Trim Tanks

[mylo]

Hey all,

I'm putting a fore/aft trim tanks in my VIIc/41 for fine control of "zero bubble". I've been in discussion with Skip Asay on this arrangement. I like it for a number of reasons:

- Realistic trim control. (That's how the big boys do it).
- Small trim tank requirement (very little space).
- Totally independent system. Not connected to main ballast control.
- Water weight in trim tanks remains constant eliminating fluctuating buoyancy issues. Only variable is in shifting that weight fore or aft.
- Cheap.
- Not complicated.
- Light weight. (Trim tanks take on neutral buoyancy when 1/2 full of water, allowing for both a subtraction or addition to water in the tank. Tanks below waterline so no added main ballast volume required. Pump and plumbing is only added weight to sub, which is minimal.

It's my opinion that what is important in this system is to be able to control the flow of the water from fore/aft tanks. Very little water exchange from the tanks would be required to trim the sub since what is happening is weight is being subtracted from one, and added to the other, in effect doubling the effect of the volume of water being exchanged. I'm thinking that a pump that has a very small flow rate is the answer. (or a pump modified in such a way). The way I see it, the actual size of the trim tanks, as long as they are neutrally buoyant when 1/2 full, is of little consequence, and that it's the volume of water being exchanged that is of most importance. Of secondary importance is the location of the trim tanks in the sub, with tanks mounted at the further extremes having more leverage and thus being more sensitive in trimming the sub given a particular volume of water being exchanged from the fore/aft tanks. For eg. If the trim tanks were 500 mls, 50mls, or 5mls, ....if 1ml of water was being exchanged from the fore to the aft tank, it would have the same net result on the trim regardless of tank size, given these tanks had the same distance between them. Am I wrong in this thinking ?

I would be interested in knowing if anybody has this type of system in their sub and what their experiences with it are. Throwing this topic out there for discussion.

Mylo

[theo]

Trim Tanks

Hi Mylo,

I found your thoughts about installing a "Trim Tank" setup of interest. I'm very new to the submarine stuff and am building the GATO sub. I am building mine from a somewhat Hi tech point of view as I can be somewhat creative in my designing process, I have designed torpedo's for my sub that have a travel range of about 35' that I have tested in my pool. Now to your project, it seems to me that you may want to look into putting in a small bladder in each end of your sub and using a/the APC-4 (that you might already have in your sub) for an automatic balance control system and have it only function 'On Command" what you want to do a balance of your sub. Just a thought of mine as you will already have the functionality of a APC-4 type unit in your sub. Any comment??

Jack

[mylo]

Jack,

I don't know what

Jack,

I don't know what an APC-4 is, but from what you said, it sounds like it's an electronic device that auto trims. I'm not particularly interested in an auto trim system, but would consider it if it could be rigged into the trim tank setup by controlling the water pump. I am more interested in the manual control of how my sub is trimmed. I may want a bow up attitude at times, or perhaps bow down, but the point being I want control of this. The "Auto On Command" idea is interesting though. I like the idea of having lots to do when operating the sub. To me, that's the whole idea. If everything is auto, a guy might as well stay home and watch T.V. My sub is big, and it's going to be slow moving, so I would like the challenge of manually trimming it while under sail. I'm convinced the key to the whole concept is a pump that just squirts a little bit of water. I need a prostate around a piece of 1/4" fuel line that squeezes if subjected to an electrical current, that's what I need. Hard to find a good used prostate though.

