H.P. vs pounds of thrust.

[hondon]

The salesman at my shop has come to me over the last few months with a repetitive question that is being asked by consumers.What is the relationship to h.p. and thrust ratings. I have explained to him that electric motors turn the prop fast with very little torque,thusly moveing a specific amount of water in ideal circumstances.There is the thrust.H.P.is determined by propshaft torque at a given RPM.A pat answer and I don't like to give pat answers.Anybody got comparison ratings for electric to small gas,and is the pat answer at least close?All my breif reaserch has come up nill.Thank you.

 

[Bear]

Re: H.P. vs pounds of thrust.

I'm not sure if this is what you mean.<br /><br />Johnson TH 2, 12,0 kiloponds (12 volt) <br />Thruster T 4800, 15,0 kp (12 volt)<br />Yamaha M 16, 14,5 kp (12 volt)<br />Yamaha M 32, 29,5 kp (24 volt)<br /><br />And for the comparison:<br />Yamaha F4, 47 kiloponds of thust ( one cylinder 112 cc fourstroke)<br /><br />Even if I cant say what kiloponds equals in Newton you can translate it to percent.<br /><br />That is the test results from a boat magazine in 1998. Factory specificatitons is sligthly higer (M 16 16,2 and M 32 31,5).<br /><br />Hope it helps.<br /><br />/Bear

 

[hondon]

Re: H.P. vs pounds of thrust.

Thank you BEAR for responding ,and you have given me some valuable comparative info.Now the question still looms.What criteria is used to determine pounds of thrust on these electric motors?

 

[trevorcday]

Re: H.P. vs pounds of thrust.

The motors make their maximum thrust when standing still, ie. no relative motion between boat and water. I always assumed that this is how the thrust ratings are created.<br /><br />Here's another way to look at horsepower comparison. Say a 50 pound thrust 12 volt trolling motor draws 30 amps (I'm guessing). That gives 30A x 12V = 360 Watts or about 0.25 hp. Since this is the power going in to the motor the output is something less due to losses in the motor, drive and prop.

 

[hondon]

Re: H.P. vs pounds of thrust.

Thank you ,MRMERC.Now I have a comparison and acutual formula to work from.That's great help.Anyone else care to wade in .I love this place.

 

[MGuckin]

Re: H.P. vs pounds of thrust.

Found this in another forum. Hope it helps<br />There is not really any direct correlation or conversion to compute horsepower from static thrust, however the following will <br />give you an approximation.<br /><br />Most modern 12 volt trolling motors draw one amp of current for every pound of thrust.<br /><br />Thrust*Voltage*Effiency=Approximate HP.<br /><br />At an assumed electrical efficiency of 95%, a motor rated at 47 pounds of thrust will consume (47 * 12.8) = 601.6 watts and deliver 601.6 * .95 = 571.5 watts of useful work. Since one horsepower is equivalent to 750 watts, this amounts to approximately 3/4 horsepower at the propeller shaft. Propeller designs may sacrifice some of this efficiency.

 

[hondon]

Re: H.P. vs pounds of thrust.

Thank you McGuckin for another usefull formula and backing up my thoughts on the corelation thing.I will jot all this info down and place it on the salesmans desk tomorrow morning,for his reading pleasure.