• Welcome to this website/forum for people interested in the Morgan 38 Sailboat. Many of our members are 'owners' of Morgan 38s, but you don't need to be an owner to Register/Join.

Propeller

bert

Bert Okma
I am interested in advice and experience with replacing my current prop with a Campbell Sailor. I have a 1983 Morgan 38, 384 with the Perkins 4-108 and Hurth 150 2:1 ratio. Currently the 16"dia. 11" pitch, three blade prop allows only 2600rpm. The Campbell folks are recommending a 16"dia with 9" or 8" pitch. They claim less slip in power and less drag while sailing. To increase the max. rpm they feel the 8" is necessary. Does anyone have experience with making this kind of change? Current postings do not directly address this situation. I want to increase the Max. rpm but I'm worried the 8" pitch will not provide enough power.
 
archives has several posts about campbell sailors. I don't remember any of the details. I also believe that if your perkins 4-108 will not turn the 16 x 11 prop over 2600 rpm then you have a higher pitch than you think or something is wrong with your engine. What do you cruise at? What speed do you get?
 
Bert,
Hang on Bert. Most of us with the Perk. 4-108 have the fixed 3 blade 16X11. We can reach 3000 rpm, wide open. Some meters might read 2900, some might read 3100. You have to allow a + or - for meter error. On Southerly with a clean bottom, we cruise 6knts at 2000rpm, 6.4knts at 2200rpm.
I would suggest that before you do anything check out the accuracy of the rpm meter, and also your speedo. I think your instincts are right about lowering the prop pitch.
Larry
 
Just to reinforce what Larry has said, Njord runs at 6 knts @ 1800 rpm and 6.4 at 2000 rpm. I am trying to determine my prop pitch. The stamp on the prop is a little hard to read but, it's either three blade 16X11 or 16X12.

Jay
 
Greg,

I have just gone thru a repower and reprop saga...and I do mean saga.

I repowered with a beta 37.5hp/3000rpm/2.1 reduction the first time. I had a 16x12 Michigan Wheel. I tryed that prop first figuring it would be close to what I needed. It was very close but needed a small (200rpm) adjustment. That said a 16x11 would have been about right for Michigan Wheel.

Campbell uses the Michigan Wheel formulars to size their props. Their rule of thumb is to use 2" less in combination of pitch and diameter than the MW formulars predict. I purchased a Campbell 16x9.5. It pushed the boat fine but it really loaded the engine. I could not get it to turn up more than 2400rpm under full thortle. The engine would gradually over heat at 2200rpm and it had other problems.

Norm at North by Northwest(Campbell) and I talked and he decide what I needed was a 16x8. I hauled the boat and changed out the prop. But I was smart this time. I cut off the shaft so I would be able to change the prop under water without dropping the rudder.

The repitch did not make 1 rpm difference and the over heat problem was still there. All I got out of the excersise was a huge case of frustration and a shorter shaft.

At this point I figured out that the engine I had just install was a lemon. Lemoms happen (but why me lord?). Beta gave me back my money and a a deal on the next engine up in thier line. I re-re-powered with a Beta 43HP/2800RPM/2:1 reduction gear engine.

Well guess what, now I need to replace the prop again. Michigan Wheel recommended a 17x12. I found one at a local prop shop used and, with the aid of a diver replaced the Campbell with a 17x12 Michigan Wheel. I did this before I put the engine in because, guess what, the new,new engine is a little longer and needs to move further back in the engnine box so if the engine were in place I would have to drop the rudder agian to replace the prop.

This engine is great and the Michigan Wheel is a perfect fit for the boat. It sings but that's another story. I have repitched the Campbell to a 16x11 and will be installing it the next time I do the bottom (spring of 2005).

I do like what the Campbells do. The boat backs better. Sailing in light to moderate air is much better. The engine does load more but seems smoother.

One more thing... I have had 2 friends that have had the same experience with Campbells - they have not been able to get their engines to reach full rpm after the re-prop. They push their boats great but rpms have been an issue.

I am gonna give Campbell one more shot. I'll let you guys know the outcome next year.

