Favorie stupid

Nobody is to blame. The pump has to be matched to a correct motor, or to a correct gear box.
This drawing will hopefully explain my point better, both engines are rated the same max power output, but have a max torque at different RPMs:



Cheers

 

Maybe someone can explain this to me. My knowlege of electrical theory is marginal. The 30 hp motor electric is rated as hi-torque motor. 208v-211v 3 phase. We run at 220 volt. Is the 208volt design, being run at 220volts, what gives it its "hi-torque" as opposed to a normal 220 volt 3 ph motor?

 

No, it is about it's constructive characteristics. See the document attached below, pages 3 to 6, where main constructive differences of AC motors are explained. I have downloaded it time ago from somewhere, so don't have a direct link anymore.
Cheers

 

Thanks for the great graph. I'm saving it. My only point is, we can't compare apples to oranges. For boat propulsion, a propeller working in water and an impeller in a pump, are doing similar kinds of work.
The direct drive electric motor is more suited, because of high torque start up, to this task than piston engines with their clutches and reduction gears.
How much electric motor do you need? A lot less than a piston engine doing same job.
Different job, like a truck or car? Maybe piston engine more appropriate.

Trains and ships use diesel electric for a reason. Efficiency.

Some ships use piston engines hooked to shafts thru gears. Lower initial costs.

It depends on your application and needs.

 

Im saving pdf too. thanks. how did you post a pdf? I've tried and won't let me

 

seems I hi-jacked this thread. Sorry

I guess its on topic if I make a stupid A__ of myself?

 

I have updated the graph, to show the engines of the same max power (plus a correct pump torque curve), as is the point I wanted to explain. Cheers!

 

Thanks.
Since I already hi-jacked the thread, let me ask one more question.
If a vessel design called for a 16 inch diam 14 pitch prop driven by 35 hp diesel with 2.5:1 reduction. but you wanted to drive same prop with direct drive electric. How big an electric motor is needed to swing the same prop? 35hp?

 

How about starting a thread dedicated to that question?

Then perhaps Jeff (BD.net admin) could move there this side-drift discussion about pumps and electric motors...

 

ok, ok is too few letters, so ok again

 

Maybe use the alternative spelling "okay" or "au quai".

 

now at this link

http://www.boatdesign.net/forums/op...otor-power-diesel-power-41038.html#post511437

 

hmmm? What's MY "favorite stupid" around boat stuff? hmmmm.
MOI

 

My wife's favorite stupid around boat stuff is me.

 

"You can learn to sail in an afternoon."

http://www.macgregor26.com/easy-to-sail/easy_to_sail.htm