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Author Topic:   Vibration

Bigwaves_us posted 08-26-2007 12:35 PM ET (US)
I have a new 2007 Boston Whaler Outrage with a Mercury OptiMax 150. At a certain speed [6-MPH] the boat has a pronounced vibration. My friend was telling me to remove the vent plug on the propeller. There is nothing in any of the owner's manuals about the plug. Coming from a large diesel [unrecognized acronym], I am new to outboards.
Thanks,
Greg
Perry posted 08-26-2007 01:09 PM ET (US)
Do you see the vent plugs on the hub of the propeller? Are the plugs removed?
Vent plugs introduce air to the prop (ventilation) and help with acceleration but I never heard of them having any effect on a boat's vibration.
If there is damage to one or more of the blades of the prop, it could be off balance and may make the motor vibrate.
Jerry Townsend posted 08-26-2007 03:27 PM ET (US)
Greg - I don't have your propeller or experience with those plugs you mention, just a lot of vibration experience.
As Perry, removed vent plugs introducing air at the hub should not affect or induce any vibration. The vibration is coming from an unbalance in the prop which may have been damaged or improperly balanced. Or the vibration could be coming from the engine. Temporarily change props and see what happens. If the vibration is still there, the problem is in the engine; if not, the prop is the problem.
If the problem is the prop and it has not been damaged, have your dealer replace the prop or have it dynamically balanced by someone that knows what they are doing. --- Jerry/Idaho
Bigwaves_us posted 08-26-2007 08:12 PM ET (US)
The plugs are still in the hub. Should they be removed?
Tom W Clark posted 08-26-2007 09:46 PM ET (US)
No, do not remove the PVS vent plugs. Removing the vent plugs will cause the propeller to ventilate, or ventilate more than it already is.
I am still unclear, are you talking about a vibration that occurs at any speed or a vibration that occurs when you are accelerating onto plane? If the latter, I would suspect you are experiencing ventilation where air is drawn into the propeller and the propeller (and engine RPM) accelerate more than thee boat speed.
When a prop is ventilating, there will be some vibration but the vibration will smooth out as the boat gains speed and the propeller regains its grip on the water.
If the vibration is the result of a damaged propeller it will be apparent throughout the RPM band and increase with engine speed.
Jerry Townsend posted 08-27-2007 01:53 AM ET (US)
Tom - I am missing something - as if a prop is ventilating, that ventilation would, I think, be somewhat uniform or random around the prop - and if that is the case, there should not be any unbalance. But, if only one (or two) blades were continuously subject to the ventilation, that would cause a vibration. Enlighten me - what am I missing? ----------- Jerry/Idaho
Bigwaves_us posted 08-27-2007 06:02 AM ET (US)
The vibration occurs in two places. The first the boat is moving around six mph. The second is around 3800 rpm. Thank fo the help.
jimh posted 08-27-2007 09:04 AM ET (US)
A vibration that occurs at low speed is fairly common and is the result of a resonance in the system formed by the propeller, the motor, the motor mounts, and the boat. Among these components, the propeller is the easiest to change, so if the vibration is really pronounced and annoying, you might consider changing to a propeller with a different number of blades.
These days when Boston Whaler designs a boat they have sophisticated computer tools and they look for resonances in the boat structure that might occur and cause these sorts of vibrations. Usually the vibration shows up in the bow railings. The structure will have a natural resonance and when the vibrations from the propeller and motor excite the hull at near its resonant frequency, it begins to vibrate.
Tell us what model of OUTRAGE you have. Maybe there is a tendency for a vibration at a particular speed in a particular hull.
Another variable in the vibration is the engine speed. Because you have a two-stroke motor the engine's vibration is twice as high as it would be with a four-stroke motor (because a two-stroke motor has twice as many power strokes per revolution than a four-stroke motor). So at a particular speed the engine vibration may be in harmony with the hull resonance.
Also the gearing is different among motors, and this is another variable. The gearing affects the propeller shaft speed. The propeller shaft speed and the number of blades on the propeller determine another input frequency for the vibration.
