Variable Pitch Propeller

[slowgoesit]

Our new to us boat is a 50’ Robert Beebe designed Passagemaker. The original owner purchased and installed a Gardner 8LXB medium speed engine, which is a massive engine! He coupled that to a Hundested, 3 blade, Variable pitch (VP) propeller. The VP actuating mechanism is in line with the propshaft, aft of the gear reduction.
The use of VP allows for several benefits.

1. You can run your engine in it’s most economical RPM, while using the blade pitch to select the speed you wish to travel.
2. You can go from forward to reverse rapidly, with no need to reduce throttle, wait for engine speed to reduce, shift to neutral, then reverse, then bring up engine RPM again for reverse.
3. If, as in our case, your boat has a hydraulic bow thruster, with an engine driven hyd. pump, you can be sitting at the dock, or wherever, and utilize the bow thruster, taking advantage of full operating pressure/volume while not moving since the engine is already at rpm. The same would hold true if you had a hydraulic anchor windlass, which, sadly, we do not.

So in practice:

1. You start your main engine, and once it’s warm:
2. Shift the reduction gear into gear (it’s a standard gear reduction with both forward and reverse, but in this case, reverse is not utilized).
3. Using the VP selector, you pitch the blades, pushing forward to go forward, and pull back to go in reverse. The blade pitch varies depending on how much you push/pull the lever.

Since the prop is always rotating clockwise as viewed from astern, the boat will walk to starboard regardless of whether fwd, or rev is selected. Cross controlling using the gear reduction in reverse may be theoretically possible, but I’m not going to risk damage to the VP actuator trying it, since the VP actuator also incorporates a separate hyd pump to move the blades.

So, for normal cruise, we select an engine RPM of 1400, and pitch the blades to obtain 7.5kts through the water.

Boat weighing approximately 85k lbs, with half fuel, half full fresh water, holding tanks empty and owners stuff on board, and running the 12kw generator, we burn right on 2.4 gallons/hr which equates to 3.125 nautical miles/gallon. Not to shabby for an 85,000 lb boat!

With full fuel tanks holding 2,100 us gallons, that is 875 running hours, with a max cruise range (no reserve) of 6562 nautical miles. So, in theory, we could go from Seattle, WA to Key West, FL without refueling. Then we’d have to take out a mortgage to refuel the tanks to full!

Since the engine driven hydraulic pump is also driving the 12kw, 120v AC generator, we have all the AC power we wish underway, without having to run the separate, standalone Isuzu 4LE2 auxilary engine, which drives a hydraulic pump which provides hyd power either to the AC generator, bow thruster, or a hyd motor that provides “get home” capability in the event the main engine fails.

The Gardner engine, new in 1978, was just north of $60k. The Hundested VP prop, shaft, and actuating mechanism is currently selling for around $40k to $50k, plus shipping from England.
The boat also came with a spare blade for the propeller, but it has never been needed.

This is a unique application of engine and drive train that I have not run across before, but since the initial cost was wrapped up in the purchase price, it didn’t end up costing any more than a comparable setup.
[FONT=&quot]We do have a little more maintenance required due to the VP actuating mechanism requiring periodic oil changes. And the VP propeller requires disassembly and lubing, I believe every 2000 hours or so, which can be accomplished during scheduled haul out with minimal tools. Overall, we’re really satisfied with the setup, and look forward to many years of use![/FONT]
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[FONT=&quot]Attached pics: Gardner 8LXB, VP propeller, and controls[/FONT]
[FONT=&quot]On the controls, the left hand lever is the gear reduction engage/disengage, only neutral and forward are used. The middle lever is engine throttle, and the right hand lever is the blade pitch for neutral, fwd and rev.
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[SteveK]

Awesome

 

[DavidM]

That is an awesome propulsion system. But not to rain on your parade, it is a very expensive one and I suspect it will never make up in fuel efficiency what it costs unless you are running thousands of hours each year, and even then I doubt it.

David

 

[KnotYet]

That is an awesome propulsion system. But not to rain on your parade, it is a very expensive one and I suspect it will never make up in fuel efficiency what it costs unless you are running thousands of hours each year, and even then I doubt it.

