Topic: Variable pitch prop (Read 8226 times)

Captain Jack · « **on:** June 16, 2009, 01:33:09 am »

Just ran across this from Harbor Models:
http://www.harbormodels.com/site08/info_pages/variable_pitch_2.htm
I recall seeing something similar to this maybe thirty years ago when I first started building. I think the ones I saw back then were manufactured by Marx.

Does anyone have any experience with these? I may want to install one on an old Shelley Foss tug that's been collecting dust for years. A forward only speed controller could be used (very cheap). It seems you could get very precise slow ahead speeds for towing and such.
The shape of the blades would also lend itself to work well with a kort nozzle, would it not?

bogstandard · « **Reply #1 on:** June 16, 2009, 08:22:58 am »

CJ,

It looks like someone has discovered a warehouse full of them and is trying to get rid.

I recently gave an unused one of these away, complete with the special extending Kardan coupling. I bought it many years ago thinking it would be perfect for using in a boat with a non throttle, one way running steam engine. But because it was so bulky and ugly, and had to fit a certain sized hull because of tube length and diameter (over 8mm) plus propellor diameter, I never used it.

A very good idea, but making it in just one size was the biggest issue, and I think that is why it never caught on.

It stated that it could be used with a 10cc IC engine. But I would use a max of 5cc because the power output has grown dramatically over the years and a 10cc I think would turn it inside out, even though it has a ball raced shaft and propellor bosses, plus the all plastic coupling would disintegrate at the first sign of major power input.

You will find that you use the throttle stick for controlling the pitch of the propellor, so motor speed control isn't really necessary. Turn the motor on, and leave it running, fwd and reverse speed is all controlled with the pitch of the blades.

Hope this helps

Bogs

Umi_Ryuzuki · « **Reply #2 on:** June 16, 2009, 09:21:33 am »

Those are the old Marx designed variable pitch propeller.
I never had one, and only ever found one picture of the originals.

For the price of that unit, you could buy two cheap F/R ESC, or
one really nice F/R Esc.

It would be a unique feature to have on a boat though.

kiwimodeller · « **Reply #3 on:** June 16, 2009, 11:25:08 am »

I have two comercially made ones, a smaller one from a Japanese outfit called WADA, sold I think by Yokohama Model Company. I have an advert from a 1980's Model Boats Mag. The other is a large Raebosch one about 4" prop size. I have also seen a similar looking smaller three blade raebosch one in a boat and working well with a steam engine. A member of our local model group has also made a couple from plans and both work well. I am looking forward to the chance to try my two out. I have never seen anything written about them to say that they do not work well. Cheers, Ian.

Captain Jack · « **Reply #4 on:** June 16, 2009, 05:56:11 pm »

Amy makes an excellent point about the ESC's. After reading the posts on the tug forum, about it's apparent lack of a true neutral position, and the diameter of the shaft housing, I'm looking at other means of a more precise control.

nemesis · « **Reply #5 on:** June 16, 2009, 06:12:53 pm »

You will find that as you put the pitch on your revs will drop alarmingly, so you have to increase your
revs/ power to compensate, hence the need for the esc. Big ships/ tugs have the same problem.
the theory is that if you can have an engine doing a constant rpm you can make it very efficient &
therfore do all the work at the prop end by changing the pitch to achieve what is required. Alas, when they tried it out the motor died, so they had to couple the throttle to the pitch control,
therefore nullifying any gain, hope that explains the problem
Nemesis

Captain Jack · « **Reply #6 on:** June 16, 2009, 06:22:51 pm »

I guess I'm never going to get the scale speed/handling thingy worked out until I can figure out how to reduce the density of water.

Colin Bishop · « **Reply #7 on:** June 16, 2009, 07:07:18 pm »

Quote

until I can figure out how to reduce the density of water

Aerate it by punping in lots of bubbles and then your boat will sink!

I believe this may have happened upon occasion during underwater volcanic eruptions, lots of gas released into the water turning it into a sort of froth which is unable to support a boat/ship.

Colin

Captain Jack · « **Reply #8 on:** June 16, 2009, 07:22:00 pm »

...and a possible expanation for occurences in the Bermudal Triangle?

Colin Bishop · « **Reply #9 on:** June 16, 2009, 07:35:09 pm »

Yes, that has been suggested!

