River rapid's boat

[B Potter]

I would like to build a boat for running the rapids in my local river. When I first started thinking about this, I wanted to use a brushless airboat, but the more I think about it, an airboat might not have enough control to maneuver in some of the tight rapids.

Next, its going to have to be a pretty short hull, again to help with maneuverability. Also I think self righting is a must, as I see it getting flipped by the large wave's alot. oh, and extremely durable. Chances are it will bounce off of some rocks every now and then.

So, can anybody give me a recomendation on a good hull to start with?

Thank you -Potter

[westbeach]

For river rapids you'll want a jet powered boat. Not sure on the self righting part on a jet boat thought! If you can find a Grapuner Jet boat, that would be the ideal hull. Or just go down to Raidentech, and pick your self a NQD jet boat, for 30$. And just upgrade the motor to a brushless and change the esc. Look on youtube for vids. They seem to haul for a cheap mod and a cheap boat. BTW the hull is ABS. Will take the beating.

[SJFE]

Jet drives are the first option for most shallow water. There can be a draw back in rapid type conditions. It may tend to get air bound. At witch point you will lose all thrust and directional control.

An alternative would ba a tunnel type drive as pictured. it would probably be more work to construct. it may also have less thrust but my bet is that it will be more reliable in your type of running conditions.
Good luck with your build.
Tommy G

[B Potter]

If you can find a Grapuner Jet boat, that would be the ideal hull. Or just go down to Raidentech, and pick your self a NQD jet boat, for 30$. And just upgrade the motor to a brushless and change the esc. Look on youtube for vids. They seem to haul for a cheap mod and a cheap boat. BTW the hull is ABS. Will take the beating.

I had seen the Graupner, but figured I'd never find one. Didnt know about the NQD, looks just about right, so I ordered one! Any recomended outrunner and esc?

Thanks Westbeach!

[785boats]

Here's mine with a Turborix 2700kv outrunner Turborix 50A ESC & 2200mah 3s Lipo.

http://www.youtube.com/watch?v=GJHFzWoL8wg

But there are many other combinations to choose from

http://www.rcuniverse.com/forum/m_7991409/tm.htm

Cheers.
Paul.

[westbeach]

Outrunners are hard to water cool, this is the motor that I have in my NQD http://hobbyking.com/hobbycity/store...hless_Inrunner. You will have to cut 1/2" around the deck underneath the cover/hatch to expose/gut the old motor/speed controller/servo. Then the fun begins. Make sure to remove the jet drive unit and clean the hotglue or whatever glue they have used. Then reinstall the jet drive and reseal the drive properly. BTW the main thing to remember is the collet is 2,3mm so the motor that I have linked is 2,3mm as well so it is a direct drop in. Screw pattern and all. Will post a pic of my NQD a little later.

Here's a NQD but with an upgraded Graupner J/D. http://www.youtube.com/watch?v=jOdSAX0gH5k

I had seen the Graupner, but figured I'd never find one. Didnt know about the NQD, looks just about right, so I ordered one! Any recomended outrunner and esc?

Thanks Westbeach!

[B Potter]

My boat came in last night, All ready to cut her open!

That boat in the video is amazing. I dont mine to be anywhere near that fast, haha.

Is this the graupner drive? Is it almost a bolt in, or does it require a lot of hull modification?

http://www.hobby-lobby.com/jetdrives.htm

Think Im going to order your motor, westbeach, and the 35a turnnigy esc. guess I'll make my own cooling coil. Battery will be a 20c 1300 3s lithium.

Unless anybody has some better recomendations. Thanks for the help!!! -Brian

[westbeach]

Brian,

Yes, it is the Graupner mini jet drive. I believe it is a drop in as the NQD is a copy of the graupner hull and pretty sure the jet as well. Bump up the MAH on the lipos to 3300. You'll have a longer run time. One a down side, my Turnigy 35A marine esc turned out to be a dud. Can't program it, nor will it run. (Others have had great success with this esc, and I guess mine slipped past the QC. When you get yours make sure you go over the unit to make sure everything is as the picture on their website. Mine was missing the SET button(switch). I guess without the switch you can't program the esc. And it's just not worth the money to send it back to HK.