David

Maybe not so great for the first owner but a nice bonus for the new owner!
As a 'gearhead' myself, I would gladly take on the learning curve of keeping it happy.

 

[Hippocampus]

Perfect set up for your use. Wonder if you follow temps to decide on pitch and how you do it?

 

[Comodave]

Pretty awesome. I would hate to pull out the credit card to pay for a fillup. Have a great time with her.

 

[rgano]

Thanks for the lesson on a unique system. I noted your concern about shifting the tranny into reverse - is there any concern that without a physical block that somebody could crank that lever all the way aft?

 

[Redhook98]

Thanks for the lesson on a unique system. I noted your concern about shifting the tranny into reverse - is there any concern that without a physical block that somebody could crank that lever all the way aft?

The Navy does that all the time. Emergency Crash-Back. Full Flank+ speed forward, and change the pitch to the opposite extreme. Pretty cool, when your expecting it. Since your not changing direction of the prop, I do not think it would effect much at all if it was cranked from one extreme to the other.



Good point though on lack of a stop.

 

[DDW]

The question is, why are there not more variable pitch props available? It is complicated, but need not be as complicated as the Hundested. The advantages are compelling, nearly all airplanes have them for similar reasons. Is anyone using an Autoprop on their trawler?

 

[rgano]

The Navy does that all the time. Emergency Crash-Back. Full Flank+ speed forward, and change the pitch to the opposite extreme. Pretty cool, when your expecting it. Since your not changing direction of the prop, I do not think it would effect much at all if it was cranked from one extreme to the other.



Good point though on lack of a stop.

You misunderstood the question. Go back and look at the description of the plant and the OP's concern about reversing the gear, not the prop.

 

[Redhook98]

You misunderstood the question. Go back and look at the description of the plant and the OP's concern about reversing the gear, not the prop.

Gotcha. That's what I get for not reading everything all the way through.

 

[sbman]

...

So, for normal cruise, we select an engine RPM of 1400, and pitch the blades to obtain 7.5kts through the water.

...

Do you use anything other than speed through water to set engine power levels with this drivetrain?

In aviation we use EGT, manifold vacuum, or manifold pressure (depending on the engine and equipment) to set the power level with the prop, I would imagine EGT would be appropriate for diesels.

 

[HiDHo]

I think it’s referred to as a controllable pitch prop. I seem to recall all props are variable pitch as seen in the blade twist.
The US Navy equipped gas turbine drive destroyers with controllable pitch propellers because the gas turbines only rotate in one direction and for better performance at different speeds.
On steam turbine drive ships it was a good throttleman that could close the ahead throttle and open the reverse throttle without lifting the boilers steam pressure safety valves when ordered “ emergency back “.

 

[dhays]

That sounds very cool. There would be a bit of a learning curve I imagine, but I really like the concept.


I too would wonder how the best pitch is selected. After a while, you would get really used to it, but I imagine an EGT would be the most valuable to make sure you are not overpropping your engine.


FWIW, someone mentioned an Autoprop. I had one on my sailboat and really liked it. However, its advantages and utility would be lost I think on a power boat. It really shown when motor sailing however.

 

[Ski in NC]

1400 rpm sounds high for a big Gardner. I thought most of them were around 900-1200.

 

[DDW]

FWIW, someone mentioned an Autoprop. I had one on my sailboat and really liked it. However, its advantages and utility would be lost I think on a power boat. It really shown when motor sailing however.

The feathering isn't necessary on a power boat, but its ability to self-adjust pitch might work very well.

A propeller has an unfortunate power absorption curve wrt to modern diesel engines. Especially the overly large ones installed in a lot of our trawlers. Mine spends the vast majority of its life at about 33% torque load. It has to, if it is able to achieve its RPM rating at full throttle. I think running it at 50 or 60% load would be more fuel efficient, the only way to do that is either variable gearing or a variable pitch prop. The Autoprop is designed to adjust its pitch to the same angle of attack regardless of shaft rpm. I'm not quite curious enough about it to spend the 7 or 8K it would take for the experiment, but wish someone else would!

