Waterjets?

[spikesliew]

Hi Everyone!

I'm nowhere near R/C and scratchbuilding standard, but was looking at the possibility of building a modern warship (or at least getting started in the next few months), but it uses the impeller-waterjet combination, instead of the props-rudder combination as the means of propulsion.

Managed to find two models that i shld be looking at from the following websites,

1. Graupner Jet Drive 2 : 2344, + Reversing Unit for jet 2 2344

http://www.westbourne-models.com/erol.h ... io%2Cs.htm

2. KMD's 28-mm-KEHRER-Jet, + Steering and reverse system similar to KAMEWA

http://www.test.jet-drive.de/vg_server/ ... language=0

Understand that most of us here are more inclined to the older ships, but question is/ are

1. Has anyone tried these systems before, and how do they fare?

2. The jets and buckets that i've found tend to cost quite a bit (w/o motors + selvos); are there any cheaper models that you might have came across?

3. Thoughts from anyone else?

Best regards
Chin Wen

[MechTech]

Chin Wen,
I have not used those brands, but I have scratchbuilt my own water jets (after a LOT of trial and error). Generally speaking they are not as efficient as props, HOWEVER, they can have faster acceleration, superior handling (can nearly turn within hull length), and give instant response to rudder controls. I actually built one on a non-scale ship that had the best of both worlds. The inlet is an open tube in line with the prop shaft so I could just hit reverse and backup (no reverse bucket). The outlet looks just like a waterjet with sterrable nozzle. Waterjets are also pefect for shallow ponds, water with lots of plants and wildlife. No more worries about destroying your expensive brass propellers. Plus they just look great! I'm thinking of building a Swedish "Visby" class corvette with two of them (just like real life). Hope that helps! - MT

[ChrisH]

I think I am going to pick up a couple of Graupner Jet Drives for a 1:72 scale project that I'm working on. I'm not sure how many I'll end up using (either 2 or 4), but I'll try to keep everyone posted.

Of course, I too would love more information.

[spikesliew]

Hi!

Yeah, guess what i like about the waterjets is the fact that by adjusting the configuration of the jets, the spray can be deflected forwards instead (without having to reverse the trottle of the model), and push the ships astern. As MT has said, the two jets could also be configured seperately to allow the ship/ model to turn almost on its spot, as compared to the more conventional rudder/ propeller configurations.

Stumbled onto this page on the Norwegian Skjold, which also runs on waterjets, at an R/c forum while i was trying to find out more about waterjets for r/c.

http://www.rcgroups.com/forums/showthread.php?t=317222



MT,

I found this for a 1/200 card model of a visby. Seems like a full-hull kit. No idea whether this is helpful to begin with? (not that i know anything about adapting paper model plans!)

[spikesliew]

Chris,

I'm more looking at KMD's 28-mm-Jet with steering and reverse system. The much lower cost (almost 50%) is the key consideration.

Looking at the ship below for my waterjet project:
http://www.stengg.com/upload/569JmPgnc9ARf5SDlEU.pdf

Question is, at 1/96 scale, the model will be just 8.96cm at the stern (ship measures 55m x 8.6m in real life). With the beam of the jets 42mm across each, common sense seems to say that 1/96 scale doesnt seem like a sufficiently large scale, does it?

I've written to KMD to ask for their advice/ recommendation, and will update you if i get anymore information.

Or are there even tinier jets with steering/ astern propulsion that we have missed out?

What are you thinking of building, Chris?

Best regards,
Chin Wen

[toiletfreak]

nice to see another Singaporean

[ChrisH]

One question about water jets before I get into specifics. Does the nozzel have to be out of the water for it to work properly? I think I may have made a mistake in my design in that the the nozzel is below the waterline.

What are you thinking of building, Chris?

I'm planning on building a very large model, which almost makes me wonder if the water jets on the market are powerful enough.

I've done some drawings of a hypothetical USN next generation guided missile cruiser. Its size, however, is more comperable to a KIROV than any previous USN cruisers. My plans were to build it at 1:72 scale, which comes out to about 12 feet (360 CMs). My initial plan was to use two Graupner or two 40mm KMD water jets, but I am starting to think the model will be seriously underpowered, even though I am looking for scale speeds in the 30 knot range rather than 40-50 of a patrol boat.

