Twin Jet Drive in a Catamaran

[lomdel]

Anyone ever tried or seen a twin jet drive build in a cat like the 32" Agitator maybe? What are the pros and cons of jet drive vs prop drive. I know with jet drive you don't need a rudder hence less drag. What size twin Graupner drive units with what size BL motor would make a 32" cat fly?

[ED66677]

The problem I see using twin jet on a cat is that if a sponson is not in contact with water the jet generates zero thrust, the cat will then turn.
IMO a jet drive is less efficient than a prop due to water friction in the "tube".

[Simon.O.]

Lombard, there is wealth of info over at RCU on jet drives. I have read a LOT of it and have come to the conclusion that water jets are cool, fun but not for high speed.
As Emmanuel (ED) said as soon as a sponson comes off the water the jet unit loses its prime and thrust is lost. It take longer for a jet unit to reprime and produce usable thrust than a conventional propellor

There are many great applications for a jet unit, I know as I have run them (full size) and come from the country that they were invented in. Ever heard of a Hamilton Jet ?? They are from here....sheep shagger central....NZ !!

I am not one to rain on anyones parade as that is outright rude. I will say that a twin-jet cat would be a lot of fun but will not scream and fly as you may want it to.

Look at full size boats and see what is there.
Jet boats are fast and fun.
Offshore Cats have twin surface drive props..............because they work
WWSR Boats are powered by Gas turbine thrust. Ken Warby knows how to do it.

Before I digress into a great speil about famous boat designers from here and Australia I will say. If you have the Jet units or can get them for a good price then consider it. Take into account that a hull that is fitted with jets has some BIG holes that will need skinning over if they are removed in favour of conventional drives.

Another thing to consider is the ''Agitator'' hull is stepped. how this will affect a jet unit intake is up for some discussion. My coin says that there will be some serious aeration prior to or within the intake to a jet-pump and that in itself is a %%$#@

Pump inlet cavitation is something I do know a little about. If I get it at work it is all bad !!

[lomdel]

Since I posted, I read a little about it on RCU and it all boils down to one thing... A Jet Cat is not efficient because at speed it not only planes, but the sponsons/water intakes is not always in contact with water and it would run erratically. Absolutely flat water would be better obviously. Would be a great idea for someone with a lot of money and time on their hands to try and build one to prove this theory once and for all...

[Diegoboy]

Time & Money I don't have. A persistent desire to attempt what can't (or shouldn't) be done? I have a ton of that! I'm gonna make one

[lomdel]

Time & Money I don't have. A persistent desire to attempt what can't (or shouldn't) be done? I have a ton of that! I'm gonna make one

I am so glad to hear that I will be a loyal follower of the build. Try and keep costs down though. The first step should be the fun part ; the wishlist What size drives for a 32"(ish) size cat so that the intake fit in the sponsons. The sponsons of the HOR 32" knock-off cat has some flat areas between the steps. Would it be enough

[lomdel]

It would be cool to hide the nozzles in the area where the stingers are usually mounted... If only it'll fit (?)

[Diegoboy]

...I'll title the build thread "Where NOT to install a jet-drive"

Sorry Lomdel, It'll have to be a "step-less" cat hull

[H2OCamel]

for a cheap experimental platform the mrp Phantom cat is flat sponsoned.

[lomdel]

The flat bottom would suck it to the water for better intake volume as well...