A/B Quicksilver lower unit going racing

Mercury Outboard  general discussion

A/B Quicksilver lower unit going racing

Postby AU52N » Fri Feb 15, 2019 9:34 pm

Aeroliner Race Boats, LLC is proud to help the student race team at Stevens Institute of Technology in their efforts for this years electric boat races.  We have provided a Mercury Quicksilver A/B Mid Section along with a newly rebuilt A/B short skeg gear case.  The power head will be an electric motor.  We also provided several propellers.  here is a link to their web site.  https://stevenssolarsplash.weebly.com/

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Re: A/B Quicksilver lower unit going racing

Postby Michael » Fri Feb 15, 2019 9:36 pm

nice to see you guys helping those kids    icon_clap.gif
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Re: A/B Quicksilver lower unit going racing

Postby outboard315 » Fri Feb 15, 2019 11:27 pm

Coupling 40's technology with a brand new motor. But to be fair that lower unit is pretty small and hydrodynamic for a old design.

They could also use the water pick up to cool the motor and speed controller like they do in rc electric boats.
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Re: A/B Quicksilver lower unit going racing

Postby AU52N » Sat Feb 16, 2019 12:44 am

There is a water pump in the gear case that will be used for the cooling.
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Re: A/B Quicksilver lower unit going racing

Postby Locomotion » Sat Feb 16, 2019 3:42 pm

Will it use 1:1 gears ?
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Re: A/B Quicksilver lower unit going racing

Postby AU52N » Mon Feb 18, 2019 9:55 pm

After consulting with the students it was determined that 16:21 gears would work better.  The motor will have the same HP as a Mark 20H and will have instant torque.

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Re: A/B Quicksilver lower unit going racing

Postby rumleyfips » Tue Feb 19, 2019 12:25 pm

Are they going to use 4 - 25 lb batteries to get 3000 rpm from the motor ?
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Re: A/B Quicksilver lower unit going racing

Postby Tom Brockmeyer » Tue Feb 19, 2019 3:12 pm

rumleyfips wrote:Are they going to use 4 - 25 lb batteries to get 3000 rpm from the motor ?


Their posted Powerpoint slides show (3) batteries weighing at 35 lbs each and the motor has 5,400 max rpm...
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Re: A/B Quicksilver lower unit going racing

Postby rumleyfips » Tue Feb 19, 2019 3:30 pm

Silly me ! I don't like powerpoint much. 5400 from 36 volts is impressive. An etek only gets 71 rpm per volt . I will go back and read their whole site.
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Re: A/B Quicksilver lower unit going racing

Postby Yellowjacket » Wed Feb 20, 2019 1:52 am

Electric motors are "torque" machines.  That is, for a given amount of windings and a given current you get a commensurate torque.  What this means is that for a given hp (torque x rpm/5252) the highest speed motor that will give you the torque will be the lightest solution.  That is, if you want a the lightest electric motor, you want higher rotating speeds.  For instance, an electric motor at 400 amps produces the same torque at 2500 rpm as at 5000 rpm.  But the 5000 rpm motor will be delivering twice the power and have the same weight as the 2500 rpm motor..  Now the voltage required to drive that current through the motor at higher speed is higher so there is no free lunch, but faster turning electric motors are lighter for a given hp. The voltage required to drive the current is a function of the "back EMF" and the resistance of the motor windings.  Back EMF is just a function of how many windings are in series or parallel.  More windings in series gives a higher back EMF, more in parallel give a lower back EMF.  The amount of current you can drive is based on the voltage supplied and the back EMF which is a direct function of winding number and rpm...  That is, a back EMF of 20 volts with a 32 volt supply means that you really have only 12 volts with of potential "driving voltage" and the current limit is the driving voltage divided by the motor resistance.   The real limit is what the rotor can handle in terms of speed.  For a given current losses are pretty much the same (losses are current squared x resistance plus the magnetic losses) so I guess I'm surprised that they would pick a motor that spins at that low a speed.  Aircraft starter generators generally turn 12000 rpm and are pretty efficient machines.
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