The Controllable Pitch Propeller, a summary.

[powerabout]

Originally Posted by baeckmo

Quote Richard: ....Baeckmo, any complaints?

What's this, am I enlisted among the grumpy ol' complainers now Richard.....grrrr! Well maybe not completely wrong today for various reasons!

About finding the pitch/rpm balance: best efficiency in a diesel is often found slightly above max torque rpm's. This fact is used to reduce the amount of guesswork needed to find the optimum setting. So, with low to medium pitch setting, give her throttle to slightly above max torque rpm, then adjust pitch until you have the speed you want. The centrifugal regulator will adjust fuel flow up to maximum possible at this rpm setting.

If you don't reach the speed wanted with max pitch at the selected rpm, that tells you she needs more power (kW, hp) than available at this rpm. That means increasing rpm's; reduce pitch and increase throttle position, say 10 % of the rpm range. Of course, having a complete fuel map at hand, or a fuel flow meter, makes it perfect, but the max torque method is often a good starting point.

If that wasnt a job for a computer, there never was one.
Just select the button 'most efficient' and let it do the rest.
cheers

[thudpucker]

Tom I know of Two.
One down near Tacoma Washington and one out in Prince William sound in Alaska.
The one in Alaska really does have some Fox.

[powerabout]

Originally Posted by RHough

Maximum Torque occurs when BMEP is highest.
Maximum Power occurs when RPM (rate of torque production) can no longer compensate for the lower BMEP at reduced volumetric efficiency.

As I understand it, a CPP allows you keep BMEP at or close to the peak torque value at much lower RPM. This loads the engine at it's torque peak values at low RPM so power output can match vessel requirements at a wide range of speeds.

What the range of RPM that allows full torque per cycle to be developed is off topic for this thread, but it reinforces the idea that a CPP and engine must be well matched to derive the full benefit of the system.

I'm struggling, but I think I have this bit right ...

Dont forget you also want to keep and eye on the BSFC, which closely follows peak BMEP but usually gets worse as the revs ( friction) go up.

[powerabout]

One question
How are the EPA regs going to allow you to run an engine and apply a load that its EPA test didnt allow for?

Or will the new electronic engines not play ball with this idea of variable speed engines with CPP and force the engine to be fixed speed?

I would of thought you need to buy a pretty big engine now not to be under the rules of TIER II and there's very little tier II that arn't electronic?

OR will we all be buying 2nd hand engines to put in out new boats... ( which you can no longer do in the EU)

[baeckmo]

Mmm, lets see if we can get a picture here....nah it comes as an attachment. Anyway, here you have an example of a fuel map. As you see, here the bsfc occurs slightly below max torque (=max BMEP) rpm. But if you aim for the torque-max rpm, you are still much better off than where a FP would consume the same power. In fact, best economy also occurs at roughly the same mean pressure as the full power pressure, or slightly below. This is a good reason to argue for a "constant torque regulator" for the CPP.

These relations are what I use for a preliminary pitch/rpm setting, not very high tech, no computer, just common sense and basic engineering.

[powerabout]

Baeckmo

I'm all for CPP's I was just stating that with so few parameters ( which you can clearly use yourself) it would be a very simple job to computerise and with a few alarms make it fool proof for the non technical.

back in the 80's I was on board several yachts that had Hunterstad manual CPP, as in wind the handle.
All the long distance travelling yachts of about 20m and up seemed to have them them.
AT about 30m yachts had full hydraulic ones.
I must admit they have seemed to have disappeared these days?

Hahhh,

who said we cannot manage a reasonable thread? Now it becomes fun!

Baeckmo,

nono I did´nt move you to another "folder". But was sure you have some fine tuning, and alas, it happened.
Thank you!

Originally Posted by powerabout

Apex 1
I like your boat and the concept
but when you start up a 750hp 500rpm engine...everybody on board is going to know its running especially if its conventially mounted, i.e crankcase to bedplate ( hull)

No, these old fashioned monsters run much quieter than a high revving modern Diesel. And of course the engine will be mounted on silencers. Even encapsulated gennies are louder!

The EPA / Tier regs are´nt touched by using a CPP. You have the same variety of using (abusing) your engine with FPP systems!
And you mean Hundested! link is in the first post.

