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Author Topic: Salt Water Darnell U37  (Read 54911 times)

unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #225 on: October 12, 2016, 06:11:14 pm »

Thank you, food for though as always. This may call for another, slightly left field, solution. Its in my head, lets not let it out just yet. Must size up the space that I have first...
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microgyros

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Re: Salt Water Darnell U37
« Reply #226 on: October 12, 2016, 07:48:17 pm »

Your external tank lends itself perfectly to what I think Andy means. Just chuck out the pressure rated cylinder tanks, probes and pinch valve and replace with a pop bottle.
If that sounds like a joke then look carefully at the wafer thin vented ballast tank in the middle picture. http://www.jotika-ltd.com/Pages/1024768/Krick_4.htm

The two bottom ports in the mostly submerged tank are connect to by a t-piece to the pump. The bubble canopy, capillary holes and fore/aft feed from the gear pump ensure there is no trapped air. The feed from the gear type pump possibly has an inverted u-bend if the water feed to the pump is below the water line, giving a couple of inches depth of water pressure. I've been assured otherwise on the last speculative detail.

Remember the Modelboats small ads for a cylinder system by David Evans? The designed-in trapped air bubble in that wtc was meant to expand under the vacuum created by two Lucas washer pumps. The air bubble method would not suit a vacformed or pop bottle tank where the only stress is from two inches of water. The bubble would also contract on diving to reduce the smallpositive buoyancy.
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Re: Salt Water Darnell U37
« Reply #227 on: October 13, 2016, 10:40:15 am »

Any sub with a high waterline is tricky when you are using a system that compresses the air inside. It becomes worse when the hull is moulded thickly, as it ratchets up displacement. Some hulls are better than others in this respect. On u-boats the use of etched metal decks can help a lot, as the metal although heavy, can be made very thin and therefore the tanks can be kept as small as possible.

Full size subs use very high pressure to store air for blowing the tanks underwater, but it's not terribly practical for modellers to replicate, plus the use of higher pressures tends to create an additional hazard best avoided.

The sealed tank water pump system is simple and pretty reliable if everything is built well enough to deal with the forces involved, which shouldn't be underestimated. You're generally looking at pressures of around 40 psi, which when spread over the area of the tank amounts to a lot of stress on the walls. Some of the later Sheerline boats used metal ballast tanks (they looked like brazed stainless steel, but not inspected one up close to confirm).

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Re: Salt Water Darnell U37
« Reply #228 on: October 13, 2016, 01:12:26 pm »




 Although I have not used one for a submarine tank, nor have I any experience of sea water submarines, a pop bottles, I used the well known brown, tooth  rotting, beverage containers, will certainly stand way  more than the pressure generated by screen wash gear pumps, some years ago I made water powered rockets to amuse my children ( not myself of course O0 ) and they were pumped up to my operating pressure of 110psi after burst tests burst tests were always over 150psi.
       I've tested the Kavan 12volt pump at 48psi some time ago, that was fresh water though I cannot see why sea water would be different, suspended sediment might be an issue for the pump but a filter can deal with that, placing two pumps in series would yield an increase in pressure.
      The 'emergency surface' system, triggered by a fail-safe, that I am building into my T Class Thrasher will use Robart r/c aircraft retraction system tanks, valves and lines. This equipment has an operating pressure of 110psi, so can well deal with the pressures of the water depth that model r/c gear can penetrate.
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #229 on: October 13, 2016, 01:23:42 pm »

Okay, I surrender ok2
Vented system is now on the radar. As I never intended to go negative buoyant in salt water, for fear of dropping the antenna below the surface and loosing signal. Therefore, remaining slightly positive buoyant lends itself to a vented system. Also as previously mentioned, everything is on board the model now, excluding a vertical vent pipe. Would 1/8" I/D be an acceptable size, or could I get away with 3/32" I/D instead?
I wish we had not sold the test tank two weeks ago now!!
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Re: Salt Water Darnell U37
« Reply #230 on: October 13, 2016, 02:46:25 pm »

Only need a small pipe- it's for air not water to go through.

A further advantage is you will have no exposed water surface to slosh, so stability of the model should improve slightly.

unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #231 on: October 13, 2016, 03:37:50 pm »

Breather pipe flush with the top of the tank, or down a few mm to retain a small bubble at the top of the tank?
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Re: Salt Water Darnell U37
« Reply #232 on: October 13, 2016, 04:13:09 pm »

I would run it completely empty or completely full with an aspirated system. So flush.

microgyros

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Re: Salt Water Darnell U37
« Reply #233 on: October 13, 2016, 04:54:24 pm »

Breather pipe flush with the top of the tank, or down a few mm to retain a small bubble at the top of the tank?

A simple tilt of a cylinder tank may not be as effective as the canopy, ring of holes, and twin drain on the vac formed tank of the Krick VII. You'd be better constructing a new tank made of plasticard.
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #234 on: October 13, 2016, 06:20:06 pm »

A simple tilt of a cylinder tank may not be as effective as the canopy, ring of holes, and twin drain on the vac formed tank of the Krick VII. You'd be better constructing a new tank made of plasticard.

