[Duncan112]

Technically even cast propellers with fixed hubs have a variable pitch in that the pitch is not constant between the root and blade tip or even across the blade width.

As regards CPP failure modes five modes have been used at various times

Full Ahead Pitch - usual and allows vessel to complete Voyage at normal service speed

Full Astern Pitch, - at least you won't plough into whatever is ahead but shock load on drive train may be significant

Current Pitch Setting - reasonable and probably the preferable option

Neutral- possibly safe but you ain't going anywhere fast.

Small Ahead Pitch- maintains some steerage but not going anywhere fast.

Only experience I had of failure was in the clutch to the gearbox, failure mode didn't matter as the Port shaft wasn't moving -

 

[woodend]

Remember well the first I docked one into P.E., in fact I still have the post card the Captain gave me. She was the Unicorn tanker 'BUFFALO' docking first discharge port on her maiden voyage. The image the post card shows is a beautiful oicture of a good South African BUFFALO and the Captain has written 'Not only is she called one but she handles like one!' As I remember she really did![=P]

 

[Derek Roger]

Technically even cast propellers with fixed hubs have a variable pitch in that the pitch is not constant between the root and blade tip or even across the blade width.

As regards CPP failure modes five modes have been used at various times

Full Ahead Pitch - usual and allows vessel to complete Voyage at normal service speed

Full Astern Pitch, - at least you won't plough into whatever is ahead but shock load on drive train may be significant

Current Pitch Setting - reasonable and probably the preferable option

Neutral- possibly safe but you ain't going anywhere fast.

Small Ahead Pitch- maintains some steerage but not going anywhere fast.

Only experience I had of failure was in the clutch to the gearbox, failure mode didn't matter as the Port shaft wasn't moving -

Thank you for that support Duncan again clarifying variable pitch on a fixed hub cast prop .
Even controllable pitch props have a variable pitch over the blade length .

 

[Don A.Macleod]

Thank you for that support Duncan again clarifying variable pitch on a fixed hub cast prop .
Even controllable pitch props have a variable pitch over the blade length .

It was dinner time in the saloon and the ship(Maihar on passage Vancouver to Japan) suddenly started to surge gently in a fore and aft motion, we all looked at each other and then the alarm went off.

The usual dash to the E/R and found an o-ring as I remember, had blown and caused loss of pitch due to low hydraulic pressure. Repair was initiated promptly and we were up to speed again in jigtime. The only time I witnessed a prop failure on these ships but it was short lived

I think you had just been releived by us Derek so you missed that wee hiccup!. Donald.

 

[uisdean mor]

It was dinner time in the saloon and the ship(Maihar on passage Vancouver to Japan) suddenly started to surge gently in a fore and aft motion, we all looked at each other and then the alarm went off.

The usual dash to the E/R and found an o-ring as I remember, had blown and caused loss of pitch due to low hydraulic pressure. Repair was initiated promptly and we were up to speed again in jigtime. The only time I witnessed a prop failure on these ships but it was short lived

I think you had just been releived by us Derek so you missed that wee hiccup!. Donald.

Hi again Donald. "O" ring must therefore have been part of the control gear either on the bridge or down the tunnel where a manual option was also available. My memories of actually pulling the hub are that the most testing time was splitting the KaMeWa collar on the shaft Intermediate shafting removed or drawn back to allow access then catch bolts screwed into the shaft end plate with copper tubing as shock absorbers then with miniscule bespoke hydraulic pumps push pressure between the collar and the shafting until the collar flew off. In reality really safe as the distance to move was small and surface area so large that as soon as pressure was released the hub only had to move a few thou but it did make a fair racket as it released. Great amusement at shoreside hammer signals between dockside and in the tunnel - One i seem to remember (sic) was "shave and a haircut 2 bits" Interesting times on these "unmanned" vessels.
Rgds

 

[Derek Roger]

Hi again Donald. "O" ring must therefore have been part of the control gear either on the bridge or down the tunnel where a manual option was also available. My memories of actually pulling the hub are that the most testing time was splitting the KaMeWa collar on the shaft Intermediate shafting removed or drawn back to allow access then catch bolts screwed into the shaft end plate with copper tubing as shock absorbers then with miniscule bespoke hydraulic pumps push pressure between the collar and the shafting until the collar flew off. In reality really safe as the distance to move was small and surface area so large that as soon as pressure was released the hub only had to move a few thou but it did make a fair racket as it released. Great amusement at shoreside hammer signals between dockside and in the tunnel - One i seem to remember (sic) was "shave and a haircut 2 bits" Interesting times on these "unmanned" vessels.
Rgds

