Prop size twin 42" cat?

[cogwheel1]

My new project is a 42" Cat. I'm running twin KB45-08XL motors on 5S initially, with 4" Stinger drives. Do I need 1/4" flex shafts or is 5mm OK? I'm having trouble finding adapters to go fron the 6mm motors to anything smaller than 1/4. Ideas?
Props!!!! I was thinking about X452's Is that enough or should I try some 3 blade X450's or larger? I'm really looking for ideas here from some with more experience than I! That should be plenty of motor for this boat to rip shouldn't it? How far should the rudder hang below the sponsons or props--any formula or ideas? My rudder assembly hangs back about 150mm to the leading edge which would put it about even with the prop nut.

[Jeff Wohlt]

If you need couplers made for that then I can do that for you 6mm to whatever.

[cogwheel1]

How much for 2 6mm to 3/16 or 5mm?

[Brushless55]

I'de like to see this puppy when your done..

[Fluid]

Depending on how fast you want to go that should be a good motor setup. 3/16" cable is fine. Prop-wise, two x455 props should give speeds in the upper 50s, perhaps a bit more if the boat is set up well and isn't too heavy. What cat are you rigging?



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[cogwheel1]

Thanks for the info. I had originally intended on running a single motor with the X452 because I already had it, but when I changed to twins I thought I would try two of them. The problem is that few sizes are available in a reverse rotation., for the left stinger drive. I'll check on the X455. 2 or 3 blade? As far as the hull--it is built in Florida and appears to be a knockoff of an Aeromarine Conquest, with a different hatch--but, not positive. The dimensions are the same, length and width and the bottom appears the same. It's a wide Cat and seems fairly light, but I dont know what a Conquest should weigh.

[cogwheel1]

Here's the problem. Either I have to run X450/3 blade, or a X457 because these are the only ones I can find in reverse rotation, or I have to run both drives left hand rotation, then I can run any prop I choose. Whats going to happen if I don't run counter-rotating drives?

[Fluid]

For sport use counter rotation is probably best. The x457s may be okay, but make certain to check for heat after no more than one minute on the first run.

Good alternatives would be the Graupner K-series glass props. They take a surprisingly large amount of power without breaking. For example, Steve normally has both K51 and K57 counter-rotating props. They are less efficient than metal props so for their size would be more forgiving amp-wise. I'd start with them.



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[cogwheel1]

Do you think that the X450/3 blades would be too little of prop? I realize that you should go down about 20% on prop when you go to a 3 blade, but I'm having trouble figuting out just what that would be(diameter and pitch wise).

[Fluid]

Twin x450/3 props would work and push the boat well enough, but top speed will suffer due to the low pitch. This is kinda new territory with the two 5S Feigao motors and an unknown cat hull, but I'd try the K51 and K55 props before I invested in a pair of S&B metal props.




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[Jeff Wohlt]

For sure...try the K55s and get a baseline.

[SJFE]

Couple things you may want to consider doing to the KB. I found mine where much smoother after having the shaft turned down to 5mm and replaced the factory bearings.
Some food for thought.
Tommy G

[cogwheel1]

Not a bad idea. The first motor I received had a bent shaft and it hadn't been damaged in shipping--at least to me. I might consider turning them down. Have you had much experience with those motors? Do they meet their kv rating? How is their amp draw?

[Brushless55]

Couple things you may want to consider doing to the KB. I found mine where much smoother after having the shaft turned down to 5mm and replaced the factory bearings.
Some food for thought.
Tommy G

great idea.. Do you have a link to some better bearings for the KB motors?