Change to Three-Blade Propeller Causes Vibration

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Author Topic:   Change to Three-Blade Propeller Causes Vibration

masbama posted 09-05-2009 03:32 PM ET (US)
For experts: I put a 17-inch pitch three-blade propeller on my 1999 Dauntless 18 with 150-HP Evinrude. It replaced a four-blade propeller. [The new three-blade propeller] works perfectly except I hear a noticeable vibrating sound from the rear of the boat or motor when [the engine speed] nears 4,000-RPM. [The vibration] stops when I steer left. It did not do this with the four-blade. Any simple solutions?
R T M posted 09-05-2009 04:08 PM ET (US)
Thrust washer missing?
jimh posted 09-05-2009 08:42 PM ET (US)
On outboard motors there is a tendency to have a vibration created when the propeller blade is shadowed by the gear case of the outboard. With a four-blade propeller, there are two blades in the shadow at once. With a three-blade propeller, only one blade is in the shadow at a time. This alters the frequency of the vibration.
For example, if you have an engine with a gear case ratio of 2:1, at 4,000-RPM the propeller shaft is revolving at 2,000-RPM. With a four blade propeller there will be two blade shadows per revolution. The frequency of the vibration will be:
2000-revolutions/1-minute x 2-vibrations/1-revolution x 1-minute/60-second = 66.6-Hz
With a three blade propeller the vibration will be
2000-revolutions/1-minute x 3-vibrations/1-revolution x 1-minutes/60-seconds = 100-Hz
Depending on the engine mounting stiffness, the boat's natural resonance, and other factors, the change from a 66-Hz vibration from the four-blade propeller to a 100-Hz vibration from the three-blade may cause an excitation of other resonances in the boat, creating a greater sensation of vibration from the propeller.
[Also, see a later comment below about how a three blade propeller would have six vibrations per revolution as each blade was shadowed first by the upper portion of the gear case and then by the lower portion. This would tend to drive the vibration frequency higher, for example, as calculated above to 200-Hz instead of 100-Hz. However, the gearcase is not the same thickness on the bottom, as usually the skeg is much thinner. This may affect the strength of the shadowing effect of the skeg on the propeller.--jimh]
jimh posted 09-05-2009 08:48 PM ET (US)
The sensation of the vibration decreases when you steer left because the coupling of the engine to the boat changes slightly. The change in coupling of the engine to the hull is sufficiently different that the vibration no longer excites the resonance in the hull.
Tom W Clark posted 09-05-2009 09:31 PM ET (US)
What four blade propeller were you formerly using?
What three blade propeller have you now tried?
masbama posted 09-06-2009 02:08 PM ET (US)
I was using a 16" 4 blade, now I use I 17" 3 blade Stiletto.
It is on a jack plate but there was never a vibration with the 4 blade. All the washers are in place.
Tom W Clark posted 09-06-2009 02:13 PM ET (US)
What 16" four blade did you have before?
How many times have you run the new propeller? Have you run it at WOT?
Is the old style rubber press-in hub or the the new square bore hub kit style?
You say you hear a vibration. Do you actually hear it or do you *feel* it...or both?
masbama posted 09-06-2009 05:38 PM ET (US)
I don't know the brand of the 4 blade; it came with the boat when I bought it and has no name on it.
I have not the new prop all that much-under 10 hours and very rarely at full throttle.
I believe it is the new Guardian hub kit type especially for this prop. (Bought through Dan's Discount)
Thanks!
mobey posted 09-06-2009 06:23 PM ET (US)
Seems possible that the three bladed prop is not in balance, or the harmonics [problem]- I've had that.
masbama posted 09-07-2009 05:22 PM ET (US)
I do fell the vibration as well as hear it. Any quick way to check if this new prop is in balance?
mobey posted 09-07-2009 07:00 PM ET (US)
This test may help in your diagnosis- With the boat in the water and the prop removed, run the motor at various rpm and see if the noise and vibrations persist.
masbama posted 09-14-2009 09:23 PM ET (US)
Well I ran the 4 blade again yesterday just to be sure and there was no vibration. I called Stiletto today and they said send it up and they will check it out. Nice people. I hope it's the prop because I don't know what else to check.
