Thrust ratings--Have they changed?

[James P]

I have to admit that when my daughter was old enough to play sports I left the world of fishing for about 10 years. When I got back into fishing it seemed the trolling motors thrust ratings were so much higher than they used to be. I remember the engine hp ratings changed at a certain point in time and wondered if the trolling motors did the same. I have a 15 or so year old 24 lb or ft. lb thrust Motor Guide that seems stronger than the same 24 of today. Could someone shed some light on this for me?

 

[JB]

Re: Thrust ratings--Have they changed?

I don't think the ratings have changed, James. They are offering stronger models these days because the boats are bigger and heavier and because fishermen lust for more power.

There is also the phenomenon of time and what it does to memory. I recall being a lot stronger ten years ago than I clearly am now.

 

[Silvertip]

Re: Thrust ratings--Have they changed?

30 pounds of thrust is still 30 pounds of thrust. Can't change that measurement. The change in outboard power came as the result of "where" they measured horsepower. It is currently measured at the prop whereas early engines were rated at the power head. Electric motors don't have a gearbox since they are direct drive and the force they exert is thrust or push not horsepower.

 

[jtexas]

Re: Thrust ratings--Have they changed?

could it be a difference in propeller?

 

[James P]

Re: Thrust ratings--Have they changed?

Thanks for the replies. I guess there would be a formula using prop diameter, pitch and rpm's . Maybe I was thinking that they may have started exaggerating the thrust ratings. I wish JB's last sentence wasn't so true!

 

[Silvertip]

Re: Thrust ratings--Have they changed?

Changing the prop on an electric motor will change thrust but not in the manner you would compare with a gas motor. Electric motors run at a fixed maximum rpm and in the case of trollers, the prop is optimized for that maximum rpm. If you added diameter and/or pitch, that motor would no longer be efficient, it would be lugging, and using electricity like crazy. Speed goes down. Conversely, if you decrease pitch, the motor runs at the same maximum speed as before the switch so again, boat speed decreases (less pitch so less forward movement) so you do not get more thrust but rather less thrust. 30# then = 30# now. Advances in motors have come in the form of run-time on a charge so the newer motors are more efficient in that regard and motors are available with over 100# of thrust.

 

[John_S]

Re: Thrust ratings--Have they changed?

Is there a standard way they are measured? I have never seen one quoted with electric trolling motor thrust ratings. I also get a little nervous when I hear "peak" thrust. Gas engines I have seen, have standards.

 

[Silvertip]

Re: Thrust ratings--Have they changed?

There are several ways one can measure thrust but it doesn't matter how you do it -- the thrust will be the same. Thrust is "push". Tie your boat to a scale and tie the scale to the dock. Turn it wide open and you should measure 30# for a 30# motor. There isn't any other measure. A 30# motor has 30# of "peak thrust", "maximum thrust" or plain "thrust". It can't deliver more but it can deliver less. Gas motors are rated in horsepower, not thrust. Big difference.