ASD vs conventional FPP propeller and rudders for 50+m AHTS tugboat

These are most likely NOT Azipods, but Schottel combi drives. They have the motor not in the gondola, but in the shaft, so they can be installed (and probably pulled) easier.

http://www.schottel.de/cache/thmb220B1158918124.jpg

I think we should know more about your requirements to come closer to a sensible solution.
When even Azipods are a possible solution for you, we have no need to think about just the first choices you mentioned.

Regards
Richard

 

there are plenty of tugs with zdrive/azipod (azimuth I should have said)shaft driven I didnt mention DE for this
http://www.keppelsingmarine.com/publications/shipbuilding.asp

Mohamed's second post says;
"I would go for a higher boat price if then the operating cost will be less with less breakdowns but needed also acceptable manueverability esp. to land people with basket from the FSO to the tug at marginal weather conditions".
When you build a twin engined PSV or AHTS these days people know you went cheap, when the market gets tough these go off hire due to the high fuel consumption.
This is bigger but you get the picture
http://www.scinicariello.it/site/augustaoffshore/index.php?ml=81609196771

PS. You can put DP on FPP they are out there ( many crew boats are starting to be DP, most are 4 engined as well)but clearly not as nice as a CPP
http://www.professionalmariner.com/...91&tier=4&id=2948B590F64B436CAABF6740670B97AE

 

sorry I dont mean azipod as that does mean electric I just mean an azimuth thruster as Apex has shown which can be installed from the top when the boat is in the water
or this
http://www.gsgnet.net/company/pdf/NII001_170510091100_GSG_Niigata_P4.pdf
http://www.nautican.com/sea_trial.htm

Re the boat in Africa, I was doing a course with one of the crew who was telling me about them operating out of a fishing village.
The boat got the contract as it was designed to allow the azimuth thrusters, main and bow to be pulled up through the deck via a dock crane knowing that it was operating on its own the oil compnay didnt want it to steam away if there was a problem.
I didnt ask if it was built that way for that contract

They all run fixed speed engines as the shaft generator needs a constant speed or you will need to run a gen set as well as your man engine and that is going to cost even more fuel.
You can idle the engines down but high performance turbo charged engines do not like this and the manufacturers usually say not to do it added to the extra maintenance of running a house gen set you lose out.
If you also need a bow thruster (close standby)you need the shaft gen as the house gen sets are never big enough to run a thruster, why would they?
You can now see why the 4 engined vessels use $1000's less of fuel per day and less fuel means less maintenance and no off hire for main engine work as you still have 3.
The combination of the pairs of engines hp ratings can be tailored exacty to suit the single engine power requirement.
You have 5000hp for towing but most of the time you do not need that much.

You havn't mentioned if the vessel needs to be DP or not?

 

good day all,

NO way we would think of what we consider too sophisticated for our area (DP vessel).

the 5000 hp will not be used most of the time as we are having only 5 export operation a month and then many times during the month material and personal transfer from and to the shore, sometimes diving operations (inspecting the pipe line, the hull of the FSO, the turret, the backup SBM, the sea chest valves, the anodes).

the idea of being able to lift the propeller up on deck sounds great. no need to be at drydock to do maintenance.

in summary i need your experience on which system is better (CPP, ASD with FPP or conventional FPP and rudder) with regards to following issues:

• cost of new build
• cost of maintenance
• frequency of breakdowns
• possibility to repair without going to dry dock
• fuel consumption
• manueverability

 

Pretty easy Mohamed,

CPP, twin engines, nothing else. See above........
Though maneuverability would be better with a Schottel combi drive. But don´t think the pull out setup is easy or cheap. And on top of that it is a Diesel / Electric setup, costing you twice the simple CPP cost, at least. And that NEVER pays back with your jobs.

Don´t let you talk into that shaft genny nonsense, this guy does not know real world conditions and applications. He did not even know the difference between azipods and Schottel drives. And the thruster argument is moot, you have most probably aux engines for the hydraulic load anyway.

A D/E system has to run the gennies, regardless of load, at constant speed, with according consumption. Though there are several of them to provide the required power, they wear out quite fast. And I know what I am talking I operated Icebreakers in the baltic, with D/E propulsion. The cost was horrible, but D/E the only proper solution for ice breaking. And this was another job I did for the fun of it:
http://www.youtube.com/watch?v=UYRE9zN6Mgc

A twin engine setup (of course NOT fixed speed thats insane) with a CPP can be run at idle for stdby operations, consuming nearly nothing, but holding position. It can be run at any required speed, fully loading the engine, reducing wear and tear dramatically, and providing the best specific consumption at ALL rpm settings. One can easily operate on one engine with the idle CPP feathered for lowest resistance.

