Hundested CPP Controllable Pitch Propellor

[slowgoesit]

We've have had several people ask us questions about our CPP (Controllable Pitch Propeller), so instead of hi-jacking someone else's thread, I started a new thread that hopefully explains ours, as we understand it. Feel free to comment if I have something wrong, or ask questions if something is unclear, or whatever. Enjoy!

Our boat, a 50' Passagemaker, designed by Robert Beebe, or Voyaging Under Power, was built with a Hundested Controllable Pitch Propeller, or CPP. Also known as a Variable Pitched Propeller. It is a 36”, 3 bladed propeller that changes pitch based on the pitch selected at the helm station.

This is a feature that is kind of out of its class for a 50’ pleasure boat due to initial purchase cost and expense of installation, but since it was already installed in the boat when we bought her, it was a “sunk cost”.

Advantages of a CPP over a fixed pitch propeller is that the engine can be run at a constant rpm, in it’s “sweet spot”, and the propeller pitched for forward and reverse movement.

Movement of the propeller blades is accomplished with the use of a hydraulic blade pitch changing transmission which is located on the main drive shaft between the main transmission (attached to the engine), and the rear stuffing box. Hydraulic pressure is generated from an internal pump using the rotation of the shaft to provide pressure. The Hundested manual states that a minimum of 500 shaft rpm is required to operate the hydraulic pump.

Since our main transmission has a 2:1 gear reduction, then the main engine rpm must be greater than or equal to 1000 rpm.

Our main engine is a Gardner 8LXB, a British made, inline 8 cylinder, medium speed engine that is rated at 173 hp at 1500 rpm. We generally cruise between 1050 and 1100 rpm, or about 73% or rated rpm.

The procedure for use is:

• Engine start and warm up like any other engine
• There are three levers at helm station, left is main transmission shift lever (only neutral and fwd are used)
• Middle lever is engine throttle
• Right lever is prop pitch
• Reduce throttle to idle (about 400 to 500 rpm)
• Ensure pitch lever (right hand lever) is in neutral pitch
• Shift transmission shift into forward
• Adjust throttle for desired rpm, in our case, somewhere between 1050 and 1100 rpm
• Adjust pitch lever for desired thrust. lever is labeled 0 (neutral) then push forward 1 to 5 positive pitch (forward), and pull back -1 - -5 negative pitch (reverse). Fuel control unit will adjust fuel to maintain the selected rpm.
• If slow speed maneuvering, pitch somewhere between 1 and 2
• If cruising, pitch around +4, +/- 1, but generally using the EGT (Exhaust Gas Temperature), also called a pyrometer, to the desired temp, usually around 600 to 620 degrees F, which will give us a through the water speed of between 6.5 and 8 knots depending on boat loading. If the boat is loaded with fuel fuel (2000 gallons, or 14,100 lbs of diesel), and provisions for an extended trip, say over 3,000 nm, it will be slower than if we have less fuel on board.

Another feature of the CPP is that since the propeller is turning the same direction whether you are going ahead, or astern, you can go from full pitch forward to full pitch aft in about 3 seconds, so it's great for panic stops, to avoid a collision or what not. No need to reduce engine rpm, shift into neutral, then reverse, then increase engine rpm again. Just pull back the pitch lever! But you'd better be holding on, because it WILL stop the boat pretty quickly!

Some idiosyncrasies with our CPP:

We run up to full cruise rpm before leaving the dock. Also, when coming into the dock. Sounds a bit weird to onlookers, who expect the boat to continue moving, or begin moving when the engine rpm is increased.
Our bow thruster is hydraulic, run off of a main engine pto, so at cruise rpm, it is VERY impressive, and can be used for unlimited time without overheating, or running batteries down.

negative: Since the prop is always turning in the same direction, even in neutral, the stern of the boat ONLY prop walks to starboard.

We have had the boat for almost 5 years now, and have cruised about 11,000 nautical miles, about 1,700 engine hours, most of which was PNW to Alaska and back to PNW, and PNW down the Pacific Coast to the Panama Canal and up to Florida.

During the majority of that time, the boat weighed in at between 80,000 and 87,000 lbs all in.