When all of these inputs align and are near a natural resonance in the hull structure, the hull vibrates. This is the cause of the low speed vibration you are experiencing.
The holes and plugs in your Mercury propeller are part of the performance vent system (PVS). The purpose of these vents is to allow control over the amount of ventilation the propeller experiences at low speeds. They are primarily of interest to boaters with very high speed potential and allow the use of higher pitch in the propeller. The higher the pitch the higher the potential boat speed. To enhance acceleration, the propeller is vented to allow the exhaust gases passing through the hub of the propeller to escape. At low speeds this action will ventilate the propeller. When the propeller ventilates it becomes easier to turn, and this allows the engine to spool up to high speed faster. Venting the propeller also dramatically increases its slip, and the boat will move more slowly than it would if the propeller were not ventilated. The effect is similar to reducing the pitch of the propeller. Once the boat reaches higher speeds, the exhaust gases tend to avoid exiting via the vents and flow only through the center hub. This ends the ventilation and the propeller then acts normally and with its normal slip and pitch.
Using PVS vents to reduce a low speed vibration problem is an unusual application of this technique. It may have some influence in that it will affect the action of the propeller. Since the propeller is one of the primary inputs in the vibration system, changing the vents may affect the vibration.
Operating a boat with a PVS propeller that has vents is something like driving a car with an automatic transmission. The propeller acts like a transmission and shifts gears, slipping a lot at low speed and then finally winding up and grabbing on at high speeds. My personal experience is that I find PVS propellers somewhat annoying and of limited application in most Boston Whaler boats which, for the most part, are not being run with extremely high pitch propellers and do not need the effects of the vents to operate properly.
A vibration that occurs at a high speed is more likely due to some imbalance in the propeller. Such an imbalance will make itself known over a wide range of speeds. If you experience the vibration at only one particular high speed it is more likely being caused by some resonance in the engine.
Tom W Clark posted 08-27-2007 10:09 AM ET (US)
Greg,
3000 RPM is right where my boat is climbing onto plane. If a propeller starts to ventilate, the motor will be vibrating, severely. Very typical. Try using more down trim when accelerating onto plane. Do not remove the vent plugs.
Jerry,
What you are apparently missing is experience operating an outboard powered boat that has a propeller that ventilates. Try it the next time you are on the water and you will see what I mean.
Bigwaves_us posted 08-28-2007 04:51 PM ET (US)
Thanks for the information. I did drop the boat off at the dealer this morning. They have been - like the boat- great. The boat is a 2007 190 Outrage with a 150-HP OptiMax.
Jerry Townsend posted 08-28-2007 05:31 PM ET (US)
Tom, you are right; I have a 1996 115 Johnson OceanRunner which has a non-ventilating prop. ------ Jerry/Idaho
jimh posted 08-30-2007 08:01 AM ET (US)
Please let us know in a follow up posting what remedy the dealer applied to correct the vibration in your 2007 Boston Whaler 190 OUTRAGE with Mercury 150-HP OptiMax motor.
Tom W Clark posted 08-30-2007 10:05 AM ET (US)
Jerry,
I meant that literally. The next time you go boating, try accelerating onto plane wit the motor trimmed out more than normal. The propeller will ventilate (ALL props can be made to ventilate) and you can then turn around and observe the power head shaking about.
When my own motors on my Revenge 25 do this they fairly shudder until they get a grip.
I so no reason to assume ventilation about a propeller would be uniform and balanced, but leave the theorizing ashore and just observe the results.
Jerry Townsend posted 08-30-2007 02:29 PM ET (US)
Tom - thanks - I'll try that the next time that I am out. ---- Jerry/Idaho
dropanchor posted 08-31-2007 01:36 PM ET (US)
What propeller are you using (e.g. Enertia, Mirage Plus)?
Bigwaves_us posted 09-01-2007 07:57 AM ET (US)
Picked up the boat from the dealer. Since none of the mechanics were around, [I] was not able to get all the details. The office clerk said the [source of the vibration problem] was with the flywheel. I'll find out how it runs later this morning.

