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Author Topic: Engel Ballast Tank and Robbe U47  (Read 5484 times)

irishcarguy

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Engel Ballast Tank and Robbe U47
« on: June 18, 2011, 02:15:26 PM »

Well maybe I becoming a little too "xxxxx" about this but here's my question on the Engel Ballast tank for the Robbe U47. I analyzing the size weight benefits of the 825 ml tank vs. the 750 ml tank. The 825 tank is 7/8 of an inch longer than the 750, and the weight with the tank and fully filled is 2.92 oz. more. By using the 750 tank I gain almost an inch of liner space in my WTC but give almost 3 oz. of additional ballast.
Any comments on this, does anyone think this Delta of weight would affect the diving and trim capabilities, or am I just nuts?
 :-))
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Mick B.

Mankster

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Re: Engel Ballast Tank and Robbe U47
« Reply #1 on: June 18, 2011, 02:20:32 PM »

A bigger tank would give you a higer surfaced waterline on the U47.  If you are not too bothered with gaining a more scale waterline, go with the smaller tank for ease of installation..

bonehead

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Re: Engel Ballast Tank and Robbe U47
« Reply #2 on: June 18, 2011, 06:36:11 PM »

I found when I did my U47 with the 750ml tank that it was a tad low in the water compared to the realistic water line and when fully blown I had about 1/2" of tower still out of the water. The 750 is a straight forward fit, need's reinforcing of the tray, and I got a lot of info off the net for the mod' but if I was doing it all again I'd go bigger to get the full static dive and better water line. My sub I sold a few years ago but it's still around and the new owner is pleased with it.... I think the slight positive bouyancy is reasuring and it only need's a smallamount of forward power to get her under. The other thing I did was servo control the front planes - did this with a low profile servo, metal geared, between the motors (if I remember correctly) with a sleeved push rod going froward over the outside of the wtc to the planes. I used a flexible model aircraft rod-in-tube and a lever in the boats rear to change the direction of the rear facing servo rod.... does that make sense? Also.... fit a leveller for the rear planes too! I can look out some more info as I think I have some instructions I printed out.
Hope this helps  :embarrassed:
Jim
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irishcarguy

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Re: Engel Ballast Tank and Robbe U47
« Reply #3 on: June 18, 2011, 10:44:07 PM »

Thanks

Jim if you have that information it would be helpful If you would like you could email it to me

John
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Mick B.

trevor v

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Re: Engel Ballast Tank and Robbe U47
« Reply #4 on: June 19, 2011, 08:53:48 AM »

my robbe U47 fitted with a 825ml tank(now sold)
http://www.youtube.com/watch?v=UhzKNmeOTs0&feature=player_detailpage
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thegrimreaper

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Re: Engel Ballast Tank and Robbe U47
« Reply #5 on: June 19, 2011, 02:54:54 PM »

I am thinking of adapting my U47 to static dive but I can't see me affording to splash out for an engal tank system was thinking of something along the lines of the system thats in my sheerline Akula question is would this be feasible considering how tight it all is in the U47 anybody converted the U47 to a static dive using other methods other than the engle system ??

regards Mark
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bonehead

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Re: Engel Ballast Tank and Robbe U47
« Reply #6 on: June 19, 2011, 03:56:04 PM »

Thanks

Jim if you have that information it would be helpful If you would like you could email it to me

John

Hi John
Have found two lot's of paper work for conversion - one printed off the internet and one I got from Pandan when I ordered the sub hull kit. As I don't have a scanner or such it would have to be by post - you're welcome to them as I won't be doing that model again - if ou want them PM me your address and I'll send them as soon as I can.
If I can remember the site I got one lot off I'll let you know or you could google U47 Engel conversion or such and see what turns up?

Cheers
Jim
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Subculture

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Re: Engel Ballast Tank and Robbe U47
« Reply #7 on: June 19, 2011, 04:14:56 PM »

The pressurized water ballast system would work, but it does need a larger volume tank than some other systems, as it only uses 50-75% of the tank volume. However if you were willing to switch battery technology to lipo or better still Lithium Life PO4, that would reduce the space needed for the battery pack by approximately half, and this would free up space for a larger tank. Also bear in mind that the engel tanks are quite slim (about 75mm diameter). You can fit a wider tank in, which will increase volume a lot.

I'm working on Roy's smashed U47 at the moment, although not right in front of me at present, but I think the inside bore of the cylinder is 10cm isn't it? Will have to measure it again. But assuming it is, a piece of 10cm acrylic pipe 23cm long will give you about 825 litre displacement with a tank 50% filled, and well over a litre 75% filled.

Another possibility if you don't mind retaining a bit of positive bouyancy i.e. top of sail just above the water, is a vented tank system. Would be very inexpensive (e.g. under 30), and that should work very well. You could use a Kavan (Ripmax) geared type pump (2L per minute) to pump in and out, no pinch valve required becuase you're not pumping against any pressure. That should give you a dive time of about 20-25 seconds. Not ultra fast but reasonable. The other way would be to use a centrifugal pump just to pump the water out, or blow it out with a diaphragm based air pump. Both of these systems would require the tank to flood using gravity as these only pump in one direction, so you need a large opening at the bottom of tank to minimise resistance. Might be a bit fiddly to incorporate that into the Robbe design.

Mankster

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Re: Engel Ballast Tank and Robbe U47
« Reply #8 on: June 19, 2011, 05:58:05 PM »

bonehead

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Re: Engel Ballast Tank and Robbe U47
« Reply #9 on: June 19, 2011, 06:30:49 PM »

The Modelbrass instructions...

http://www.modelbrass.com/U47Modifications.htm

To John....
This is one of the one's I have and very good too :-))..... Probably the more usefull of the two. I had the Modelbrass deck on mine, which is VERY good and well worth it. The net cutter was fiddly and you do need a good soldering iron with a small and very HOT tip. Come's out a treat tho'! The deck attachment method uses the capstans as screws, which means the whole deck will come off and gives good access.
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Subculture

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Re: Engel Ballast Tank and Robbe U47
« Reply #10 on: June 19, 2011, 06:49:53 PM »

Unfortunately, I don't think Jason is producing those decks anymore, despite the website still being active. Jeff Larue in the States did produce a set of brass decks on a small batch order basis, but you need to get half a dozen people together in order to geta  set of those.

Etched brass decks have a further advantage- being thinner than the kits plastic version, it should reduce the displacement, although the slots were narrower, which might even things up a bit. You might need to take a bit of lead out of the belly though to compensate for the brass being about eight times the density of ABS, or use some lighter batteries!

Dream Arts do some very nice CNC milled plastic decks to go alongside their range of replacment conning tower kits, not cheap, but will go a long way to improving the scale fidelity of the Robbe model, as the supplied deck is nothing like the original boat.

Subculture

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Re: Engel Ballast Tank and Robbe U47
« Reply #11 on: June 19, 2011, 08:44:59 PM »

Just took my measuring tape to Roy's U47- the cylinder is 9.5cm internal diameter, so 10cm tubing is out.

9cm PMMA tubing is available. If you can fill the cylinder to 75% full, a 20cm long tank should get you to the same waterline as an 825ml engel tank, maybe a tad longer if allowing for the tank endcaps and internal baffles. You have 50cm space from the motor bulkhead to the front cap. So that gives you an additional 30cm for batteries pump and pinch valve- that should be ample space.

The equipment tray will need serious modification for this to work however.

Andy
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