propeller question

[circle hook]

my 135 HP 1990 runs 5200rpm with a 19pitch alluimum prop, but when i try my friends 17pitch stainless the max rpm is only 4800 i thought that the lower the pitch the higher the rpm does the stainless run slower because its heavery than alluimium thanks bob

 

[Lyle29464]

Re: propeller question

Check the diameter. The stainless will bite more with more cup. Maybe your prop is worn out.

 

[circle hook]

Re: propeller question

the pitch marks are clear and the props dont look damage at all i have a 13 pitch i never tryed i also have a 16 pitch 4 blade thats stainless, what pitch would you start with on a 21 alluimum starcraft the boat only weight 900 lbs and the motor is a 135 HP black max these props are costly so i am trying any thing i can get my hands on thanks Bob

 

[Lyle29464]

Re: propeller question

The 19 sound fine? why change it.

 

[jimmbo]

Re: propeller question

There are a few things that could account for the drop in rpm. Your 19 alum might be venting and and the resulting slippage is allowing a higher than normal rpm. It might be an older design that has no cupping. The 17 SS may just grip the water better and doesn't slip as much. It may have be tweaked as in more cup or even pitch.

 

[circle hook]

Re: propeller question

so witch one would be better on my boat the stainless 17p @ 4,800 rpm or the allummium 19p @ 5,200 rpm because still the engine is suposed to run at 5,500 rpm i believe would the stainless at 4,800 do any damage to my engine

 

[Lyle29464]

Re: propeller question

you need to be able to turn 5500 If you were over 5000 fully loaded I would not worry but 4800 max is not enought.

 

[circle hook]

Re: propeller question

What a difference i tryed the 2 propellers again laast time it was in a different part of the river and on windy days and tide changes today i did both with in an hour apart and now got 5,400 rpm wioth the 17P stainless and 5,200rpm with the 19P alummium prop and the trim played a huge role in that the boat is so touchy in effecting the speed,rpm, & fuel GPH I also tryed a 16P 4 blade stainless, prop but it was about an inch smaller than the other 2 and i got the same results as the 17P but 2 gallons per hour less. what do you think leave well enough alone at 5,400 rpm with the 17P stainless or keep trying with a 17P alummium next Thanks Bob

 

[steelespike]

Re: propeller question

Just rpm doesn't mean much.You need the gps speed at each wot rpm.
you need to figure gph against speed.You also need to evaluate hole shot
and ability to plane with a load.And is the motor able to operate within its recommended rpm range.

 

[Lyle29464]

Re: propeller question

Your lucky you have all the props. Do your tests with your normal load. The 16 sounds good if you get a better hole shot and a good cruise speed. I would not worry about a 1 or 2 MPH loss at top end.

 

[Texasmark]

Re: propeller question

2 cycles are like wild mustangs.............they like to run. Get them around the upper limit and they are happy. Run them at the lower limit, you get poor performance, gunked up rings, exhaust ports, plugs and all that.

Mark