Dual Jet Challenge

[Eodman]

My son has challenged me to do a dual drive jet this winter! To that end ---what would be a good hull for this project?

Me being a Cat man I think I would like to consider a Catamaran also, I know I know it would be difficult but if I can get it to run it sure would be sweet!

Just need to Identify a cat hull that has wider sponsons! Again not looking to race just fun and cool factor!!

Any input Guys -Looking in the 30 to36 inch range!

Any mono hulls would be considered also need a flatter ride pad!

Just gathering info for now .... have to finish rebuilding my twin outboard Cat ---going with Graupner GTX820's from Steven!

I have to clarify - we are talking about water jet here!!!!

[lomdel]

There has been previous threads here on OSE regarding this with concensus that the ride attitude of a catamaran with a jet intake in each sponson would be extremely difficult to make work. The sponsons are not always in contact with the water at the same time and therefore thrust on each sponson would differ during runs. If you can find a mono with a rather wide flat ride pad, and mount the intakes as close to each other as possible (touching), it could work... (Proboat Formula Fastech??)

With a bit of butchering maybe the NQD Tear Into could also work... http://www.rcuniverse.com/forum/m_7991409/tm.htm
This could make for an INSANE little boat with twin 380 BL motors!!

[lomdel]

I just went and measured my Thundercat 31 flat ride pads, they are 32mm wide on each side. That would also make for a suitable catamaran hull (if you really want to go cat), bit heavy, but with twin 540 BL motors and 2x Graupner jet drive units ( http://www.offshoreelectrics.com/pro...?prod=grp-2344 ), weight would not be a problem... Just find out how wide the intake grate is first, obviously.

[areseaer]

I just went and measured my Thundercat 31 flat ride pads, they are 32mm wide on each side. That would also make for a suitable catamaran hull (if you really want to go cat), bit heavy, but with twin 540 BL motors and 2x Graupner jet drive units ( http://www.offshoreelectrics.com/pro...?prod=grp-2344 ), weight would not be a problem... Just find out how wide the intake grate is first, obviously.

That is the boat I was thinking would work.
Maybe use the nacelle method like I used in my shockwave 36.

[Diegoboy]

Hey Lomdel,
I haven't forgotten about This

[lomdel]

Hey Lomdel,
I haven't forgotten about This

Then you and Eodman can have a parralel build right here on this thread. See who can come up with the best solution for a twin jet drive cat/boat! That is a challenge!!

[crabstick]

There has been previous threads here on OSE regarding this with concensus that the ride attitude of a catamaran with a jet intake in each sponson would be extremely difficult to make work. The sponsons are not always in contact with the water at the same time and therefore thrust on each sponson would differ during runs. If you can find a mono with a rather wide flat ride pad, and mount the intakes as close to each other as possible (touching), it could work... (Proboat Formula Fastech??)

With a bit of butchering maybe the NQD Tear Into could also work... http://www.rcuniverse.com/forum/m_7991409/tm.htm
This could make for an INSANE little boat with twin 380 BL motors!!

Thats mine!!! hahaha

[lomdel]

Any progress on your decision yet, Eodman?

[Eodman]

Yeah --- I'm 99% sure I'll try it! Just need a little more info - like which graupner drive will stand up best to brushless, or better yet is brushless the way to go!

I really like Catamarans so I just need to figure out the best one for it! I've been thinking about how to compensate for lose of thrust when 1 sponson is out of the water --- haven't come up with much but I do have one thought!

Got a few more weeks of good water running so the build season is not in full swing yet.

[Eodman]

Because you may be on & off the throttle alot I might be better served using brushed motors --- less heat build up!



I just know I'll have to run the hull wetter to keep the intakes in the water!


Although I do have 2 brand new super vee motors sittin in the parts bin!

[785boats]

I've put three jets in a scale model of the Wallypower 118" with no problems.
Two drives should work fine in my opinion. I thought that in a hard turn the outside jet would suck air, but it doesn't. Mind you it is a big boat & sits low in the water but gets up & planes on the last 1/3 of the hull. Just like the real thing. The jets are also home made so probably not as efficient as your commercial units. Here's a couple of pics to give you an idea.
Cheers.
Paul.

Sorry , I should have read more closely. I see you're still leaning towards a cat.

[Eodman]

That looks like a sweet install! Very neat too!

[785boats]

Thanks.
I've got one of those cheap NQD Admiralty cats that I bought (super cheap) to try some jets in as an experiment but never got round to it. I too was worried about the differential thrust as one jet breaks the surface & loses thrust. All I could see was wild spinouts. Maybe a small scoop over/around the rear of the intake might help pull the hull down onto the water. Who knows?
Cheers.
Paul.

[Eodman]

Well as I do more research - I've looked at all the jet drives that Graupner offer(5 in all) and when you look at the distance from where the unit passes thru the hull and where the intake begins(from the stern) it appears that model # 2347 would locate the intakes the furthest back!

My thinking is if I run the hull a little wet, a little heavier in the stern and then trim the steering jet inwards a bit on both, it may compensate for some of the steering problems of the sponsons being out of water! Again trial & error because as you move the jet off center you lose some propulsion!

Lay out I think should be jet drive, motor & esc in sponsons and batteries on the tunnel to give the most adjustment for CG. I have no idea where CG would end up on a build like this.

I think on a pond with smoother water -- this kitty would just get up and go!

[lomdel]

Also consider a stepless sponson design hull to suck the boat to the water...