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Author	Topic: Vibration
Bigwaves_us	posted 08-26-2007 12:35 PM ET (US) I have a new 2007 Boston Whaler Outrage with a Mercury OptiMax 150. At a certain speed [6-MPH] the boat has a pronounced vibration. My friend was telling me to remove the vent plug on the propeller. There is nothing in any of the owner's manuals about the plug. Coming from a large diesel [unrecognized acronym], I am new to outboards. Thanks, Greg
Perry	posted 08-26-2007 01:09 PM ET (US) Do you see the vent plugs on the hub of the propeller? Are the plugs removed? Vent plugs introduce air to the prop (ventilation) and help with acceleration but I never heard of them having any effect on a boat's vibration. If there is damage to one or more of the blades of the prop, it could be off balance and may make the motor vibrate.
Jerry Townsend	posted 08-26-2007 03:27 PM ET (US) Greg - I don't have your propeller or experience with those plugs you mention, just a lot of vibration experience. As Perry, removed vent plugs introducing air at the hub should not affect or induce any vibration. The vibration is coming from an unbalance in the prop which may have been damaged or improperly balanced. Or the vibration could be coming from the engine. Temporarily change props and see what happens. If the vibration is still there, the problem is in the engine; if not, the prop is the problem. If the problem is the prop and it has not been damaged, have your dealer replace the prop or have it dynamically balanced by someone that knows what they are doing. --- Jerry/Idaho
Bigwaves_us	posted 08-26-2007 08:12 PM ET (US) The plugs are still in the hub. Should they be removed?
Tom W Clark	posted 08-26-2007 09:46 PM ET (US) No, do not remove the PVS vent plugs. Removing the vent plugs will cause the propeller to ventilate, or ventilate more than it already is. I am still unclear, are you talking about a vibration that occurs at any speed or a vibration that occurs when you are accelerating onto plane? If the latter, I would suspect you are experiencing ventilation where air is drawn into the propeller and the propeller (and engine RPM) accelerate more than thee boat speed. When a prop is ventilating, there will be some vibration but the vibration will smooth out as the boat gains speed and the propeller regains its grip on the water. If the vibration is the result of a damaged propeller it will be apparent throughout the RPM band and increase with engine speed.
Jerry Townsend	posted 08-27-2007 01:53 AM ET (US) Tom - I am missing something - as if a prop is ventilating, that ventilation would, I think, be somewhat uniform or random around the prop - and if that is the case, there should not be any unbalance. But, if only one (or two) blades were continuously subject to the ventilation, that would cause a vibration. Enlighten me - what am I missing? ----------- Jerry/Idaho
Bigwaves_us	posted 08-27-2007 06:02 AM ET (US) The vibration occurs in two places. The first the boat is moving around six mph. The second is around 3800 rpm. Thank fo the help.
