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Author Topic: "crackerbox" problems  (Read 4098 times)

Martin [Admin]

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"crackerbox" problems
« on: January 31, 2008, 09:24:34 AM »

Via email to Mayhem....

Hi, I have a flat bottom crackerbox that barrel rolls violently in fast turns do you know how i can solve this problem?
Its a 1/4 scale C-box 46" long & 16" wide running on gasoline. Zenoah 260pum Engine. the bottom @ the ride pad is completely flat & the edges are sharp.

Could it be tripping up on the sharp edge?

regards Keith
USA
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DickyD

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Re: "crackerbox" problems
« Reply #1 on: January 31, 2008, 10:07:08 AM »

Slow down ! Sorry couldn't resist. :embarrassed:
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Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

Martin [Admin]

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Re: "crackerbox" problems
« Reply #2 on: January 31, 2008, 10:25:51 AM »


Additional details added below (above depending on your forum setup!)

Morning DickyD!  ;)
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keith

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Re: "crackerbox" problems
« Reply #3 on: January 31, 2008, 10:31:09 AM »

That actually works to  ;Hello everyone. Im a Gas & Nitro model boater from the USA. I look forward to talking R/C boats with you all!  8)
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keith

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Re: "crackerbox" problems
« Reply #4 on: January 31, 2008, 10:42:30 AM »

Thanks for posting my question for me. Martin. :) Im running a sub surface octura X472 prop
With a octura wedge rudder behind it. The skeg is a shark fin shape and is directly below the engine in the center of the hull. the 24oz fuel tank is on the starboard side.
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BJ

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Re: "crackerbox" problems
« Reply #5 on: January 31, 2008, 07:39:41 PM »

So first of all, how much does it weigh and where is the centre of gravity/balance.
You could try talking to a guy called Ron Olson in the US - he seems to be a good source of knowledge over that side of the pond and is on most of the forums over there.
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keith

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Re: "crackerbox" problems
« Reply #6 on: February 01, 2008, 07:00:03 AM »

Hi, I have already talked to the guys over hear. beside's ive already been kicked off every form hear in the US.   :police: 8) :police: The boat is setup per crackerbox setup guidelines its got nice speed & attitude in the straits, but in the corner without warning she pops off the water and cork screws high into the air. i have tried just about everything to stop this from happening but it still does. the boat weighs 14Lbs & the CG is 30%
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w3bby

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Re: "crackerbox" problems
« Reply #7 on: February 01, 2008, 08:50:20 AM »

No personal experience of the crackerbox but the blowing off sounds familiar for that class. If I remember correctly this is what the guys said made the class was fun, you have to DRIVE the boat. It is likely that you are correct and the boat is side slipping (even with a skeg) and tripping on the chine.
If you have trim tabs on the transom the boat can also trip over the outside edge of the port tab. I believe they were bending an anti-trip on the outside edge of the port tab to stop it digging in when turning.

simple sketch        \________ but not such a steep angle.

Hope this is of use....

BJ

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Re: "crackerbox" problems
« Reply #8 on: February 01, 2008, 10:49:05 AM »

Does it do it when you turn anticlockwise or just clockwise?

Is the hull heavier on one side and if so which?

Weight and % distance from transom sound OK

Then there is W3bby's trimtabs question - some boats have a pair of outer tabs and a pair of inner tabs.
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scoop

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Re: "crackerbox" problems
« Reply #9 on: February 03, 2008, 05:51:00 PM »

Hello, 

Try ditching the skeg, then angle the bottom leading edge of the rudder so it is 5 degrees towards the bow, ie 5 degrees from perpendicular to the transom. It think what is happening is the stern is lifting in the turns causing the bow to dig in and barrel roll. Angling the rudder as above causes the stern to dig in on a turn and sit down making for tighter stable turns, this has always worked for me.
Does your boat presently weave about a bit in the straights?
Also if you are running two turn fins ditch the port side one and set the starboard one to perpendicular to the transom. Let me know how you get on.

Regards Scoop
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martno1fan

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Re: "crackerbox" problems
« Reply #10 on: February 05, 2008, 02:14:12 PM »

Hi, I have already talked to the guys over hear. beside's ive already been kicked off every form hear in the US.   :police: 8) :police: The boat is setup per crackerbox setup guidelines its got nice speed & attitude in the straits, but in the corner without warning she pops off the water and cork screws high into the air. i have tried just about everything to stop this from happening but it still does. the boat weighs 14Lbs & the CG is 30%
Hi mate check this build thread out might give you a few ideas also check out the site ive also linked lots of info on there for you  O0.just click on the pics and theres info about them too.seems the balance has to be way forward on these hulls compaired to some monos.16-17" from transom.so your ballance seems a bit far back according to what they say on that site.
mart

http://powerpete.20megsfree.com/photo3.html


http://groups.msn.com/OxfordCountyCrackerboxes/home.htm
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GARY C

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Re: "crackerbox" problems
« Reply #11 on: April 16, 2008, 11:34:18 AM »

Via email to Mayhem....

Hi, I have a flat bottom crackerbox that barrel rolls violently in fast turns do you know how i can solve this problem?
Its a 1/4 scale C-box 46" long & 16" wide running on gasoline. Zenoah 260pum Engine. the bottom @ the ride pad is completely flat & the edges are sharp.

Could it be tripping up on the sharp edge?

regards Keith
USA

Hi Keith,

Please vist www.modelgasboats.com   then click onto Insane Boats Hardware. They sell hardware for the crackerbox including a special left trim tab called a "NON TRIP"  this prevents hooking and spining out on the turns. Picture is shown of the hardware.
Hope this is of some help.

Gary.
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