In that time we have burned just over 4,000 gallons, for a burn rate of about 2.4 gallons/hour, and a “mileage” of about 2.71 nautical miles/gallon. * Note: fuel burn includes fuel used for generator and diesel fired hydronic heat as well, so actual fuel burn just for propulsion is somewhat (slighlty) less, and mpg slightly more.

There is a definite learning curve associated with a CPP. Three levers instead of two, propeller walk, etc.

We have been extremely happy with the CPP, and with the combination engine/CPP performance.

 

[DDW]

Questions:

Do you have reverse in the transmission, and if so can it be used with the CPP? Maybe the CPP transmission can't be run in reverse? If you could reverse, you could have the prop walk the direction you wanted. Dashew used to tout this as an advantage of the Hundested.

With the Gardiner, pretty hard to get instantaneous numbers, but have you ever tested the fuel economy effect of the CPP in a controlled way? The only methodical test I've seen on a trawler with variable pitch is the one done by a Great Harbor owner, using Autoprops vs fixed pitch. The difference in cruise economy was significant, though the payback would be decades. However the range improvement pays back immediately.

 

[slowgoesit]

The main transmission is a fully functional transmission with fwd and reverse, but the reverse is locked out with a bar on the shifter at the transmission. I had considered reversing for prop walk to port, but according to Hundested the hydraulic pump in the Hundested transmission is designed for one direction input.

I have no way of comparing fuel economy with a fixed pitch prop as Beebe designs were one off, no two boats identical, or even very similar, and I've never run into another with a Gardner engine.

We consider the current setup to be pretty economical, as the word is used with boats at any rate, and although it might be nice to know exactly how much (if any) gains in efficiency the Hundested CPP provides, I have no way of comparing it.

 

[mvweebles]

Unfair question but I'll ask anyway: If you had a choice between two otherwise identical boats, would you go with the one with CPP, or the one with conventional F/R direct drive reduction?

Peter

 

[slowgoesit]

CPP, hands down!

 

[Comodave]

Sounds neat but hate to think what a new system would cost.

 

[Jeff F]

Thanks for the explanation. So what happens at < 1000 RPM? Do the blades stay in the flat (neutral) orientation until there is sufficient hydraulic pressure to increase pitch?

 

[slowgoesit]

Thanks for the explanation. So what happens at < 1000 RPM? Do the blades stay in the flat (neutral) orientation until there is sufficient hydraulic pressure to increase pitch?

Jeff, I don't know how the CPP could react below 1000 rpm, and I have no desire to operate outside of the parameters of the manufacturers instructions! It might be nice to know just for kicks, but not if it could possibly cause damage to the CPP or transmission.

 

[Jeff F]

Gotcha. I reread your process, and had a look at the manufacturer's web site. I get now how it works. I've looked at Hundested props out of the water, but didn't understand the pitch control unit.

My confusion was in thinking that hydraulic pressure is required for the prop to operate. I see now that it's required for pitch adjustment. Once set at a given pitch no pressure is required.

I can understand recommendations against making pitch changes at less than 1000 rpm. Maybe I'm missing something, but why not go to max pitch at 1100 rpm and then adjust throttle down to get desired EGT/boat speed at less than 1000 rpm?

 

[PierreR]

My last boat that I built was a 26' trawler with a SABB H2 (18hp @ 1,900 rpm) and SABB 19" 2 blade CCP. The boat was a full displacement heavy weight at 8,700# with 750# keel ballast and paravane stabilizers. Cruise was between 950 rpm and 1,600 rpm CCP was mechanically controlled by a lever and load was set with an exhaust gas pyrometer. There was no reverse gear and you could go from full forward pitch to full reverse pitch in about a second at not more than 1/2 throttle. Gear case was 2:1 reduction with forward and neutral.

At 950 rpm she sounded like the African Queen and delivered 5 knots at 14 nmpg if, you were not making electricity from the 150 amp alternator. To make electricity you, had to be as much as 1,350 rpm for the same speed and 8nmpg. The electric coffee pot sucked away 6mpg.
Fuel was 80 gal, water 70 gal and holding tank 20 gal.
The drive train was expensive but more than made up for it in fuel mileage. I would be glad to have a CCP again with all of it's grease points and fuss.

