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# Physics/DC Motor

Question
I have a sailboat which has a 12 V DC motor driven bow thruster rated at 8 HP or 5.884 KW. I run the system with a dedicated battery bank consisting of two batteries of 245 amp hour batteries for a total available amps of 490. The thruster is use during docking and only in short durations usually less than a minute or two. Will the horse power be less if I provide less than the 490 amps?  I frequently see others using a smaller (amp hour) battery bank.  Does not this diminish the available motor HP?  Is there a linear relationship between amp hour and horse power?

Of course it will be less during the time you use less amperage.  And yes, the relationship is relatively linear.  However, it's not like you should go out and decrease the battery power of your motor.  The term of HP or HW are power terms, the amp-hour terms are the total energy stored in the battery itself.  If you need it, you'll have it by keeping the same battery energy.  Power is just raw energy thrust, energy/time.  Energy is the total amount that the system is keeping in store for you.

Physics

Volunteer

#### Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.