At this point, I need to find out how many jets I'll need, and I may need to scale my project down to 1:144 so it's manageble and doesn't cost a small fortune.

I'll see if I can post one of my drawings later tonight if you're interested.

Question is, at 1/96 scale, the model will be just 8.96cm at the stern (ship measures 55m x 8.6m in real life). With the beam of the jets 42mm across each, common sense seems to say that 1/96 scale doesnt seem like a sufficiently large scale, does it?

1:96 scale may be a bit on the small side if you plan on using two jets as in the real ship. I hate to suggest to anyone they build a bigger model because of the additional storage space and cost in building the model, but maybe 1:72 would work out better in this case?

Thanks for the information! I hadn't found the KMD site before this post, so that was just what I needed.

Chris

[MechTech]

Thanks Chin Wen,

The Skjold photos are cool. I bet he gets a short run time though. He's running fans and waterjets! That sucks some serious power.

If you haven't seen them, one vendor for Graupner drives:
http://www.hobby-lobby.com/jetdrives.htm
I didn't get your link for the Visby, but I have seen it. It's only an idea for now. I have to finish my current large ship model first.

ChrisH, On the same link, check out the glow powered drive at the bottom.

Jet drives don't have to be above water. In fact, mine is in the water and I believe it gives me more thrust being forced against the water outside.

Chat with you later. - MT

[spikesliew]

Hi MT,

Ooops... silly me... ...you've already seen the link to the Visby, but here it is, nontheless:

http://www.card-models.com/product.php?product_id=53

Thanks for the link to Graunpner. The 'GR2349 Mini-Jet Drive ..... $ 39.90' sure looks like a suitable candidate! I'll write in to hobby-lobby, and see what they say (if a set of two will fit into the stern). No news from KMD for the time being. Will keep you guys posted once i get anything!

Hello, Chris,

Wow... at 3.6m, it's an awfully big project, isnt it? Will certainly love to see what you've planned out!

Does the nozzel have to be out of the water for it to work properly?

I do tend to agree with MT on the waterjets. I'm certainly not an expert, but i would think that ideally, as much as you might see a fair bit of 'wash' above the water surface when the jets are in operation, the jets shld be submerged (at least at the waterline level) to ensure that the maximum trust is directed in the stern to push the vessel forward.

Perhaps one reason why the jets seem to be partially out of the water is that the vessels might not have been completely loaded (and consequently weighed down) at the time the pics were taken? Pure speculation here.

http://www.naval-technology.com/projects/visby/

'1:96 scale may be a bit on the small side if you plan on using two jets...maybe 1:72 would work out better in this case?'

Yeah Chris, 1/72 might be a more viable option..good balance between the 2 scale too. was actually contemplating of doing in 1/48 if all else fails. But that [1/48] would mean that it will take up a HUGE amount of space in the house! Perhaps a key consideration for deciding on the two scales is the availablilty of fittingf from Sirmar and other suppliers. Any idea where i can get stuff like the 76mm Oto Melera gun (I'm really not that good in scratchbuilding) in 1/72 scale?

Any advice would be greatly appreciated!

Hi, Toiletfreak,

Good to see ya around too!

[ChrisH]

Here is a REALLY LARGE graphic of my CG-74. I used the 40mm KMD water jets in this drawing, so you can get an idea of the size of the ship in relation to the jets that I am tenatively planning on using.

If you have dialup, you may wanna skip clicking on the link. It's in scale, so really, really big.

http://home.centurytel.net/cthjlh/graph ... lightI.jpg

[MechTech]

ChrisH,
I think you need to change your designation to "BB."
It looks great! I'd suggest four waterjets and some kind of azimuth thruster. Check out Austal's site if you haven't already (this is a PDF download for trimarans):

http://www.austal.com (for the regular site)
http://www.austal.com/download.cfm?Down ... CC3C2D1D40 (for some cool internal/layout views)
They show some good arrangements for LCS-2 and another trimaran.
An actual ship like your design could ruin your whole week if you were on the "other" side!

I'm seriously considering a trimaran someday because I build small and they are so stable. Take care. - MT