Colin

hama · « **Reply #10 on:** June 16, 2009, 07:50:02 pm »

Hi all!
I have one of those and put it on an old Banckert tug i have, it worked great and it's no problem with rpm´s. The biggest problem with this unit is that it's totally out of scale. I tried it out of curiosity and because I didn't have anything else at the time. Many years ago I bought a very nice Raebousch prop that is out of production. It is a lot bigger and I believe I showed it here in another thread some time ago. I haven't yet found a big enough hull to put it in, but some day. I would love to see a range of CP-props if they can be made at a reasonable price. After all most vessels, except the smallest and the biggest, have them. One way of using them is to have the engine revs at a maneuvering rpm and just use the pitch when maneuvering. Some systems have a combinator that controls both rpm and pitch with one control lever, if so there can be a computer that controls the load on the engine and adjusts the rpm and pitch at any given time.
All the best!
Hama

Captain Jack · « **Reply #11 on:** June 16, 2009, 08:09:20 pm »

Quote from: Captain Jack on June 16, 2009, 07:22:00 pm

...and a possible expanation for occurences in the Bermudal Triangle?

My ability to spell leaves alot to be desired today! Or perhaps, I should go and locate my glasses?

Bunkerbarge · « **Reply #12 on:** June 16, 2009, 08:14:11 pm »

Firstly I have to say that I'm the lucky chap that Bogstandard passed his unit on to and I fully agree it is let down by the fact that the length is fixed. I also have a much older brass Raebosch unit which is very nicely made but needs a new bearing and trimming the blades but it will be OK then.

As for real ones I have sailed with a combinator system on main propulsion and I have sailed with fixed speed units driven by electric motors for thruster use. If the motor revs drop significantly when you apply the pitch then, for my money the motor doesn't have enough torque. I do believe though that elecronic speed controllers give you far more control with less to go wrong and are a lot cheaper than controllable pitch props for motor use. There real benefit to me is to control the speed of non reversible steam engines which can sit there and chug away while all the control is done by the prop. I would always incorporate speed control as well though, whether by a combined linkage to the steam valve of via a seperate servo. I think these units are a bit unecessary on the end of an electric motor, which are so easy and cheap to control nowadays.

Just a point of interest here as well, the term variable pitch propeller is quite wrong, even though used quite regularly by manufactuers. All propellers are of a variable pitch design with the pitch decreasing in proportion to the distance from the centre line. The correct term for these devices is a Controllable Pitch Propeller or CPP as quite rightly stated by Hama.

Bryan Young · « **Reply #13 on:** June 16, 2009, 08:21:15 pm »

Quote from: Colin Bishop on June 16, 2009, 07:07:18 pm

Quote
until I can figure out how to reduce the density of water

Aerate it by punping in lots of bubbles and then your boat will sink!

I believe this may have happened upon occasion during underwater volcanic eruptions, lots of gas released into the water turning it into a sort of froth which is unable to support a boat/ship.

Colin

Please please Do Not Bring The Theories Of The Bermuda Triangle into this! !

Colin Bishop · « **Reply #14 on:** June 16, 2009, 08:50:03 pm »

Quote

Please please Do Not Bring The Theories Of The Bermuda Triangle into this! !

Wasn't me M'lud. Atlantis is more my scene....

Colin

bogstandard · « **Reply #15 on:** June 16, 2009, 08:53:53 pm »

If you remember, the Marx one was released many years ago, when IC was in full swing. Not a modern day gizmo as suggested by the advert.

I personally think it was to give fwd/rev control to IC engines rather than anything else. At one time, most scale boats had IC engines installed instead of the modern day electric. So unlike IC racing where it is forwards only, having fwds/rev would have definitely been a feature that people would want on their scale boats.

The literature supplied with the unit gave the same impression. But as I stated in my first post, modern day IC engines have more than double the power output of the early offerings, and so they would most probably be ideal for that application, but limit it to the smaller range of engines.

