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Author Topic: Salt Water Darnell U37  (Read 54909 times)

Sub driver

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Re: Salt Water Darnell U37
« Reply #100 on: October 10, 2013, 03:19:11 pm »

Hi.
I use stainless washers under mine, lot more durable than fibre which will break up.
notice you have some oversize holes in the perspex lid for the bolts to pass through.
Mine are a lot tighter tolerance plus a
silicone gasket so deformes around the bolt filling the gap. You might try o rings under the stainless washers to fill the gap as it were.

hope its of use........keep the faith nearly there.
regards sub.
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #101 on: October 10, 2013, 04:18:07 pm »

I ask as some of the bolts seemed to leak more as I tightwened them, possibly pointing to the washers deforming as I tightened down on them. I will try both the fibre washers under the stainless ones, and the stainless on their own. I am using hand cream as a hatch seal at the moment, purely experimental and easier to clean up afterwards than vaseline. However it might be back to vaseline as well.
My perspex lid 'tolerances', shall we call them? I blame the fitter who opened them out to 5.5mm and some to 6mm. You would expect better after doing this for thirty years. We learn by our mistakes but I think I have been 'round the clock' once already and am now making all the old mistakes again :-)
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #102 on: October 10, 2013, 04:55:44 pm »

And two suggestions for o-rings that I read and didn't sink in. Will factor that option in also, cheers :-))
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triumphjon

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Re: Salt Water Darnell U37
« Reply #103 on: October 10, 2013, 06:02:03 pm »

how often does the perspex lid need to be removed ? ( i prefer my models to stay above the water  ) ive a couple of yachts with hatches that are occasionally immersed , im using roof and gutter sealant ( bought from toolstation ) to form the " gasket " the hatch is kept in place with m4 stainless bolts with washers under the heads . jon
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Footski

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Re: Salt Water Darnell U37
« Reply #104 on: October 11, 2013, 10:18:15 am »

Simply stunning work.. :-))
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #105 on: October 11, 2013, 05:05:03 pm »

Thank You :-)) .

Best result so far, 15mm washer first, fibre washer second, M5 nut last. Pressure tested to fifteen pumps with a bicycle pump ( a bit over the top, I know, but its a good test. ), now only leaking the smallest amount UNDER the neoprene soft seal. Hopefully at more 'operational' pressure this wont be an issue.
Next job, get it to float......
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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #106 on: October 15, 2013, 05:25:05 pm »

Yay, It Floats!!!
Yay, No Leaks!!!

Air pump wont work once the sub is pressure tight, Stuff A Bucket!!!

Anyway.. it appears that the little piston pump is unable to reduce or increase the pressure in the main two compartments in any way. Once the screw top is released an audible hiss can be heard as the compartment re-pressurises to atmosphere, so thats a bust {:-{ .

Plan B, water tank. I have a redundant trim tank for a surface boat, now cut in half. Baffles under construction and three alternative geared water pumps tested for suitability. The sweetest is also the slowest at over 70 secs, the noisiest is also the fastest at about 25 secs. I have repaired a Norbert Bruggen Ballast Tank Switcher, water sensor now working. all that remains is buttoning up the tank and making more holes in the sub bulkhead. Dimensions of said tank 75mm dia x 195mm long, rough estimate is 800 grams of lift, I think...
I am planning to vent the tank into the RC compartments, I assume a pinch valve would be recommended for the water feed? The pumps seem to suffer from a little 'blow back', however a water sensor turning the pump off is of little use if water still seeps through the pump when submerged, despite not running!

Anyway, photos show the model floating in the pouring rain, in our team test tank. Now with excessive amounts of foam in place ( Trimmable as needed ), also the placement of the EPO foam blocks along the length of the model. I can highly recommend EPO Foam, just dont know where to get it. The blocks I am using were purchased from an RC Aircraft stand at Hop Farm about 3 years ago as cheap offcuts.




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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #107 on: October 15, 2013, 05:28:35 pm »

Please note giant 'Salt Water' antenna. This will be trimmed a bit and is entirely removable for static display or that holy grail of coastal dwelling submariners, fresh water :}
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GAZOU

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Re: Salt Water Darnell U37
« Reply #108 on: October 15, 2013, 05:44:07 pm »

the basin is not bulky in exhibition? %)

beautiful underwater :-)) :-)) :-))
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Subculture

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Re: Salt Water Darnell U37
« Reply #109 on: October 15, 2013, 06:24:01 pm »

Unless you are using a peristaltic pump, then you will need some way to block the flow of water back through the pump to maintain trim.

You can purchase diaphragm air pumps very cheaply that will work much better than the old USE pump.

Davy1

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Re: Salt Water Darnell U37
« Reply #110 on: October 16, 2013, 08:46:44 am »

Before you junk everything again, I would just check on the original Darnell air pump - it should work better than you describe.

I'm puzzled about its inability to pump anything and it was such a simple system. Have you got the original air reservoir in the bow?

