Folding or Feathering Prop Advice

[Robert E]

Jan, we had three blade Max props on two boats; a Norseman 447 and Columbia 41. Both were reliable. Our current boat is a Nonsuch 33 which is fitted with a Gori three blade. Sail faster with feathering prop, but do more maintenance. Fixed props are cheaper and reliable. Here is the best data I have come across on evaluating folding and feathering propellers. I highly recommend it. Best, Robert
Folding and feathering propeller test

[Jim Cate]

Originally Posted by CarinaPDX

Not all feathering props are inefficient, or allow changing of pitch. Probably the oldest design out there is the Luke, which dates back nearly a century. It has efficient curved blades and is a simple, sturdy construction in bronze. The stops are machined into the bronze - they can be altered by the factory or a good machine shop but not by the owner and certainly not in the water. The downside is that it needs to have a low viscosity grease pumped into the hub occasionally, which can be done underwater.

For racers it is important that a prop have the absolute least drag under sail, even at a substantial loss of performance under power, which is the case for most feathering and folding props. For cruisers I feel that a small loss of performance under sail (i.e. much better than fixed but less than other feathering/folding props) is acceptable for a large increase in efficiency under power, which is what the Luke offers.

Automatic Feathering Propellers, P. E. Luke. Full Service Boatyard, Boothbay, Maine.

Greg

Those are interesting props for sure! I wish they showed a bit about the mechanism in the hub, for the pix are kinda underwhelming in detail. Some detail about the gearing, etc would be helpful.

However, I can't agree that the Luke does offer a large increase in efficiency over the Flex-O-Fold going forward. How do your reach that conclusion? Better than flat blade feathering props, sure, but the F-O-F has shown very high efficiency in tests... better than most any competitor, including fixed blades.

And there is no info about maintenance and longevity for the Luke. There have been posts here on CF relating the need for rebuilding Max props after only 1500 hours or so... not acceptable to me, so I wonder about the Luke.

And for what it is worth, re service life for F-O-F props: Ours now has some 4400 hours usage (13 years full time cruising). The maintenance has been to remove any growth and then stuff some grease into the gear pocket when hauled for bottom paint... intervals ranging from 12 to 18 months, plus renewing the anode when required and then applying Prop Speed... and that's it. Result? No perceptible wear to pins or blades, no slop in any plane, no pitting or discoloration of hub or blades. Pretty damn impressive to me, and in complete contradiction to the upthread post saying that folders have wear problems (some do, these don't).

I have no interest in the F-O-F company, but have found their product to be unusually high quality compared to their competitors (and I have owned and used several of those over the years).

Jim

[CarinaPDX]

Originally Posted by Olddan1943

The sure expensive.

Actually they are on the low side of the bronze feathering prop market, along with the MaxProp. The top of the market is $4k-$5k. Other materials can be less expensive but you get what you pay for.

Originally Posted by Jim Cate

However, I can't agree that the Luke does offer a large increase in efficiency over the Flex-O-Fold going forward. How do your reach that conclusion?

I didn't. I said nothing about Flex-O-Fold. I did make some generalizations, which may not apply to the F-O-F. From the research I did at the time I bought the Luke I found that its efficiency was far ahead of other feathering props. Folding props are a completely different matter - it seems universally they are the best at minimizing drag under sail, but the performance under power varied all over the map, and usually not great. The curved blades of the F-O-F puts them at the top of the folding props for efficiency, just as the Luke's curved blades do for feathering props. If I were to buy a folding prop I would certainly put F-O-F at the top of the short list. But I wouldn't buy a folding prop. YMMV.

Greg

[lateral]

I decided to go flex-o-fold but then in the folded position the blades would clip my rudder, so had to go feathering.

[billknny]

Originally Posted by Olddan1943

No shaft locking feature other than the transmission?
I would think that would put strain on the transmission without lubrication.

Errr... it is LOCKED, that means it is not moving... why would you need lubrication? This by far the most common way of keeping a prop from turning and is completely appropriate.

Separate shaft locks are usually only needed on hydraulically shifted transmissions, some of which can not stay locked in reverse without the engine running. Sometimes VERY fast boats also need a lock in case the prop unfolds at high speed, it can reverse spin the engine against its compression.

Also, you do have to be careful with a MaxProp. Buried in the manual very deeply is a "feature": Do not stop the engine when it is turning in reverse (or was last running in reverse). The blades will not feather. It is a "feature" if you have a shaft alternator so you can force the blades to turn as the boat sails. If you want to be sure they feather as you expect, it is best to stop the engine while in forward. (No... that will NOT hurt anything, just do NOT leave the transmission in forward while sailing. If it turns, that is bad for the clutch--on most transmissions.)

[Olddan1943]

Originally Posted by billknny

Errr... it is LOCKED, that means it is not moving... why would you need lubrication? This by far the most common way of keeping a prop from turning and is completely appropriate.

Separate shaft locks are usually only needed on hydraulically shifted transmissions, some of which can not stay locked in reverse without the engine running. Sometimes VERY fast boats also need a lock in case the prop unfolds at high speed, it can reverse spin the engine against its compression.

Also, you do have to be careful with a MaxProp. Buried in the manual very deeply is a "feature": Do not stop the engine when it is turning in reverse (or was last running in reverse). The blades will not feather. It is a "feature" if you have a shaft alternator so you can force the blades to turn as the boat sails. If you want to be sure they feather as you expect, it is best to stop the engine while in forward. (No... that will NOT hurt anything, just do NOT leave the transmission in forward while sailing. If it turns, that is bad for the clutch--on most transmissions.)