Bogs

catengineman · « **Reply #16 on:** June 16, 2009, 09:08:45 pm »

Quote from: nemesis on June 16, 2009, 06:12:53 pm

You will find that as you put the pitch on your revs will drop alarmingly, so you have to increase your
revs/ power to compensate, hence the need for the esc. Big ships/ tugs have the same problem.
the theory is that if you can have an engine doing a constant rpm you can make it very efficient &
therfore do all the work at the prop end by changing the pitch to achieve what is required. Alas, when they tried it out the motor died, so they had to couple the throttle to the pitch control,
therefore nullifying any gain, hope that explains the problem
Nemesis

I have the pleasure of being an engineer aboard a vessel with CPP and a shaft Alternator giving 3300 Kw there are several points to bring to attention
the engine speed is controlled by its governor to maintain a constant speed to keep volts etc at the correct rate
the CPP is controlled by hydraulics and has limit control which will restrict or reduce the weight put through the gearbox therefore keeping the engine at the constant speed.
A CPP ship has some advantages over a fixed pitch prop in that the forward to astern is not hindered by waiting for the shaft to stop

I have been an engineer aboard a direct drive tug, a single screw tug, several twin screw tugs and ships with and without korts and a tug with VS drive, I like the CPP as the engine is run at a constant + - a few rpm
Just my outlook on things

I would like to have a CPP model though as said there is no great need with the electric drives we use as ESC's are so easy to set up.

Jonty · « **Reply #17 on:** June 16, 2009, 10:09:59 pm »

As I posted in another thread quite recently, there is a device called the HPI Savage reverse module. This is designed for IC model lorries, but will presumably work for a non-reversing steam engine. Cheaper and simpler than a variable pitch prop.

Malcolm Reade · « **Reply #18 on:** June 17, 2009, 06:55:01 am »

Does anybody have any drawings, or explanation of how a VPP works?

Malc

Umi_Ryuzuki · « **Reply #19 on:** June 17, 2009, 07:35:39 am »

Quote from: Malcolm Reade on June 17, 2009, 06:55:01 am

Does anybody have any drawings, or explanation of how a VPP works?

Malc

I keep these archived..

Malcolm Reade · « **Reply #20 on:** June 17, 2009, 07:50:53 am »

Brilliant! Thank you.

Malc

catengineman · « **Reply #21 on:** June 17, 2009, 07:53:08 am »

http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/brochures/product/propulsors/cpp.pdf

This may help as well "LIPS" system is the one I am used to

R,

norry · « **Reply #22 on:** June 17, 2009, 08:54:13 am »

...Hi Guys...

I bought a matching pair on E-Bay a while ago & passed them on to another member of our club to use with a steam engine...

I have pictures of them somewhere...

...Best Regards...Norry

fooman2008 · « **Reply #23 on:** June 18, 2009, 05:39:15 am »

Having had experience with full scale variable pitch propellers (USN Spruance class) both from the point of standing helm watches and working on mooring with them. I can testify that variable pitch is definitely not the say all and do all for slow speed maneuvering or precision helsmanship. At anything less than (I think it has been almost 20 years) less than 11 knots the engines are always turning 55 rpm, since the propellers can never be entirely flat (due to the curve of the blades) or entirely feathered (to shut down one shaft for fuel or noise reduction), makes it a royal pain in the butt to moor to a buoy since the ship can never be entirely stopped. Beyond that speed the shafts stay at 100% pitch and the throttles are advanced. In case of emergency (someone shooting at you) they have the availability to advance the props to 102% (war emergency) and squeeze a few rpms out of the engines along with higher pitch. With a Chief Engineer who didn't care about whether we hurt the engines and a clean bottom they had us at just under 41 knots, about shook us to death, and had a rooster tail higher than the fantail (12 feet), but she was moving (made it pretty twitchy to steer too)! Something that had no throttle (up until a set speed) such as a steam tug I would think VP props would be great. Just do notexpect the kind of fine maneuvering ability that a good ESC will give you. For a tug or something that requires slow and fine adjustment this is not a system I would use.
Foo

derekwarner · « **Reply #24 on:** June 18, 2009, 07:33:07 am »

fooman2008.... the second picture is a DDG....many years ago I worked on the GMLS13 & the 5"/54 gun mounts of the Australian DDG's....& naturally were steam turbine & fixed props

The RAN also had FFG's with VPP, but no Spruance Class ...although in 1986 I inspected a vessel of that class ......... Derek

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Author Topic: Variable pitch prop (Read 8226 times)

Captain Jack

bogstandard

Umi_Ryuzuki

Captain Jack

Captain Jack

Captain Jack

hama

Captain Jack

bogstandard

catengineman

Malcolm Reade

Umi_Ryuzuki

Malcolm Reade

catengineman

fooman2008