Lugging?

[tomxdana]

What is lugging a motor? I've been reading threads and someone mentioned that with the wrong prop you can kill your motor. I'm looking to go from 11 3/4 x 19 to a 13 x 19 by the recommendation of a Mercury dealer, salesman, and a prop calculator I found online. My prop died and they didn't sell a 11 3/4 and started looking into the correct prop for my boat. What would the symptoms be? If I can't get to wot rpms is that lugging? Would you expect to see with the change in diameter prop? I believe I had to much throttle with my old prop. Meaning I never had it all the way forward or it would exceed the 5200rpm. I also only run it by myself so I didn't know if that was normal.

Thanks

 

[kenmyfam]

Re: Lugging?

You need to know the max rpm range for your motor and then be at the mid to high end of that range.
Example, your motor max rpm = 5,000 to 6,000
You should be between 5,500 and 6,000 rpm at WOT with your "normal" load. Anything less and you are running the risk of lugging.
Look for other responses from people out here that are absolute experts at this.
This is an example only, you must find out the details for your motor before changing anything.

 

[steelespike]

Re: Lugging?

You didn't say what boat/motor you are running also would be good to know your present max rpm and speed.Generally prop diameter is a product of prop design and not considered in prop selection except regarding clearence.
That said the 1 1/4 inch increase could have some slight affect on reducing rpm.
give us your present specs, motor and boat.You certainly aren't likely to lug the motor with that prop.

 

[Silvertip]

Re: Lugging?

Since we don't know what motor you have we can't offer much help. However, understand that there are two prop characteristics to consider (actually more but these two are what most people need to consider) and those are diameter AND pitch. Diameter is a function of prop design so you will see props designed for a given gear case size vary in diameter by about an inch from the lowest pitch to the highest in the range. You are apparently going from a prop designed for a smaller gearcase to a one for a larger gearcase so I would first make sure you are buying a prop that is INTENDED for use on your engine. 13 - 13-3/4 inch props are typically installed on intermediate size gearcases. 11-3/4 - 12-1/2 inch props are typically used on 40 - 50 hp motors. The reason I mention this is that if you are over reving as easily as you say you are, then the change you are making may be wrong for two reasons (diameter and pitch). One inch of pitch (up or down) typically provides an engine rpm change of 150 - 200 rpm. Tell us what boat, motor (make and year), and current WOT rpm. A short burst at WOT will not hurt anything. Only then can we tell you whether you are on the right track or not. I would suggest that you are on the right track ONLY if the original prop was the wrong diameter (incorrect prop for that engine gearcase).

 

[tomxdana]

Re: Lugging?

I need a prop for my Trophy 1802 ( year 2002). Mercury 125hp 2 stroke. I bought the boat used last year and don’t know whether or not it had the right prop. There are numbers stamped on it. 2038 with a space then 19. The prop actually measures 11 ?. I went to West Marine and when they looked up the quick silver replacement the book listed 12 ? x 21 or 13 x 19 for my size boat. I never opened it all the way because I didn’t want to exceed the 4750-5250 rpms recommended by the manufacturer. ( I also haven't had more than 3 people making it tough to test wot )I use my boat primarily for fishing with 2 to 3 people aboard. At this point gas mileage would be more of a priority than speed. I can't test wot because my prop is dead right now but it was higher than the 4750-5250 the manuf. suggests.

I since did some research at Trophy and found that the boat comes with the 12 3/4 x 21. This also agrees with the Mercury recommendation. Going up in diameter and pitch is scary because I don't know if the smaller prop is on there for a reason or if it was just something the old owner got his hands on.


I put my info into this prop calculator and it recommended the 13 x 19.
http://turningpointpropellers.com/propellers_101_cm.htm

Its between the 13x19 or the 12 3/4 x 21. I'm leaning toward the 13 x 19. Going to buy tomorrow so any input would be appreciated.

Thanks,
Tom

 

[tomxdana]

Re: Lugging?

Bottom line. As long as my rpms are within specified range at wot and normal conditions I don't have to worry about lugging?

Thanks again,
Tom

 

[Gary H NC]

Re: Lugging?

Yes,Like stated if you can run in the upper limit of thr RPM range with the usual weight on board it should be fine. The 21 pitch will lower your rpms by 300 to 400. The 13 X 9 sounds like it would work fine.
Just my opinion there are a lot better prop guys here than me..

 

[kenmyfam]

Re: Lugging?

Try to get one from the dealer to "test" before you buy. A lot of them will let you test a couple of different ones to see which one works best for you. As long as you buy one from them when you decide which one is for you there should be no worries.
Good Luck and let us all know.

 

[propper_advice]

Re: Lugging?

EDIT When your company establishes a business contract with iboats we can then permit soliciting!!