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U47 trouble, need help

R/C Submarine modelers

Postby g2tiger » Sun Oct 05, 2003 5:46 pm

Gents,

Need some advice/help. I have a robbe U47 with the accurate Armor conning tower, updated motors from ships n things, dual MCD speed controllers and the dual ships n things batteries. It is stock other than these items. My trouble is that when fully set up with both batteries it sinks, then if I take out one of the batteries it rolls over and to add insult it leaks at the rear seal.

Should I stuff some foam in the saddle tanks? I did try to remove 40mm of the lead weight as the instructions reccomend to lighten her so she would stay above water but this may have contributed the rolling problem.

Sad to say there is a big regatta this weekend and I was hoping to show off, there is this guy with a 1/48 scale Gearing Destroyer.....

What does the brain trust think?

Thanks in advance.

Charlie
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Postby safrole » Mon Oct 06, 2003 12:15 pm

I have read elsewhere that the conning tower you have is solid resin and quite heavy, which is probably your major culprit for the rolling. Maybe you could hollow it out a bit and replace with some foam? Lightening your tower (if possible) would surely help the rolling tendency due to the reduced keel mass that you needed to offset your extra components.
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Postby Carcharadon » Mon Oct 06, 2003 6:10 pm

Charlie, I don't know if this is any consolation but I had a major failure with my sub just a few days ago. I had to salvage parts from my other 7 ft. sub and then readjust the ballast on my 4 ft. sub. I took the sub out to my test pond five times today but I finally got it working right. So as of today everything looks good for Saturday. Hope to see you there.
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Postby Lundberg » Tue Oct 07, 2003 4:28 pm

Hi,

I've had problems with the U-47 "rolling over" as well, the main part of the problem was the weight of the Accurate Armour conning tower but another part was also that I had removed a part of the led keel weight.

(I sawed off the led keel weight a long time ago in order to test a higher water line.)

What I did to fix the problem was that I used my Dremel and sanded the inside of the tower walls A LOT. If I don't remember incorrectly I took away 1/3 of the initial weight, I think I made a posting some time ago (in the Tips & Tricks forum) with the exact numbers.

/Bjorn




Edited By Lundberg on 1066160885
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Postby g2tiger » Mon Nov 03, 2003 7:10 pm

Thanks for the input gents,

I have been working a lot lately but have managed to add some foam to help with the overweight delima. Also, I still have a leak around the joint where the two hulls come together. I tried a trick to the joiner screw, but it did not work, the leak is still there. My next move is to create a spacer for the "O" ring to try and get a better seal. I think the screw is not able to tighten enough because of a possible misalignment of space of the hull shape. If you understood that, my hats off to you!

Anyway, I will continue my testing and I will reduce the weight of the CT. By the way, I did remove a lot of material with the dremel, but possibly not enough.

Charlie
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Postby wellington » Mon Nov 03, 2003 11:56 pm

Charlie
I put on the Accurate armour tower about 3 years ago. I did not hollow it out. It is solid. I removed no weight from my boat and added weight to get the water level to the edge of the deck. This was done to allow it to dive better. I also have ships and things engine modification. My boat has never rolled, even at full speed turns on the surface and below water. in hindsight I would hollow out some of the tower but I am not about to take it off. As to leaking I have added a narrow elastic in front of the o ring so it adds a bit of help to seal the rear hull to the front. I would like to replace my o ring but cant seem to find a replacement. Hope this helps
Cheers
Dave Goddard
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Postby safrole » Wed Nov 05, 2003 1:07 pm

You can get stock O-rings from SubConcepts.
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Postby g2tiger » Sat Nov 22, 2003 6:37 pm

Gents,

I have been reading your postings with interest, thank you for the input. I have made an expander for the "O" ring. I used plastruct and cut out a 4 mm "doughnut" that is 104mm diameter. This matches the rear area where the seal rests against the housing. I am amazed that I still have a leak as evidenced by bubbles forming along the joint when soapy water is applied and air is forced into the hull through the supplied tube designed to check for leaks.