Rhough

As I understand it, a CPP allows you keep BMEP at or close to the peak torque value at much lower RPM. This loads the engine at it's torque peak values at low RPM so power output can match vessel requirements at a wide range of speeds.

Right this time!

Thanks peers, that was what I had in mind!!! Staying on topic and finding out if everyone interested, has his share and probably profit!

Regards
Richard

[baeckmo]

Originally Posted by powerabout

Baeckmo

I'm all for CPP's I was just stating that with so few parameters ( which you can clearly use yourself) it would be a very simple job to computerise and with a few alarms make it fool proof for the non technical.

Of course it's a peace of cake to arrange a computerized control. Problem is that I am totally allergic to "overcomputerization" of marine equipment. I see computerized engine controls, computerized safety devices high and low. Local pilotvessels here seldom leave port without one or more electronic alarms are manually reset or detached because of obvious malfunction. We have a fleet of passenger vessels serving the population in the archipelago, my neighbour is a ce there. In his evening prayer he now adds ".... and almighty father, take away all the electronic junk and give me
the mechanical injection pumps back".......!

Originally Posted by baeckmo

and almighty father, take away all the electronic junk and give me
the mechanical injection pumps back".......!

He obviously has this in mind!



And he is dead right!

I had one of them, a old Buckau Wolf in a 35m passenger ship, she had more than 100.000 hrs on the clock. Piston rings and bearings were reported as replaced several times, in the unbroken engine service report manuals! Nothing else.

[powerabout]

it makes less high freq noise but getting rid of the low freq is much harder and that will be structure born.
Just think of the weight of the piston and rod plus the explosion that needs to be absorbed with each bang?

How heavy is that engine?

You will need to invent an isolation system for it as I very much doubt you can buy the bits.
That will make for a nice project.

I have a mate who does that type of work ( here in Asia) and he gets involved in some very interesting projects

Originally Posted by powerabout

it makes less high freq noise but getting rid of the low freq is much harder and that will be structure born.

How heavy is that engine?

You will need to invent an isolation system for it as I very much doubt you can buy the bits.
That will make for a nice project.

The engine is ten tonnes. And believe me, I have operated these engines, you usually do´nt hear them in the wheelhouse!

The engine mounts are off the shelve, no need to reinvent them. Although they are quite different from average rubber mounts. (and cost twelve times as much). Do´nt have the info at hand. But here on Proboat, page 43 top right you find a much similar one.
http://www.proboat-digital.com/proboat/e20090809/

Regards
Richard

[PAR]

Any vessel that has a 10 ton engine better not be heard in the wheelhouse.

[troy2000]

Originally Posted by apex1

He obviously has this in mind!



And he is dead right!

I had one of them, a old Buckau Wolf in a 35m passenger ship, she had more than 100.000 hrs on the clock. Piston rings and bearings were reported as replaced several times, in the unbroken engine service report manuals! Nothing else.

This is a little off-topic, but I work in a natural gas line station, where the gas is compressed to send it on towards the Los Angeles area. Some of our main units have been in service since 1948, and have over forty years of actual running time. That's somewhere in the neighborhood of 350,000 hours....

They're twenty-foot long, straight 8 cylinder, 2-cycle engines that run on natural gas (of course), with natural aspiration, closely related to old marine engines. When you fire one up, the floor starts shaking under your feet; in the days when we had all or most of the fifteen original units running, the parking lot shook like the deck of a ship, and pictures on the wall in the office bounced and rattled.

Nowadays, we've replaced half of them with two Caterpillar units. They're 16-cylinder, four cycle monstrosities that run at 1000 RPM instead of the 300 RPM of the old Clark units, and they're so automated and computerized that it seems like they're down half the time. Not to mention the vibration problems that take out wiring and various air, water and oil tubings on a regular basis....when they go down, we fire up the original simpler, bulletproof units, and keep making rate.

Straight sixes are the smoothest of common designs - not that straight-eight is common (I feel them shaking up here!).

Originally Posted by mark775

Straight sixes are the smoothest of common designs - not that straight-eight is common (I feel them shaking up here!).

Right on the spot! For that reason I have choosen a straight six. You hardly hear or feel them outside of the engine room.

But yes, we are a bit off topic.