Folding / Feathering Props

Originally Posted by senormechanico

Hugosalt,

I've got a 2 blade Gori which I'm thinking of replacing. It works fine, but the vibration I get during motoring is really depressing. The shaft is straight, the motor mounts and alignment are fine.

Maybe I'm all wet, but I suspect it's because of the straight edges on the blades causing pressure pulses on the hull.

Flexofold is on my list as is the Varifold, as both of them have rounded blade design.

What is your experience with the Flexofold regarding vibration, and what did you replace?


Steve B.

Sounds like you need a careful evaluation before you pin your hopes on a different prop shape.

Before I'd blame the shape of the edges of the prop, do you know what the tip clearance between the prop and hull is? If too small that would be a prime suspect in annoying vibration.

You might be better off going with a slightly smaller diameter, 3 blade, prop.

[Alan Wheeler]

Most of us don't have saildrives and so our props are held at a 10-25 degree angle to the flow.

I assume you mean the down angle of the shaft. So how does affect the drag??

2...sails faster
3...points slightly higher (bonus) than with fixed prop
4...motors better/less rpms,no problem in reverse/stop
5...no maint. or maint issuses

So how does the prop folding allow you to point Higher??

Can not aggree with comment No.4 though. I have heard this so often with self pitching props. It is simply worng to ahve this happen. I can not stress enouhg, the Motor MUST be able to rev to it's Max Continuous RPM or within 10% of it. To have the engine run at lower RPM and achieving hull speed is bad new's for the engine and results in poor handling of the boat in tight places like a Marina.

And I am not so sure about No.5 either, but seeing as I do not have one, I can not comment apart from, the more complex an item, the more likely for something to go wrong at sometime.

[senormechanico]

hugosalt,
I'm not sure of the clearance measurement, but I'll put the boat on my grid in the next few weeks for a quick bottom slosh. I will definitely measure all the clearances then.
Steve B.

Originally Posted by Alan Wheeler

I assume you mean the down angle of the shaft. So how does affect the drag??


So how does the prop folding allow you to point Higher??

Can not aggree with comment No.4 though. I have heard this so often with self pitching props. It is simply worng to ahve this happen. I can not stress enouhg, the Motor MUST be able to rev to it's Max Continuous RPM or within 10% of it. To have the engine run at lower RPM and achieving hull speed is bad new's for the engine and results in poor handling of the boat in tight places like a Marina.

And I am not so sure about No.5 either, but seeing as I do not have one, I can not comment apart from, the more complex an item, the more likely for something to go wrong at sometime.

Alan,

It's no surprise to you I'm sure, that people switch from one type of prop to another and they credit the new "TYPE" prop with all kinds of improvements, when they actually had the completely the wrong sized prop in the first place!

Shaft angle does have an effect on the drag of a feathered prop. With an angled shaft the blades can not all feather to fully slipstream. Drag is certainly nowhere near a fixed prop, but, at least in the lab, it would measure out as higher that a shaft in full line with the flow. Folding props also show a higher drag on an angled shaft, because they project a larger area into the flow, but it is a smaller number. But we are talking small fractions of very small numbers here. More suited to the salesman than the cruising sailor.

When I switched fro a 2 bladed fixed to a 3 blade feathering, almost all of the improvements in motoring performance I found had nothing to do with feathering, but the three blade design, carefully pitched. Sailing performance and reverse thrust are the two things that I can credit the feathering design with. But pointing higher? I was wondering about that myself.

Bill

[ireaney]

Anybody tried or had any experience with the Autostream feathering props, they seem to get good write ups, made of SS and supposed to be very good!!!

[Hubec]

Alan, First I'll reply to your comment on my "angle of flow" point; Anytime you see an ad for a feathering/pitching prop they show a pic of the prop in sail configuration with the camera directly inline with the prop shaft. This is supposed to highlight how little frontal area is available to obstruct the flow. My point was that in the case of a shaft drive boat the flow isn't in line with the shaft, therefore there is more of an obstruction than you might think. I readily admit that this is a very small point, I just wanted to bring it to people's attention, as I suspect a folding prop suffers less from this real-world-reality than a feathering/pitching one.

I also have to defend hugosalt's point #4, as it's a big part of the reason I just bought a folding prop (Flex-O-Fold) for my Catalina 350. Unfortunately Catalina sells the 350 with an undersized fixed prop, and so in my case the engine is never producing anywhere near 100% power and the boat can't get to hull speed under engine alone. You might now say; "Well just get a properly sized fixed prop!" Okay, but that would further comprimise my sailing performance. Of course this is Catalina's excuse for the small prop in the first place.

Oh, and while I'm at it I believe the "pointing higher" comment referred to the fact that anytime you increase headway, with no increase of leeway your track made good will point higher. I personally doubt this would be an observable difference but it will certainly help (a very little bit).

[The Mons]

We have had an Autostream 3 blade feathering prop for three months.

So far, we are very happy with the increase in performance with the new prop. The other benefit is that the shaft does not rotate under sail. This reduces wear on the cutlass bearing and also make much less noise.

We first thought that we would have to manually stop the shaft or go into reverse to get the prop to feather. As it turns out the prop seems to feather itself when the shaft is not under power.

Reverse is very effective.