So how do you keep the shaft from turning?

[silversailor]

I've just finished my 12th season with my KIWI feathering prop on a monohull saildrive. It's fabulous and priced reasonably with excellent service if ever needed. The blades are made of some space age resin, not metal, and don't accumulate growth, easily adjustable and simple to maintain. Recommended highly.

[roberthowell]

look at kiwi prop they have a composite blade feathering prop for half the price of max prop. have had one on my bene 44 for five yrs now no problem and a spare blade is only around 100 dollars

[CruiserAD]

Thanks for all the answers! Greatly appreciated!
Seems like the F-O-F 3-Blade has a lot of fans here. Will certainly look closer at that one!

[a64pilot]

Originally Posted by Olddan1943

So how do you keep the shaft from turning?

Once feathered, there is no drive to turn the shaft.
It may very slowly rotate if it’s a particularly free shaft with little friction maybe, but that ought to be a very slow rotation if at all.

I know it’s not what we are discussing, but however I remove the drive on my Autoprop whether by placing in neutral or turning the engine off in any position, it stops and never rotates again.
However very fast sailing on my boat is 7.5 kts, she has touched 8, but was overpowered and needed to be reefed at that speed.

[Zzmeyer]

I’ve had both maxprop and now flexifold. I would have stuck with maxprop on my new boat but was told it wasn’t recommended on a yanmar saildrive so went with flexifold and it has been as good in both forward and reverse as my maxprop. The drag of two fixed props is big so your thinking is spot on.

[smj]

We had fixed props on our old 36' catamaran that had Yanmar 3gm30's for power. We replaced them with maxprops while hauled then splashed the boat. At low rpm's the maxprops would clatter back and forth between being folded and opening up to drive the boat. It turns out they'd had this problem with the 3gm's before just neglected to tell me. Ended up going back with the fixed props and returning the maxprops, an expensive failure on my part.

[Tornadosailing]

I went with Brunton Autoprop on my new to me FP Salina 48. I had virtually no experience with this boat and fixed props outside of the pre-purchase sea trial, so it's hard for me to make a solid comparison. I made the decision on the Autoprop based on recommendations of a couple of other FP owners, and knowing I didn't want to be dragging a couple of 19" 3 blade props around all the time.

There are a few pros and cons I've found with the autoprop. On the pro side, the blades present exactly the same profile forward and reverse, which is a properly curved blade not flat. I love the control they give me at the dock. Also a big pro, on my way from Maryland to West Palm Beach last week, we picked up a stray piece of line somewhere around Charleston. It was clearly wrapped up pretty good, and we shut it down. By the time we had got to West Palm, the prop had completely shed the line and we free and clear of it. Another pro has to do with the prop self pitching due to hydrodynamic forces. When motoring the props increase their pitch to give you great speed with very little fuel consumption. This allowed us to motor at over 7kt and 1200rpm. This got us a net of .6 GPH per motor.

On the con side, it seems that most of it is a learning curve. Because of the design of the props, simply putting the motors into neutral, and the subsequent water flow over the props, causes them to flip into the reverse position and gives you a big bump and a clear slowdown for a second. The props will then windmill in reverse until you shut the motor down and put it back in gear. What we learned was that it's much easier to simply shut the motor off in gear. No bump and no slowdown.

The con side of the self pitching props is the loss of top end speed. With the fixed props we could get to 10.5kt @ 3200rpm. When the boat nears hull speed the extra drive pressure on the blades causes the pitch to flatten out, and cost us right at 1kt top end speed. Not that I care, because I'm not going anywhere that I need to motor at 10.5kt for hours on end, but if impressing your friends with over 10kt motoring speed is important to you....

Also we have a problem that appears to be particular to the combo of the Salina 48 and Autoprops. If you put the sails up and put the motors into neutral prior to shutting the motors down, not only do you get the bump and slowdown, but the windmilling in the reverse (and probably partially feathered) position causes the boat to round up uncontrollably. I believe this is from the close proximity of the propeller ahead of the undersized rudders. The big Autoprops are likely mixing the water in such a way as to destroy any and all lift generated by the rudders. I have a report from another Salina owner with the same issue. He's been working on this issue for two years and is going to confirm the "fix" of shutting the motors down in gear this week.

[Tia Bu]

I've had fixed props (two boats) and an Autoprop (one boat). While I like the Autoprop, I'm not sure I'd pay the extra money to put one on a cruising boat that already had fixed props.

A racer would be different, but for cruising? There's always something else to spend the bucks on!

[CruiserAD]

Except from the drag I also think that leaving the fixed props constantly milling while sailing will wear the saildrives unnecessarily. Putting the gear in reverse to stop the turning is explicitely not recommended by Volvo (the forces on the saildrives are too high).

I had a intense communication with the flex-o-fold reperesenatative in Denmark. Apart from being extremely repsonsive and helpful they also gave me a price for two 3-blade F-O-Fs which was app. the same price I would have to pay for one 3-blade feathering prop from another reputable company in Germany. Makes me think...

I will go and have a closer look at the F-O-F props at the BOOT in Düsseldorf in January and if that also convinces me, then it's a deal.