Mylo

[fgauer]

Mylo,

At least there are small

Mylo,

At least there are small peristaltic pumps out there - now to find a good source of surplus ones cheap!

http://www.randolphaustin.com/supplemen ... Series.pdf

Frank Gauer
Tustin, CA

[mike dory]

Mylo, My friend, Tell us

Mylo, My friend, Tell us what type of ballast system are you going to be using Then we maybe able to talk trim tanks. I'm sure Skip told you all this but There are two basic types of trim tanks (1) Those that take on water because you have lighten up your boat ( This maybe because you have fired off all of your forward torpedoes or if your using a Propel type ballast system, which I wouldn't recommend, in such a large boat. You have used up alot of air blowing tanks and need to replace the weight. Or (2) You just want to be able to have a bow up or bow down attitude for say running on the surface. ... As for Using an APC (Auto pitch control) Trust me, your going to need it. Skip will tell you the same thing. Your eyes can not see the settle changes in your boat's pitch, in time for you to make the changes nessary to keep your boat level. Looking through water can be very miss leading. This is particurly true of type V11 boats in a turn. The bow always wants to go up. Having an APC on your rear diving planes is the only way to go. You can always over ride the APC, should you wish to make some slight trimming changes But dont leave the dock without one on board... Pay close attention to what Skip as told you. He's taking his time to share with you at least 35 years of experence building great running boats...... Best Wishes ... Mike Dory

[mylo]

Mike

My main ballast system is

Mike

My main ballast system is going to use a "low pressure blower" combined with on board pressurized air. The blower, from my understanding, is simply an air pump. The blower can be activated once the intake line, which is mounted up high in the tower (yet concealed) is above waterline. This blower then pushes the water out of the main ballast tank through the outlets in the bottom. To get the sub so that this intake line is above water, you can either "drive" the sub up that way, or use a little bit of reserve air to create a slightly buoyant state, bringing the sub up. The benefit I see to this system is that the blower system itself is very simple and reduces greatly the amount of pressurized air needed. The pressurized on board air also doubles as an emergency blow. As well, I am going to mount a "neutral buoyancy" piston tank right inside the main ballast in order to be able to dial the sub in given any water condition.

THAT....is the plan for my main ballast.

The trim tanks are going to be neutrally buoyant when 1/2 full as well as below waterline, thus having little to no effect on any weight/balance issues. I don't want anything that takes on, or purges water. My trim system is going to be fully enclosed with water simply being transferred from one tank to the other via a pump that can be switched to pump in either direction.

As for APC, if it's a must have, then it is. I like the idea of the APC being connected to the planes and NOT the trim system. I can see where the APC controlling a consistent depth while operating would be very nice. The trim system is for me to be able to make minute changes in the sub's trim....quite simply. It has to sit in the water perfectly, surfaced or submerged, and I want to be able to control that remotely.

I fully realize the wealth of knowledge such guys as Skip Asay bring to the table. If it's one thing I do well, it's listen when people talk. .....I'll sort out my opinion afterward.

Mylo

[skip asay]

Mylo said -
“If the trim

Mylo said -
“If the trim tanks were 500 mls, 50mls, or 5mls, ....if 1ml of water was being exchanged from the fore to the aft tank, it would have the same net result on the trim regardless of tank size, given these tanks had the same distance between them. Am I wrong in this thinking ?”

No, not at all. But if you use the 10” long tanks you initially described, you’ll be wasting a lot of space and setting yourself up for too much extra work in constructing baffles. KISS definitely applies here.

Other than that, you’ve hit the nail on the head. Reducing the pump’s output volume is relatively simple. A.) Run it on less voltage. B.) Put restrictors in the hose.

APC-4 is an Automatic Pitch (leveling) Control (Mikessubworks has them) which drives the stern planes servo and, courtesy of a very sensitive chip, keeps your boat level when underwater. With APC - 4, you have a choice of controlling it from the TX or letting it “stand alone” (no signal input).

I see no reason why one of these could not be used as an automatic trim control. (See my post in RC Modeler:Auto Trim) But whether automatic or manual, the important thing is that very little water should be moved between the tanks. Read that as the volume of water should move slowly. As a matter of fact, the trim tanks themselves really only need to be about 1 - 2 feet apart in a boat as large as yours. This has been shown in Bud Lederer’s boats. Bud’s been using trim tanks for many years.