Scare you enought?

Fairwinds and Rum Drinks,

Vic C.
 
You have to remember that if you go with a to large of diameter prop, you run the risk of cavitation. There is a point where you can get the prop to close to the hull. Another point to consider, diesels like to be run at about 75-80% of the full power for full efficiency. The ideal situation is to calibrate first your tach and then your speedo with a gps. If you run your engine for long periods of time at slow rpms, the engine developes carbon build-up enternally.
Jim
 
Jim,

That is exactly the point. And, exactly why you need to as exact as possible when selecting a prop. And why not being able to turn the engine up with the Campbell has been a concern.

We have plenty of room to swing a 17" prop by the way. If there is a problem with room it is with the "deadwood" forward of the prop.

 
The last time my boat was out of the water, I measured about 2 1/2 or 3 inches clearance between the prop edge and the hull. I have 16 RH 11 prop by the way. A 17 inch prop would be max. I believe the area in front of the prop is shaped to allow water to flow freely and it is quite a distance from the prop. Cavitation is caused by a hard surface next to the prop edges, i.e. the hull. There is a formula for this minimum distance but it is on the boat. It may be 10% of the diameter of the prop.
Jim
 
When I propped for my Med Cruise, I put the german feathering Sailprop 17x11, similar to the Maxprop, half the cost. I was told by the manufacturer that the rule of thumb or I should say fingers is 2 fingers clearance to the hull is sufficient. When I was in France, I had it worked on because of rpm problems too and balance. My ol' 3QM30 just wasn't going up - they reconditioned the prop, found the prop had struck something and was a wee bit out of true. They also found my shaft off a bit which they worked also. The whole thing cost $175. I was happy, the boat did run much smoother. Now I still have the problem of the dead motor mounts and broken springs in the clutch...

That's this year..
 
Thank you for all of the valuable information. Things have changed dramaticly. As a result of study, advice and a shaky transmission analysis report I replaced the Hurth 150 2:1 with its newer model ZF12 2.6:1. The dealer and mechanic recommended this after conducting an analysis. They felt strongly that consistant runing at or near 2000rpms was not good for the engine. I kept the Michigan Sailor prop 16x11. I just returned from extended cruising. The rpms are way up. She will turn 4000 which puts the clean bottom, flat water above 7 kts. However that is really too high of a rpm and it takes 3000+ rpm to hit 6 kts consistently. With 20 kts and waves head on I can't hold 5kts without going up to 3400+ rpms. Engine and transmission seem to be fine now. I do not over heat.

Now I'm looking to increase prop and change to a Cambell sailor or the Sailprop mentioned above. For the Cambell Sailor I'm thinking 16x11. But what I just read about the lower rpms makes me think 16:10 might be better. I'm open to all input.
 
What engine are you talking about? On any engine, you should look at the engine power curve. Most engines should be run at about 70-80% of max rpm's. I would not say that 2000rpms is bad for the engine. The worst thing is a possible build-up of carbon but it should no effect on the transmission. Prop size and pitch depend on the boat and engine. I would reccommend a prop shop for your questions.
 
Could I take this thread in a slightly different direction for awhile? Jim mentioned cavitation. I have a Perkins 4-108 on my M-384 with 16x11 prop. If I am going forward at say 5 - 6 knots and shift into reverse and give 1/3 throttle or more I get this rumbling sound like the boat is being dragged down a gravel road. I thought the engine was coming through the cockpit floor! After looking in the engine room while a friend repeated the "all stop" manuver I saw no movement of the shaft or engine that could have caused the rumbling sound. Could this be cavitation? I'm not sure if cavitation has a "sound".
By the way, Vic, I really had a good laugh (not at you but with you) as I read your 4/1 post. I have had similar experiences. Sometimes when making an apparently simple change we set off a domino effect of unexpected events.
Regads
Rick
 
Are you kidding? Why shift into reverse while moving forward at 6kts. and then not expect "rumbling" sounds? You are attempting to change the flow of water two feet under the surface.
 