Tom W Clark posted 09-14-2009 09:45 PM ET (US)
The folks at Stiletto are always helpful. Just great people to deal with.
I will be very surprised if they find the prop is out of balance.
I remain perplexed as to why you would be experiencing a vibration at all though. Keep us posted.
masbama posted 09-15-2009 02:00 PM ET (US)
I will. The only other thing I can think of is the jack plate induces vibration because of what jimh said above but everything is bolted tight and sturdy. Also-I noticed that the 4 blade fits a little tighter to the gear case than the 3 blade but we are talking a very, very minute amount.
masbama posted 10-11-2009 04:39 PM ET (US)
Update-I received my Stiletto prop on Friday. They checked it out and said it was indeed out of balance (strange for a new prop) so I checked it out today and the vibration was even worse. It still goes away when turning left but gets more pronounced when turning right; to the point of fearing something will break. This all happens above 3300 RPM's and trimming or lifting up makes it worse also. It's mounted on a CMC powerlift jack plate but everything seems bolted tight and sturdy. I'm going to call Stiletto tomorrow but I don't know what else they can do. This is strange. Any thoughts?
acassidy posted 10-11-2009 08:18 PM ET (US)
Actually happens often because when it is pressed on the rubber hub it can compress rubber more on one side than other making it off center. Was told one time that sometimes a prop like this will center itself eventually running it, Any shaking is bad for the motor, good to replace it.
weekendwarrior posted 10-12-2009 04:04 PM ET (US)
Your description of the vibration makes me think it's outside of normal vibrations. You said there was a minor difference in fitment between your old and new prop; any chance you have a prop with a hub that is not exactly the correct hub for your motor and the prop is actually not staying perfectly centered on the shaft? A prop that is crooked can definitely cause a vibration.
weekendwarrior posted 10-12-2009 04:05 PM ET (US)
Your description of the vibration makes me think it's outside of normal vibrations. You said there was a minor difference in fitment between your old and new prop; any chance you have a prop with a hub that is not exactly the correct hub for your motor and the prop is actually not staying perfectly centered on the shaft? A prop that is crooked can definitely cause a vibration.
masbama posted 10-12-2009 05:05 PM ET (US)
weekendwarrior-I'm thinking the same thing. The hub seems to fit and go on straight but it does not fit as snug as my 4 blade. Very, very close but not quite as close. It may be the thrust washer too. I don't know but I do know that when over 3200 RPM's it vibrates bad-especially when turning right. I'm just running out of theories. I may get another 3 blade prop-if I can-and see if the same thing happens.
crabby posted 10-12-2009 09:16 PM ET (US)
Wouldn't a 3 blade prop have 6 shadows per revolution? (one for each blade on both the upper part of the gearcase and for the skeg, since there is no alignment as with a 4 blade prop)
deepwater posted 10-13-2009 04:01 AM ET (US)
I dont recommend running your motor in gear when out of the water but you might see if there is a slight wobble to the prop at slow speed or low RPMs
jimh posted 10-13-2009 09:04 AM ET (US)
Crabby--I agree. A three blade propeller would have six instance in each revolution where the blade was shadowed. Good observation.
Tom W Clark posted 10-13-2009 03:14 PM ET (US)
It is not at all unusual for a rubber hubbed prop to have its hub slightly out-of-alignment. It will self center the first time the propeller is run.
It IS unusual for a new propeller to produce a vibration and if a second replacement propeller produces the same vibration, then I suspect it is something other than the propeller.
masbama -- Is the replacement propeller rubber hubbed or is it square bore?
outragesteve posted 10-13-2009 05:19 PM ET (US)
Possible tweaked prop shaft. Pull the prop and check for any "wobble": Any shop should be able to use a dial indicator and see if the runout is withing factory (Evinrude) spec. Good luck!
masbama posted 10-13-2009 09:20 PM ET (US)
Would the "wobble" be the shaft moving when jiggling when the prop is off?
