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Old Nov 19, 2012, 09:17 AM
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United States, MI, Royal Oak
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Chidago, looks like a great performing boat youve got there! What motor are you running in that?
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Old Nov 19, 2012, 09:38 AM
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Thank you J, I appreciate that..

My uncle bruno lived in Royal Oak, so did I when I first started at Chrysler, moons ago..

I am using a 3900kv turnigy, 3s, Graupner jet, 3 degrees up trim on the jet, .010 clearance on the impeller to stator distance, 60a turnigy marine ESC.
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Old Nov 19, 2012, 11:10 AM
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Hey very cool, yeah I love Royal Oak, its my second time living here now. Would you happen to have a link to the motor you are using? Ive got two motors that I got for this boat, but one seems too high at 4800kv and one too low at 2100kv lol.....
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Old Nov 19, 2012, 12:03 PM
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Sumner surf

Looks quick, what is the rotor to nozzel diameter ratio you are running?

Here's my Coroplast scratch build surfing in the Pacific ocean

Yellow NQD Jet Boat Sumner Surf FPV high tide in the surf jumping clear of the water, going vertical (11 min 24 sec)


https://maps.google.co.nz/maps?saddr...p=1&sz=19&z=19

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Old Nov 19, 2012, 01:14 PM
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LOL !! ...Nick, you put waves in a new perspective..we aint got creeks like that... great vid.

JG, just go to the hobbyking site, under boat motors, its the 3900kv brushless with water jacket, 40 bucks, I think? or, close to it..

When talking with Sandy at Graupner, before I could pick power, I wanted to see what the jet could take rpm wise..he said 20-25k..on the 3s, thats 43k UNLOADED..loaded, I figured 30+, and if it overran it, I would just dial some throttle out of it..dont know what it does turn, but, at any throttle level, even like 85%, wide open still accelerates the boat, so, it seems right.

I saw one run on 4s, sick holeshot.., but, it breaks a lot.. I wanted trouble free, best I can, this package was cost efficent, and hit the power just right for my usage..But, the speed it runs now came from working with, and tuning the boat..I had to add tabs, made a difference for me, but, that could be because of my rigging inside, too..

All of em are individual in how they run, by the vids I've watched..

nqd rc jet boat. sickly powerful. brushless 14.8v (1 min 1 sec)
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Old Nov 19, 2012, 01:23 PM
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Mad fast I want one
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Old Nov 19, 2012, 01:36 PM
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I'm using air cooled having cooling no issues with the motor @ 26 Amps 264 Watts on the watt meter on a Turnigy 3C 198 grams. Its a 20 inch boat around 700 grams at launch. Like doing FPV getting a ducks eye view . Akaroa harbor
FPV Yellow Boat Akaroa Harbor 19-11-12 NQD Jet Turnigy 2632 3800kv Turnigy 3C 2200mah Lipo (3 min 33 sec)


More vids http://www.youtube.com/user/nickatredbox/



P2632 Brushless Outrunner 3800kv
RPM: 3800kv
Max current: 32A
No load current: 11.1V/3.2A
Internal resistance: 0.036 ohm
Weight: 51g
Diameter of shaft: 2.3mm
Dimensions: 26mmx32mm

Its a deep V so it will never be as fast as yours, I have the cheap and cheerful NQS's US$69 for four units. I have tinkered with impellers but am currently running stock.

My ESC is an Turnigy AE-30 with a big heatsink

Currently developing a drop in power module with servo motor jet and ESC as I am building for a friend



The idea being the aluminum which is embedded into hull and in the water will act as a heatsink for the ESC

Happy jet boating I have 2 jet pumps in stock may build a twin hull speed moster with 2 X 4500 KV heli motors ! POWER !
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Old Nov 19, 2012, 03:45 PM
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Quote:
Originally Posted by chidago View Post
Rim, I tried heating it, the plastic softens to bad to let the joint go..it aint the glue they use inside, so I gave up..but, a GREAT idea..lemmie know if you find a way to get it loose, please.

I finished tuning mine, problem is, its a shortie, cant do anything about that, and to keep the pump hooked up better, it would need waaay more hull, or a different design..my problem with everything is I take stuff to a extreme, and eveything has a limit by nature..

Water, by its nature, doesnt compress, and, volume cannot be scaled down, the engineering degree my father paid for, so many years ago, still works..