 

[Bmarler]

Interesting topic. I get the advantages using of using this in open water. Properly loading the engine at all speeds is possible, and is the major selling point of the system I’d guess.
But close quarters maneuvering and docking seems like it would take some getting used to. I spend most of my time in neutral, no shaft rotation. With a cpp the shaft is rotating at speed the entire time, making prop walk. I’m sure you get used to it, but like anything unusual it takes some practice.

 

[slowgoesit]

Gotcha. I reread your process, and had a look at the manufacturer's web site. I get now how it works. I've looked at Hundested props out of the water, but didn't understand the pitch control unit.

My confusion was in thinking that hydraulic pressure is required for the prop to operate. I see now that it's required for pitch adjustment. Once set at a given pitch no pressure is required.

I can understand recommendations against making pitch changes at less than 1000 rpm. Maybe I'm missing something, but why not go to max pitch at 1100 rpm and then adjust throttle down to get desired EGT/boat speed at less than 1000 rpm?

Jeff, I suppose it would technically be possible to do what are suggesting, but we're perfectly comfortable with running at 1050 to 1100 rpm. At that speed, the engine sound is not uncomfortable at all, and I would rather run the engine at 73% rated rpm than at say 50%. Just not a lot of interest in experimenting with other settings when what we do has been done by us, and the previous owner for the last 37 years with good results.
besides, why add another necessary step (increasing engine throttle to above 1000 each and every time we wished to adjust propeller pitch?)

 

[slowgoesit]

Interesting topic. I get the advantages using of using this in open water. Properly loading the engine at all speeds is possible, and is the major selling point of the system I’d guess.
But close quarters maneuvering and docking seems like it would take some getting used to. I spend most of my time in neutral, no shaft rotation. With a cpp the shaft is rotating at speed the entire time, making prop walk. I’m sure you get used to it, but like anything unusual it takes some practice.

Brian,
There was definitely a learning curve associated with the CPP. This is the first boat I've had with one, although I'm very familiar with variable pitch propellers in aircraft.
Lots of "firsts" for us with this boat. For instance, this is the first boat we've owned that had a bow thruster. I've always had single engine boats, and never owned a boat with a bow thruster before. We did just fine without bow thrusters, never realizing they were necessary for safe operation of my boat! The things we learn as we get older. . . That said, our bow thruster, especially since it is hydraulic, is really handy!
Other "firsts" include:

• first boat with a washer/dryer . . . BONUS!
• first boat with a water maker
• first boat with LiFePO4 batteries
• first boat with solar
• first boat with ice maker
• first boat that can hold 2000 gallons of diesel
• first boat with power winch for dingy raising/lowering, total game changer!
• first boat with stabilizers (paravanes)
• first boat with radar

The list goes on. Needless to say, we feel spoiled when we go cruising!

 

[Jeff F]

Jeff, I suppose it would technically be possible to do what are suggesting, but we're perfectly comfortable with running at 1050 to 1100 rpm. At that speed, the engine sound is not uncomfortable at all, and I would rather run the engine at 73% rated rpm than at say 50%.

Hmm. Compare fuel consumption to max rated capacity for the engine. Not to argue, but I have a hard time believing that Gardner would suggest that this high rpm is needed to support a constant load of < 40 HP.

I've always thought that one of the big advantages of a CPP was reducing engine RPMs for low load operation. It surprises me that this unit hasn't been used to achieve those goals

 

[slowgoesit]

Hmm. Compare fuel consumption to max rated capacity for the engine. Not to argue, but I have a hard time believing that Gardner would suggest that this high rpm is needed to support a constant load of < 40 HP.

I've always thought that one of the big advantages of a CPP was reducing engine RPMs for low load operation. It surprises me that this unit hasn't been used to achieve those goals

At a cruising weight of between 78,000 and 90,000 lbs, at 6.5 to 7.5 kts, 73% rated engine RPM, and abut 75% pitch on the CPP, I suspect we using more than <40 hp to move our boat, but I could be wrong.

 

[Jeff F]

At a cruising weight of between 78,000 and 90,000 lbs, at 6.5 to 7.5 kts, 73% rated engine RPM, and abut 75% pitch on the CPP, I suspect we using more than <40 hp to move our boat, but I could be wrong.