The 4 blade has a round, rubber hub and the new 3 blade is a square type that you tap into the prop. Why does it NOT vibrate when the 4 blade is used?
Tom W Clark posted 10-13-2009 09:23 PM ET (US)
masbama,
I want to make sure this prop is installed correctly. It should not wobble on the prop shaft at all.
Can you tell me exactly what hub kit you have? Did they send a Quicksilver Flo-Torq or Guardian SQ-Lok hub kit?
What is the part number of the hub kit and what parts were included?
masbama posted 10-14-2009 10:53 AM ET (US)
I was sent the Guardian SQ-Lok Hub kit #DE-502. The instructions came with it but were incomplete. It came with a thrust washer (which does not seem to go down the shaft as far as my 4 blade one does-yes, it is put on correctly), the rubber bushing which I had to hit with a mallet to go all the way on (didn't seem like a good way to do it but that is what the instructions say) and a prop nut spacer. I had a similar issue getting the cotter pin on, not unlike MR.T's thread in this performance forum about his Turbo Prop. There is a very small give when I pull the prop back after it is secured. I wonder if the prop is still out of balance?
Tom W Clark posted 10-14-2009 11:35 AM ET (US)
OK, good, the #DE-502 is the correct hub kit.
I do not understand how the instructions can be incomplete; they are printed on a single 8-1/2" x 11" sheet of paper, though I do note some unforgivable typographical errors.
Yes, the thrust washer provided may fit differently than the thrust washer you had. That is how it should be.
It is also very common to have to tap the hub insert (which is NOT made of rubber, but of DuPont Delrin, a hard plastic) into the propeller. It is important that the hub insert be fully seated. The SQ-Lok hubs usually seat nicely. The Flo-Torqs are the worst; some fit, some you have to really beat down.
The propeller nut should be torqued to about 50 foot/pounds and then advanced until the nut aligns with the next cotter pin slot.
Once the nut is tightened, there should be NO movement between the prop and the prop shaft. It IS normal for a prop shaft to have some fore-and-aft play but it should NOT wobble side to side.
The other thing to verify is that the hub insert has the black plastic bushing snapped in place at the forward end. This helps hold the hub insert and prop centered on the prop shaft. It is like the bushing used on Flo-Torq II hub kits for the Rev 4, Trophy Plus and Tempest Plus propellers.
masbama posted 10-14-2009 01:01 PM ET (US)
Tom:
I do not recall a black plastic bushing that snaps on. Should it have comewith the hub kit?
Thanks!
Michael
Tom W Clark posted 10-14-2009 01:07 PM ET (US)
Yes, the bushing would have already have been snapped into place and may appear to be integral with the hub insert, but it is a separate part.
Its part # is 54040.
masbama posted 10-14-2009 06:19 PM ET (US)
Tom: I spoke with the nice Stiletto folks today and their tech person was not in but will give me a call tomorrow. Very good folks. I mentioned a plastic bushing but they were not aware of any nor was it included in the hub kit's list of parts. I googled the Flo Torq II and saw the piece you referred. Would I be able to order it from the Stiletto folks?
Tom W Clark posted 10-14-2009 06:25 PM ET (US)
The bushing is not shown or mentioned in the drawing because it comes already snapped into the hub insert. Just look at the hub insert and it will be apparent.
masbama posted 10-14-2009 08:45 PM ET (US)
I found it. Took off the prop and put it back on. Everything looks just fine except the part # I have on mine is #52040. Could that be the problem; it is fitting in snug.
masbama posted 11-01-2009 06:20 PM ET (US)
Well I feel I must give an update to my situation. I talked to the super folks at Stiletto and they are awesome! They sent me a Bay Pro III, four blade, 17" prop to try. I did that today and the results were perfect. No vibration, stellar hole shot with almost no bow lift, tight in turns and fuel economy very close to the three blade. Low rpm's keep it on plane too. This is the perfect prop for this boat. I believe all the suggestions of trim tabs and doel fins, etc. can be eliminated with this prop. The folks at Stiletto are incredible and so is this prop!

