Tuesday, January 24, 2012

Re: [Electric Boats] Re: 30 ft C&C/ Colombia 30

 

yup, if a motor skipped out on ya, you'd definitely have to power down and run slower to limp it home, for remaining motors not to get overloaded. theyed handle 1/2 speed for a bit.
I'm just talking an "if" for some reason a motor burns up, things still happen.
 
I have a limited experience (a good one) with a 24v 250w 2600rpm scooter motor,
I ran it on 12v for 1/2 rpm, direct drive to a youngprops T-6, and it never got warm.
so much smaller a boat tho, 5/16 rod through 3/8 hard brake line = perfect fit!
there was about .004 clearance between shaft and tube, I did a gravity feed column to it for 50wt oil, same as a typical model boat, just larger.
on half voltage, that motor still had really amazing torque for its size, very likely a great combo for something simple like an electric kayak. I probably couldda also got away with swinging one of young's 7" prop, the motor ran that cool on 12v.
the boat was a slightly narrowed (and lighter) electric inboard version of svensons-com's "Bebop", which is just a cute kid size runabout toy. it'd do 3.5-4mph about all day long, stereo (with 2 10's and horns) thumping the whole way.. a fishermans nightmare!
 
I'd almost be tempted to say use 36v motors fed 24-26v.. it'd maybe sacrifice a little efficiency, maybe not! windings never getting warm can be better than internal resistance and heat robbing it, and the long term reliability only goes up, even if runtime is slightly shortened. spinning slower probably also pulls less amps and build less heat..
honestly.. I'm also thinking the real torque is more a function of the motors magnets,
that scooter motor spun slower but there sure wasnt any lack of torque!
another tidbit about the scooter motor I played with, it wasnt "notchy" and didnt slow down really fast when the shaft spun by hand, so in a triad, if one let go, it'd be more like an idler pulley, not adding a buncha load to the other two.. but idk if they're all like that.
it was brush type, neutral timed, would power forward or reverse same speed.
 
I sure like the potential hull speed of something 30ft, 8.5mph is decent if it'll do it.
 
 

--- On Tue, 1/24/12, John Green <v_2jgree@operamail.com> wrote:

From: John Green <v_2jgree@operamail.com>
Subject: [Electric Boats] Re: 30 ft C&C/ Colombia 30
To: electricboats@yahoogroups.com
Date: Tuesday, January 24, 2012, 9:47 AM

 
Hi,
Regarding the use of multiple small motors. That is my plan, but the
idea of running partial power via having some motors non-powered does
have an annoying snag.
Due to the lack of excess power available, the gearing has to be such to
give torque loadings that are slowing the motor group (when all motors
are running) only to a comfortable situation regarding amps and heat.
Taking a single motor of a group out will increase the 'slowing' effect
on the remaining motor(s), probably/possibly taking it/them out of a
useable range as far as amps/heat and continuous duty goes.
The simple resolution though, is to have a second pulley/belt set
available, with corrected ratios. Especially with toothed belts, and
spring loaded tension pulleys that can be hooked back clear, the
changeover would be quick to do.

John

4b. Re: 30 ft C&C/ Colombia 30
Posted by: "KEN" rekkamurd@yahoo.com rekkamurd
Date: Mon Jan 23, 2012 10:21 pm ((PST))

"roll your own".. funny expression no doubt, but pretty much what I had
in mind pointing at the "monsterscooterparts.com" site, I dont know what
kind of power requirements your 30 footers really need, the 24v 900 watt
motors (1.2hp each) if 80% efficient is 1hp each..
they spin about 2500 rpm and belt or chain joining em at whatever
reduction would be simple enough. same for replacement if one takes the
proverbial dump, theyre not spendy.
if theres 3 of em and one comes unglued, still got the power of the
other 2 and can limp it home? not that it'd be a long trip with your 1hr
runtime requirement.

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