[B Potter]

Wont the extra weight of the 2000mah cause the motor/esc to run hotter, and make the boat slower off the line? Longer run time does sound nice though...

Im assuming the graupner drive uses ball bearings and flows better than the drive I have now?

Thans again for all the help WB! I'd still like to see some pictures of your setup! -Brian

EDIT: Order placed...

Motor

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4194

ESC

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7377

Lipo

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10099

Now the waiting game begins....

[damfurst]

Brian, Just a couple of things about the Gaupner mini jet drive. I did put that one in my knock off and it is very close to fitting but you do have to cut a little bit on the hull both bottom and transom to make it fit. The other thing is there are no ball bearings in the mini jet drive. Brass bushings yes. You can get a bearing for the front of the drive from Boca. The other thing is the impeller shaft is 3mm as opposed to 2.3mm kn the knock off. Also the motor mount on the mini jet is for a 540 size motor, however there are adapter plates that one can buy for the smaller brushless motors to fit or you can make your own. One other thing is that there are replacement impellers available for the Graupner while there are none for the knock off. The jet drive in the video from bigbird22 is a 29mm while the mini jet is 19mm same as the knock offs. He did post pics of building it over in the jet drive thread on rcuniverse.

As far as a bigger battery being a problem they really aren't. You sometimes need that weight to keep the intake engaged in the water when running rapids. I usually run 9.9v life batt in mine 2300mah and have had great results. 3s will make it faster but not necessarily better when it comes to rapids. hope this helps.

[sundog]

I wouldn't change the jet drive until you need to! It's a clone of the Graupner except for the 2.3mm shaft (you're not going to bend the shaft). These are fun boats, I put a 3200kv outrunner in mine and it scoots. http://www.youtube.com/watch?v=8LiVQzF4EDQ That is a good choice of battery/voltage/amp for this boat, you might puff a 1300. Jet drives require more amps than surface or submerged props. While these boats are fun on flat to rippled water they aren't very good in medium or larger rapids as the nose catches water and goes under easily and you get aeration from the frothy water that also puts a stop on things until you gain control again. But they are fun to run elsewhere. You won't regret owning one, the ABS hull can take a beating (unlike fiberglass) and with a mesh intake mod you can run right up on shore when done.

[785boats]

Brian.
I agree with Sundog. There's no real need to replace the jet until the existing one is flogged out.
Spare impellers are available for these boats & in aluminium too.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=270488051742&ssPageName=STRK:MEWAX:IT

I run a 2200mah 25c lipo in mine & there's no weight problem.
As for cooling an out runner, I don't bother with mine. It's got more than enough power to drive that little jet so it doesn't get hot. The only cooling on the boat is for the ESC.
These boats are supposed to be fun, not expensive. I only got one because I had the motor, ESC, servo, batteries etc lying around not being used. so it seemed like a fun thing to do.
Cheers.
Paul.

[westbeach]

Brian,

Here's the pics, sorry for the delay. Had issues loading the pics.
I am using 2200 mah 3s lipos and not 3300 as I had stated in an earlier thread. Sorry for the confusion. The one pic shows the upgraded grate over the jet drive. The one that comes built in is made of plastic and is not great at keeping out pebbles that will ruin your impeller. Probably one of the mods you will want to take care off right off the bat.

Wont the extra weight of the 2000mah cause the motor/esc to run hotter, and make the boat slower off the line? Longer run time does sound nice though...

Im assuming the graupner drive uses ball bearings and flows better than the drive I have now?

Thans again for all the help WB! I'd still like to see some pictures of your setup! -Brian

EDIT: Order placed...

Motor

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4194

ESC

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7377

Lipo

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10099

Now the waiting game begins....

[westbeach]

Dude, I would have to kick you in the nuts for suggesting this crappy aluminum impeller. But seriously have you not kept up on the thread?
This is a quote from that thread "They are pieces of crap and, as eTokyoPop said it best, "an aluminum can eating hippopotamus could crap out a better product" lol "

Spare impellers are available for these boats & in aluminium too.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=270488051742&ssPageName=STRK:MEWAX:IT

Cheers.
Paul.

[damfurst]

Hey Westbeach, What did you use for your intake screen? It kinda looks like it's off a pump or something.