Prop Pitch

[Justinde]

Hi All

When I bought my boat, It had the 'standard' prop, an alloy 19" pitch prop, and an unknown stainless prop. I just found out the s/s prop is a 17" pitch. The guy that found out for me suggested that I would still pull 45mph, but at about 1000rpm more....... I don't want to over rev my engine, so obviously I will be careful as to how I run her. I am more than happy with 40mph@5500rpm. Question is- do I use the 17" prop, or replace the alloy prop with another 19" prop, or do I go to a larger/bigger pitch ( say 21"). Any suggestion/thoughts?

 

[jerryjerry05]

Re: Prop Pitch

The stainless at 17 is basicaly the same as an aluminum 19.The motor should rev about the same.
If you change the prop to anything that makes the motor lug your gonna hurt the motor.Stick with what you have.
Most small boats usually hit bottom before a big boat does.I don't like stainless on a small boat as they tend not to break when you hit something.The prop shaft or the drive shaft will break or twist and lock the shaft in the powerhead.The aluminum will break off an ear or two and save the shafts.
Even though they have a shock hub that doesn't always give.
Stick with what you have.If you want more speed,get a bigger motor.Or leave the wife /kids/dog/coolers and you best bud at home.Jerry

 

[Frank Acampora]

Re: Prop Pitch



Well, Justin, Given the same load, if you go to the stainless prop, here is what will happen: Stainless gives about 200-400 more RPM than the same aluminum prop. Dropping down in pitch gives about 400 RPM more. If the stainless is cupped, that will drop RPM by about 200 less than if not cupped.

SO: The stainless will run your engine (Under the same load) at anywhere from 400 to 800 more RPM. (not knowing the particulars, I can't tell exactly). Additionally, there is a good chance that even at the higher RPM, you will lose top speed with the lower pitch prop. You need pitch to go fast.

The engine itself will not be harmed by the increased RPM. My 125 on a 14 footer is turning 6000RPM and probably is good for more. However, 15 gallons of fuel in about 1 1/2-2 hours at WOT is a lot. here are a couple of photos of it at speed. Center photo is with the rebadged 125 and the others are with a 90. Stock engine with a 12 X 21 stainless cupped cleaver prop. 55 MPH with the 90, 60 with the 125.

However, if you have someone skiing, especially slalom, the stainless would be a good choice as the load will be more and the boat will accelerate faster.

Wakeboarding and tubing would not need the lower pitch but the increased loads would make the prop a good choice.

Generally speaking, I prefer a stainless prop but in your case I would agree with Jerry: Stay with the aluminum prop you have on now UNLESS you are doing water sports.

 

[Justinde]

Re: Prop Pitch

Thanks guys- problem is with the alloy prop the mechanic that looked at the boat broke one of the blades of my prop- maybe about 1" off the end of one.

Do I try to repair what I have, sell the s/s prop and replace with a 19" alloy, or, get a 21" alloy? I use our boat atm for fishing and family fun. No skiing as yet- the kids are too little. Maybe some tubes this summer.

Thank you in advance.

 

[jason32038]

Re: Prop Pitch

Try a piranha prop. The hub kit is only $80 and the blades are $20 each. The blades are designed to break when you hit bottom and you can also swap out blades to a different pitch easily depending on how you're boating on a certain day.

 

[Frank Acampora]

Re: Prop Pitch

You can have the aluminum prop repaired economically. One inch off one blade is nothing and a good prop shop will weld it as good as new. I would keep the steel prop for later and either buy a used or new prop or have the old one repaired. Do not go up in pitch as these engines do not have the oomph to swing high pitched props. Stay with 19 pitch. If money becomes easier, a nice 19 pitch stainless prop cupped will work just fine. Or, you can investigate re-pitching your steel prop to an 18 or 19 and cupping it.

 

[jerryjerry05]

Re: Prop Pitch

Fix the one you have.5500 is optimum.Try the stainless see what you get.Post the results.J