I always like reading HP and efficiency related threads. Some educational posts.
One always has to keep in mind that there are always two things necessary to establish HP, that is FORCE and VELOCITY. One is not enough. Please correct me if I'm wrong.
In the case of linear motion, HP = k * F * V where k is a units conversion constant which I think is 1 if you use consistent units such as watts, newtons, and meters per second. In the case of rotary motion, its HP = k * Torque * Rotational Rate.
The linear case applies to boats and rockets.
So, for a boat I've always thought about making a plate to attach the motor to which had load cells (force sensors). Then, using this force along with water speed you should be able to measure the Power (HP, or KW) actually delivered to the boat. I think one would have to be wary of the force vector that is being measured, if there were an angle error that could throw off the measurement. It might even be worthwhile to have 3 triangularly configured force sensors and depending how the thrust plate is hinged some might have to measure positive and negative forces. I would probably also include some kind of mechanical adjustment so that I could change the thrust angle of the propeller.
Then, if you could make such a measurement of power delivered to the boat, then also measure the voltage and amps going into the motor you would be able to get an overall efficiency factor, compare different props, thrust angles, bollard force (tie to your dock so V = 0) etc in order to optimize performance. In fact this could give performance data over the entire speed curve for a boat.
It also occurs to me that when to bow rises, this requires a static force that may not contribute to motion against the water, not sure how to compensate for that. Of course raising the bow in planing is beneficial too, but maybe not until you are on plane.
Comments ? And, if anyone has done this or if there are posts relating to this please comment.
In order to optimize anything you need a good measurement system.
--- In electricboats@yahoogroups.com, "scott" <audeojude@...> wrote:
>
> Just remember that though bollard testing is a good component of your investigation that strong pull in a bollard test doesn't directly relate to top end speed. You can have an engine prop combination that pulls less on the bollard test but that gets more high end speed. Speed range has more to do with the prop than the engine. However even this isn't absolute.. You truly need to match the engine/motor to the prop to get best efficiency/speed. Mismatched engine/motor/prop combinations will eat power, cause fuel consumption to skyrocket and reduce engine/motor life.
>
> --- In electricboats@yahoogroups.com, "John Green" <v_2jgree@> wrote:
> >
> > Hi, thanks for the responses.
> > It seems that there is no instant answer, too many variables. But that pulling test seems the info I really wanted!
> > Seems that with 3 minnkotas, take out the resistor speed controls, add model airplane props, and it would be like having one minnkota extra!
> > So, from these responses plus the other topics lately, it would seem once again that the electric setup can be done using low cost parts. The controller being so low cost to compare with switches is good too.
>
No comments:
Post a Comment