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Old 06-02-2019, 09:49 PM   #1
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Feathering prop?

Anyone know if there is any such thing as a feathering prop for a 1.75" shaft, 25 to 26" dia? Current props are 4 bladed. I do not currently have the pitch available. Would need both a LH and RH. I am thinking of streaming one (with shaft brake) and running on one for long range efficiency.

Probably Ginormisly expensive if available, but I just wanted to know if anyone is aware of one.

I don't have a boat yet, but just checking out possibilities. Thanks.
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Old 06-02-2019, 10:38 PM   #2
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I've seen these used on big sailboats. I'm sure you can check sizing etc on their web site

http://www.maxprop.it/2014EN/index.html

I like them, because the reverse thrust is the same as the forward thrust. And the pitch is easily adjustable with set screws. Not cheap though.
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Old 06-03-2019, 12:11 AM   #3
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They were made, I don't know how small they go. It's a whole new shaft because the control is in the shaft center. I've seen 2 kinds. One uses hydraulic pressure to change the pitch with the oil flow down the shaft center, and the other has a shaft within the main shaft that moves in and out changing the pitch. It has a control box behind the trans. and can be controlled from the wheelhouse. I can't remember a brand name but they were on the web. Mostly used in small fast ships and commercial boats. Last time I looked (about 10 years ago) they were 10-20 thousand for a 36" wheel. Most don't completely feather, but just give a wide range of pitch control.

Some I saw on minesweepers were run w/o a transmission and the blades go flat for neutral.

I don't think on a yacht you'd ever save enough fuel to pay for the props.
Rolls Royce marine division is one I remember. I don't think they do small.



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Old 06-03-2019, 01:23 AM   #4
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There are plenty of feathering props in that size. One problem with most feathering props is they are not as efficient as a normal prop, because the blades are built without twist and therefore not on true pitch. They must do this or the prop will not stop turning when feathered. You may want to look into folding props instead, such as the flex-o-fold, Gori, etc. An advantage to them is they are less vulnerable to debris strike damage when folded. Still not going to be as efficient as a normal prop, but better than a feathering. Another option is the Autoprop, not sure if it goes that big but I think so.
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Old 06-03-2019, 06:43 AM   #5
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Thanks for the replies. I checked out Max Prop, but without having the exact pitch of the props I can't get a quote. I will look into it more, but it looks like any efficiency I would gain by streaming one would be lost with the loss of efficiency from the different contours of the blades, plus the cost of new shafts, etc. Thanks for all the help though!
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Old 06-03-2019, 06:48 AM   #6
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Luke has been making feathering props since the 20's or 30's

They fit a conventional shaft .

Most feathering props were created for sail boats to reduce the drag while sailing..


When Luke started many large sail boats added an engine which was frequently offset to the vessels center line.

Lukes blade areas are much higher than racing sail boats style props to move bigger boats.

Luke automatic Feathering Propellers, P. E. Luke. Full Service Boatyard ...

www.peluke.com/marine-hardware/boat-props/
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Old 06-03-2019, 07:45 AM   #7
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Decades ago Sneckies (Scandinavian motor cruisers) similar to my Albin-25 appearing at left had feathering props instead of F/N/R transmissions. The control was mechanical, manipulated by a lever through the cockpit floor. Norwegian relatives of my wife's cruised all over Europe in such a vessel.
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Old 06-03-2019, 09:28 AM   #8
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You are kidding yourself if you think you will save significant fuel by shutting down one engine and feathering/braking the other one.


Take a look at the attached graph. The Alaskan based data was done by Bob Lowe and I know he reported it correctly. FWIW he didn't find significant difference between freewheeling and braking a fixed pitch prop.


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File Type: pdf Fuel economy graph- one engine vs two.pdf (53.4 KB, 31 views)
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Old 06-03-2019, 09:58 AM   #9
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We had a Gori folding prop on our wing engine. I donít know how efficiency compares to a fixed prop, and also agree that the savings from alternating engines will be very small, and only get worse with the reduced efficiency of a folding prop.
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Old 06-03-2019, 10:28 AM   #10
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If you do the math on the reduced speed and fuel burn over time, there is not a lot of benefit. The engine would be grossly undersized as a single and the load increased exponentially. Not worth costing thousands on engine life to save 10's on fuel.

Consider load like trying to pedal a bike in the highest gear. It's not about speed, it's about resistance. A feathering prop would be insignificant compared the small single engine and the mass of the boat.
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Old 06-03-2019, 12:09 PM   #11
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Although I appreciate the input, too many responders appear to be jumping to the conclusion that I am trying to save money. That was not the object of my post. I am interested in increasing RANGE and ENDURANCE in areas that may not be conducive to regular fuel stops. I believe in making decisions based on research and facts, not on "not invented here thinking". Hence my post to which I received some very good leads and thoughts for further research! My experience with variable pitch/feathering props is from aviation, both as a pilot, and as a mechanic, rather than boats.
Regarding the fuel economy graph, although I appreciate the input, the premise behind the graph assumes FIXED pitch screws, NOT feathering screws, so it's not really relevant to the discussion as I never mentioned freewheeling a fixed pitch prop, besides freewheeling brings up an entirely different series of issues ie; is the "freewheeling" shafts transmission getting properly lubed/cooled since the engine is not running, do you need to install a shaft brake, is the coupling getting lubed, etc.
Even using the term "fuel economy" with boats this size is living in a fantasy land!
And lastly, although we are currently "boatless", we aren't totally lacking in experience with trawler ownership or experience. We're just trying to make the best purchasing decision based on wants, needs, budget, assumed cruising area/usage, etc.


Thanks again to all who responded!
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Old 06-03-2019, 12:51 PM   #12
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They do not lend themselves well to retro fitting but a CPP (controlible pitch prop) would be by far the most efficient.

