help - possible spun prop 15hp johnson 1992

[acalabro]

hello all. this is my first post as i am new to boating as well.
i own a 1992 15hp johnson on a 14' jon boat total load (motor, 2 persons, gear) on water is 450-550 pounds and i am experiencing symptoms of what i believe to be a spun prop.
Ever since the first time i took it out 2 months ago i have had this happen: get out of idle zone, go to throttle up and 1/2 throttle accelerates and moves boat fine then getting to 60-90% throttle the rpms continue to go up but it picks up the boat for a second then drops it but rpms are still high as i am engaging throttle (feels like all symptoms of spun prop from what i've read).
what i am wondering about is why this only was happening SOME TIMES. so, i took my prop off and looked at it and it had a little bit of shredded rubber so i took it and got it re-hubbed.
First time out with new prop this weekend: planed out fine off the ramp, i thought it had solved the problem, moving from spot to spot, no problems. then at end of day i was going full speed and i was making a 45-65 degree turn to make a circle to pick up the top of a cooler that had fallen out and slowed down to get it, went to accelerate again and i experienced the symptoms like before i put a new hub on, motor slipping. did i spin another hub by making a turn and exerting that force on the motor? the prop is sst, not sure what pitch.
Funny thing is, this happened about a mile from ramp so i stopped as i could not accelerate, put it in neutral, then reverse for about 20 yds, then put back in forward and it picked up and planed us back to the ramp!
any input is appreciated as i am confuse as what to do. after taking it off when i got home, it had a little shredded rubber again so it is prob spun.

 

[steelespike]

Re: help - possible spun prop 15hp johnson 1992

Sure sounds spun.You can double check by drawing a waterproof line across the hub and body of the prop and test run it.

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

Really, as a newbie, I would like to know if these symptoms only happen sometimes when powering up. Like I said, I put it in reverse and idled about 20 yards then put it back in forward and powered up and it planed out like nothing was wrong. Does a spun prop actually give you performance SOME TIMES? I've had the exact same thing happen before I had it re-hubbed.

Had a normal day until I made a turn at almost full speed, that's when the symptoms started again. Could this cause a spun prop?

Thanks in advance !

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

also i want to add in that when it struggles to plane and revs up as its trying to pull the boat up, the wake seems very large and deep for my small boat not weighing more than 500-600 pounds

 

[steelespike]

Re: help - possible spun prop 15hp johnson 1992

Does the motor have a whale tale or hydrofoil?
My limited experience with spun hubs occasionally a hub will spin but then work normally
until just the right conditions it spins again. Usually once spun it will appear again at about the same power
and get progressively worse.
Can you get us some pictures of your motor setup.especially the anti vent plate Just above the prop.
Is the bottom clean and smooth Anything that could disturb the water near the prop?Jons usually have 4 or 5 keels
these could cause problems.
How wide is the bottom?What size is the prop?

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

Thank you for your response steelespike!
There is no hydrofoil on my motor and the prop is 9.25" diameter, not sure what pitch. The boat didn't go over any heavy seaweed, only light grass. The grass seems light enough to not cause a problem, seems very light, haven't hit anything either. Been operating in 15-15 ft. in open bay waters. I uploaded a video going top speed right before the symptoms started occurring. Right after this video, I made a 45-55 degree turn to the left at about 85% throttle and then slowed to pick up something that had flown out of the boat. Upon starting again, the motor exhibited the symptoms of a spun prop. video url: http://youtu.be/L8UOnV9GnL8

The bottom of the boat is 3.5 ft. wide.
I'm going to go ask the prop shop tuesday morning where I had it re-hubbed if the thrust bushing should be where it's at. It appears that the thrust bushing doesn't go all the way in to the prop like it did before I had it re-hubbed, the hub leaves about 1/9" of the bushing outside of the inside of the prop, (it goes as far in as the hub allows it, leaving 1/9" out). Obviously when the prop is spinning it's going to thrust against the bushing and compress the hub inside the prop with this condition. I will have pics and info on what they said at the prop shop tomorrow afternoon-evening or so. Is it possible they could have given me the wrong size hub? This is the only prop shop in the Tampa Bay area believe it or not.
Also I need to confirm that it is spun by marking it and test running it but that wouldn't be until this weekend.
I'm guessing you will probably need more info and pics to really pinpoint the problem, I'm working on it.
Thanks again for your help.