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Author	Topic: Change to Three-Blade Propeller Causes Vibration
masbama	posted 09-05-2009 03:32 PM ET (US) For experts: I put a 17-inch pitch three-blade propeller on my 1999 Dauntless 18 with 150-HP Evinrude. It replaced a four-blade propeller. [The new three-blade propeller] works perfectly except I hear a noticeable vibrating sound from the rear of the boat or motor when [the engine speed] nears 4,000-RPM. [The vibration] stops when I steer left. It did not do this with the four-blade. Any simple solutions?
R T M	posted 09-05-2009 04:08 PM ET (US) Thrust washer missing?
jimh	posted 09-05-2009 08:42 PM ET (US) On outboard motors there is a tendency to have a vibration created when the propeller blade is shadowed by the gear case of the outboard. With a four-blade propeller, there are two blades in the shadow at once. With a three-blade propeller, only one blade is in the shadow at a time. This alters the frequency of the vibration. For example, if you have an engine with a gear case ratio of 2:1, at 4,000-RPM the propeller shaft is revolving at 2,000-RPM. With a four blade propeller there will be two blade shadows per revolution. The frequency of the vibration will be: 2000-revolutions/1-minute x 2-vibrations/1-revolution x 1-minute/60-second = 66.6-Hz With a three blade propeller the vibration will be 2000-revolutions/1-minute x 3-vibrations/1-revolution x 1-minutes/60-seconds = 100-Hz Depending on the engine mounting stiffness, the boat's natural resonance, and other factors, the change from a 66-Hz vibration from the four-blade propeller to a 100-Hz vibration from the three-blade may cause an excitation of other resonances in the boat, creating a greater sensation of vibration from the propeller. [Also, see a later comment below about how a three blade propeller would have six vibrations per revolution as each blade was shadowed first by the upper portion of the gear case and then by the lower portion. This would tend to drive the vibration frequency higher, for example, as calculated above to 200-Hz instead of 100-Hz. However, the gearcase is not the same thickness on the bottom, as usually the skeg is much thinner. This may affect the strength of the shadowing effect of the skeg on the propeller.--jimh]
jimh	posted 09-05-2009 08:48 PM ET (US) The sensation of the vibration decreases when you steer left because the coupling of the engine to the boat changes slightly. The change in coupling of the engine to the hull is sufficiently different that the vibration no longer excites the resonance in the hull.
Tom W Clark	posted 09-05-2009 09:31 PM ET (US) What four blade propeller were you formerly using? What three blade propeller have you now tried?
masbama	posted 09-06-2009 02:08 PM ET (US) I was using a 16" 4 blade, now I use I 17" 3 blade Stiletto. It is on a jack plate but there was never a vibration with the 4 blade. All the washers are in place.
Tom W Clark	posted 09-06-2009 02:13 PM ET (US) What 16" four blade did you have before? How many times have you run the new propeller? Have you run it at WOT? Is the old style rubber press-in hub or the the new square bore hub kit style? You say you hear a vibration. Do you actually hear it or do you feel it...or both?
masbama	posted 09-06-2009 05:38 PM ET (US) I don't know the brand of the 4 blade; it came with the boat when I bought it and has no name on it. I have not the new prop all that much-under 10 hours and very rarely at full throttle. I believe it is the new Guardian hub kit type especially for this prop. (Bought through Dan's Discount) Thanks!
mobey	posted 09-06-2009 06:23 PM ET (US) Seems possible that the three bladed prop is not in balance, or the harmonics [problem]- I've had that.
masbama	posted 09-07-2009 05:22 PM ET (US) I do fell the vibration as well as hear it. Any quick way to check if this new prop is in balance?
mobey	posted 09-07-2009 07:00 PM ET (US) This test may help in your diagnosis- With the boat in the water and the prop removed, run the motor at various rpm and see if the noise and vibrations persist.
masbama	posted 09-14-2009 09:23 PM ET (US) Well I ran the 4 blade again yesterday just to be sure and there was no vibration. I called Stiletto today and they said send it up and they will check it out. Nice people. I hope it's the prop because I don't know what else to check.
