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post #6 of Old 05-08-2007
Jeff_H's Avatar
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At least as described, this is not a well concieved idea and is a far more major a modification than has been suggested. To begin with the website says Mars Brushless motor is a suitable substitute for a 3-12 hp diesel. An Atomic 4 is a 25 hp engine that generally requires an 18 to 24 hp diesel as a replacement.

But even if the Mars Brushless motor offered suitable power. the project is huge, far beyond what is suggested on the Mars Site. As I think of the step by step process below, it makes an Atomic 4 rebuild sound like a real bargain;
  • Remove Atomic 4 and tanks;
  • Build a structurally sound base for the motor. This is a legless motor and so you need to fabricate both a set of motor beds and the brackets that can take the torsion and rigidly distribute the loads to the beds.
  • Here is where it gets complicated. The propeller shaft is supported by the coupling in all three axis's. So you need to find and fabricate a mount for a thrust bearing and shaft end bearing.
  • Typically electric motors drive the shaft by cogged belt or chain, which means finding suitable pulleys, belts or chains and designing a tensioning device.
  • Build boxes capable of supporting the batteries. Batteries are bigger and heavier than the fuel tank they replace if they have close to an equal run time. The batteries need to be secured at all angles of heel. The boxes need to acid resistant. If you use lead acid batteries they boxes should be vented to the atmosphere and have a blower to prevent overheating during recharging and to carry away the explosive gases.
  • Add chargers with adequate capacity for the large capacity batteries.
  • Re-ballast the boat to get her back on her lines since the center of gravity of the batteries and motor will most likely be extremely different than that of the Atomic 4 and fuel tanks.
The real problem with electric powered cruising boats is the size of the batteries required to operate refrigeration, nav instruments, running lights, and autopilot between charges. You probably could buy a small rebuilt diesel with a warrantee and install it far more simply.

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