Rick:

Cavitation will cause the noise that you are talking about. The energy created by the propeller going against the flow of the water past the boat causes vacuum bubbles to form around the propeller. These bubbles are causing the rumble. I'm sure you are aware that turning the boat, if you have the sea room, is a more efficient way of slowing the boat down.
 
To Frank and Anonymous
Hope you don't think I'm nuts. The action I mentioned in my post was part of a mechanical survey of my Morgan 384. The noise was unexpected to say the least. This action was also performed on my Morgan 323 and Ranger 33 during survey sea trials. No similar noise on either boat. Frank, thanks for your feedback that the noise is most likely cavitation.
Regards
Rick
 
Thank you for all of the valuable information. Things have changed dramaticly. As a result of study, advice and a shaky transmission analysis report I replaced the Hurth 150 2:1 with its newer model ZF12 2.6:1. The dealer and mechanic recommended this after conducting an analysis. They felt strongly that consistant runing at or near 2000rpms was not good for the engine. I kept the Michigan Sailor prop 16x11. I just returned from extended cruising. The rpms are way up. She will turn 4000 which puts the clean bottom, flat water above 7 kts. However that is really too high of a rpm and it takes 3000+ rpm to hit 6 kts consistently. With 20 kts and waves head on I can't hold 5kts without going up to 3400+ rpms. Engine and transmission seem to be fine now. I do not over heat.

Now I'm looking to increase prop and change to a Cambell sailor or the Sailprop mentioned above. For the Cambell Sailor I'm thinking 16x11. But what I just read about the lower rpms makes me think 16:10 might be better. I'm open to all input.
I just came across this thread on ZF12 gearing change to 2.6:1. It seems prior owner did the same on our 384, and we struggle with same speed/rpm issues mentioned. Did you ever re-size the prop or solve in another way?
 
My guess, just a guess, is that a 2.6/1 gear is a little more reduction than what a Perkins needs/wants. That then requires more rpm or more pitch than the standard 16x12 or 16x11. The engine should turn up in to the 3000s at a minimum. Prop diameter is limited by aperture. Mark Pearson just installed a Yanmar 45 and went with a 16x14 MaxProp. To learn about problems with under-runn ing diesels, check out Attainable Adventure Cruising.
 
Thanks for the reply Terry! We still have the 16x11, and thus at the higher reduction requires higher RPM to get any speed - e.g. 3,000 rpm to get 5 kts. In lieu of swapping the transmission for the ZF12 at 2.1:1, was wondering if Jay increased pitch of prop to get a little more load on the engine and speed. I guess mathematically, it would need to be quite a jump to match the 23% increase in reduction. Perhaps a 16x11*1.23 = 13.5, unless increasing prop size. I've read in other threads a 17" prop was doable without cavitation but probably the max. A MaxProp would be wonderful, but a transmission swap would likely be cheaper...
 
Well, I am no expert, just "propeller-curious," Mark has a 16x14 prop that works very well with his new Yanmar with a reduction gear close to yours. The issue with "over-propping" is whether you can put the engine up to a full loaded rpm and, if not, whether the lower rpm/load will glaze the cylinder linings. With my 16/11 prop and a 1.88/1 ZF15, I cruise at 2000-2200 rpm. I have only once in 25 years run the engine above 3000. Are my cylinders glazed over? Perhaps. I don't know. The old Perkins always starts and runs, but it uses some oil and things are beginning to break or otherwise need replacement, so I am installing a Beta 35. Ted Brewer spec'd the boat for the Yanmar 30. I would recommend joining Attainable Adventure Cruising and then reading the discussion about diesels. I would also urge you to find a reliable diesel mechanic and a knowledgeable prop shop and talk to them about your issues.
 
Thanks Terry. I share your curiosity and skill level :). I signed up for Attainable Adventure Cruising and will be digging into their article this weekend. Our (rebuilt) Perkins was installed shortly before we became owners, thus she only has around 750 hours. Runs great otherwise. I'll circle back if we change anything to document in the forum. This is a really great resource.
 
Back
Top