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

Reputable prop shop (which put my new hub on) said prop isn't spun after they looked at it and did a test. They said it could be ventilating if anything. I've marked it so next time (this weekend if the weather permits) I'll be able to see if it spins. If it exhibits symptoms like before I will make a good vid and post.
next possible reason is ventilation because of wind/chop conditions on light/small boat, I presume since it gets up with no problem some times.
Will update sunday night.

 

[steelespike]

Re: help - possible spun prop 15hp johnson 1992

Is the antivent plate (just above the prop) about even with the bottom or slightly above?

 

[Texasmark]

Re: help - possible spun prop 15hp johnson 1992

Sure sounds spun.You can double check by drawing a waterproof line across the hub and body of the prop and test run it.

ditto

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

alright, ran it 14 miles today and the mark on the hub did not show that the hub spinned at all. The anti-vent plate is about even with the bottom of the boat. I uploaded a video with the boat powering up and planing out no problem then one that I took a couple minutes after that showed the symptoms. I'm not sure what could be going on since I know the prop is not spun.
Check out the video http://youtu.be/ZZnHDWMmGbM . I guess it could be what's known as ventilating, see where the anti-vent plate is at and bottom of boat in video! I just don't understand why this happens some times but not others in virtually same wind/wave conditions. As you can see in the first part of the vid, the boat starts moving along just fine without any slippage and I powered up fully and was able to get a pretty good speed like it should! Then other times I can't get going more than 6-10 mph.
It feels like this: throttle goes from idle, to about mid-power just fine, going into the top end however it feels like it "slips" and makes a different sound, (could be sucking air, don't want to conclude this however). For example, it feels like I would be driving a car and at a certain point once I start to speed up push the clutch in almost all the way.
link to vid http://youtu.be/ZZnHDWMmGbM

also see other normal performance, (LAST WEEK), at WOT : http://youtu.be/L8UOnV9GnL8 the problem occured on this day before & after the video was shot as well!


Any expert help is much appreciated! thanks for your responses!

 

[jestor68]

Re: help - possible spun prop 15hp johnson 1992

I find your comment early on about reversing for a short time, then everything was all right, interesting. That indicates that you were able to clear something that was obstructing the water flow to the prop. After watching your videos, I am certain that you are experiencing ventilation of the prop (which is an old, out dated design).

I recommend you spend $118(here at iboats) on a Solas Saturn SS prop for your Johnson. They are 9-1/4 x 8,9,10, and 11 pitch.

That big keel right in front of the prop is not helping matters. The SS prop, with it's double cupped blades is better able to deal with those conditions, and will likely solve your problem.

If money for the SS prop seems too much,even the Solas Amita(aluminum) will out perform your old prop at just $64.94 for the prop and thrust washer.

My Merc prop selector calls for a 9" pitch for your boat/motor combo.

The current design props are much better than your old OMC prop. Even the Solas aluminum props have some cup on the blades and will out perform your old prop, which I doubt has any cup at all.

 

[steelespike]

Re: help - possible spun prop 15hp johnson 1992

I agree that big fat keel right in front of the prop is almost surely causing problems.
also with that keel it wouldn't take much weed to start problems.
The prop suggested may also help.
You might research the Turning Point Rascal. Said to deliver ss performance for aluminum prices.
If you don't have a money to change a props; lower the motor a notch.
Also the the boat didn't look planed out for the relatively light load.Too much rooster tail it seems to me it should be planed right out
with an almost flat wash out the back.The motor rpm seemed high for the apparent speed.
You can't fully evaluate your setup and performance without the pitch, and normal; rpm and gps speed. Some cells have a gps app and an induction tach will get the rpm.

 

[pootnic]

Re: help - possible spun prop 15hp johnson 1992

I'd just try lowering the motor a bit.
Although maybe a new type prop may help,to me it almost seems like you have a short shaft motor on a long transom.

