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Jet Drive selection

Old 09-15-2007, 12:17 AM
  #1  
shishtawoo
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Default Jet Drive selection

Well I’m building a 7.5 ft scale battle ship, but I want to use jet drives instead of standard props. If I go with jet drives I was wondering if it would be better to use two Graupner GR2340 or four Graupner GR2345. I’ll be powering the units with two 400w brushless motors.


http://www.hobby-lobby.com/jetdrives.htm
Old 09-15-2007, 09:17 AM
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Flabum
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Default RE: Jet Drive selection

I believe your manuverability would be extremely limited with those. Plus, they are designed with speed, not weight in mind. I'd stick with props and rudders.
Old 09-15-2007, 11:53 AM
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Default RE: Jet Drive selection

I actually think you'll have very good maneuverability with jets. However your model is huge, I don't think either of those drive are near big enough for your boat. You'll need to look at MHZ drives. The trick to good maneuverability is making the drives independent. Separate throttles and reverse buckets. If you add a stern thruster and a bow thruster, the boat could do anything, sideways diagonal turn a dime.........etc. The MHZ drive are expensive, like $400 a piece, but they're big enough, you could also look at KMB drives, jet-drive.de. With them I'd look at twin 40mm drives. They're actually your best bet.
Old 09-15-2007, 12:16 PM
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shishtawoo
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Default RE: Jet Drive selection

So 4 of these drive couldnt cut it, one will power a 35 inch hull so since my hull will be 91 inches i thought 4 would be overkill.
Old 09-15-2007, 02:32 PM
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Default RE: Jet Drive selection

They would power it, but there is a question wether it would power it well. [&:]

Better to put four jet drives on one of these US Navy ships.
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Old 09-15-2007, 04:07 PM
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LClark
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Default RE: Jet Drive selection

OK Umi, where did you get this pics....I would like to check those beauties out further
Old 09-15-2007, 04:21 PM
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Default RE: Jet Drive selection

So 4 of these drive couldnt cut it, one will power a 35 inch hull so since my hull will be 91 inches i thought 4 would be overkill.
It doesn't really work like that. Assuming similar models at the different sizes, one is almost three times the length of the other. Also three times as wide and three times as deep, 3x3x3=27. A LOT more power.
Old 09-16-2007, 12:25 PM
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Quicksilver1
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Default RE: Jet Drive selection

I still recommend twin 40mm drives. Heck a real jet ski uses an 80mm drive. Your boat will be as big as a jetski so.....yeah you need a lot of power. Four small drives will get you something like 5kg of static thrust, not enough. Bigger drives will be much more efficient. It will definitely move with 4 drives, but it'll handle horrible, wont move fast at all and be twice as complicated as twin 40mm's.
Old 09-22-2007, 08:29 PM
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texas_hippie
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Default RE: Jet Drive selection

I gotta tell you, I just installed jet drives in the Dumas American Enterprise. Jet drives are designed for a FLAT transon, that is at a 90 degrees rake from the keel! I can't recall any battleship that has a flat transom (vs. rounded). You really have your work cut out for you here. I can't imagine how it's gonna work, shipmate. Don't forget to plan for the reversing buckets that you're gonna need if you want the vessel to back up! Secondly that model is gonna be far from scale. If you make it work though, post some pictures. Good luck!
Fair winds...and following seas.
Old 09-23-2007, 10:12 PM
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headhunter23
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Default RE: Jet Drive selection

I had the same issue when I purchased my jet drive... which one. The graunaper ones were somewhat nice but there was f all for information on them. After reading up enuff, special thanks to quicksilver for all his posts and testing, decided to look at the kehrer jet drives. http://www.jet-drive.de/vg_server/cu...bau&language=0

not sure if that will get u too the english version, if it just gets u to the front, click enter and top left there is an american/English flag so you can convert it to whatever language. Anyways the details and specs on what jet drives do and size of boat, motors etc is all there. Those Germans are great at getting the details. Hope the info helps.


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