If asked I would guess the "doughnut" is about 1/2mm in thickness, I can check the package. I was thinking the "O" ring was not sealing and the "doughnut" would help make the screw joiner and seal tighter by adding space making the joint tighter. This may not be the case. I noticed the leak is on the starboard side. What this means I do not know. Any thoughts on this fustrating issue? The joint where the two hulls come together seams to be the issue. It is as if I cannot get one side to pull tight enough to make contact and seal. Should I make a second "doughnut" and see waht happens? Does anyone think the seal area may have an unforseen problem?


As for the Accurate Conning tower, I removed about 1/8 or more from the inside of the tower. This has lightned it considerably. My main concern is the leak right now. Does or has anyone done any work to the joint where the two hulls come togather?

Thanks for the advice guys, I just need some more if you have it.

Charlie
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Postby tsenecal » Sat Nov 22, 2003 9:07 pm

Charlie,

two possible things i can think of about your o-ring problems...

1) is there a knick in the o-ring itself? check and see if the o-ring is visibly knicked first, second is to physically move the o-ring around the end cap to see if the leak also moves.... check to see if the end cap itself has a knick or a seam in it that might be causing the o-ring to not properly seat.

2) I actually purchased a grease made for mountain bikes for their axle shafts, crank cases, bearings etc. it is 100% synthetic and 100% water proof. I originally bought it as packing grease for the stuffing boxes, where it works great, but in addition I now run a thin bead of it around the little gasket in the front and around the o-ring in the back. It has allowed me to make the wtc water tight with much less tension on the front screw.

Tim
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Postby PHPH » Mon Nov 24, 2003 3:52 am

Although I've never had any leakages around the O ring seal, i alweays keep this area HEAVILY smeared with vaseline, & even with the increased presure caused by my internal ballast system so far no problems & its now starting its 2nd year.
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Postby Lebeau » Sun Nov 30, 2003 6:29 pm

Hello...

I too am building the U-47. I have stopped at the construction of the "mid-section". I am afraid that I will sand back to much off the vacuum formed pieces, resulting in a poor seal. Is there a rule of thumb? Any advice or suggestions? I want to do it right the first. I see or read nothing in the instructions, that really indicates how far you should sand the ends back, once the edges/"lip" has been trimmed away.

Thank You

Stephen

PS: To ensure that I can be reached, here is my email and phone.

lebeau0@hotmail.com

(307)-321-1823

Thanks again...
Lebeau
 

Postby kd6hq » Sun Nov 30, 2003 8:03 pm

Lebeau

You might want to look at this web site : http://www.marinerc.com/submarines/u47_const2.htm

Only one end of the tube / hull should be sanded to be flush with each other. Please look at the above web site it covers the basic construction of the U 47.

Good luck
Don

Keep the faith.....
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Postby tsenecal » Tue Dec 02, 2003 9:34 pm

Lebeau,

the vacuum formed parts of the hull offer no integrity to the water tightness of the WTC. all 11 basic pieces are merely cosmetic. The reason they have you sand the edge down is so that the size of the gap between the stern and forward sections of these vacuum formed parts is as small as possible. To see an excellent example of a different way to solve this problem, please take a look at the following link to see how one can add additional "bulkheads" to reduce the gap to an almost invisible line. (frames 4, 5, & 6 cover the seam between hull sections). I used this technique on my sub and the results are very very good.

http://www.wingsontheweb.com/u47/u47-4.html

Tim
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Postby boatbuilder1 » Thu Dec 04, 2003 12:27 am

charlie
the cut I told you about didn't work ?
did you try to desolder the screw joiner and lengthen it ? this should work and give you a tight seal let me know
chuck
charlie



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Postby MIT » Thu Dec 11, 2003 10:28 pm

Any updates on this leak.

I too have a Robbe U-47 that I was going to start on this winter.

I will be installing an Engel 750 piston tank in it and the CT from Accurate.

The motors will be Graupner 400FG with a 2.33:1 gearbox.

Props I am still looking at. (any suggestions ???)

This "leak" has raised some concerns I had regarding this model. Did you try the vaseline suggestion ? Seems like the easiest one. I presume that the O-rings had no kinks ?


Nick
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