jimh	posted 08-27-2007 09:04 AM ET (US) A vibration that occurs at low speed is fairly common and is the result of a resonance in the system formed by the propeller, the motor, the motor mounts, and the boat. Among these components, the propeller is the easiest to change, so if the vibration is really pronounced and annoying, you might consider changing to a propeller with a different number of blades. These days when Boston Whaler designs a boat they have sophisticated computer tools and they look for resonances in the boat structure that might occur and cause these sorts of vibrations. Usually the vibration shows up in the bow railings. The structure will have a natural resonance and when the vibrations from the propeller and motor excite the hull at near its resonant frequency, it begins to vibrate. Tell us what model of OUTRAGE you have. Maybe there is a tendency for a vibration at a particular speed in a particular hull. Another variable in the vibration is the engine speed. Because you have a two-stroke motor the engine's vibration is twice as high as it would be with a four-stroke motor (because a two-stroke motor has twice as many power strokes per revolution than a four-stroke motor). So at a particular speed the engine vibration may be in harmony with the hull resonance. Also the gearing is different among motors, and this is another variable. The gearing affects the propeller shaft speed. The propeller shaft speed and the number of blades on the propeller determine another input frequency for the vibration. When all of these inputs align and are near a natural resonance in the hull structure, the hull vibrates. This is the cause of the low speed vibration you are experiencing. The holes and plugs in your Mercury propeller are part of the performance vent system (PVS). The purpose of these vents is to allow control over the amount of ventilation the propeller experiences at low speeds. They are primarily of interest to boaters with very high speed potential and allow the use of higher pitch in the propeller. The higher the pitch the higher the potential boat speed. To enhance acceleration, the propeller is vented to allow the exhaust gases passing through the hub of the propeller to escape. At low speeds this action will ventilate the propeller. When the propeller ventilates it becomes easier to turn, and this allows the engine to spool up to high speed faster. Venting the propeller also dramatically increases its slip, and the boat will move more slowly than it would if the propeller were not ventilated. The effect is similar to reducing the pitch of the propeller. Once the boat reaches higher speeds, the exhaust gases tend to avoid exiting via the vents and flow only through the center hub. This ends the ventilation and the propeller then acts normally and with its normal slip and pitch. Using PVS vents to reduce a low speed vibration problem is an unusual application of this technique. It may have some influence in that it will affect the action of the propeller. Since the propeller is one of the primary inputs in the vibration system, changing the vents may affect the vibration. Operating a boat with a PVS propeller that has vents is something like driving a car with an automatic transmission. The propeller acts like a transmission and shifts gears, slipping a lot at low speed and then finally winding up and grabbing on at high speeds. My personal experience is that I find PVS propellers somewhat annoying and of limited application in most Boston Whaler boats which, for the most part, are not being run with extremely high pitch propellers and do not need the effects of the vents to operate properly. A vibration that occurs at a high speed is more likely due to some imbalance in the propeller. Such an imbalance will make itself known over a wide range of speeds. If you experience the vibration at only one particular high speed it is more likely being caused by some resonance in the engine.
Tom W Clark	posted 08-27-2007 10:09 AM ET (US) Greg, 3000 RPM is right where my boat is climbing onto plane. If a propeller starts to ventilate, the motor will be vibrating, severely. Very typical. Try using more down trim when accelerating onto plane. Do not remove the vent plugs. Jerry, What you are apparently missing is experience operating an outboard powered boat that has a propeller that ventilates. Try it the next time you are on the water and you will see what I mean.
Bigwaves_us	posted 08-28-2007 04:51 PM ET (US) Thanks for the information. I did drop the boat off at the dealer this morning. They have been - like the boat- great. The boat is a 2007 190 Outrage with a 150-HP OptiMax.
Jerry Townsend	posted 08-28-2007 05:31 PM ET (US) Tom, you are right; I have a 1996 115 Johnson OceanRunner which has a non-ventilating prop. ------ Jerry/Idaho
jimh	posted 08-30-2007 08:01 AM ET (US) Please let us know in a follow up posting what remedy the dealer applied to correct the vibration in your 2007 Boston Whaler 190 OUTRAGE with Mercury 150-HP OptiMax motor.
Tom W Clark	posted 08-30-2007 10:05 AM ET (US) Jerry, I meant that literally. The next time you go boating, try accelerating onto plane wit the motor trimmed out more than normal. The propeller will ventilate (ALL props can be made to ventilate) and you can then turn around and observe the power head shaking about. When my own motors on my Revenge 25 do this they fairly shudder until they get a grip. I so no reason to assume ventilation about a propeller would be uniform and balanced, but leave the theorizing ashore and just observe the results.
Jerry Townsend	posted 08-30-2007 02:29 PM ET (US) Tom - thanks - I'll try that the next time that I am out. ---- Jerry/Idaho
dropanchor	posted 08-31-2007 01:36 PM ET (US) What propeller are you using (e.g. Enertia, Mirage Plus)?
Bigwaves_us	posted 09-01-2007 07:57 AM ET (US) Picked up the boat from the dealer. Since none of the mechanics were around, [I] was not able to get all the details. The office clerk said the [source of the vibration problem] was with the flywheel. I'll find out how it runs later this morning.