I shall stick with the tube that is fitted for now, it's built and secured in the model. i still don't quite understand the ring of holes on the top of the Krick Type VII. to replicate that on my bigger boat, would I not need either many pipes rising up from the tank, or as you suggest, a plasticard version of the Krick tank, that fits my sub, with many holes?
I like the idea of the single breather pipe being as high as possible, maybe a 'voicepipe' in the top of the conning tower, rather than above the water line,but not necessarily visible when surfacing.
Of course, the only concern, which I cannot check until the sub is re-assembled, is will the high power pump be happy sucking air through a 3/32" dia tube, but not then start sucking air from the radio compartment also, as it did when the sub was bolted shut. My hunch is that it wont be an issue, but it is a powerful pump.
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Re: Salt Water Darnell U37
« Reply #235 on: October 13, 2016, 07:04:04 pm »

What pump is it you have again? I'm assuming it's a geared pump.

microgyros

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Re: Salt Water Darnell U37
« Reply #236 on: October 13, 2016, 08:23:37 pm »

If the holes are the correct size they should vent any air trapped above the lowest end of the pipe but not negate the pipe's drawing of air when it just breaks the surface.  There is no air vented to the  water tight compartments, just hose connections to the pump. One from the pump terminates in the free flood, the other to both ends of the tank base, via a T-piece. Don't ask me how the tank doesn't just fill from the small pressure of a few cm depth. I don't know.

I've recognised the occasional model using the system with a three-compartment cylinder wtc, one with a row of holes in the centre section, one with a dome, one with external water tubes. At least one other had made the vent and drain points in the bulkheads when the tube was white pvc.

However I have not spoken to this kit developer or producer. Tugmad George has the kit instructions.
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tugmad

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Re: Salt Water Darnell U37
« Reply #237 on: October 13, 2016, 08:54:51 pm »

The Krick ballast tank
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tugmad

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Re: Salt Water Darnell U37
« Reply #238 on: October 13, 2016, 08:57:10 pm »

Larger view
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tugmad

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Re: Salt Water Darnell U37
« Reply #239 on: October 13, 2016, 08:58:05 pm »

The other half
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tugmad

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Re: Salt Water Darnell U37
« Reply #240 on: October 13, 2016, 08:59:40 pm »

The actual tank
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #241 on: October 13, 2016, 11:42:36 pm »

What pump is it you have again? I'm assuming it's a geared pump.




It is a Darke Horse 20 (something) litre 12v to 20v geared pump. Fully reversible.
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #242 on: October 13, 2016, 11:48:59 pm »

Tugmad, thanks for posting images of the Krick system. I think its the lateness of the hour, but I am more confused now than I was before!!
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tugmad

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Re: Salt Water Darnell U37
« Reply #243 on: October 14, 2016, 07:36:19 am »

Yes it does seem a bit weird but as far as I can make out  from the very sparse instructions, the idea is that the boat is ballasted to a surfaced waterline with the tank empty, then to get it to the diving decks awash state the tank is filled,it holds 375Ml .the boat is then dived using the forward planes only,I am looking at making the after planes work,but have not got to that stage yet.
On the good side is that the boat has positive buoyancy at all times.  ( possibly? )

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Re: Salt Water Darnell U37
« Reply #244 on: October 14, 2016, 11:52:10 am »

Not familiar with that pump, but it looks like a gear based unit, so no worries. If you find the tank is now too large, then you can either reduce the tank, or add some foam in the conning tower, which will increase displacement and improve submerged stability.

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Re: Salt Water Darnell U37
« Reply #245 on: October 14, 2016, 12:40:09 pm »


Yes it does seem a bit weird but as far as I can make out  from the very sparse instructions, the idea is that the boat is ballasted to a surfaced waterline with the tank empty, then to get it to the diving decks awash state the tank is filled,it holds 375Ml .the boat is then dived using the forward planes only,I am looking at making the after planes work,but have not got to that stage yet.
On the good side is that the boat has positive buoyancy at all times.  ( possibly? )


  For my sub I am building a very similar system, the boat is a wet hull with wtc and is ballasted to waterline, a Kavan gear-pump fills a pair of saddle tanks to decks  awash, a small piston tank will then get the boat to 'periscope depth' or varying with temperature/density the boat is then in the top few cms of water where it can be visible and  it is dived dynamically being held level by commercially available electronic gubbins. As mentioned in a previous post, failsafe triggers an air release system to blow the 'pumped tanks' and up she comes if something goes really wrong, battery fail, signal loss(timed),safe depth exceeded, a separate timer system will blow a buoyancy bag and float.
   Well all that is the theory of the system, of which the component parts have been thoroughly tested and I'm happy with, but because of the poor quality of the molding, particularly the top heavy piece, I have had great difficulties getting the boat to balance which has meant lots of rebuilding of that half of the hull, and so I've not done a full out of sight pond test- -maybe next year?
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #246 on: October 14, 2016, 12:44:28 pm »

Patience is a virtue when it comes to subs. Take your time and get it right. One of the advantages of most sub models is that they are too big to throw out of a window :}
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Re: Salt Water Darnell U37
« Reply #247 on: October 14, 2016, 04:19:53 pm »




 Patience ? :} Perhaps we are patients to endure building working model submarines, and with an unknown neurological quirk %% %%


  Yes Sir! Difficult through a window sideways maybe, but sometimes tempting to throw it, or parts of, just like a spear through the same opening into the scrap skip outside the workshop <:(
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Re: Salt Water Darnell U37
« Reply #248 on: October 14, 2016, 07:37:51 pm »

You can make a very simple bu effective trim tank using a peristaltic pump, with a balloon flexible tank running inside a small tube to constrain its proportions. This only has to be volumed to about 1% of the overall displacement to giev you the ability to trim the boat for all water conditions.

Pumps are very inexpensive e.g. http://tinyurl.com/jrg2tm8

unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #249 on: October 14, 2016, 08:21:05 pm »

You can make a very simple bu effective trim tank using a peristaltic pump, with a balloon flexible tank running inside a small tube to constrain its proportions. This only has to be volumed to about 1% of the overall displacement to giev you the ability to trim the boat for all water conditions.

Pumps are very inexpensive e.g. http://tinyurl.com/jrg2tm8




They are nice little units, the 12v ones at the bottom of the page look useful too.
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