 

[slowgoesit]

That is an awesome propulsion system. But not to rain on your parade, it is a very expensive one and I suspect it will never make up in fuel efficiency what it costs unless you are running thousands of hours each year, and even then I doubt it.

David

Maybe not so great for the first owner but a nice bonus for the new owner!
As a 'gearhead' myself, I would gladly take on the learning curve of keeping it happy.

David, KnotYet nailed it. We paid pretty much going rate for a similar boat having a Cat, or a Cummins, and a fixed pitch prop, so the money has already been spent, but the high initial costs were not passed on to us to pay! Both the Gardners, and the Hundested VP prop arrangement are still supported, and parts are readily available. They both seem to last forever if properly taken care of, and I have voluminous maintenance records since the boat was built. Oil samples were all great, the same mechanic has maintained the boat for the last 26 years. I hired him for a day to pick his brains, and the Sellers hired him to be present for the survey and sea trail to answer any questions that arose.

 

[slowgoesit]

Perfect set up for your use. Wonder if you follow temps to decide on pitch and how you do it?

400 to 450 degrees on the EGT appears to be the sweet spot for engine efficiency. The PO set the engine EGT alarm to go off at 500 degrees. Gardner says EGT is good for up to 600 degrees, so the PO was conservative, but that's okay with me.

 

[slowgoesit]

Pretty awesome. I would hate to pull out the credit card to pay for a fillup. Have a great time with her.

I don't think we would fill up completely unless it was a great deal, or we were in for some extended cruising. That said, the capacity is there if needed.

 

[slowgoesit]

Thanks for the lesson on a unique system. I noted your concern about shifting the tranny into reverse - is there any concern that without a physical block that somebody could crank that lever all the way aft?

That is a concern of mine, negative habit transfer and all that, so if there is not a physical block on shifting the gear reduction into reverse (I haven't checked yet), there soon will be!

 

[slowgoesit]

Do you use anything other than speed through water to set engine power levels with this drivetrain?

In aviation we use EGT, manifold vacuum, or manifold pressure (depending on the engine and equipment) to set the power level with the prop, I would imagine EGT would be appropriate for diesels.

Yep, I expanded on that a little in post 18. By the way, I'm fixed wing rated, helo rated, instrument/commercial, etc, etc. Also A&P.

Short answer, yes, I use EGT, no MAP on a diesel. Good question though!

 

[slowgoesit]

I think it’s referred to as a controllable pitch prop. I seem to recall all props are variable pitch as seen in the blade twist.
The US Navy equipped gas turbine drive destroyers with controllable pitch propellers because the gas turbines only rotate in one direction and for better performance at different speeds.
On steam turbine drive ships it was a good throttleman that could close the ahead throttle and open the reverse throttle without lifting the boilers steam pressure safety valves when ordered “ emergency back “.

I'm used to the term variable pitch, and that is what Hundested calls it as well. But controllable pitch prop works too.

 

[slowgoesit]

That sounds very cool. There would be a bit of a learning curve I imagine, but I really like the concept.

I too would wonder how the best pitch is selected. After a while, you would get really used to it, but I imagine an EGT would be the most valuable to make sure you are not overpropping your engine.

FWIW, someone mentioned an Autoprop. I had one on my sailboat and really liked it. However, its advantages and utility would be lost I think on a power boat. It really shown when motor sailing however.

1400 rpm sounds high for a big Gardner. I thought most of them were around 900-1200.

To address both comments, I set the rpm, then adjust pitch to speed desired using EGT to find sweet spot. For slower speeds I can reduce engine rpm to as low as 1050 rpm. That is about the minimum that the Hundested needs to provide adequate hyd pressure to actuate the VP prop.

On cruising at 1400 rpm. The maximum rpm for the 8LXB is 1500, and according to Mike, the owner of Gardner Marine in England, it is designed to operate at that rpm continuously as long as EGT of 600 degrees is not exceeded. He also said 1400 rpm, properly loaded, should result in an EGT of somewhere between 400 and 500 degrees.

