New prop for my 390

Jan 12, 2015
38
beneteau oceanis 390 herzelia
Hello 390 owners,
I have a Perkins Prima M50 on my 390
What are your propeller's dimensions?
I'm thinking of buying a Maxprop easy. Recommended diameter? Pros and cons?
Thx
Yoram
 
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Slider

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Sep 1, 2014
93
Beneteau 37DK Alameda
I have a Beneteau 37. I purchased a 3 blade Bruntons Varifold. it runs smoother than the original fixed prop with no change in power. KINGpropulaion 703-430-4118. Dr. Rodertick Sampson will work with you for a perfect fit.
 
Jan 12, 2015
38
beneteau oceanis 390 herzelia
Thanks for the info.
May I ask how much it cost?
The Maxprop is at least 3500$.
Thx
 
Jan 4, 2010
1,037
Farr 30 San Francisco
kiwiprop, much less expensive feathering prop, mine worked well after it was adjusted. Initially it was set too fine.
 

Slider

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Sep 1, 2014
93
Beneteau 37DK Alameda
The Varifold was about $1400 I think it was 13' 25mm shaft. Call the Dr., he is fun to talk to. He is an English Naval Engineer. Has the spec on all the boats, but will have you fill out a form to make sure you get the correct prop. I have had it for 3 years. You will like it, and it will be free shipping.
 
May 17, 2004
5,025
Beneteau Oceanis 37 Havre de Grace
We also have a Beneteau 37 and upgraded to a flexofold this winter. Cost was $2035 for a 16"x12" 3 blade on a 25mm ISO hub. It replaced a 17"x12" fixed prop. So far speed under power seems about the same, and under sail seems at least a quarter knot faster in light-moderate wind.
 
Jan 12, 2015
38
beneteau oceanis 390 herzelia
Again, thanks for the info.
I'll call the Dr. next week.
Slider, Why did you prefer the Varifold over the Autoprop?
It seems as if the big advantage of the Autoprop is that the pitch is not set but the optimum pitch is set according to the engine speed and the boat speed.
I don't know the dimensions of my prop and am afraid to get one that will be under powered. The current prop is to small because the engine can rev up to 3800 rpm in gear when the manufacturer states that the max rpm should be 3000 (Perkins Prima M50) and my boat is very slow when motoring.
Would appreciate more advise...
yoram
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
.... The current prop is to small because the engine can rev up to 3800 rpm in gear when the manufacturer states that the max rpm should be 3000 ...
A prop will not make your RsPM increase. What does the engine do in neutral, wide open? THAT is what you should get in gear, wide open, if you have the proper prop. If you can do 800 over the engine's spec, then you have a different problem- maybe a governor?
 
Jan 12, 2015
38
beneteau oceanis 390 herzelia
Do you think that max rpm in idle and in gear should be the same? What about the drag of the prop? It has to effect the rpm in gear.
 
Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
If the prop pitch is correct (and prop is clean etc) and the governor is set correctly, the governor will control the RPM to the same point at WOT (wide open throttle) .. but if the RPM is going that high, you are probably "under propped" that is, not enough pitch to load the engine enough..
RPM Verified with an optical tachometer?
 

Slider

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Sep 1, 2014
93
Beneteau 37DK Alameda
They make the 3 blade Varifold 16" to 32". I think mine was a 16"X12". I have the Yanmar 29hp engine and make over 6 Knots at 3000 rpm. You have an M50, is that 50hp? Your 39 can't be much heavier than the 37. I don't know anything about the Autoprop, but have had a good experience with the Varifold at a lower price. Call the Dr. he will get it right!
 
Jan 12, 2015
38
beneteau oceanis 390 herzelia
Haven't checked the rpm with an optical tachometer. Good idea. I'll do that next week.
Thanks
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Do you think that max rpm in idle and in gear should be the same? What about the drag of the prop? It has to effect the rpm in gear.
Yes, that is the normal check-out procedure. Just do it and see what it does.
 
Jan 12, 2015
38
beneteau oceanis 390 herzelia
Hi,
Bought and rpm optical tachometer and went for a sea trial today. Below are the results:
There are 3 columns in the table:
"rpm gauge", "measured engine rpm", "shaft rpm"

1000, 710, 330
1600, 1058, 497
2000, 1457, 680
3000, 2115, not measured
3550, 2522, not measured

The max rpm measured is 2522 yet it should max out at 3000 (WOT). Thats what the manufacturer states. This means that I am over propped.
How does this effect my engine? the speed of the boat?
How will a correct propeller affect the speed of the boat?
Thanks
Yoram
 
Last edited:
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
There should be a small hole in the back of the tach. Stick a small flat blade screwdriverin there and adjust the tach to it reads correctly.

Les
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
I'm in the same position you are max is about 2600 and max is listed at 3200. I don't have any smoke unless under very heavy loads (towing another 35' boat) and then it is very light. So I have other higher priorities for my time and money. Btw I've had the for just over a year.

Les
 
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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
By your new optical, your max RPM was 3550, not 2522. SO, now the question is, how accurate it the optical? (maybe time the second hand on a clock?) You read these speeds in neutral, didn't you? Excess RPM above the spec means you have some other problem, but perhaps the manufacturer just recommends the 3000 as CRUISING RPMs, not max? IIRC the suggested crusing RPM is 80%, so 3550 x .80 = 2840, so not all that far off. Also, calculated your tranny is 2.14 geared.
 
Jan 12, 2015
38
beneteau oceanis 390 herzelia
It was measured when the engine is in gear.
The rpm was measured on the crank shaft which is the correct engine rpm. It was 2522. the tachometer showed 3550 but I guess it is faulty and need adjustment.
I don't think I have excess rpm. I think its the other way around.
Graphs provided by the manufacturer show that the max rpm should be 3000 and the gear ratio should be 2.14.