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[srcampb]

How large ( length, displacement) of a model has anyone seen or heard of that was powered by single or twin water jet drives?
 
I'm interested in scale speeds, rather than racing type applications.
 
Thanks!

[Umi_Ryuzuki]

I've seen a 24" Graupner catamaran ferry in Tualatin Oregon.
The Graupner Moonraker used three of the larger jet drives and was 1470mm long and 284mm wide.
And Keher Modelbau Berlin makes a couple of one meter long jet boats. I like the Stridsbåt 90 Police version.


Also, one of the guys back East built up the LCS-1 USS Freedom
3'-11" ( 1200mm) It runs on two graupner mini jet drives.
http://www.youtube.com/watch?v=CZq0TB5QqzI

And Takahashi, in Japan built up the LCS-2 Independance.
It runs on four custom built jet drives and is also 1200mm long.
http://www.youtube.com/watch?v=bspVcOORADY&list=UUi9QDf9IXkTVPQ89Qd6Qmqw&index=7

http://www.rcgroups.com/forums/showthread.php?t=1013059

 

[BrianB6]

May 2012 Model boats magazine has a build of USS Independence using a Graupner jet unit 5.   The boat is 1162 long (4')

[srcampb]

Thanks for the responses, all.
 
The 47' Canadian motor life boat hull I'm building really isn't turning out as well as I had hoped. So, I'm trolling around for another project.
 
I've come across the USN PBR type river patrol boats that utilized two water jets for propulsion. There are LOTS of accessories and figures in 1/6 scale that would work great on an RC model.
 
But, in 1/6 scale I'm looking at a model that's 64" long, and the most daunting part, would weigh 65 pounds or more depending on the source you use for displacement of the real boat.
 
is this too big for a couple of the larger water jets (KMB 40mm?) available on the market? I've got plenty of weight budget for batteries, but do these jet drives have enough "OOMPH" to drive a boat that large at any reasonable voltage?
 
Thanks again, and looking forward to any words of advice from the forum..

[Norseman]

One thing you might need to consider when selecting your water jets / motors / batteries is I think the max rpm before cavitation occurs.

Dave

[chris gillespie]

Dave do you not sleep, or are you on guard dog duty 

[Norseman]

  I have an appointment in February at a sleep clinic Chris - 4 hours at most and then I wake up with headaches    I'm not really a tired guy though.

On the bright side I have a nice pibber hull and two jet drives in the shed .... and this scotch is really quite good.

Dave

[srcampb]

Dave,
 
Do you think a pibber in 1/6 is even feasible? What scale is yours?

[Umi_Ryuzuki]

SWASHDRIVE jets are no longer available, but the whole series of drives and
sprint boats were 1/4 scaled. http://imageevent.com/justaddwata/myboats/jets

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

http://www.youtube.com/watch?v=t7ufCLieCps

So 1/6 would be possible if you found the correct size of drive and motor combinations.
Graupner and KMB are the two most common drives. Hobby King purports to have an
aluminium drive, but I rarely see it available or in stock.

[pettyofficernick]

Not as big as your PBR Scrambp, I am in the process of building a 1/24th PBR from Deans Marine, with a Graupner Mini Jet, no room for 2 so I have only fitted 1 to see if it all works out. Early days yet but here is a couple of photos of progress to date, waiting for postie to deliver the brushless motor etc, which should be in the next couple of days.

[Norseman]

Hi Scrampb
I was persuaded by HS93 to buy a pibber hull like his latest buy (at 1:16 plus plans) purchased from some nice people at Nautical Marine Models.  They are located at Burscough Bridge in Lancashire. The hull doesn't appear on their site and it was one of three prototype hulls. Very nicely done and I think they will do more. http://www.nauticalmarinemodels.co.uk/index.htm so the idea was parallel builds but any machining would be Peter's domain.

KMB in Germany offered the four water jets we needed and in my opinion they are better built than Graupner. KMB were good to deal with. Some info below and in there you can see there is an effective range of rpm so banging on the biggest baddest motor isn't the answer - the correct choices just as Umi says.  Peter and I were going to go Lipo and Brushless .... Peter said choosing the motor wasn't straight forward (the maths were beyond my knowledge) and that was as far as we got (Peter died last Monday).  Your large scale build will sure be a 'stand out' model on the water .... if you can just get the speed, so plan to go light wherever you can.

40mm see http://www.jet-drive.de/index.php?page=shop.product_details&flypage=shop.flypage&product_id=32&category_id=11&manufacturer_id=0&option=com_virtuemart&Itemid=17

28mm see http://www.jet-drive.de/index.php?option=com_virtuemart&page=shop.browse&category_id=4&Itemid=17

Dave

[pompebled]

Hi Scrampb,

I'd contact Kehrer and ask if they think a realistic scale speed is possible using two Ø40 mm jets in a 64" hull.

As you're not after high speed, I think it'll be no problem.

Keep in mind though; operating a jet is considered 'hard labour' for the motor selected, so don't skimp on the Wattage when looking for suitable motors.
You'll need a lot of torque, so either big four-poled inrunners, or similar sized outrunners, which have even more torque.
Don't go beyond 16000 rpm under load, it'll only create cavitation.

That size will most certainly be a real presence on the water!

Keep us posted.

Regards, Jan.

[philk]

check out this video of a jet lifeboat. it's 54 inches long

http://youtu.be/Jn2QxbhaJUs

phil

[Norseman]

Is that the A Team Boatyard's Alan Noble's boat?

Dave

[srcampb]

Dave,
 
I had read elsewhere on Mayhem of Peter's untimely passing; hope you continue on with your PBR build.
 
The lifeboat video is most encouraging. That's significantly more speed than I think I'll need; maybe I can trade off a little velocity for the ability to push my heavier (?) boat around.
 
I'm going to start investigating the 40mm Kehrers in greater detail. Probably speak with the folks in Germany.
 
From looking around a bit at brushless motors, it looks like inrunners are easier than outrunners to water cool? (I've only used brushed motors in previous boats, so brushless is a whole new world to me.) Appears I should consider water cooling the ESC's as well?
 
Once again, Thanks all!
 
Scott

[john goodwin]

Scott


There was a build on here from Hannu - both he and friend built a water cat patrol boat at 1/10 scale making it 146cm long or 57 1/2 inches in English money.


One was powered by a single 40 mm kehrer jet on an ic engine the other twin 40mm kehrer jets on brushless electric.


Watercat 1300 Patrol 1:10 scale brushless twin-jet


hope this helps a bit more


John

[philk]

yes it is

Is that the A Team Boatyard's Alan Noble's boat?

Dave