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Old Jan 24, 2013, 09:03 AM
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Scub, the kmb has a big old hole in the bottom.. kinda looks like one of my old girlfriends..

The only thing I dont like about the kmb is how you have to pull your watercooling..the nozzle is so close fit to the bowl, you have no ability to get to the bowl..trust me on that. so, its gotta be on the nozzle, and to me I dont like the look of it going back and forth.

Some run a normal water pick up on the bottom of the hull. I wanted the pressure, my stuff gets hot..its a big esc, and a 2400 watt motor, need the volume that the jet gives, so, its where it is.

Trouble with this grate/screen issue is that the water still gotta get in, and at a high volume. if you put a small screen over it, the overall open area it shuts off starves the pump for water, catch 22..not being the expert on crawlin, in most vids I've seen, seems most of the guys run the grates.

Screaming the motor when you're grounded aint helpin anything but suckin rocks..driving technique gotta play here too, if it were a prop boat, no one would be gassing it if it went aground, knowin its gonna wreck the prop..same applies, we know the weak spot..cant suck a rock if it aint suckin..

Mad, to properly use a turn fin, it must have a 90 degree angle to the water when the boat is in its heeled over position on that side..

So, with the boat on a flat surface, on its chine, use a square, make it 90 to the water..size depends on the boat, depth of the fin into the water is a tuning issue, which I'll deal with when we have soft water again, just deep enough to stop the boat from spinning out..

Most boats use 1, as we just do right turns, races are just rights. but, this aint a race boat, so, 2 fins, this way its got equal hard turn ability..
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Old Jan 24, 2013, 11:10 AM
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Originally Posted by chidago View Post
1)Trouble with this grate/screen issue is that the water still gotta get in
2)Mad, to properly use a turn fin, it must have a 90 degree angle to the water when the boat is in its heeled over position on that side..
1)The problem when you're crawlin' is that you are often in very shallow water and if there is a fine gravel bed to the stream or any weed about then although you are definitely not grounded and you're squirting like a good 'un there is still the potential for FOD as the current whips stuff up. My screens are diamond shaped and very narrow wire with fairly large holes so the amount of obstructing metalwork is no more than on a grate, although I accept the fact there are transverse elements, rather than all being fore-and-aft, may make it more restrictive. And its nothing like as strong as the Steve type, that's for sure. Time, and Scub, will tell how his take on it performs in the real world. As I said in my reply to Scub, it seems to work in Oz

2)Well, that makes perfect sense. I'd only seen fins on race-type models where, as you say, we're only going clockwise.Well mostly. The Naviga 'M' type of course favoured in Europe has 1 turn to the left but there are 4 rights so people concentrate on the right turnability. Your explanation for boats designed to turn as hard both ways clears it up for me.
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Old Jan 24, 2013, 11:30 AM
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Mad, just wanna stop the spin outs on this one..
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Old Jan 24, 2013, 01:01 PM
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Mad, just wanna stop the spin outs on this one..
Should certainly do that. Only problem is you'll have to wait 3 months to find out. Unless you know someone with an Olympic size hot tub
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Old Jan 24, 2013, 01:07 PM
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Thanks guys! My dad is a freelance photographer, (now retired) so I suppose I have likely inherited some skill from him.

Mad, the mountain in IMG647 is Mt. Baker, the one in 644 is Mt. Shuksan, and the image was captured from a ridge near the top of Mt. Herman.

As far as the grate situation goes, chi hit the nail on the head with the point about driving technique; if I stick it on a sand/gravel bar, I try to resist the urge to gun it and dislodge the boat. That's almost certainly going to mean a shredded impeller! However, sometimes you aren't aware of what's under the boat, or you can't resist, that's why I've shredded 2 of them so far!
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Old Jan 24, 2013, 01:13 PM
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AHA !! I knew there was some photo professionalism there somewhere....
Impellers are like props, they dont last forever, part of the game..I keep a inventory of em, thats why I went with the graupner, parts are easy and quick for me to get,and now, kmb stators, too..

I keep 3 of everything, when I bust something, I re order, always have 2 extra cause if it will go wrong, it does.
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Old Jan 24, 2013, 02:26 PM
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Hi Gang
I don't have much rocks and whitewater near me, but I do live on the Wisconsin River. I have a couple of small 18' range sailboats, an Aquacraft Mini-mono, and an evolving homebuilt airboat.

Question for another thread, but boy does that airboat heat up motors and ESC's. The Mini-mono goes great but cavitates a bit and seems to suck water in more than I would have expected, (kind of a pain when I have been taping the hatch before each run).

