Please help -- Cavitation problem???? - RC Groups
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Feb 16, 2013, 11:18 PM
Registered User

Please help -- Cavitation problem????

please help- trying to get my boat to run
I am having trouble getting my boat to run-- not sure what to do and ready to give up

For background,
I bought a V hull from someone (new) that is 52" long and has a weedeater motor (23cc?) , i bought a 1/4 " flexdrive and propeller 6417 prop (3 blade) and have the Prop mounted 120mm back from the transom ( stinger type setup ).

I have gone numerous times and changed various pitches etc and all I get is CAVITATION.

Is the boat too heavy perhaps. It seems to me to be quite heavy?? - will this matter??

What are the causes of cavitation??

Thanks soo much!!
I put a lot of effort in and cant get things to go!

Any help appreciated!!
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Feb 16, 2013, 11:36 PM
RC boat Rock Star
It's the wrong prop! What it appears that you have is a lifting prop which is made for hydroplanes, not mono hulled boats. Those things wil cavitate like crazy on your hull.
If it's an ABC prop, they're made in 10, 20 and 30 degree props. A 10 is a high-lift, 20, low lift and 30, low-to no-lift.
The diameter is awfully small also at only 64mm which can add to your problem as it isn't getting enough bite in the water. With that Zen you want something closer to a 70mm.
Feb 17, 2013, 02:04 PM
Registered User
Thanks for helping

Looking at the props I have, I actually tried 2 diff props
1) One was a Arrow Shark RC Boat High Performance Prop - AS6717/3 Mod Prop that i bought from ebay

2) The other was a 470 aluminum propeller 70mm dia 98mm pitch for 1/4" prop shaft that i bought from aliexpress

There are no people in my area here that have RC boats, so when I bought this stuff I was unaware of perhaps what I needed

Both these props seemed to cavitate, The more throttle I gave -- the slower the boat went. I expected the boat to race off-- but this has not happened at all.

Is the stringer perhaps not long enough?? to cause the prop to be above the water??

I looked at many peoples builds on these forums and it doesnt seem that my hardware setup is any different??

Could you point to a propeller that might be more appropriate for this kind of boat. I went to abc props but did not really understand what kind of prop i might need

Thanks soo much
Feb 17, 2013, 02:16 PM
RC boat Rock Star
With a 6717 oe 470 you shouldn't be having any problems with cavitating so I'd be looking at strut/stinger height as it may be too far up. Yeah, I know that this sucks as it's a lot of hassle to move it up or down.
If it's just cavitating on the launch then try giving it a toss into the water if you're just dropping it in and hitting the throttle. A nice level toss is all it needs.
Start from the last one first then work you way back as it's the easiest and cheapest way.
Pictures help if you have any. A transom shot would be great, right at it, top or side.
Feb 17, 2013, 03:48 PM
Registered User
thanks for getting back!!

I think the problem is that the drive is not low enough on the transom

I actually drilled a hole lower on the transom to get the drive lower than was initially placed!

Problem is I think I didnt put it far down enough

I tried to attach a photo to see if you agree
Last edited by gzmann; Feb 17, 2013 at 05:01 PM.
Feb 17, 2013, 06:29 PM
RC boat Rock Star
If that's a new hole and the old one is above then yes, that was way too high! That position looks a lot better.
That appears to be an older Warehouse Hobbies setup where they used an Octura rudder. It is newer than the original as yours has the strut extender bracket.
The picture is a little fuzzy but that's what I getting from it.
Feb 24, 2013, 10:20 PM
Registered User
Mark Anderson's Avatar
Give it a good throw and leave the throttle just above idle until the prop hooks up, more throttle won't help. We use a modified x470 3 blade.

Feb 28, 2013, 02:38 AM
Registered User
Thanks for all the help

I decided to lower the drive on the transom. I redrilled the drive in the fibreglass and reglassed everything.

Amazingly--- IT WORKED!!
Feb 28, 2013, 10:10 AM
Suspended Account
It should be lower to get it to work even better. flush with the bottom of the bottom hull with a stinger setup. Normally it should be 1" below the bottom of the hull for the best result.

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