Tom W Clark	posted 09-14-2009 09:45 PM ET (US) The folks at Stiletto are always helpful. Just great people to deal with. I will be very surprised if they find the prop is out of balance. I remain perplexed as to why you would be experiencing a vibration at all though. Keep us posted.
masbama	posted 09-15-2009 02:00 PM ET (US) I will. The only other thing I can think of is the jack plate induces vibration because of what jimh said above but everything is bolted tight and sturdy. Also-I noticed that the 4 blade fits a little tighter to the gear case than the 3 blade but we are talking a very, very minute amount.
masbama	posted 10-11-2009 04:39 PM ET (US) Update-I received my Stiletto prop on Friday. They checked it out and said it was indeed out of balance (strange for a new prop) so I checked it out today and the vibration was even worse. It still goes away when turning left but gets more pronounced when turning right; to the point of fearing something will break. This all happens above 3300 RPM's and trimming or lifting up makes it worse also. It's mounted on a CMC powerlift jack plate but everything seems bolted tight and sturdy. I'm going to call Stiletto tomorrow but I don't know what else they can do. This is strange. Any thoughts?
acassidy	posted 10-11-2009 08:18 PM ET (US) Actually happens often because when it is pressed on the rubber hub it can compress rubber more on one side than other making it off center. Was told one time that sometimes a prop like this will center itself eventually running it, Any shaking is bad for the motor, good to replace it.
weekendwarrior	posted 10-12-2009 04:04 PM ET (US) Your description of the vibration makes me think it's outside of normal vibrations. You said there was a minor difference in fitment between your old and new prop; any chance you have a prop with a hub that is not exactly the correct hub for your motor and the prop is actually not staying perfectly centered on the shaft? A prop that is crooked can definitely cause a vibration.
weekendwarrior	posted 10-12-2009 04:05 PM ET (US) Your description of the vibration makes me think it's outside of normal vibrations. You said there was a minor difference in fitment between your old and new prop; any chance you have a prop with a hub that is not exactly the correct hub for your motor and the prop is actually not staying perfectly centered on the shaft? A prop that is crooked can definitely cause a vibration.
masbama	posted 10-12-2009 05:05 PM ET (US) weekendwarrior-I'm thinking the same thing. The hub seems to fit and go on straight but it does not fit as snug as my 4 blade. Very, very close but not quite as close. It may be the thrust washer too. I don't know but I do know that when over 3200 RPM's it vibrates bad-especially when turning right. I'm just running out of theories. I may get another 3 blade prop-if I can-and see if the same thing happens.
crabby	posted 10-12-2009 09:16 PM ET (US) Wouldn't a 3 blade prop have 6 shadows per revolution? (one for each blade on both the upper part of the gearcase and for the skeg, since there is no alignment as with a 4 blade prop)
deepwater	posted 10-13-2009 04:01 AM ET (US) I dont recommend running your motor in gear when out of the water but you might see if there is a slight wobble to the prop at slow speed or low RPMs
jimh	posted 10-13-2009 09:04 AM ET (US) Crabby--I agree. A three blade propeller would have six instance in each revolution where the blade was shadowed. Good observation.
Tom W Clark	posted 10-13-2009 03:14 PM ET (US) It is not at all unusual for a rubber hubbed prop to have its hub slightly out-of-alignment. It will self center the first time the propeller is run. It IS unusual for a new propeller to produce a vibration and if a second replacement propeller produces the same vibration, then I suspect it is something other than the propeller. masbama -- Is the replacement propeller rubber hubbed or is it square bore?
outragesteve	posted 10-13-2009 05:19 PM ET (US) Possible tweaked prop shaft. Pull the prop and check for any "wobble": Any shop should be able to use a dial indicator and see if the runout is withing factory (Evinrude) spec. Good luck!
masbama	posted 10-13-2009 09:20 PM ET (US) Would the "wobble" be the shaft moving when jiggling when the prop is off? The 4 blade has a round, rubber hub and the new 3 blade is a square type that you tap into the prop. Why does it NOT vibrate when the 4 blade is used?
