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Thread: Prop Recomendation.......?

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    Member Akgramps's Avatar
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    Default Prop Recomendation.......?

    Question about prop for a 20 foot boat w/ a 140 HP Johnson.
    I tried a 3 X 14 X 19 first and was able to hit 6300, yesterday I tried a 3 X 14 X 21 and max rpm was about 5500, we were relatively light (~800 pound load).

    I am sure we were at redline with the 19, and I think it could pull a little more pitch.

    Can anyone make a recomendation? This 140 was built by Suzuki, so essentially the same motor as a DF140.

    This is a relatively flatbottomed riverboat, we go out on the ocean once or twice a year, and would run a prop on any long trips on the Tanana or the Yukon, so I think, I prefer a aluminum prop?

    Anyone ever try/use a pro-pulse prop?
    Thanks
    “Nothing worth doing is easy”
    TR

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    Default

    Quote Originally Posted by Akgramps View Post
    Question about prop for a 20 foot boat w/ a 140 HP Johnson.
    I tried a 3 X 14 X 19 first and was able to hit 6300, yesterday I tried a 3 X 14 X 21 and max rpm was about 5500, we were relatively light (~800 pound load).

    I am sure we were at redline with the 19, and I think it could pull a little more pitch.

    Can anyone make a recomendation? This 140 was built by Suzuki, so essentially the same motor as a DF140.

    This is a relatively flatbottomed riverboat, we go out on the ocean once or twice a year, and would run a prop on any long trips on the Tanana or the Yukon, so I think, I prefer a aluminum prop?

    Anyone ever try/use a pro-pulse prop?
    Thanks
    What is the recommended WOT rpm? I thought it was around 5800 to 6000 RPM's.


    Well as far as pulling more pitch I am not so sure.....if the 19" is at redline and the 21" dropped 800 rpm's you are about where you need to be with the 19 fully loaded. Normally a change of 2 inches in pitch is worth about a 400 rpm change but in your case it was twice that. You could have the 21" repitched to a 20". The other thing was one cupped and the other not, this is also about a 200 rpm change.

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    Default !

    Quote Originally Posted by Dupont Spinner View Post
    What is the recommended WOT rpm? I thought it was around 5800 to 6000 RPM's.


    Well as far as pulling more pitch I am not so sure.....if the 19" is at redline and the 21" dropped 800 rpm's you are about where you need to be with the 19 fully loaded. Normally a change of 2 inches in pitch is worth about a 400 rpm change but in your case it was twice that. You could have the 21" repitched to a 20". The other thing was one cupped and the other not, this is also about a 200 rpm change.
    The book says 5400-6200, I was hoping some one would pipe up and tellme about some super duper, killer 3 X 20 aluminum prop.....................!
    “Nothing worth doing is easy”
    TR

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    That was quite a drop in rpm's.
    How new are the plugs and the filters?
    Something more is going on then just the prop if you have the right 21" prop.
    Hope you find the right prop.

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    Quote Originally Posted by Badriverman View Post
    That was quite a drop in rpm's.
    How new are the plugs and the filters?
    Something more is going on then just the prop if you have the right 21" prop.
    Hope you find the right prop.
    170 hours on the motor, new plugs this spring, filters I haven't changed, it has three fuel filters, one is a Racor, I drained that one a week ago and really, very little junk came out?

    Both props were 3 bladed OEM props.

    Motor runs ok? I have very little experience w/props, what makes you think something else is going on?
    “Nothing worth doing is easy”
    TR

  6. #6

    Default had the same problem

    I had the same problem when I wanted to re-prop my engines. When it was new and empty I could hit WOT no problem, but once I loaded my gear, gas and water, I couldn't get close. So I went down in size and there wasn't much selection, so I had to chose what was the best trade off for what I'd be doing most and pick the prop that would suit the most common situation and accept the fact it wouldn't be optimal for the occassional situations.

    If it's a flat bottom river boat do you want aluminum though? if you hit anything they will bend fairly easily. On the other hand, if you hit something hard a stainless prop will transfer the jolt to the lower unit and potentially do damage there.

    Personally I went stainless because there is alot of wood in the water where I am most of the time and I don't like getting bent props all the time. Soft wood is generally not damaging to the lower unit either.

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    Quote Originally Posted by heathjohnson View Post
    I had the same problem when I wanted to re-prop my engines. When it was new and empty I could hit WOT no problem, but once I loaded my gear, gas and water, I couldn't get close. So I went down in size and there wasn't much selection, so I had to chose what was the best trade off for what I'd be doing most and pick the prop that would suit the most common situation and accept the fact it wouldn't be optimal for the occassional situations.

    If it's a flat bottom river boat do you want aluminum though? if you hit anything they will bend fairly easily. On the other hand, if you hit something hard a stainless prop will transfer the jolt to the lower unit and potentially do damage there.

    Personally I went stainless because there is alot of wood in the water where I am most of the time and I don't like getting bent props all the time. Soft wood is generally not damaging to the lower unit either.
    Still learning the prop thing.....! I was going off the advice that it was better to sacrifice a prop then a lower end?
    At least until I figure what the best pitch is.

    I finally got the parts for the Pro-Pulse I bought off of Craigs. It was missing a washer so I haven't been able to test it yet. Its a variable pitch prop, thinner blades than aluminum so similar advantages to a Stainless in that regard. supposed to be tougher than Aluminum, but not as tough as SS?
    I dont know??? It maybe a bunch of smoke and mirrors..........
    “Nothing worth doing is easy”
    TR

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    Quote Originally Posted by Akgramps View Post
    170 hours on the motor, new plugs this spring, filters I haven't changed, it has three fuel filters, one is a Racor, I drained that one a week ago and really, very little junk came out?

    Both props were 3 bladed OEM props.

    Motor runs ok? I have very little experience w/props, what makes you think something else is going on?
    The high pressure fuel is suppose to be changed every year.
    Pain in the rear and kinda expensive but well worth the trouble.
    Will look at the other type of prop i have on mine.

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    I am also running turning point props.
    They are a little smaller diameter at 13 1/4 but also have the vent holes in them.

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    I heard of an Optimax that was running low in RPM's on jet and they found a bad spark plug wire.

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    Post best to test props/pitch

    your boat is a little heavy... if u have a "core" my mec props would fit i have 17 thur 23 pitch ,...i "no matter what the load ( teseted with regular load)" have always lived with the prop with the highest speed to rpm # started with a 15" and ended at 23 .......... mph went from 27/29 to 34/39 on the lite loads (5'x 20' with 90 and teflon bottem)
    WHEN IN DOUBT> THROTTLE OUT.......

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    Default more testing

    I think I gotta it, ran the ProPulse 4 blade tonight, tried with 18 pitch first and ran just under 6200. I then adjusted it to a 17 and hit the rev limiter at 6450, quite obvious when that happens, sounds like it drops one cylinder, either spark or fuel.

    In any case, everything is working great, I installed a Permatrim cavatation plate and it works very well.
    once on step I could play with the trim and raise the motor and you could defintely feel the "sweet spot".
    I didnt measure it but I was able to raise it up untill the cav plate was ~ 2" above the roof of tunnel. Its pretty cool having all that adjustment.

    So, I think I am ready for our yearly trip to Homer this weekend, Woo-Hoo........

    Thanks for all the great input........John
    “Nothing worth doing is easy”
    TR

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