Bustitup Sprintcat 40 need help

[bustitup]

someone tell me what this needs?

scorpion outrunner 4025 1674kv on 6s2p turnigy 5000's, Turnigy 180 esc, prather 235 prop....57mph...temps where fine 140 esc, 170 motor

I couldnt turn left and beached it....nothing broke but why is it porpoising?

SECOND RUN

[crabstick]

Man, it made it a fair way up the bank!

where is your COG ?

How long is teh rudder?

[bustitup]

Man, it made it a fair way up the bank!

where is your COG ?

How long is teh rudder?

COG is 11.5 and the rudder is about 2" below the prop....the bottom of the stuffing tube is about 5/8" above the bottom of the sponsons

[Raydee]

Not sure and I know you commented on my CG but yours just looks to far forward compared to every other Sprint I have seen built.

[bustitup]

It seems if I was to far forward there would be LESS chance of porpoesing?

Not sure and I know you commented on my CG but yours just looks to far forward compared to every other Sprint I have seen built.

[knpc]

Those numbers seem about right. My cog is 11.5'' and the bottom of my strut is 1/2'' above the bottom of the sponsons and 0 deg. I do have a bigger rudder, the bottom of my rudder is almost 4'' below the bottom of the strut.

[crabstick]

Try going forward on the cog and see if it sits down.

[Raydee]

It seems if I was to far forward there would be LESS chance of porpoesing?

If you have a powerful motor and a big prop the boat will want to lift the nose out of the water BUT then if the CG is forward the weight will slam it back down. I have done this with my Delta Force hull, by accident I had the cells to far forward and the front end was jumping up and down the same way.

[Raydee]

Might also just be the wrong prop for the hull. I know mine loves a 3 blade prop.

[knpc]

Is the strut level? I got a little porpoising when I tried going a couple deg kick up on the strut.

[Fluid]

The most common cause of porpoising is running the prop too deep. The Prather props have more lift than the Octura props and so would act like they are running deeper regardless of the strut setting. Set the sponsons flat on a table and raise the strut 1/8" more. Angle the strut so it has about 1 to 2 degrees of 'up' angle at the prop end and see if this helps. Yuo may want to try a prop with less lift like an Octura x452.

The prop is on the small side for the hull but that may be all the motor can handle. My HK4025/1100 spins an x455 just fine on 1P but the higher Kv of your motor means less torque.



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[Rumdog]

I didn't notice any porpoising in the vid.

[bustitup]

I didn't notice any porpoising in the vid.

well not sure if you would call it porpoising but listen to the whine of the motor ......its not a steady whine......it sounds like the prop is catching and letting go intermittently

here is a video of the first run where you can see the boats slight bouncing

click here

[knpc]

You can hear it and see it in the roostertail better in that video. I would think its causing unnecessary amp spikes and heat. I'll be interested to know what adjustments will fix it, it will be good to know for future reference if the same problem in encountered.

[bustitup]

You can hear it and see it in the roostertail better in that video. I would think its causing unnecessary amp spikes and heat. I'll be interested to know what adjustments will fix it, it will be good to know for future reference if the same problem in encountered.

also look and listen to my first turn where I get off the throttle and you can hear a spinning or slipping of the prop

from suggestions that have been given here especially from Fluid and Raydee ....my next move is to go up to a prather 240.....if his theory of prather having more lift is right than my 235 prather may be lifting but its not big enough to hold the hull "up" under full load...so the bigger prop may help....with all that waisted energy of lifting and dropping this boat should hit 60+ easily..........both videos at 57mph I have the hammer down even into the turns....I may also move the batts towards the back a little after the bigger prop

another thing is why the heck am I running a left hand oval?..LOL