I'm refurbishing a Darnell Type XXI here:

http://www.theassociationofmodelsubmariners.com/t1092-darnell-type-xx1-graham-s-dad-s-boat-for-refurbishment

The first post shows the original boat "as received" and you can see the original air reservoir. I checked the pump over and after fixing a few leaks I thought that the air pump was serviceable and that the original Darnell dive system could be made to work.

So I would have a look at the original system before going to more time and trouble.

David
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U-33

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Re: Salt Water Darnell U37
« Reply #111 on: October 16, 2013, 10:16:09 am »

For such a basic, simple idea, that little USE/Darnell set up always worked well...once you could get the boat trimmed up properly. The late Bernie Wood had a twin pump/twin air bag system in his famous Darnell U boat, and it always worked perfectly...lovely level static dives, and it looked so realistic when diving under way (I expect you've seen it at some of the shows we did back in the day, Alan?)


If I can find it in my archive collection, I have some video footage of Bernie's boat in action at the Plumpton Show back in the early 90's, I'll have a hunt for it and post it up here if anyone would like to see it.




Rich
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Rich

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Re: Salt Water Darnell U37
« Reply #112 on: October 16, 2013, 12:07:26 pm »

If you're referring to the boat that was built by Jim Ward, that was converted to a modular system by Nick Burge in 1991, the boat was a test bed for the system which was later commercially produced by Craycraft.

It featured a single hard ballast tank with a custom made twin cylinder compressor. The two cylinders were to prevent the pump loading up against itself, as the compressed air was stored in the forward compartment with the compressor. You can also circumvent this by placing the compressor in another compartment, or by making a small discrete enclosure for the pump to sit in.

U-33

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Re: Salt Water Darnell U37
« Reply #113 on: October 16, 2013, 12:22:29 pm »

No Andy, I was talking about Bernie's original Darnell U boat.



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Rich

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unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #114 on: October 16, 2013, 12:40:09 pm »

I do remember those days, Hat, Badges, Beard, Bernie Woods :-) .

The piston unit is not one of the cast units by USE but a brass affair with flywheel. It works perfectly well with all the lids open, taking about 70 seconds to inflate the bag, however, once buttoned up, nothing. Once the twist caps were released, there was a rush of air in or out, depending on how I tested the setup, then it would work.
I am proceeding with a water tank, but making no alterations to the model just yet. If I can get the air system working, great, if not, everything is removable anyway and I have more than enough bouyancy to accomodate weight variations in the internal layout.
When I started this project, the aim was to get back into the underwater mind set. I am glad I didn't start with a tube system, which would probably have been relatively trouble free. This project, setbacks, chaos, leaks, tech problems, loving it. Must be mad %%
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Re: Salt Water Darnell U37
« Reply #115 on: October 16, 2013, 12:52:19 pm »

How have you got this air system set-up?

Do you fill/prime the bag with the boat out of the water, then use the pump to suck air out of the bag, and store under pressure, or do you use the pump to pull a vacuum in the chamber to fill the bag?

unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #116 on: October 16, 2013, 01:05:57 pm »

I have tried both, so far with the same result. I am wondering if the pump is running too fast to 'bite' the air, similar to an over revving impellor pump/fan. Seems unlikely, but anything is possible. The fore and aft compartments are interconnected, so its a big reserve of air.
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Re: Salt Water Darnell U37
« Reply #117 on: October 16, 2013, 01:12:23 pm »

No don't think so- positive displacment design. My money would be the valves are probably leaky. Is your pump an oscillating model?

unbuiltnautilus

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Re: Salt Water Darnell U37
« Reply #118 on: October 16, 2013, 01:18:12 pm »

Single Cylinder oscillating.
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Re: Salt Water Darnell U37
« Reply #119 on: October 16, 2013, 01:36:09 pm »

Do you have a check valve inline with the pump and bag?

Sub driver

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Re: Salt Water Darnell U37
« Reply #120 on: October 16, 2013, 02:47:24 pm »

Hi.
try some one way valves in the system, I use windsceen washer non return valves....work a treat. Available from most auto suppliers.
Regards
Sub.
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Davy1

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Re: Salt Water Darnell U37
« Reply #121 on: October 17, 2013, 08:49:25 am »

 
Hope this helps show the original Darnell setup. (I connected it up and photographed it 30 seconds ago!)
Dead simple:
- No need for one way valves - you need flow in both directions.
- No pressurisation of your WTC - unless you have a very worn, leaky steam engine.
Hope this helps your setup.
David
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Re: Salt Water Darnell U37
« Reply #122 on: October 17, 2013, 08:52:25 am »

Looks like it might be a drain on the system.

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Re: Salt Water Darnell U37
« Reply #123 on: October 17, 2013, 08:54:23 am »


I had that setup, it was quite power hungry.....
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Re: Salt Water Darnell U37
« Reply #124 on: October 17, 2013, 09:06:47 am »

I was referring more to the backdrop of the picture. ;)
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