On the OD box there was a small filter ( strangling hole filter ) which had to be cleaned / checked regularily ; if this plugged up the pitch would go to full ahead . That is what happened to Mahsud when she hit the dock wall in Colombo putting back the bow 22ft . Had to sail to Hong Kong for repairs ; Class allowed her to sail in the damage condition as the collision bulkhead was intact.Allan Attack flew out and took her to drydock ; I have some pictures of the damage which I will post when I lay my hands on them . The old man was demoted ; he could have clutched out or used the emergency stop ; he only informed the engine roon at the last minute and Davie Meek cluched out but it was too late .

 

[sternchallis]

Great amusement at shoreside hammer signals between dockside and in the tunnel - One i seem to remember (sic) was "shave and a haircut 2 bits" Interesting times on these "unmanned" vessels.
Rgds[/QUOTE]
As an apprentice often did the odd drydock job and remember the hammer signals.
Something like ,
1 knock -Ahead
2 Astern
3 Shaft In
4 Out

7 smoko or tea up!!
So we had to clamber up the dockyard steps then down the gangway, by which point we were ready for a cuppa.

 

[skilly57]

Duncan112 - I've got another failure mode for you.
Stone Manganese Marine "Seffle" type CPP - each blade about 750 Kg - doing about 167 rpm - dinner time one peaceful night in August 1984, off Nelson, NZ, on arrival from Brisbane, Australia. Master (R.I.P.) decided to do a control check while approaching harbour limits - masts started to leap around a bit, accommodation started moving as well - rushed below and found O.D. box & muff coupling seemingly doing large eccentric circles. Master refused to allow clutches to be pulled until alongside wharf (over an hour). Finally stopped shaft, trimmed ship down by head, engaged turning gear, and told 3/E to start rolling the shaft. Blade 1 - Ok. Blade 2 - Ok. Blade 3 - had to ask 3/E over VHF why he had stopped the turning gear - "I haven't stopped it at all", he replied. Oh F#*K!
One blade had snapped off inside the hub, and all the others were cracked in the same root area!
Ship towed to Wellington (130 miles away) - then laid up there for 6 months awaiting new propeller from SMM. Stern tube bearings also stuffed - flown back to UK for re-metalling as well.
I have a vague recollection of working out the out-of-balance couple at the time - was about 298 tonnes - explains the unhappy stern tube bearings!
1985 replacement propeller continued cracking blades - eventually replaced prop & shafting with Berg system in 2003 - should have gone RR Kamewa though.
The ship is still running today (having now carried 10.4 million tonnes of cargo), still with the original operator, but now 38 years since keel was laid, so replacement finally on the horizon at the end of this year.
Last photos shows active rudder - 4 tonne thrust from rudder motor & propeller is very handy stern thruster & emergency propulsion system - power is supplied by cables coming from steering flat via hollow rudder stock, as do hydraulic pitch control hoses.
I sailed from 1979 - 1990 on her, and have been back on again since August last year. A bit like pulling one's old comfy slippers on again!
Skilly

 

[sternchallis]

And as Lt. Philips would say " Oo Narsty" regarding the stern tube bearing.

For those old enough to remember the Navy Lark and HMS Troutbridge.
Still heard occassionaly on Radio 4 Xtra.
Left hand down a bit. Crash.

 

[NoR]

Were I a shipowner I wouldn't have anything to do with CCP unless operating ferries, tugs/OSV. The list of shipowners who invest in unnecessarily complex equipment which breaks down expensively and inconveniently is a very long one.

I would go for tried, tested and reliable before anything else. Oh, and one other thing. All the kit must be inboard so that the crew have at least a fighting chance of fixing it..........I guess that rules out pods.

 

[Varley]

For many years DNV required CPP on vessel with a shaft generator - regardless of the technology used to generate.

