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Help with powering Fast passenger ferry or crew/ supply vessel

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Help with powering Fast passenger ferry or crew/ supply vessel

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Old 05-14-2018, 04:41 PM
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KAF
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Default Help with powering Fast passenger ferry or crew/ supply vessel

Hi to all,
My name is Kenneth and I'in currently in the design stage of having a Fast offshore crew/supply vessel built. So far the design process is going real good. The model with be 63" long and 15 inches more or less wide. Will have a twin screw set up, but as I am new to electric and never had any brushless motor experience I don't know that size motors/ESC/batter to get. I forgot to mention that, I will be operating each motor independently with a radio that had a stick to throttle each motor separately. I would like to see around 25-30 mph and have as long a run time as possible. I don't know if these are reasonable goals, but any help would be greatly appreciated. The green ferry in the pictures below does about 34 knots.

Thanks in advance, Kenneth

Last edited by KAF; 05-14-2018 at 04:54 PM. Reason: Add more information
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Old 05-15-2018, 06:04 AM
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If the real thing is 25 metres long, and capable of 34 kt, a model 63" long would be about 1:15 scale. Speed scales as well as size, which is why test tanks work. A realistic hope for top speed would be about 8 kt. Apart from providing power to get high speed, the hull design will have limits on what speed it can go and stay the right end up. Again, this is why test tanks have been considered very useful things by ship designers over the last couple of hundred years.
If you know the power available for the original, you have a good starting point for guessing at the power needed for realistic performance, but speed and endurance are not usually compatible given the limited energy storage available within a model boat.
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Old 05-15-2018, 01:08 PM
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KAP, Here are a couple of websites that may help you. The motors are Astro Flights brushed 800 KV . Each one is running on a 14 cell battery pack. They are set up with counter rotation. Keep us posted. Dan
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Old 05-15-2018, 01:17 PM
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KAF
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Awesome Dan, thanks for sharing your video and information. It gave me hope that I can get some type of a decent speed. I will post pics as I get the final design from Mike and as the build progress.
I greatly appreciate your help. Guys.
Kenneth
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Old 05-16-2018, 05:27 AM
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Good morning to all once again.
I need a bit more help, what length stuffing box should I use in a boat that is 63" in length. I am on MACK Products website and the longs I see for 3/16 shaft is 12" long. Would that be long enough? Or is there somewhere else if I need to go longer? Thanks for you help. Kenneth
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Old 05-21-2018, 03:13 PM
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Okay, how about I throw a few questions back at you?
1) How far is it between the shaft strut and the motor?
2) How much stuffing box does it require to get the shaft through the bottom of the boat?
3) Does the entire shaft need to be contained in the stuffing box?
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