You get a very good idea from fuel consumption 2.4 gph is probably very close to 40 HP.

 

[SarahSeed]

We've have had several people ask us questions about our CPP (Controllable Pitch Propeller), so instead of hi-jacking someone else's thread, I started a new thread that hopefully explains ours, as we understand it. Feel free to comment if I have something wrong, or ask questions if something is unclear, or whatever. Enjoy!

Our boat, a 50' Passagemaker, designed by Robert Beebe, or Voyaging Under Power, was built with a Hundested Controllable Pitch Propeller, or CPP. Also known as a Variable Pitched Propeller. It is a 36”, 3 bladed propeller that changes pitch based on the pitch selected at the helm station.

This is a feature that is kind of out of its class for a 50’ pleasure boat due to initial purchase cost and expense of installation, but since it was already installed in the boat when we bought her, it was a “sunk cost”.

Advantages of a CPP over a fixed pitch propeller is that the engine can be run at a constant rpm, in it’s “sweet spot”, and the propeller pitched for forward and reverse movement.

Movement of the propeller blades is accomplished with the use of a hydraulic blade pitch changing transmission which is located on the main drive shaft between the main transmission (attached to the engine), and the rear stuffing box. Hydraulic pressure is generated from an internal pump using the rotation of the shaft to provide pressure. The Hundested manual states that a minimum of 500 shaft rpm is required to operate the hydraulic pump.

Since our main transmission has a 2:1 gear reduction, then the main engine rpm must be greater than or equal to 1000 rpm.

Our main engine is a Gardner 8LXB, a British made, inline 8 cylinder, medium speed engine that is rated at 173 hp at 1500 rpm. We generally cruise between 1050 and 1100 rpm, or about 73% or rated rpm.

The procedure for use is:

• Engine start and warm up like any other engine
• There are three levers at helm station, left is main transmission shift lever (only neutral and fwd are used)
• Middle lever is engine throttle
• Right lever is prop pitch
• Reduce throttle to idle (about 400 to 500 rpm)
• Ensure pitch lever (right hand lever) is in neutral pitch
• Shift transmission shift into forward
• Adjust throttle for desired rpm, in our case, somewhere between 1050 and 1100 rpm
• Adjust pitch lever for desired thrust. lever is labeled 0 (neutral) then push forward 1 to 5 positive pitch (forward), and pull back -1 - -5 negative pitch (reverse). Fuel control unit will adjust fuel to maintain the selected rpm.
• If slow speed maneuvering, pitch somewhere between 1 and 2
• If cruising, pitch around +4, +/- 1, but generally using the EGT (Exhaust Gas Temperature), also called a pyrometer, to the desired temp, usually around 600 to 620 degrees F, which will give us a through the water speed of between 6.5 and 8 knots depending on boat loading. If the boat is loaded with fuel fuel (2000 gallons, or 14,100 lbs of diesel), and provisions for an extended trip, say over 3,000 nm, it will be slower than if we have less fuel on board.

Another feature of the CPP is that since the propeller is turning the same direction whether you are going ahead, or astern, you can go from full pitch forward to full pitch aft in about 3 seconds, so it's great for panic stops, to avoid a collision or what not. No need to reduce engine rpm, shift into neutral, then reverse, then increase engine rpm again. Just pull back the pitch lever! But you'd better be holding on, because it WILL stop the boat pretty quickly!

Some idiosyncrasies with our CPP:

We run up to full cruise rpm before leaving the dock. Also, when coming into the dock. Sounds a bit weird to onlookers, who expect the boat to continue moving, or begin moving when the engine rpm is increased.
Our bow thruster is hydraulic, run off of a main engine pto, so at cruise rpm, it is VERY impressive, and can be used for unlimited time without overheating, or running batteries down.

negative: Since the prop is always turning in the same direction, even in neutral, the stern of the boat ONLY prop walks to starboard.

We have had the boat for almost 5 years now, and have cruised about 11,000 nautical miles, about 1,700 engine hours, most of which was PNW to Alaska and back to PNW, and PNW down the Pacific Coast to the Panama Canal and up to Florida.

