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Jan 14, 2015, 10:53 PM
Jetdrives R Us
sundogz's Avatar
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Wow, phase change pigment. My wife said it almost looks alive. Rob the bank, make your getaway in this boat and bystanders would be describing 4 different boats. Wonder what it will look like in the sun? Way cool.

Flexator, it there a diagram or template you could post? It sounds like you need 42mm (1-13/16" )height in the transom measured from the bottom of the intake, so you'd need it in your hands to get that measurement - or maybe use a template.
Last edited by sundogz; Jan 15, 2015 at 08:10 AM.
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Jan 15, 2015, 02:13 PM
Free my speech
BACKEMFNRG's Avatar
That is tough as nails in the video, Kudos on your lamination skills!!!

I've asked someone in PM if the Aluminum impeller (sp) can be sharpened and balanced like I do with surface drive props on race boats. Can they be sharpened or is a jet drive impeller a different animal??
Jan 15, 2015, 03:11 PM
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flexator's Avatar
Flexator, it there a diagram or template you could post? It sounds like you need 42mm (1-13/16" )height in the transom measured from the bottom of the intake, so you'd need it in your hands to get that measurement - or maybe use a template. (quote)
This is from there website,
http://www.kehrer-modellbau.de/en/fa...et28-jet-drive
It is 42mm without using the outer transom ring.

I've asked someone in PM if the Aluminum impeller (sp) can be sharpened and balanced like I do with surface drive props on race boats. Can they be sharpened or is a jet drive impeller a different animal?? (quote)
BACKEMFNRG, The only metal one I've seen is the from Mickiebeez, It is not sharp. Maybe he can tell us?
Jan 15, 2015, 03:26 PM
Jetdrives R Us
sundogz's Avatar
Thread OP
A regular (surface piercing) prop is thinned and sharpened to lower resistance by allowing it to cut through water easier. An impeller commonly has the same thickness throughout - it is designed to push water - the outer (square)edges riding against a tunnel 'wall'. The leading edge is often sharpened, but not the stator edge, which is left square like the back of a rudder to reduce drag.
Jan 15, 2015, 03:39 PM
Jetdrives R Us
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Quote:
Originally Posted by flexator
Perfect. I should have thought of that!. This tells it all - Thx, Flex.
Last edited by sundogz; Jan 15, 2015 at 04:27 PM. Reason: verbage
Jan 15, 2015, 05:10 PM
Registered User
hi guys, just thought id add a few projects here, this is the stage of the marathon hull and the larger version that i painted and will be fitted out with a jettec unit and 300pum petrol donk. the other hull was a boat i built for a customer , inlayed with carbon, my own jet unit and hull. Aparently the customer was going with a aquacraft ul~1 motor on 4s.
Jan 15, 2015, 08:33 PM
Free my speech
BACKEMFNRG's Avatar
Nice stuff so far and thank you for the response regarding the impeller. Just a UL-1 motor? Whatever works... Decent motor but, new you can get something better cheaper. If it was in your box already, then that's just efficient.

I am surprised to see a power robbing motor coupler there... Graupner makes couplers with a small flex in between, This would cut down on vibration and make motor alignment not as critical. Just my .02, remember I'm just learning about this stuff.
Jan 15, 2015, 08:53 PM
Jetdrives R Us
sundogz's Avatar
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For the larger drives, I make mine out of couplers and a piece of 5mm flex cable.

Mickie, nice paint! I am jealous. I have never been able to paint worth a hoot. If I lay down a layer with a rattle can and it doesn't run I get giddy.
Jan 15, 2015, 10:31 PM
Registered User
Im familiar with that type of coupler setup, yes your probably right about they being not as critical with the setup, but i always set up the motor inline with the jet unit shaft, because of this i have never had any issues with the uni joints. I supply these with the jet unit kits.
this boat went over there in the states, aparently he had a ul~1 motor laying around.
Mick
Jan 15, 2015, 11:05 PM
Free my speech
BACKEMFNRG's Avatar
Quote:
Originally Posted by sundogz
For the larger drives, I make mine out of couplers and a piece of 5mm flex cable.

Mickie, nice paint! I am jealous. I have never been able to paint worth a hoot. If I lay down a layer with a rattle can and it doesn't run I get giddy.
That's cool. I've done that before a long time ago. Now they have couplers with reverse threads so it won't ever come lose, not saying yours does or will.
Jan 16, 2015, 08:55 AM
Jetdrives R Us
sundogz's Avatar
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I don't think a reverse coupler would help much in this application. The flex turns the collet (part which is clamped to the impeller shaft) and the outer shell (part you tighten) follows. It doesn't have enough mass to resist the momentum. If you could apply enough spin fast enough it could unscrew, but it won't happen when an impeller shaft is tagging along. At least that way of thinking has served me well over the years.

Mickie 's right - if you have things in alignment there is no power robbed. It is like a solid coupler except that it absorbs some of the startup 'shock'. It is always important to have everything lined up - it helps prevent bearing, bushing or liner wear (which does rob power)
Last edited by sundogz; Jan 16, 2015 at 09:11 AM. Reason: clarification
Jan 16, 2015, 09:47 AM
Jetdrives R Us
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Thread OP

ALIGNMENT and BALANCE


I'm glad you brought up the subject of alignment. Someone is selling a kit that's supposed to reduce vibration by replacing the solid impeller shaft with a flex in a liner. IMO this may cause other problems including water leaks, air leaks - causing drop outs (aeration) loss of power, and accelerated rear bushing wear - which don't occur with the OEM shaft if it's kept greased. The real cause of the vibration is the coupler. The boat is furnished with a cheap, not quite balanced coupler which can raise havoc in a small jet drive. Get a better quality coupler, make sure the motor is aligned (you may have to enlarge the mounting screw holes to do this), and your problems are solved. I have upgraded several Tear Into's and have several bad 2.3mm couplers to show for it (I don't know why I'm saving them). Jeff Wohlt (rcraceboat.com) makes some of the best couplers available and has made many for me. But most any aftermarket coupler will be better than the OEM part.
Last edited by sundogz; Jan 19, 2016 at 01:24 PM. Reason: removed extranious information
Jan 16, 2015, 06:00 PM
Registered User
marathon hull joined, after testing of this one i will pull another hull out of the mold, make any necessary adjustments then make a mold from that.
Jan 16, 2015, 07:57 PM
Jetdrives R Us
sundogz's Avatar
Thread OP
The bottom of that hull (looking less buoyant) gives you a secure feeling that the intake will always be in deep water, and to see the full size boats under way with only the intake touching the water is too cool. Looking forward to seeing the maiden.
Jan 17, 2015, 11:38 AM
Registered User
Hey Dave and Marc good to find friends on this thread which I've already read. Starting to get back into the hobby again and like you guys love jet drives. I look forward to posting more here over time. The projects you guys have posted look interesting.


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