is no part of the sub still above the surface of the water once the additional ballast is taken onboard.

In theory one can adjust the ballast volume so as to get a submarine to 'hover' at a(ny) given depth, but in practice this is very difficult for our models. A very fine level of control over the movement of water in the ballast tank would be needed. Given that level of control, then the amount of additional ballast (water) that needs to be taken on is directly dependent upon the density of the water you are running in.

So all that said, if there is still some portion of the sub above the surface of the water, then the amount of water required to exactly compensate for bringing it to the water's surface would be the volume of water that is displaced by whatever is still above the surface.

Also, please be aware that running r/c subs in brackish (part saltwater) or saltwater will present difficulties in getting the radio signal to penetrate down to where the sub is.

-does this help?

Jeff
Rohr 1.....Los!

JWLaRue
SubCommittee Member

Posts: 3897
Joined: Wed Aug 31, 1994 6:00 pm
Location: Annapolis, MD

### Re: New member with question: About calculating divetank

Brackish water is hopeless with conventional R/C gear. You will have to run an aerial to the water surface. This will limit your depth to just a foot or two at the most.

An alternative would be to run a boat with an umbilical, like the ROV's. Clearly this would mean your boat is tethered, but it would afford you perhaps more flexibility than radio if there is no freshwater to sail the boat.

In reality trying to judge the depth of a boat accurately by eye is very difficult, even when you have perfect water, with good clarity and still surface. In a sea you have zero chance. Concentrate on getting a good reliable watertight enclosure, and chose a simple subject to start with.

May I suggest you get in touch with SubComScand chapter leader Bjorn Lundberg. he is very experienced in this hobby, and lives in Sweden, and is always looking to hear from fellow enthusiasts. he may also be able to suggest some good fresh water sailing sites.

Andy
'Why are you staring at an empty pond?'

Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk

Sub culture
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Posts: 2895
Joined: Fri Feb 21, 2003 6:55 am
Location: London, UK

### Re: New member with question: About calculating divetank

You say that it´s nearly impossible to hover??
There is a lot of pic´s and films on the net of subs crusing at steady depth so it can´t be totally impossible??
But i will be prepaired for some dificulties to come for sure.
Sad to hear thar brakich water is hopeless, i thougt that it woulb be pretty ok? This is an drawback for me.
Isn´t there any way around this?? Any way to increase signalstrength?
After all, there is 2013 now, we schould have been able to come upp with some kind of solution.
This project will be kept werry simple in the beginning. Later more "gadgets" can be added.
I will present an buildlogg later.
Now i have to spend several ewenings to surf this forum to see all the new info that is avaiable.

// Mats W
Mwd
SubCommittee Member

Posts: 8
Joined: Mon Nov 11, 2013 12:23 pm
Location: Stockholm, Sweden

### Re: New member with question: About calculating divetank

Mats,
Welcome! You definitely can maintain a depth with forward motion, but to truly hover (zero movement up or down and forward or backward) as I understand it is not obtainable. You can give the illusion of hovering, but in time the sub will creep up or down.

We are in 2013, but the laws of physics and laws regulating bandwidth take precedence. Anyway you have the right attitude, start simple! I was taught to crawl, walk, then run. Look forward to your build and we all have had frustrations, we are here to help you.

Mike Dory used to sail in brackish water in California. He left a couple of inches of antenna above the surface and had a longer than usual delay on his fail safes just in case he did go below the surface or a wave covered his antenna. You will gain a lot of experience doing just that and it will build skills.

Again welcome to SubCommittee and this fantastic hobby!

Peace,
tom
If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

salmon
SubCommittee Member

Posts: 548
Joined: Sat Jul 16, 2011 2:35 am

### Re: New member with question: About calculating divetank

Hi Mats,

Tom has it right. With the sub moving (typically forward), the dive planes act to counter the tendancy for the sub to rise or sink.

I have a 1/24th scale Seehund that uses a homebuilt dive module that has an Engel piston for the ballast tank. With some add-on electronics, I can get really, really close to hovering (no forward or rearward motion) but the sub will start to sink after a minute or two....but in the meantime it does look good just apparently 'sitting' there!

-Jeff
Rohr 1.....Los!

JWLaRue
SubCommittee Member

Posts: 3897
Joined: Wed Aug 31, 1994 6:00 pm
Location: Annapolis, MD

### Re: New member with question: About calculating divetank

Difference between deph-holding during hover ore mowing forward..hum.
Delay in the failsafe..have read that somewhere fefore but forgotten..?
Learning new stuff every minut here.
Thank´s guys.

// Mats W
Mwd
SubCommittee Member

Posts: 8
Joined: Mon Nov 11, 2013 12:23 pm
Location: Stockholm, Sweden