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

I find your comment early on about reversing for a short time, then everything was all right, interesting. That indicates that you were able to clear something that was obstructing the water flow to the prop. After watching your videos, I am certain that you are experiencing ventilation of the prop (which is an old, out dated design).

I strongly recommend you spend $118(here at iboats) on a Solas Saturn SS prop for your Johnson. They are 9-1/4 x 8,9,10, and 11 pitch.

That big keel right in front of the prop is not helping matters. The SS prop, with it's double cupped blades is better able to deal with those conditions, and will likely solve your problem.

If money for the SS prop seems too much,even the Solas Amita(aluminum) will out perform your old prop at just $64.94 for the prop and thrust washer.

My Merc prop selector calls for a 9" pitch for your boat/motor combo.

The current design props are much better than your old OMC prop. Even the Solas aluminum props have some cup on the blades and will out perform your old prop, which I doubt has any cup at all.

You did notice that the prop I'm using is SS? it is aftermarket, they painted it black when they rehubbed it, I don't know how old it is it could be 5 it could be 12 years old. It does look like it doesn't have much, if any, of what's known as cup though. You can see the prop briefly at 2:38 in the first video, does it look like it is an outdated design? Could having this outdated design and lack of cup cause this problem to occur ONLY SOME TIMES but not others like in the second video http://youtu.be/L8UOnV9GnL8 where I'm skimming along? However I would say it happens more often than not. It seems to happen randomly without a noticeable difference in wind/wave conditions.
The next step is buying a new prop for it, if this one, even being SS, is indeed outdated.
Thank you all for your input

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

also, i'm wondering if maybe exhaust gases could be escaping from the sides in the ~1/4" gap between the prop and casing and causing cavitation. i wonder if this little space could be causing this, if so, why is it only happening part of the time.

 

[steelespike]

Re: help - possible spun prop 15hp johnson 1992

I don't think the 1/4" is a problem
It is possible the ss prop is a weak design and sometimes a prop just won't work on a particular application.

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

ok turns out the solas props on iboats doesn't have any extra cupping. the sales rep that i talked to said that all three available for my motor are "general putpose" and she said they are'nt double cupped. what i did find out from anoyher prop shop guy us that my SS is indeed the original OMC prop and is "weedless" if that has any significance.
He carries the solas alluminum and will take an exchange if the one i buy doesn't work out. He told me to try trimming the motor up one notch instead of having it all the way down, that air could be gettin in that way.
this is what ill try on sunday

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992



delayed Sunday.

 

[Geezer11]

Re: help - possible spun prop 15hp johnson 1992

I wonder what happened to the poster with this problem. I had the identical problem with my 25 HP Evinrude, on a larger but similar boat to his. Mine also has a ridge (I guess its called a keel) right in front of the prop. I watched his video &, at the point it was about to plane, the motor would sound like it was reving up & the boat would not plane or go any faster. My problem was identical & my motor made the exact sound as his. At first I could not understand it because I had determined that the prop was not spun & the sound the motor makes is a different sound. It sometimes would barely plane with my wife in the front, but would not plane at all with my much heavier grandson in the front. Finally it dawned on me that with, the type fishing I was doing (mullet), the supplies I had were much heavier than with my usual freshwater fishing with the same 2 partners. After many years of having my motor trimmed in one position, I lowered the trim by one notch. Instead of being in the neutral position, it is now trimmed in a little. I couldn't believe the difference. With my big heavy grandson, 2 five gallons buckets of mullet bait & all, it now jumps up on a plane with no problem. The irregular motor sound is completely gone.

Hopefully, my experience will help someone else with this problem. It would be nice if people who post a problem & then get it resolved, would always take the time to post their resolution.

 

[acalabro]

Re: help - possible spun prop 15hp johnson 1992

Yeah I eventually got to take it out this last weekend and didn't have a problem, didn't change anything on how the motor sits or anything but for some reason she ran outstanding. I actually bought a new boat on 9/8 Saturday a Lucraft 15'6" with a '90 50hp Force. I figured I was in need of a larger boat anyway and got a good deal on it. First time out on it will be this weekend. A guy at a marine shop said to try trimming up as well. That's where the problem is/was.