 

[Irish Rambler]

The Gardner's are a cracking engine, just the sound of the starter brings back many memories for me.
Incidentally they were one of the first to use low rev high torque in trucks, along came the Swedes with Volvo, Scania etc with their high revving units at 2,800 rpm which found favour for a while but they've all gone back to Gardner's concept of low rev high torque.
Well maintained they'll see you under the sod first.
My brother has one in his boat, built in 1947 and still in regular use.

 

[sean9c]

I've shared this video before, it's a favorite. The crank he keeps turning is the control for the cpp, cranking between fwd and rev.

Years ago I helped a friend rebuild a Hundested CPP pitch adjustment mechanism, it was pretty simple and nothing was super precision, you got the feeling that it was built to last and not require a bunch of maintenance.
I look at boats for sale in Norway, the majority of small commercial fishing boats I see use a cpp.

 

[FF]

One big delight in your setup is the std gear box.

Sometimes fish boats just use the pitch adjustment as neutral, .

The hassle is the engine usually requires more RPM on morning starts till it settles down, which can mean motion . Simple enough to increase the RPM and adjust for no motion before shut down , but a surprise the first time!

 

[Hippocampus]

The original Artnauticas 58s were single engine mated to a cpp. Think the concept is long been validated and still a excellent choice in small recreational boats. Multiple vendors offer them. Dickey, alubot and others continue to put them in recreational boats. Us Americans maybe behind the curve on this.
The only downsides I can think of is it’s service point that requires a haul and god forbid you entangled the prop resulting in a sudden stop. Would think many boat bucks to fix. Not just replacing the screw. Even maxprops on sailboats are expensive to replace or repair.

 

[dannc]

...
Since the engine driven hydraulic pump is also driving the 12kw, 120v AC generator, we have all the AC power we wish underway, without having to run the separate, standalone Isuzu 4LE2 auxilary engine, which drives a hydraulic pump which provides hyd power either to the AC generator, bow thruster, or a hyd motor that provides “get home” capability in the event the main engine fails.
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Excellent information. Thank you!

Has there been any problems with the hydraulics? Failed pump, leaks, etc.

What is the brand of the hydraulic generator?

I have been considering a hydraulic generator for a variety of reasons so I am curious has to the brand and how well it has been working.

Thanks,
Dan

 

[slowgoesit]

Excellent information. Thank you!

Has there been any problems with the hydraulics? Failed pump, leaks, etc.

What is the brand of the hydraulic generator?

I have been considering a hydraulic generator for a variety of reasons so I am curious has to the brand and how well it has been working.

Thanks,
Dan

Dan, about 12 years ago, the "get home engine" was replaced with the Isuzu engine. At that time, the hydraulic motors on the get home and the main engine were also replaced, as well as the hydraulic motor on the generator. No problems related to, or experienced regarding the hydraulics so far.

Pics: On the hydraulic pump on the main engine, belt replacement for the alternator and engine driven bilge pump requires slipping the coupling to the hyd pump, so on the last belt change, the owner positioned three new belts over the shaft, and zip tied them out of the way to allow a quick belt replacement if needed. This is the type of care/due diligence that is present through out the boat and is one of the things that sold us on the boat.
Also pics of the 12kw generator and data plate. One of the down sides of having 120vac generator power available anytime the main engine was running, is that the PO never saw the need for an inverter to supply 120vac power for small loads when anchored. If he needed 120vac power, he started the Isuzu. That is one of the changes we will be making. I want to upgrade the electrical system to include lithium batteries, Victron Quartro plus 5k inverter, 50 amp shore power, and 1600 watts of solar panels. This is not a "repair", but rather an upgrade/outfit because of the manner in which we intend to use the boat.

 

[dannc]

Thank you very much for the info and the photos! That is really helpful and interesting.

The hydraulic generators I have been looking at are driven by a PTO attachment, usually on the transmission, and not engine belts like yours, not that that really matters. Just interesting. I think most of the hydraulic generators are being used in construction equipment and fire/rescue vehicles. Some of the companies have been in business for many decades, Stamford has been around for over a century!

Having hydraulics opens up other uses, as you mentioned, the windless and bow thrust, along with pumps, air compressors, etc.

Thanks,
Dan