We don't know how many anodes it eats through yet.

The only problem that we have had with the prop is that at certain RPM mid 1500 to 2000 ranges when the boat is building speed, the prop makes a lot of noise. I suspect that this is due to the flat blades and wash being thrown against the bottom of the hull.

[hugosalt]

Where to start!

Wheels,
I really don't know how the folding prop allows me to point "slightly higher". I'd like to think Hubec is on to something...What I do know is that after sailing the same boat
for thousands of miles for over 20 years, all else being equal, the boat points
"slightly higher" with the new prop... Oh almost forgot!... Quote from Kiwi Props:
"Our experience hard on the wind in 15 knots, boat will point 10 degrees higher over
fixed prop". Now I don't know if I am buying 10 degrees but I might give them
the benefit of the doubt of say maybe... pointing "slightly higher".
Addressing point 4...Before new prop, boat was under propped (indicated in original post, new prop 15/11 old 14/9) had to push motor well beyond normal 85-90% rpms to try to approach hull speed...now can achieve hull speed with proper 85-90%
rpms ...hence bringing us back to point 4..".motors better/less rpms" granted this time around with proper (if you will) explaination).
Addressing point 5..."No maint/maint issuses "...the prop is simple basic, not the least
bit complicated. Not even necessary to grease as required by some others!
must qualify... maint comments are after only 1 year, however after spending a lifetime 40 + years of owning, moving, operating, buying, selling, building, rebuilding, small delicate and complicated heavy equipement I might go out on a limb here and
stand by "No maint/maint issuses.
pause ...while I climb down off my soap box...

Totem... would like to hear from you after your install and use of F-O-F prop for a
while to see how your research and conclusions hold up...good luck!
"very low drag while sailing
good motoring performance
mechanicly very simple
making it easy to maintain"

Hubec...good luck with your prop, let us know how it works out
and thanks for your forward thinking and humanity!

[svTOTEM]

hugosalt – I will report back this summer on how the F-O-F works out.

Some of the performance and maintenance comments surprised me. No one prop is right for all boats; there are just too many variables. I do not see this as comparison of subtleties; as in a 100th of knot performance improvement. Instead it’s about what works best for the particular boat and cruising requirement. In the NW, most sailors I know have a MAX prop. It’s a fine prop; however I know a few cruisers that have had problems with them. One in particular, a Stevens 47 like mine, somehow the pitch setting changed and the blades would jam on the zinc - while cruising in Mexico. They had to haul the boat to fix it.

Flex-O-Fold is simpler mechanically. I don’t know of anything on a boat that cannot fail, but less chance of failure – even if only slightly less – works for me as I close in on departing for a 5 year cruise. A fixed prop is too much drag. A feathering prop has a bigger footprint to hit objects when sailing. Maybe a folding prop doesn’t work as well in close maneuvering, although I haven’t spoken to a F-O-F owner that has problems. And I like to be anchored out…

[fstbttms]

Originally Posted by svTOTEM

I know a few cruisers that have had problems with them. One in particular, a Stevens 47 like mine, somehow the pitch setting changed and the blades would jam on the zinc - while cruising in Mexico. They had to haul the boat to fix it.

It is virtually impossible for the pitch settings to change accidentally on any Max Prop. Further, even if this did somehow occur, the blades would not come into contact with the zinc. The blades rotate through the same space regardless of pitch.

What most likely happend is the wrong Max Prop zinc was installed. Max Prop changed the shape of the prop hub and the zincs their props use several years ago. Newer Max Props require a round-base zinc as opposed to the older, triangular-base zincs. Older Max Props can use either zinc. If the old-style triagular-base zinc is installed on a newer Max Prop, the blades will indeed come into with contact the zinc and will not rotate properly.

[svTOTEM]

I only know what I was told by the couple that owns the stevens 47 that had the problems. Oh, and they are both Boeing engineers, so safe to say reasonably mechanical. And they have a lot of cruising miles under the keel. Maybe there full of crap, but I'm inclined to believe them

[fstbttms]

Originally Posted by svTOTEM

Maybe there full of crap, but I'm inclined to believe them

OK, again, it is not possible for the blades to come into contact with the zinc due to a change in pitch. Simply not possible. I don't mean that it is unlikely to happen, I mean it is impossible. The prop simply does not work that way. So somebody is mistaken. And it ain't me!

[tburgess]

Hey folks, I have a 3 blade folder prop (gori) and would like to hear how other's with folding props (gori or other) manage "freewheeling" while sailing. On my last boat I had a Max prop (feathering). I was able to feather the prop by shutting the engine down in forward. This alloiwed me to avoid locking my transmission in reverse. The last boat was a mono hull with a shaft, the new boat is a multi with saildrives. Locking my engines in reverse folds the props and stops freewheeling but the Yanmars get stuck in reverse even though I shift back to neutral. This causes starting problems after we sail for a while. I confirmed this starting problem (transmission locked in reverse) with Mack Boring but they are not offering any good alternatives to help fold the props.

[senormechanico]

tburgess,

How about hitting reverse, then going right back to neutral? Does it still lock up?
My Volvo md2020 doesn't ever have a problem with that scenario.

Steve B.

[ggladd]

I put the j prop on my LaFitte 44 last year and have been very pleased with the performance.