In the mid 80's I raced, pro, full size jets, and in the 90's I owned part of a jet boat facility, Tahiti
Caribbean, great boats, was part of the parent company that owned berkley jets, Hardin Marine, who did all the jet conversions from normal market jet boat builders..

Vic Hardin was a good guy..died in the early 90's, family didnt pursue boats anymore..

Geez, I got long winded..

Anyway, I changed my CG a little, its done..short vid for ya, and a few pics of one of my Caribbeans..

http://vimeo.com/53790481
You could try adding a rudder to the bottom of the steering nozzle to keep it planted in the turns.
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Old Nov 19, 2012, 05:15 PM
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i think its the form of the hull that lifts the hull when doing turns.

a flatter hull would be a solution, but on the other side that would make it very unstable.

i'm having the same problem even after having a heavy motor and battery and lipo.
counter effect is, making it havier takes out speed..

the original size jetsprints don't seem to have that much problems losing prime, looks like they have better prime due to better intake capacity (suction?).
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Old Nov 19, 2012, 05:46 PM
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Canada, ON, Markham
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Here's the motor and cooled mount I'm running:

http://www.hobbyking.com/hobbyking/s...dProduct=12201

http://www.hobbyking.com/hobbyking/s...dProduct=11173
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Old Nov 19, 2012, 05:56 PM
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Rim, the surface area of the full size boats is so much greater, and water only fills a gap, so to speak, at a given rate..volume cannot be scaled down, and, I agree, hull design is the issue here, but, its a $40 pool toy, we are lucky we got what we got, as they say..
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Old Nov 19, 2012, 06:18 PM
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I have had cavitation also. There seems to be 2 types

One is like when you jump a wave and even with the throttle on it recovers thrust when the boat reenters the water.

The other is at full speed typically with a 3C or more, the drive sucks air during normal running and it seems the only way to get the drive back is a full stop, then the thrust returns on the next throttle up. I'm pretty sure its not foreign object ingestion.

This happens on both single and twin installations I have built, on a twin typically on one drive at a time never seen it do it on both

Worthy of further research I think?
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Old Nov 19, 2012, 07:53 PM
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Fire had a great idea with a small rudder..

Rim, load cavitation is caused HERE by huge rpm, and even tho its a pump, its not a self priming pump..it needs water there..the rpm we are spinning at, creates a bubble of air...had it also happen on my full size jets when I used a droop snoot on them..had to start the engine while dropping the boat in the water..nature of a pump.
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Old Nov 19, 2012, 08:22 PM
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So a larger pump turning at lower rpm would be the solution?
But how much larger? A 30 mm jet would have an crossectional area a of 7 cm² and my current one has a 20 mm impeller 3.14 cm ² logically then if its like plane props the massive 45% diameter increase would require 45% less pitch to maintain the same motor load?

With a plane prop pitch has an influence on max speed, I think the rule of thumb is
Plane_Kph = PitchInches * RPM / 800
Is there a similar calculation for water do you know?

On full size boats I have seen very big hulls with small outlet nozzels I assume this is to increase exit velocity of the water, could a larger slower turning pump and a smaller nozzel give better speed?
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Old Nov 19, 2012, 09:53 PM
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First, the pump inlet is to small..goes back to cant scale down volume..a bigger pump, such as the KMB 28mm, will of course put out more water, so, you CAN run lower rpm for = boat speed..

Real problem is exactly what Rim was talkin about, its too short, and not a good hull design, but, its a TOY..wasnt ment to run fast, or, have big $$ spend on design..

Nozzle outlet size is a tuning tool, on the real boats, we use .030 at a time down, on a lot bigger exit hole..wouldnt even guess on how you could tune this small outlet.

Also, real jets have wear rings inside, to hold the tolerance around the impeller..we have a gap thats huge, even for a real one..playing with a clearance ring between the impeller and the drum would work here, well..

I will be doing that on my KMB.


A jet boat, has to have a semi v setup, with a flat pad at the stern to work correctly..trying to mount em in a deep v without a pad will always give some cavitation on turns, and some as the boat rises up on the chines..

Steve at sic rc is gonna be doing a 22 inch boat after the holidays, he tells me, I think he does nice work, hes into it, AND at very fair prices..

The bigger hull will be on the size of the KMB jet sprint, and also use the KMB 28mm, with the option of the 40mm KMB..the maniac version, which I gotta do..
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