Tom W Clark	posted 10-13-2009 09:23 PM ET (US) masbama, I want to make sure this prop is installed correctly. It should not wobble on the prop shaft at all. Can you tell me exactly what hub kit you have? Did they send a Quicksilver Flo-Torq or Guardian SQ-Lok hub kit? What is the part number of the hub kit and what parts were included?
masbama	posted 10-14-2009 10:53 AM ET (US) I was sent the Guardian SQ-Lok Hub kit #DE-502. The instructions came with it but were incomplete. It came with a thrust washer (which does not seem to go down the shaft as far as my 4 blade one does-yes, it is put on correctly), the rubber bushing which I had to hit with a mallet to go all the way on (didn't seem like a good way to do it but that is what the instructions say) and a prop nut spacer. I had a similar issue getting the cotter pin on, not unlike MR.T's thread in this performance forum about his Turbo Prop. There is a very small give when I pull the prop back after it is secured. I wonder if the prop is still out of balance?
Tom W Clark	posted 10-14-2009 11:35 AM ET (US) OK, good, the #DE-502 is the correct hub kit. I do not understand how the instructions can be incomplete; they are printed on a single 8-1/2" x 11" sheet of paper, though I do note some unforgivable typographical errors. Yes, the thrust washer provided may fit differently than the thrust washer you had. That is how it should be. It is also very common to have to tap the hub insert (which is NOT made of rubber, but of DuPont Delrin, a hard plastic) into the propeller. It is important that the hub insert be fully seated. The SQ-Lok hubs usually seat nicely. The Flo-Torqs are the worst; some fit, some you have to really beat down. The propeller nut should be torqued to about 50 foot/pounds and then advanced until the nut aligns with the next cotter pin slot. Once the nut is tightened, there should be NO movement between the prop and the prop shaft. It IS normal for a prop shaft to have some fore-and-aft play but it should NOT wobble side to side. The other thing to verify is that the hub insert has the black plastic bushing snapped in place at the forward end. This helps hold the hub insert and prop centered on the prop shaft. It is like the bushing used on Flo-Torq II hub kits for the Rev 4, Trophy Plus and Tempest Plus propellers.
masbama	posted 10-14-2009 01:01 PM ET (US) Tom: I do not recall a black plastic bushing that snaps on. Should it have comewith the hub kit? Thanks! Michael
Tom W Clark	posted 10-14-2009 01:07 PM ET (US) Yes, the bushing would have already have been snapped into place and may appear to be integral with the hub insert, but it is a separate part. Its part # is 54040.
masbama	posted 10-14-2009 06:19 PM ET (US) Tom: I spoke with the nice Stiletto folks today and their tech person was not in but will give me a call tomorrow. Very good folks. I mentioned a plastic bushing but they were not aware of any nor was it included in the hub kit's list of parts. I googled the Flo Torq II and saw the piece you referred. Would I be able to order it from the Stiletto folks?
Tom W Clark	posted 10-14-2009 06:25 PM ET (US) The bushing is not shown or mentioned in the drawing because it comes already snapped into the hub insert. Just look at the hub insert and it will be apparent.
masbama	posted 10-14-2009 08:45 PM ET (US) I found it. Took off the prop and put it back on. Everything looks just fine except the part # I have on mine is #52040. Could that be the problem; it is fitting in snug.
masbama	posted 11-01-2009 06:20 PM ET (US) Well I feel I must give an update to my situation. I talked to the super folks at Stiletto and they are awesome! They sent me a Bay Pro III, four blade, 17" prop to try. I did that today and the results were perfect. No vibration, stellar hole shot with almost no bow lift, tight in turns and fuel economy very close to the three blade. Low rpm's keep it on plane too. This is the perfect prop for this boat. I believe all the suggestions of trim tabs and doel fins, etc. can be eliminated with this prop. The folks at Stiletto are incredible and so is this prop!