These little Jet Boats have totally caught my attention. If there is any reason for me to skip the jetdrive in favor of props please tell me about it. If not the HobbyKing ADS400L 3700 kv 600 watt watercooled motor looked good along with the
HobbyKing 50A Boat ESC 3A UBEC
or Turnigy Marine 60A Brushless Boat ESC
or Birdie 70A Brushless Boat ESC w/5A BEC

I figured I might run 3S 1000 to 1600mAH Lipo's, hopefully 40C or better.

If I am way off on these or if someone has an opinion about what to avoid here, please share some of your knowledge with me.

Thanks
John in Merrill
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Old Jan 24, 2013, 03:05 PM
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Hi Gang
I don't have much rocks and whitewater near me, but I do live on the Wisconsin River. I have a couple of small 18' range sailboats, an Aquacraft Mini-mono, and an evolving homebuilt airboat.

Question for another thread, but boy does that airboat heat up motors and ESC's. The Mini-mono goes great but cavitates a bit and seems to suck water in more than I would have expected, (kind of a pain when I have been taping the hatch before each run).

These little Jet Boats have totally caught my attention. If there is any reason for me to skip the jetdrive in favor of props please tell me about it. If not the HobbyKing ADS400L 3700 kv 600 watt watercooled motor looked good along with the
HobbyKing 50A Boat ESC 3A UBEC
or Turnigy Marine 60A Brushless Boat ESC
or Birdie 70A Brushless Boat ESC w/5A BEC

I figured I might run 3S 1000 to 1600mAH Lipo's, hopefully 40C or better.

If I am way off on these or if someone has an opinion about what to avoid here, please share some of your knowledge with me.

Thanks
John in Merrill
I think your choices will work just fine, except I would plan on using 3S 2200mah batteries; they fit in the hull just fine, and you'll get way more runtime vs a 1600. Also, be prepared to make a few mods to the drive if you want to use all of the RPM's from that 3700kV motor. You will have to smooth out any sharp edges in the drive, probably add bushings, and make sure you have proper impeller/stator clearance to prevent cavitation at high RPM's.

The only drawback to a jet drive is that they're not as fast as their prop driven counterparts, but they can still be just as fun if not more fun in other aspects!
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Old Jan 24, 2013, 03:05 PM
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AHA! someone close to me..!! you will love the jet, john, they are a blast..
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Old Jan 24, 2013, 03:06 PM
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Also, chi, could you dremel a notch out of the KMB steering nozzle somewhere to make room for a bowl pickup?
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Old Jan 24, 2013, 03:08 PM
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Lot of good info here, take the trime to read the thread, it will pay off for ya..

The power of choice is a mid 3000kv on 3S..Steves boat covers all the rest, there are build outs on everything on the thread, or links to em..I have slim pickings on streams too, but, I got a few..welcome to the thread, great bunch of men here.
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Old Jan 24, 2013, 03:14 PM
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Fire, not really..you gotta see the thing..wasnt thought out for cooling on the side..works well as it is, thats per kmbs drawings..
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Old Jan 24, 2013, 03:38 PM
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Originally Posted by jgestner View Post
Hi Gang
If there is any reason for me to skip the jetdrive in favor of props please tell me about it.
No-one on here will try to dissuade you. We are all jet nuts. Welcome to the addiction clinic.

Take Chi's advice and read the thread from the beginning. Will take a while but there's such a wealth of information here.

Other than that my only advice at this stage is to heed what Fire says about using bigger lipos. And bushings or bearings. With a 600watt motor the 1000 or even the 1600mah lipo will give disappointing run times, and the 1000s in particular might struggle to provide the amps for long even if they are rated at 40C. Go for 3s 2200 at least, or even a bit bigger with that motor. If the jet bug bites you won't want to be coming back in to change batteries every 4 or 5 minutes. And with that amount of thrust the plastic main body won't last too long before it gets worn without the bushing.
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Old Jan 24, 2013, 03:50 PM
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Originally Posted by Firehawk989 View Post
Mad, the mountain in IMG647 is Mt. Baker, the one in 644 is Mt. Shuksan, and the image was captured from a ridge near the top of Mt. Herman.
Thanks. I'll look it up on GooEarth.
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Old Jan 24, 2013, 04:28 PM
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Yup, the mod jet from Steve,or the Graupner jet, there are bushings..

Personally, I use 4400ma 3S, gives me decent run time..

Later in the year, Im going to actually find a glue that will work, and make a insert to put a real BEARING, not a bushing, in for the motor side of the jet, but got to run it on the flow bench to make sure it wont inhibit any flow...the rear aint gonna be difficult to do a bearing, not really needed there, it stays cool, and lubed by the water, but bearings are nicer for the friction aspect.
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