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Author Topic: Salt Water Darnell U37  (Read 54807 times)

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Re: Salt Water Darnell U37
« Reply #25 on: October 24, 2012, 05:40:53 pm »

Water is really the only practical solution for a pumped system. Glycol based antifreeze lubricates as well as killing off any bugs, however i wonder if it may have an effect on the plastics used in the pumps? I have run a water cooled computer for about ten years, and that runs on normal tap water, with no antifreeze, and I've never seen a bit of algae or stagnation in the water, despite all the warnings written on the web about needing special additives etc.

Mercury is used in some fullsize vessels, and being about 13 times the density of water, you wouldn't need to move much to get the same effect. But even assuming you can find a supplier, it's nasty stuff, and you don't want it getting into the watertable if you were unlucky enough to spring a leak.

However I prefer the system David mentions. Don't forget the shiftable weight could be placed in the wet area if space is tight. You can control the weight via a watertight gland or bellows.

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Re: Salt Water Darnell U37
« Reply #26 on: October 24, 2012, 06:19:13 pm »

Okay, could a shiftable ballast sytem be fitted either forward of the existing watertight compartments, or aft, and still be effective, or does it need to be around the mid-point of the model? Also could it be fitted above the screw down lid if it used only a small amount of weight but with a greater deflection fore and aft?
My brain stopped working about an hour ago and all the above seems totally sensible to me at the moment, I may need a lay down in a darkened room for a bit....
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Re: Salt Water Darnell U37
« Reply #27 on: October 24, 2012, 06:33:02 pm »

Yes that isn't a problem. Generally you can get about 40mm linear shift on a standard servo. The further you can move the weight the less weight you require to get an equivalent tilt (law of moments). Mounting above he lid of the compartment is possible, but this won't help the stability of the boat, as it will reduce your metacentric height.

How many degrees of tilt do you want, and do you know the overall weight of the boat (roughly). Regarding the weight, the battery pack is often used, but could also use a lead weight, or if you have some a block of tungsten which is about 80% denser than lead, not easy stuff to work with though, so lead is probably best!



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Re: Salt Water Darnell U37
« Reply #28 on: October 25, 2012, 05:59:25 pm »

Dont know the weight of the boat at the moment, in fact I am not sure it will float with the big D cell batteries on board. I have got back up Sub C packs in the wings just in case, its all a bit 'seat of the pants' at the moment, mind you, thats how we learn :-)



This was the sort of effect I was looking for, something to integrate into our WWII Convoy Display. So the tilt angle is intended to be quite severe, or as severe as a 20" deep lake will allow anyway.
I wont be attempting anything ambitious with this model, so no mods to the installed trim system.Its just intended to get me back under water after 22 years. The next serious build will have bells AND whistles attached, and I like the idea of trimming the boat 'Ram Up'. Keep those pesky slave trading ships at bay :}
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Re: Salt Water Darnell U37
« Reply #29 on: October 25, 2012, 06:01:16 pm »

Actually, I have been hacking away at the model structurally, which I consider fair game, but internals, dont muck about with stuff you dont understand...or have long forgotten.
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Re: Salt Water Darnell U37
« Reply #30 on: October 25, 2012, 07:04:51 pm »

The angle of tilt in that photo looks like about 15-20 degrees.

I've not owned a Darnell boat, so I don't know what they displace. At a guess I would think somewhere between 7-10kg submerged, perhaps a little more. So if you want to go the servo route, and assuming you manage to get between 20-40mm linear movement you will be looking at somewhere between 0.7-2kg of weight to shove about. With the ballast tank system, the weight would be a lot less, because you are moving it over a greater distance.

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Re: Salt Water Darnell U37
« Reply #31 on: October 26, 2012, 04:26:57 pm »

Well, trimming issues aside, I have started hacking again. The  extended lay up time allowed me to stare at the model and be overly critical about its appearance. The main issue being the lack of slot above the saddle tanks. The problem being that I have got the lid to fit perfectly without any flexing to fit. if i start hacking it about, it may not fit so well.
But why let that stop me :-)
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Re: Salt Water Darnell U37
« Reply #32 on: October 26, 2012, 04:31:00 pm »

Thank you Permagrit, for making a difficult job that much easier...
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Re: Salt Water Darnell U37
« Reply #33 on: October 26, 2012, 04:38:15 pm »

The reason for the slots? So I could add just a little bit more pressure hull under the upper casing, visible through the new slots. This needed building up with something, so out with the Glass Fibre Repair Paste. Just one point, before applying, abrade the surface vigorously, I forgot and paid the price....
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Re: Salt Water Darnell U37
« Reply #34 on: October 26, 2012, 04:50:44 pm »

Following a bit of judicious filling and sanding, I was able to apply a bit of Humbrol 87 Steel Gray to see what it looked like.
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Re: Salt Water Darnell U37
« Reply #35 on: October 26, 2012, 04:54:31 pm »

Black over the top of the newly re-defined saddle tanks, notice the gradual loss of the original camoflage scheme <:(
New scheme to follow %%
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Re: Salt Water Darnell U37
« Reply #36 on: October 30, 2012, 11:02:27 am »



This was the sort of effect I was looking for, something to integrate into our WWII Convoy Display. So the tilt angle is intended to be quite severe, or as severe as a 20" deep lake will allow anyway.

