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Author Topic: rudder, prop and prop shaft question for a beginner  (Read 1374 times)

big yim

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rudder, prop and prop shaft question for a beginner
« on: April 28, 2010, 10:21:42 am »

Is there a rule of thumb to say what size rudder you need? I am planning a large ish bait boat and don't really know which ones to get? How do you know which propellor to get too?
I also don't know how to connect the motor to the prop shaft? All I have on the motor is the part that sticks out which has a little groove cut into it. So how would this attach itsself to a prop shaft?
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malcolmfrary

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Re: rudder, prop and prop shaft question for a beginner
« Reply #1 on: May 02, 2010, 05:24:58 pm »

The rudder should reach down to the bottom of where you think the prop wash will be in the water, and come up as far as the top of the prop wash.  A depth/width ratio of about 5 deep to 3 wide should be about right.
Prop diameter, as a rule of thumb, a smidgen smaller than the motor diameter, and with less blades than the motor has poles.
It sounds like your motor has a shaft with a flat on it to accept a fitting with a grub screw.  To connect to the prop shaft you get a grub screw fitting, a universal joint fitting and a fitting to suit your prop shaft.  To take up bad alignment, call that two UJs and a centre coupler.
Whether the prop and motor will propel your boat as you want it depends on the hull design, the power of the motor, battery voltage and whether the prop can translate that power into forward motion.
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"With the right tool, you can break anything" - Garfield

hmsantrim

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Re: rudder, prop and prop shaft question for a beginner
« Reply #2 on: May 02, 2010, 07:42:07 pm »

Hi Big yim.
              you would be better going to a model shop or boat club where you can be physically shown how its done
 
             which is a lot better than trying to have it explained on paper.  Its not rocket science but when you don`t know how
 
             its done those trying to explain may as well be talking Greek.  I am just about to put a motor in a boat and I can send a pic

            so you can see the parts to help you match them to the words.   


                                      cheers
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