engine size for 84" cat?

[rick jacobson]

engine size for 84" cat?

I am wanting to know if twin 35cc quickdraws would be enough power a 84" cat over 50 mph or would I have to go with inline twin 35's on each side to get that kind of speed? Maybe their is a another choice of engines out their that would be better suited for it just do not sure. Any info would be great. Thanks Rick.

 

[nitrotoys]

Re:engine size for 84" cat?

Your best bet is to ask the guys on Jims RCBoat dock.

mainly nitro here, but more and more gas guys are checking in.

I would go with 2 full mod 260s.

that QD 35 heavy, or inline 50cc QD.

Its not all about the "engine" In the boat. its your setup, and PROP is where you squeeze more speed out of it.

 

[speakerboy]

Re:engine size for 84" cat?

rick .. like nitro here told u its not the engine power .. but the power to weight ratio what will bring it to 50 mph ... for ur info .. 2 times more weight needs 4 times more hp to reach the same speed ... thats a good rule .. dont forget !!

i think 2 QD 25 engines will do the job .. than again i am realy angainst 2 engines . its a hell of a job to keep them running the smae rpm lets not say stall ....

than again .. ever seen the german guys run such boats wit 2 MHZ 30 cc twins per sponsor .. 7 minutes running = 2 liters nitro .. but does run more than 65 mph .... massive !!!

 

[[email protected]]

Re:engine size for 84" cat?

Maybe you can beg someone to sell you one Mathe engine. They are supposedly as fast as 2 QD's, so I've been told by the gas guys. But, those are also the guys that say gas is better than nitro. LOL

 

[izitbrokeyet?]

Re:engine size for 84" cat?

84" !!! you may have to rent a slip fer that big mutha.

 

[izitbrokeyet?]

Re:engine size for 84" cat?

doing some curve extensions, I'm guessing it will take at least 17 HP to get you over 50mph even at a relatively light weight.

 

[izitbrokeyet?]

Re:engine size for 84" cat?

I ran the calcs again using a "best fit" curve, and the larger end defined by full scale boats with power plants that bring them to 50mph. The "best fit" curve brings the required HP up to 20HP for an 84" boat. The Curve extension #of 17hp is better because it incorporates more typical HP/weight ratios that you will find with a R/C boat.

With that said....it looks like it will take at least two motors to get you to 50MPH

 

[Bob Kensill]

Re:engine size for 84" cat?

I built two 84" apache boats for Bonzi Sports that had twin 2-cylinder Quickdraw 70cc engines. The engines were counter-rotating. Top speed of these boats was over 80mph. The speed-limiting factor was prop availability.

Bob Kensill

 

[Propjockey]

Re:engine size for 84" cat?

84 inches at 80+ MPH!! WOW!

How did they sound?

 

[Rick Jacobson]

Re:engine size for 84" cat?

Thanks for all the info. Do you have any pics on that 84" Apache? Would like to see the setup on it. Thanks Rick

 

[Ron Olson]

Re:engine size for 84" cat?

It is a bad boat! Bob showed me some pix of it at a swap meet in Grand Rapids 2-3 years ago after he built it. He told me the price tag too, I hope that you have deep pockets!

I found one shot of it:

http://www.bonzisports.com/BONZISPORTS/Pic...ngineinhull.jpg

 

[Mike Hughes]

Re:engine size for 84" cat?

You could also ask the manufactor about their recomendations for power plants.

Mike

 

[nitrotoys]

Re:engine size for 84" cat?

Ok Just how do you launch this boat, I am guessing 28-34 lbs. And 84 inchs.

I have launched a 57 inch boat before, this is STILL BIGGER. Crane it down to the water or what?

 

[Mike Byer]

Re:engine size for 84" cat?

1 of these will do ok.

http://www.pixhost.com/pixm/mbawks/p1010500.jpg

 

[rhomodel]

Re:engine size for 84" cat?

I suggest one of these, saw it running on an 90inch mono

http://www.mhz-engines.com/database/genera...anguage=english

 

[izitbrokeyet?]

Re:engine size for 84" cat?

wow rho......that 28hp should do the trick with horsies to spare

it appears we have similar thoughts on power ratios....

 

[Rick Jacobson]

Re:engine size for 84" cat?

Very impressive. Anybody here in the states sell the MHZ or Rotax motors? Rick

 

[rhomodel]

Re:engine size for 84" cat?

I think you have to contact MHZ directly. The 28 Hp is mainly torque so a gearbox en twinprops would be better I think. And yes you need hp to move a big boat quickly. This rotax angine has been watercooled and Ernest Savarsky ( owner MHZ) said he had it done somewhere specially for him. If you ever buy that engine make sure you also have the coorect carb with it. It needs a big aone and the 90 inch mono I saw did not have a large enough carb to let it really rock. The electric starter is really helpful as it is quite an effort to put the boat in the water.

Julius

 

[Bob Kensill]

Re:engine size for 84" cat?

The 84" boats weighed in at 65lbs. I would pre-start each engine and then put the boat in the water and re-start the engines. The engines were clutched and had one waterpump for each cylinder and one direct feed. At idle the boat sounded like a racing snowmobile. At full throttle it sounded like a formula one car.......sweeeeeet! You had to baby the throttle to get the boat on plane,but once the props grabbed,the boat would accelerate like a rail dragster! The props were from England and cost $100.00 each.

 

[rhomodel]

Re:engine size for 84" cat?

I emailed to MHZ and they think the Rotax is too big for a 84 cat, they adviced twin engines in combination with their outdrives. The outdrives can be changed easilly of rotation by installing a different cran. They didn't specify which engines however. Take a look at http://www.mhz-engines.com/Seiten/frameset.htm and shoot them an email or better call ( and keep in mind the time difference).

Julius