During the majority of that time, the boat weighed in at between 80,000 and 87,000 lbs all in.

In that time we have burned just over 4,000 gallons, for a burn rate of about 2.4 gallons/hour, and a “mileage” of about 2.71 nautical miles/gallon. * Note: fuel burn includes fuel used for generator and diesel fired hydronic heat as well, so actual fuel burn just for propulsion is somewhat (slighlty) less, and mpg slightly more.

There is a definite learning curve associated with a CPP. Three levers instead of two, propeller walk, etc.

We have been extremely happy with the CPP, and with the combination engine/CPP performance.

Really appreciate you breaking down the CPP operation and quirks -super helpful for anyone considering one. Sounds like it’s been a solid setup for your cruising.

 

[PierreR]

Interesting topic. I get the advantages using of using this in open water. Properly loading the engine at all speeds is possible, and is the major selling point of the system I’d guess.
But close quarters maneuvering and docking seems like it would take some getting used to. I spend most of my time in neutral, no shaft rotation. With a cpp the shaft is rotating at speed the entire time, making prop walk. I’m sure you get used to it, but like anything unusual it takes some practice.

When the prop is in zero pitch it is not creating any prop walk. With the bow thruster I could walk the boat straight sideways. By quick backing and then forward thrust on the rudder.
Not so with my present twin engine boat

 

[rslifkin]

You get a very good idea from fuel consumption 2.4 gph is probably very close to 40 HP.

Those Gardners are particularly efficient, up there with the better modern diesels typically used in recreational boats. I wouldn't be surprised if 2.4 gph on that engine is 45+ HP (but definitely not more than 50).

 

[PierreR]

Those Gardners are particularly efficient, up there with the better modern diesels typically used in recreational boats. I wouldn't be surprised if 2.4 gph on that engine is 45+ HP (but definitely not more than 50).

I don't remember Gardner diesels being particularly fuel efficient but the were rugged, slow turning with lots of torque so you could run a larger diameter more efficient propeller and get the fuel milage with them.

 

[rslifkin]

I don't remember Gardner diesels being particularly fuel efficient but the were rugged, slow turning with lots of torque so you could run a larger diameter more efficient propeller and get the fuel milage with them.

I did some digging and found an old post where some information on this had been compiled. It looks like the 175hp Gardner 8LXB is spec-ed to burn 8.4 gal/hr at max output, which is 20.8 hp-hr per gallon. That's right up there with the more efficient modern turbodiesels. A lot only manage 19 - 20 hp-hr per gallon, and something like a 2 stroke Detroit can be as bad as 16 - 17 hp-hr per gallon (and most gas engines will be down around 10 - 12 hp-hr per gallon).

Big, slow turning engines like the Gardner can be very efficient, although being big and naturally aspirated, I'd expect it suffers a little more efficiency-wise under light loads than a smaller turbodiesel would. But it's still going to be at least competitive with modern engines in terms of fuel burn.

 

[slowgoesit]

Kurtis, when at flat, or neutral pitch, and cruise rpm, the boat stern still prop walks to starboard, just not as much as with some pitch engaged (either fwd, or reverse).
I also have to agree with rslifkin on fuel economy. Whether it's the Gardner, or the Hundested CPP, or a combination of the two, I think 2.7 nmpg at 6.5 yo 7.5 kts for a boat that averages around 85,000 lbs is pretty darned good!
Our Gardner is the 8LXB, an inline 8 cylinder engine. In some respects, our boat would have done just fine with the 6LXB. I know of at least one other Beebe similar to ours that has a 6LXB and has cruised extensively. Besides, it would have given us about 18" more space fore/aft in the engine room!

 

[PierreR]

Kurtis, when at flat, or neutral pitch, and cruise rpm, the boat stern still prop walks to starboard, just not as much as with some pitch engaged (either fwd, or reverse).

I kinda forget that my engine/ prop installation had very little down angle. Probably less than 5 degrees. The angle of the shaft and prop to the water line is a huge part of prop walk. I also had a two blade propeller.