The angle of the bow in this photo of U-505 was due to the crew having started scuttle the boat.
http://www.history.navy.mil/faqs/faq91-1.htm
Were you planning on an authentic scuttling action?  %%
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Re: Salt Water Darnell U37
« Reply #37 on: October 30, 2012, 11:42:49 am »

Right oh!

Coming back to your original question. I would suggest something like car antifreeze - or a water/methanol mix. Something in there to kill the bugs but still tolerant of some water leakage.

David

What about Automatic Transmission/power steering fluid? denser than water and not quite as toxic as mercury

Then again there are Marine safe Hydraulic fluids tho slightly more expensive
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Re: Salt Water Darnell U37
« Reply #38 on: October 30, 2012, 12:00:00 pm »

How much denser than water is transmission fluid? I wouldn't have thought it was very much.

The other thing you need to be mindful of is compatibility with plastics. Water is fairly inert, although most plastics do absorb water especially if left wet over extended periods, although I would expect pumps designed for windscreen washers to be made from plastics that are very resilient in this respect (nylon and acrylic are probably the worst plastics with regard to absorbig moisture). However other fluids may cause the plastic to break down.

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Re: Salt Water Darnell U37
« Reply #39 on: October 30, 2012, 12:10:38 pm »

Im not sure exactly... will find out and get back to you

Didn't think about the oil and plastics thing.... one for for experimenting with I guess
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Re: Salt Water Darnell U37
« Reply #40 on: October 30, 2012, 12:35:01 pm »

How much denser than water is transmission fluid? I wouldn't have thought it was very much.

Water has a density of 1 kg/l, (salt water is around 1,020 kg/l) - ATF is around 0.85-0.86 kg/l so it's actually lighter than the water.

Your best bet if you're using a sealed system for the trim tanks, is to use either demin or de-ionised water :-))


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Re: Salt Water Darnell U37
« Reply #41 on: October 30, 2012, 02:18:56 pm »

Looks like de-mineralised water or its like is top of the list, possibly with some sort of winter additive type of thing to give it a nice blue tint. I will be able to see it then.
Scuttling action? Yes :-))
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Re: Salt Water Darnell U37
« Reply #42 on: October 31, 2012, 12:59:59 pm »

My main concern with your set-up is the tanks themselves. With an unbaffled pair of tanks situated a long way past the centre of gravity, any slosh in there will I think result in some unpredictable handling.

I would think of fitting either spherical tanks (solvent weld some plastic hemispheres together from EMA's) or make some cylindrical tanks mounted end up. These will give little to no slosh.

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Re: Salt Water Darnell U37
« Reply #43 on: October 31, 2012, 01:24:34 pm »

I will give this some thought, maybe a little bit of lateral thinking is called for.......
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Re: Salt Water Darnell U37
« Reply #44 on: October 31, 2012, 02:20:59 pm »

whay not use the bladders instead of tanks like the TT Neptune?
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Re: Salt Water Darnell U37
« Reply #45 on: October 31, 2012, 02:55:04 pm »

You could use balloons inside the tanks.  The natural elasticity will keep the water from sloshing about Change them now and again, as they can degrade as the air gets to the rubber.

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Re: Salt Water Darnell U37
« Reply #46 on: October 31, 2012, 05:03:18 pm »

I have spoken to my friendly neighbourhood upholsterer, who has dropped off a selection of man made fibre pillow/sofa stuffing material. Similar to cotton wool in look, but drains/dries quickly. Seems to take up about 5% volume in a cup of water and drains off in about ten seconds. As I couldn't find the stuff they put in F1 Car fuel tanks, and cannot get baffles through the neck of my fuel tanks, I will test this. It may well need a fuel filter fitted in line between it and the pump, although it does not seem to 'fray' easily.
This is me being stubborn :} as I have already made my nice brass frames for the tanks. However, notes are being taken for the next project, so thank you for the ongoing input, greatly appreciated as always, and hopefully helpful to others along the way :-))
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Re: Salt Water Darnell U37
« Reply #47 on: October 31, 2012, 05:24:48 pm »

stuff they use in motorsport fuel tanks is available from  MERLIN MOTORSPORT  , based at castle coombe racing circuit , wiltshire !
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Re: Salt Water Darnell U37
« Reply #48 on: October 31, 2012, 05:42:43 pm »

They use it in aeroplane fuel tanks too I believe. I've not seen or heard of it being used in a submarine before. Unnecessary if you use a ballast system which doesn't employ an exposed water surface.

It must reduce the volume of the tank by a fair bit, and I'd be a bit conserned by the risk of bits breaking off and possibly clogging the pump.

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Re: Salt Water Darnell U37
« Reply #49 on: October 31, 2012, 05:55:19 pm »

wouldnt wire wool do the job?
Grendel

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