Two versus three bladed Max prop

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Gary Wyngarden

Gary Wyngarden

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Mar 4, 2004
347
Hunter 37.5 Orcas Island, WA
I'm having a now two-year-old continuing problem with shaft/prop vibration that I'm spending alot of money on and not getting resolved. The prop is a 17 inch two bladed Max prop. We've done all the usual stuff: shaft alignment, had the shaft checked to ensure it's striaght and not damaged, new cutless bearing; removed and realigned strut, new engine coupling. The Prop has been back to PYI twice to check balance. Nothing seems to help. The vibration is somewhat better but still unacceptable with my two bladed fixed pitch prop (17x15). Having told my story to PYI, they are recommending I replace the two blade Max prop with a three blade and have suggested they will give me a deal and a trade in on my old prop. Anyone done this tradeoff with success? Any other ideas? Gary Wyngarden S/V Wanderlust h37.5
 
J

jayden

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Aug 10, 2005
4
- - San Francisco
better prop

Look at Variprop. Ive cruised 27000 miles with a Maxprop vibrating.After a lot of research I must say Im most impressed with Variprop. Extremely helpful and knowlegable people as well.And no vibration.
 
Seattle Scott

Seattle Scott

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May 6, 2004
916
Hunter 37C Seattle
Gary, take the deal

if it really is a "deal" but it can't be the prop, since you have unacceptable vibration with your fixed blade. My only lame advise is to keep poking around forward of the coupler; tranny bearing? motor mounts? Rubber dampener for the coupler that PYI sells?
 
Tsehum Pete

Tsehum Pete

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Apr 26, 2005
286
Beneteau Oceanis 390 Tsehum Harbour, BC, Canada
Prop Woes

Gary, Having spent spent a bunch of money with PYI to resolve this problem, why not suggest to them they loan you a perfectly balanced 3-blade Max-prop and then test it out? The 3-blades VP's are installable and adjustable by a diver and generally are a better designed unit. My boat-sitter has a doctor's stethoscope with six-foot tubes and can find any vibration on a boat. Maybe PYI need a doctor with long arms? Props are incredibly expensive and the diagnosis should have turned up the problem by now. Peter
 
Tsehum Pete

Tsehum Pete

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Apr 26, 2005
286
Beneteau Oceanis 390 Tsehum Harbour, BC, Canada
Prop Woes II

Gary, Another thought. Have you pumped the prop hub full of lithium grease? Adding a zinc to the shaft? Maybe it's creating an imbalnce condition. Peter
 
OldCat

OldCat

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Jul 26, 2005
728
Catalina , Nacra 5.8, Laser, Hobie Hawk Wonmop, CO
Do you have the problem . . .

Do you have the problem at all RPM? Or, only in a narrow RPM range - like your typical cruise RPM?
 
Fred Ficarra

Fred Ficarra

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Dec 2, 2003
4,245
- - Seabeck WA
Gary, It's the prop and they know it. That's why

the deal. As I understand your situation, the fixed prop works fine. Correct? If the Maxprop is properly installed, (tight hub and correctly indexed) then your problem is dynamic in nature. That means that it only manifests it self when operating. A blade could be out of index or miss-manufactured. If the guys at PYI don't spin-balance/test your prop, but only weigh the components, they'll never know if it's out of balance. It's just like your car tires. Remember bubble balancers? OK, that said, the people at PYI are good folks. But,,,,, there comes a time when we all need to assert ourselves. After two years and the elimination of all other possible causes, I think your time is at hand. IMHO,,,of course.
 
S

Steve

Have you tried . . .

Have you tried disconnecting the propshaft (at the coupler) and running the engine at different RPMs? If there is still vibration, then the problem is on the engine side. If there is no vibration, then it is on the propshaft/prop side. If the prop is out-of-balance, or one of the blades' pitch was changed (ever so slightly and not visible to the eye) by hitting something, then you could get significant vibration. Good Luck!
 
D

Dave Sharp

I did exactly that!

Gary, Our last boat had a 2 blade Maxprop. That boat had an IOR type strut that had too much vibration with the two blade Maxprop. Due to other circumstances we replaced it with a three blade Maxprop. The vibration was gone. I will, however, say that our present boat, H376, now has a three blade Kiwi-prop that has been great. The price was certainly right at around $1200 including shipping. But it's just been one year with it. Good luck.
 
Gary Wyngarden

Gary Wyngarden

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Mar 4, 2004
347
Hunter 37.5 Orcas Island, WA
Prop Woes

Thanks to all for your input. We have vibration even with our fixed pitch prop but it's worse with the max prop. It's more noticeable at higher RPM's. Once over 1800 you really become aware of it. I'm talking to a different boatyard now and will give them a chance at it. Their comment was that the three bladed max prop might be better, but if everything else is right, the two blade shouldn't vibrate. Very frustrating, very expensive. Gary Wyngarden S/V Wanderlust h37.5
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Gary, a bent shaft will create

vibration not matter what your propeller is doing. My Islander has an aperture and my three blade doesn't cause any noticeable vibration even when allowed to free wheel while sailing. But the old sailerman 2 blade didn't either. If the propeller tips are too close to the hull you can get a pressure thump as the blade passes the hull.
 
OldCat

OldCat

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Jul 26, 2005
728
Catalina , Nacra 5.8, Laser, Hobie Hawk Wonmop, CO
Gary - Some Physics -

Some Physics - and they may not apply to your situation. The interaction of the prop and the hull create a vibrating force at "Prop blades x RPM /60 hz". IF, and it may be a significant if, there is some part of the system that happens to resonate at 2*1800/60 hz, then balance, etc does not matter - it will pick up the energy comming off the prop and hull and amplify the vibration to where it is a problem. Hence, the three blade prop might solve the problem, just because it moves the frequency of the forcing function. Also, two perfectly good 2 blade props might have different amplitude if one drives the system harder than the other. One idea is to try any good three blade and see what happens. If the problem does not go away, I would think it is somewhere other than the prop. But, then, with all the money spent - you'd think the pro's would have found it?!?!? Just because stuff is balanced - does not mean it will all work together, especially if you have any drive train mods on the boat. If you want real fun with these types of problems, try my other hobby, modify a 4x4 and chase these gremlins around for months. Best o' Luck, OldCat
 
T

Tom S

I think OldCat might be on to something

I was thinking the same thing. There might be some unique harmonics happening . Gary -- A few quick questions. Do you have a bronze shaft or a Stainless steel shaft? A bronze will be much much more flexible than a SS shaft. I have a heavy autoprop and changed to SS and any vibrations I had went way down. I am assuming you have about a 1" shaft -- How far is the prop from the Strut? Ideally it should be no more than 3/4" from strut. The further the prop is the more torque and thus vibrations induced
 
Gary Wyngarden

Gary Wyngarden

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Mar 4, 2004
347
Hunter 37.5 Orcas Island, WA
Thanks Again

Oldcat's theory is indeed an intruiging one. The fixed pitch prop is 17x15 which is I believe the original prop Hunter put on these. The Maxprop is also 17 inches so I'm thinking distance from the hull wouldn't be a problem. The shaft is one inch stainless. I don't know how far the prop is from the strut. But the harmonic theory is a new possibility for sure. Thanks again. Gary Wyngarden S/V Wanderlust h37.5
 
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