As for the pump, I’ve used model airplane fuel pumps we got from Hobby Lobby in all of Bud’s boats for trim systems as well as periscope mechanisms. And, like Timex, “they keep on ticking”.

Skip Asay

[mylo]

Skip,

I went with a

Skip,

I went with a 10" long tank because that was the distance I had between bulk heads, and I wanted the tank mounted firmly on the bulk heads. I suppose I could have built some sort of mount between the bulk heads, but I was just thinking....heck, ...just have the trim tank long enough to reach in the name of KISS, really.

Funny story about the "fuel pumps". I went into my local hobby store asking for an "r/c plane fuel pump". The guy was adamant that there was no such thing, that r/c engines do not require a fuel pump. I insisted that it was an "r/c plane fuel pump" that I needed. ......no such thing....... how can that be, Skip Asay told me he used a fuel pump. Nope.....no such thing. Finally....the guy said, "Maybe you are looking for an electric pump to pump fuel into and out of an r/c plane fuel tank to fill it".

.....uhhh.....yeah, ......that's what I mean. ....do you have one of those.

Mylo

[mylo]

Skip,

My sub is 105" long.

Skip,

My sub is 105" long. The center of the fore trim tank is 22" from the tip of the bow, mounted low in the hull. The center of the aft trim tank is 24" from the tip of the stern, mounted low in the hull (same as fore tank), making the centers of the trim tanks 59" apart.

In your opinion, using a outer tank diameter of 1" (material wall thickness 1/16"), how long should I make the trim tanks ? (I don't EVER remember a question like this in grade 12 math class....I KNOW I would have paid attention to that).

Mylo

[skip asay]

Mylo -

A 1” diameter tank

Mylo -

A 1” diameter tank with 1/16” wall with a length of 4” will hold 1.33 ozs. of water. With 59” between tanks and taking into account the leverage available, the 5/8 oz. should be more than enough to do what you want. The trick is the very first time you trim your boat, make sure each trim tank is 1/2 full. If you’re going to use the piston tank trim inside (or below) the main ballast tank, make sure that’s 1/2 full. Then do all the adding weight and foam as needed until the boat sits perfectly level with just the upper rim of the conning tower at the water’s surface. Now activate the pump for just a second or 2. You’ll be surprised at how much effect that has.

As I said in my PM, try to mount the tanks vertically.

Skip Asay

[mylo]

Skip,

4" it is, I'll

Skip,

4" it is, I'll cut the ends off my 10 inchers and put new end caps on. I can fiddle with my mounts and build a few more pieces to make a smaller tank work. The design of my bulk heads makes compromises to install torpedo tubes fore, and a pressurized air bottle aft. That, combined with my dive plane / rudder control rods just doesn't make a vertical trim tank possible as much as I like the idea.....too much junk in the way. I'll have to keep them horizontal, mounted low in the hull.

I ordered an electric fuel pump. By simply adjusting the voltage, can I adjust the volume being pumped ? How do I adjust this voltage, wire a light dimmer switch in there ?? ....don't laugh....I'm serious.

Mylo ......one.....small.......step........at.........a .........time

[Guest]

You can vary the voltage,

You can vary the voltage, but it's a very crude method of speed control.

All you need is a bi-directional ESC. These work by switching the current on and off very quickly- they vary the current to the motor- the voltage remains constant. This has two advantages- it's more efficient and the motor has more torque.

Power (in watts) = Volts (emf) x current (flow of charge)

For calculating ballast tank volume in a cylinder Pi (3.14) x inside radius of tank squared x length of cylinder. Very simple.

For strange shapes and/or partial volumes, I find this site really useful-

http://grapevine.abe.msstate.edu/~fto/t ... index.html

Saves breaking out the slide rule!

This place supplies peristaltic pumps-

http://www.williamson-shop.co.uk/

They're not cheap though, and you can always make your own- probably the simplest kind of pump to make.

Andy