Also being shut down much of the time should reduce maint.

On a new build the cost is not excessive .

An EGT gauge is required to optimize performance.

One of my pet concepts for a world cruiser would be a single shaft CPP bolted to an LST style transmission.

These mount 2 engines , either or both can power the shaft.

To me twin engines is a fine idea , but 2 exposed shafts , much unfun.
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Old 06-03-2019, 01:05 PM   #13
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There are folding propellers and then there are feathering or variable pitch propellers.

The variable pitch props are the ones mentioned that sometimes have the hollow shaft for the control rod that changes pitch. These are often found on vessels that use fixed RPM engines as the propellers are used as throttles and gears. Folding prop, which as mentioned are common on sailboats and on wing engines, are simpler, provide less drag but are also less efficient.

I agree with many of the comments already made, the lost efficiency from the inherent design of a variable geometry prop will most probably never be made up with any fuel savings (range) from switching back and forth on engines. You might extend range some by using fixed blade props and shaft brakes. BTW some marine gears are fine with freewheeling, others are not.

Also these type (variable/feathering) props are commonly found on much larger vessel than one that would use a 1.75 shaft so sourcing may be difficult.

The airplane analogy, like a P3 on ASW patrol extending time aloft by shutting down engines just doesn't work well in a boat.

One other thing to note is that for expedition use these variable geometry props are not as robust as a regular fixed blade prop. They seldom are as smooth and will often create more vibration or structure borne noise than a fixed blade prop.

There are also gear boxes made, usually from industrial parts, that combine 2 engines into 1 shaft. These are often seen on OSV's, again, much larger vessels than ours.

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Old 06-03-2019, 03:26 PM   #14
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OK, I take your point that the graph I posted wasn't really on point. So think about this: a sailboat usually picks up a half a knot under sail when switching from a locked fixed prop to a feathering prop.

That translates into a diesel engine driving the boat picking up 10-15% in fuel mileage.

YMMV.

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Old 06-04-2019, 07:17 AM   #15
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"That translates into a diesel engine driving the boat picking up 10-15% in fuel mileage."

Hardly worth contemplating on a cruiser that burns 2 or 3 GPH .

A 10 hour run would save 2 to 4 GPD , might be a long time to save the prop cost.

Now if the fuel burn is measured in hundreds of GPH or tons per day savings would be different.
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Old 06-04-2019, 08:51 AM   #16
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"That translates into a diesel engine driving the boat picking up 10-15% in fuel mileage."

Hardly worth contemplating on a cruiser that burns 2 or 3 GPH .

A 10 hour run would save 2 to 4 GPD , might be a long time to save the prop cost.

Now if the fuel burn is measured in hundreds of GPH or tons per day savings would be different.
Right, and if 2-4 GPD is going to make a critical difference during an voyage then you're perhaps in the wrong kind of boat for the trip.

It's laudable to plan for ideal situations/efficiencies. But it's often a fool's errand to get hung up on "the numbers" or other specifics versus finding the right boat overall.

There is no perfect boat. But there are ones with imperfections that will make ownership more annoying than others might. It's sometimes hard to see this 'forest for the trees'.

Fixating on efficient/range when you're really never going to be in situations that are ever going to require it is one example. Or serviceability factors when you're not going to the one doing the work. Sure, on paper lots of things are arguably important. But none of them will matter if the boat doesn't provide and all-around enjoyable experience.
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Old 06-04-2019, 09:36 AM   #17
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We used to cruise on one engine when we need extra range and it made a significant difference. We went from 7 knots on two engines at 1200 RPM to 6 knots on one engine at 1200 RPM. Fuel flow from 12 LPH to 6.5 LPH.



The WOT for our engines was 3000 RPM so a load was not an issue at all and our transmissions did not require the engine to be running while free wheeling.


We used to alternate the engines about every 4 hours to keep the operating hours and wear the same. Did hundreds of hours like that.
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Old 06-04-2019, 10:12 AM   #18
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We used to cruise on one engine when we need extra range and it made a significant difference. We went from 7 knots on two engines at 1200 RPM to 6 knots on one engine at 1200 RPM. Fuel flow from 12 LPH to 6.5 LPH.



The WOT for our engines was 3000 RPM so a load was not an issue at all and our transmissions did not require the engine to be running while free wheeling.


We used to alternate the engines about every 4 hours to keep the operating hours and wear the same. Did hundreds of hours like that.


Iíll wager that 90% or more of your fuel savings were a result of slowing down from 7 Kts to 6 Kts

This is a very common misinterpretation of the fuel savings, or misattribution of the cause of the fuel savings.
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Old 06-04-2019, 10:33 AM   #19
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Take a look at the Autoprop. This is a 3 blade with true pitch, the blades are arranged to adjust their pitch by themselves, due to the offset in the pivot point. They will change their pitch with rpm or load. If you lock the shaft they will feather. For what you are trying to do they might be the solution.
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Old 06-04-2019, 11:23 AM   #20
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Iíll wager that 90% or more of your fuel savings were a result of slowing down from 7 Kts to 6 Kts

This is a very common misinterpretation of the fuel savings, or misattribution of the cause of the fuel savings.
With one engine down for a whole summer, I kept rough track of fuel consumption on a single. It was down to close to exactly 1/2 of my usual MPG on twins at 8 knots, running on a single at 6 knots. The single engine was never run at increased throttle, so I expect the fuel burn on that engine to be the same as before losing the twin.

I would expect, though I haven't tested the theory out, to be down to below 1/2 of my 8 knot consumption by slowing to 6 knots, though still running on two engines.

With the drag of a non engaged prop and the inefficiency of pushing the boat at an angle, correcting with the rudders, I would expect running on one engine to be less efficient than on two.
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