 

[NoR]

With CPP (of which I know very little) is there a connect between engine power and pitch. That is to say as pitch is increased or decreased is engine power adjusted accordingly. For instance many prop driven aircraft have constant speed units whereby pitch is altered to maintain constant RPM within certain power settings. In the case of engine failure it's important to feather the blade asap to avoid drag as the pitch fines off to maintain RPM as power decays. So I wonder if it is possible to feather a CPP to reduce drag in the event of engine breakdown in a ship with two or more props.

 

[Derek Roger]

With CPP (of which I know very little) is there a connect between engine power and pitch. That is to say as pitch is increased or decreased is engine power adjusted accordingly. For instance many prop driven aircraft have constant speed units whereby pitch is altered to maintain constant RPM within certain power settings. In the case of engine failure it's important to feather the blade asap to avoid drag as the pitch fines off to maintain RPM as power decays. So I wonder if it is possible to feather a CPP to reduce drag in the event of engine breakdown in a ship with two or more props.

CPP can run either at constant revs and adjust the pitch to adjust speed or in some cases when fitted with a " combinator " the prop speed and pitch are combined to give the most fuel efficient result over all engine speeds .
Regards Derek

 

[skilly57]

NoR,
The photo of the 400 hp rudder motor in post #48 shows the 4 blades in the feathered position (ie., "stowed position"), so there is no drag. On start up (not initiated unless ship speed is below 6 knots), the hydraulic pump turns the blades through 90 degrees, then the electric motor starts with the blades at Zero pitch. The master can then apply Ahead or Astern pitch as required, although most only apply Ahead pitch, then turn the rudder 80 degrees either way to get thrust in the desired direction.
I have sailed on around 12 ships with CPP - unless they have shaft alternators fitted, the CPP is generally fitted with Combinator Control so the rpm & pitch are applied together. Some also have the Constant Speed option as well as Combinator Control, but using the latter enables the option of applying greater pitch at a lower shaft speed, so is more economical on fuel and often drops the engines out of the resonant rpm range, making the engine room a nicer place to work in and stopping the accommodation from shaking.

Skilly

 

[Derek Roger]

All the Brocklebank / Moss Tankers had shaft alternators so ran at constant speed . On Maihar and Mahsud the shaft alternator was used for the bow thruster and at sea for electrical supply allowing the generators to be shut down which was a blessing as we had Paxmans which were a nightmare .
On the tankers one main engine was run in port with a shaft alternator to provide power for the cargo pumps which negated the need for a big hot inefficient boiler and steam plant to run the cargo pumps ; also provided enough waste heat to use the ex gas boiler for domestic steam supply . Quite a neat set up .
Derek

 

[Varley]

Derek,

Indeed, but now well-dated technology allowed that without the shaft remaining at constant speed (and so seeming to need CPP). Paxmans were not a pre-requisite but strangely that is where I first came across them too (not "them" for SGs. "It" for the Paxman!).

 

[OLD STRAWBERRY]

Well done Boy's at leats my original question seems to have taken off. My original question related to the old "Samson" class steam tugs(MOD) did they have variable pitch propellors. Was it a question of some did and some didn't. Not sure if I had a reasonable answer as yet. Were old steam tugs able to have CPP or VP propellors??.

 

[Jim S]

Re the Samson Class 3000 hp tugs built 1953/54 in Aberdeen although it was possible there would have been no real advantage in equipping them with Controllable Pitch Propellers - Steam Reciprocating engines being capable of good manoeuvring capability. Additionally the class were twin screw albeit with a single rudder.
The cost alone would not have been favourable.

Jim S

 

[OLD STRAWBERRY]

Hi Jim thanks for that. I did have cause to wonder. I had been talking to a friend who was convinced that the PAS Steam Tug Samson had variable Pitch propellors but I think He may be getting mixed up with the "Confiance" Class that did. Thanks all for your input. Last question when was it that VP or CPP Propellors were first introduced, how far do they go back in years?.

 

[Stephen J. Card]

Pielsticks = PielSTOPS!!!!!


A bit more on UTC STATESMAN. She was built in Japan (Kure) for Moran Towing, New York as ALICE L MORAN.

She came down to Bermuda for a stint on Salvage Station... 1966 I think. She arrived almost 24 hours late. She missed the island and had to turn around and find the way back. Not a good start!