 

[slowgoesit]

I did some digging and found an old post where some information on this had been compiled. It looks like the 175hp Gardner 8LXB is spec-ed to burn 8.4 gal/hr at max output, which is 20.8 hp-hr per gallon. That's right up there with the more efficient modern turbodiesels. A lot only manage 19 - 20 hp-hr per gallon, and something like a 2 stroke Detroit can be as bad as 16 - 17 hp-hr per gallon (and most gas engines will be down around 10 - 12 hp-hr per gallon).

Big, slow turning engines like the Gardner can be very efficient, although being big and naturally aspirated, I'd expect it suffers a little more efficiency-wise under light loads than a smaller turbodiesel would. But it's still going to be at least competitive with modern engines in terms of fuel burn.

So, 2.4gph/8.4gph x 173hp gives us just under 50 hp being produced at 1050 to 1100 rpm. That sounds about right. Our engine design is rated at 175hp at 1500 rpm, but the data plate on the engine states 173hp at 1500, so I am assuming 173hp is a dyno reading for that specific engine. The engine was built in 1978, was shipped to Hong Kong, then was installed new in our boat in the Philippines sometime during the 1978-1982 build. The engine currently has about 7,300 hours on it. Time is not exact because there was a 2 year period from 1987 to 1989 when the hour meter was not working, and the previous owners estimated from speaking to the sellers that it was used about 500 hours during that time. We purchased her with estimated 5,500 hours, and we've put about 1,800 hours on the boat since we purchased her in January of 2021.
Except for fluid changes, anodes in the cooling system, and periodic valve lash adjustment, per the Gardner service manual, the first required maintenance is to remove the heads, and the cylinders, and to replace all the fresh water cooling system O-rings, then reassemble. This is recommended to be done at 30,000 hours, so given that we have another 22,700 hours to go until the next scheduled maintenance I think we're good for few more years.
The Hundested CPP recommends greasing every 5 years of operation, so it is about due, even though the interval is established assuming commercial use. But we'll do that at the next haul out.
The Hundested transmission oil change interval is more often, at about every 300 hours.
Overall, during our ownership of 5 years, 1800 hours, and a little over 11,000 nm, including 3.5 year full time liveaboard, except for periodic drive shaft lubing (every 50 or so hours), and scheduled oil changes, (recommended every 400 hours, but per recommendations of Blackstone labs, from oil analysis, we've extended that out to 500 hours). They keep recommending longer and longer intervals, but we're not planning on going more than 500 hours, our entire drive train has been pretty much maintenance free.

 

[Jeff F]

Here's a power curve. 90 HP available at 800 rpm.

 

[twistedtree]

Most applications of CPPs are for their benefits as a transmission, and less so for efficiency or other reasons. I think there are two typical use cases:

Ships with slow or medium speed diesels. I gather the Gardner falls into this category, but I think it's at the faster extreme. Most I have seen operate in a narrow range from about 800-1000 RPM. And bigger ships are in the 100-200 rpm range. The challenge is that with a fixed reduction gear, and a fixed prop pitched for full power at max RPM, min RPM is still moving the boat too fast. There just isn't enough RPM range to cover dead slow to full ahead. Enter a CPP, and now you have infinitely variable load at whatever RPM you like.

The other use is for motorsailers where the amount of "boost" you want to give the sails, and the prop rpm and pitch to accomplish that, varies widely depending on boat speed, wind speed, and wind direction. A CPP lets you dial in just the right RPM and pitch to match any situation.

With most modern diesels, the engine's rpm range with a fixed reduction gear is a remarkably good match for a fixed prop pushing a boat from dead slow to full ahead. As a result, there is little gain from a CPP. You might be able to find a more "comfortable" engine RPM for a give speed, or get slight MPG gains, but in their normal operating range, there is actually very little variation on the fuel consumption per HP produced (BSFC). So a CPP that allows operating at different RPM points with the same output HP, makes little to no difference in fuel efficiency. As a result, the cost and complexity of a CPP is seldom worth it, which is why you don't see them very often.

I suspect that when Beebe built Scot's boat he was experimenting with all this, and now Scot's the beneficiary. But I think it would be pretty hard to justify the cost of one in a build today unless there were some special circumstances.

 

[dannc]

A good discussion about CPP's from a cost and expense perspective is on Kasten's website, Controllable Pitch Propellers.