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Aug 10, 2005, 07:19 PM
Registered User

prop shaft angle???


Hi!
I have a problem with prop angle too i think.I have tryed the things pompebled described in the thread below, but the prop just sucking air and almost wont move, the prop is under water to start with but as soon i try to go forward the prop just sucking air.Can it be the angle or the length of the shaft or what?

Its a Speed vee with Graupner Hydrospeed Flexdrive and brushless setup.
Any ideas what im doing wrong??
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Aug 11, 2005, 02:02 PM
Boaters are nice people.
Could you post some pics of the boat?
From the side, top, bottom and rear, preferably not at an angle so I can see how the components relate to eachother.

Which motor are you running? what RPM? which prop? how many cells?

Without this info, longdistance diagnosing is hard.

Regards, Jan.
Aug 11, 2005, 03:58 PM
Useful Idiot
The prop sounds as if it's not set deep enough or that it's too small for the brushless motor and is cavitating because of that.
Aug 12, 2005, 06:01 AM
Registered User
Hi sorry forgot to tell about the setup, motor is a Mega 22/20/2 and rev 2800rpm/v im running it with 8 cells but will go for 3or4 lipo when i get it running, the prop is a 42 mm graupner and the shop told me that the motor should go with 37 to 45 mm prop.
I was traying to lower the prop even more today and moved the prop axel under the boat insted and now it goas a little faster but still not like it should ,the prop still goas in the air (my friends torpedo boat is faster).I read that the propaxel should be 10-15% of the boat length now its just 2" and the hull is 31" can that be a problem.
Thanks Christian
P.S Im from Sweden so sorry for my bad english.
Aug 12, 2005, 07:18 AM
Registered User
MikDee's Avatar
From the Pics, your prop is too deep to be surface drive, most of it is submerged,,, Your motor can't unwind fully because that 42mm prop is too big for submerged running!,,, This will just cause drag, and excessive heat. Get yourself a 35mm prop, as submerged drives use for your size boat, OR put the driveshaft straight out the lowest point on the hull, and move your outdrive up, & back, at least 1" using a block of balsa, or plastic, or a homemade bracket, so that your propshaft is level, and just below the hull bottom,,, The bottom line is 1/2 your prop needs to be in the water, and the other 1/2 out, You need to air out that prop for it to work right, thats why race boats have a big roostertail!
Aug 12, 2005, 07:53 AM
Registered User
MikDee's Avatar
Wait, it just occurred to me what your problem is, I see in your pics the batteries are in the front of the boat, no wonder your props out of the water!,,, Whatever you do to change this, you must have your (center of gravity) COG (balance point) at the last 1/3 of your boat,,, if your boat measures approx. 690mm, the COG or balance point with batteries in should be about 230mm, from the transom. Use this equation with your measurements. Otherwise, your boat will be what we call "plowing", or digging in at the bow.
Aug 12, 2005, 08:25 AM
Registered User
Thank you very much, i will spend some time in the garage to do some rework on the boat.
Maybe i buy a alu strut assambly, then i can use it on a mono race hull as well.
Regards Christian
Aug 12, 2005, 08:45 AM
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MikDee's Avatar
Your hardware is just fine, when it's setup right,,, don't waste your money on better hardware unless you plan to race, by the way make sure your trim tabs are 1/16" above the bottom (don't know what that is in mm?) or they will drag, in fact you may not even need them, because they do slow you down a little bit. But, you may eventually need a spin/turn fin on the right side.
Aug 12, 2005, 08:56 AM
Registered User
MikDee's Avatar
Personally I would notch out sides of the back wall under the hatch where your reciever is, to slide the batts in on their edge alongside, but slightly behind the motor, this way you could adjust your COG as needed by sliding the batteries in, & out. Make sure to fasten your batts before running also.
Aug 12, 2005, 10:29 AM
Registered User
I split the batt in half and slide each stock in the side, mach perfect.
What do you think of the hull and the motor shold it pick up some speed do you think?
I thought the hull would be perfect becaus its so light but maybe a little week i dont now?And the motor should be a very fast one (the lokal store told me)so guess if was disappointed when my friends torpedo with a much slower AXI brushless motor could go circles around me!
Aug 12, 2005, 11:46 AM
Registered User
Hmm!! the lokal shop have tricked me its not a 22/20/2 the last letter was switched from a 2 to a 3 thats maybe why it was slower,when i finally got the prop under water.
Aug 12, 2005, 12:04 PM
Useful Idiot
Alan at www.astecmodels.co.uk/ probably knows as much about the correct propellors for Mega brushless as anyone.
Aug 12, 2005, 01:30 PM
Boaters are nice people.
Quote:
Originally Posted by chrilla
Thank you very much, i will spend some time in the garage to do some rework on the boat.
Maybe i buy a alu strut assambly, then i can use it on a mono race hull as well.
Regards Christian
Hi Christian,

I've attached a picture of my 12 cell monohull. It's not a flex-shaft with a strut, but it gives you an idea where the prop should be located and where the shaft should exit the transom.

Let us know if you need more pictures.

Regards, Jan.
Aug 17, 2005, 04:29 PM
Registered User
I have done some work on the boat and extend the prop shaft.But does the shaft need to be level with the hull bottom?Now its slightly angeld down as you can see on the pic,but need to be if the prop should be half over and half in the water, if i have it level then just the prop blade would be in the water.
The prop is about 3" from the transom.
Aug 17, 2005, 04:59 PM
Boaters are nice people.
This is looking much better!

Just give it a try and see how she runs.

The idea of a surface piercing prop is that only the blade is in the water, everything else will create drag...

Regards, Jan.


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