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Alignment of Rudders and props

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Old 10-04-2019, 06:23 PM
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Default Alignment of Rudders and props

Hi I am building a 5’ pt boat would like to know if I should Align the props with the rudders , twin props twin rudders 2 775 Brush motors
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Old 10-04-2019, 07:59 PM
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Short answer - yes. With your submerged drive you will get better steering at low speed with the rudders directly behind the props. A fellow club member has a large dual-motor PT and with the rudders behind the props, he has great maneuverability.


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Old 10-05-2019, 01:33 AM
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Originally Posted by Got RPM View Post
Short answer - yes. With your submerged drive you will get better steering at low speed with the rudders directly behind the props. A fellow club member has a large dual-motor PT and with the rudders behind the props, he has great maneuverability.


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....although it is often considered sensible to offset the rudders by the width of the propshaft. This makes life a lot simpler when servicing the prop shaft later on should the need arise to withdraw the shaft. Having to remove and replace the rudders is generally a PITA that is best avoided. Makes not a scrap of difference to the handling.
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Old 10-05-2019, 05:26 AM
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i am going to power this boat with two 775 brush motors 1/34 three blade props can u tell me if the onyx 1060 esc I going to use 2 of them and 3s 11.1 5200 lipos x2 will work and I plan on removing one of the bec from one of the esc hook up on a y I am also going to run servos to make the gun Mounts to turn back a Fourth I plan on using a Funabashi 6x airplane 2.4 radio I use when I use to fly any help on this stuff Will be very much appreciated thanks Rye
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Old 10-05-2019, 09:19 AM
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No idea how those motors behave with those props, but to get anything like scale performance is going to need motors that swallow about 500 watts between them, or 25A each on 3S. Usual rule of thumb for brushed motors is "prop to have smaller diameter than the motor can, should also have fewer blades than the motor has poles". I'll let you read the specs on your preferred ESC and decide on the level of derating needed. With sensible motor choice, this normally results in a cool running motor and good run times.
The numbers relating to brushed motors usually just refer to the can length, what goes on inside is a big unknown. The same size can might hold a motor that will swing a huge prop quite happily at modest revs. or, with different windings, might rev beyond belief but only with a very small prop for a fast boat. Its a big model of a fast, powerful boat that was very thirsty at high speed. The model will have the same behaviour.
I am sure that you will get lots of suggestions of what combination of brushless motor and ESC will work well. Probably the best way to go.
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Old 10-05-2019, 02:31 PM
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Thank you very much for the help I appreciate it I’ll take any suggestions RYE
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