One can service the entire drive train from the inside, and the prop blades, as mentioned, can be replaced relatively easy by divers even on the open ocean.

The FPP is as expensive or above CPP cost, depending on the gearboxes required. Has a far higher consumption, due to its inefficiency at all rpm but one. Is much slower in maneuvering. Cannot be replaced at sea.
Gearboxes require regular service and bring massive weight.

Pod drives like the classic Schottel provide higher maneuverability at higher initial cost, and have the same disadvantage as the FPP in terms of fuel consumption and weight.

Azipods being a D/E installation, have the least efficiency in terms of fuel consumption and maintenance cost, but the best maneuverability and possible "finetuning" of power requirements in finicky jobs. The service and replacement cost of any D/E installation makes them by far the most expensive solutions though.

Looking at your average job requirements my recommendations stands without any doubt,
go CPP.

Regards
Richard

 

Do yourself a favour Mohamed, just browse the internet for 50m PSV/AHTS so you can see how they are configured.

Will this be a oil company owned vessel (who cares about the fuel consumption) or separately owned and operated?
Reliability, fuel consumption and down time seem to be your issues.
Its possible in a psv/ahts to run non stop and be ashore for such a short time that you barely get to shutdown your M.E's. and use your small house gen set are you getting the picture re the shaft gen set design that most are.
(I wouldnt expect this design to work for a fishing boat)

Nothing wrong with twin cpp (thousands of them out there) and one bow thruster of which you say will be 500hp so hence you see you will need to run a gen set of about 750kw to run the vessel and the thruster so hence you can see doesnt make a lot of sense whilst you also have at least a 2500hp engine running doing almost nothing hence all 99% of all ofshore support vessels have shaft gen sets.
But clearly there is calculation to be done running the main at constant rpm versus idle and a large gen set in slighty larger vessels the maket has spoken and they are all cpp constant speed with shaft gen sets and some a are multi engined to also keep the onsumption down. I posted a link above shows a 4 engined psv)
So your vessel now has 2x 2500 main engines and 2 750kva gen sets which look silly running the house load when you dont need the thruster so you have a 3rd gen set for dockside plus your emergency to make class, alot of kit in a small boat.
Apex's fishboat spec would most likely have hydraulics running non stop, I would be intersted to see if you can find a psv/ahts vessel spec like that but on a psv/ahts the gearbox creates it own hydraulic power for the cpp and everything else has its own powerpak as for most of the time you are not using any other powered device.

Your on board house/hotel gen sets only need to run that load and maybe the deck crane and tugger winches alongside, any other operation has the main engine(s) running hence the config of most vessels having shaft gen sets.

There's another config I have had a captain tell me about and it did have a large enough gen set to run the forward azimuth thruster so they could shutdown the main engines when on stanby and still have control, makes sense


These guys are probably the top of the game on vessel design have a look through their site.
http://www.ulsteingroup.com/Kunder/ulstein/cms66.nsf/pages/x_y_z.html?open&qm=wcm_2,3,0,0

Here's a pod thats not a shottel and not electric
http://www.wartsila.com/Wartsila/gl...ropulsors/2009/propac-st-selection-tables.pdf

browse the internet and you can find this;
http://www.marifor.com/showthread.php?t=2407

I notice that at 5000hp for 60tbp most vessels are a little larger like this which seems typical
http://www.namcheong.com.my/ships.php?id=66

further reading

http://www.wartsila.com/Wartsila/gl...dia_publications/brochures/product/propac.pdf

http://www.wartsila.com/Wartsila/sw...zerland/Ship_Power_Product_Catalogue_2010.pdf



Happy reading

 

Nice you mentioned Ulstein, no doubt one of the best yards for such vessels.

They actually build two AHTS vessels with exactly the setup I recommended!
And they install Schottel CPP`s for good reason.

You should give up contradicting me in this field mate, you obviously are miles away from first hand knowledge and this is a ballpark way above your head.

Why must every occasion with you end in a senseless debate? Are you unable to keep your mouth shut when you are not firm on the subject matter?

Regards
Richard

edited: sorry but it really pisses me off, to discuss senseless appliances like Azipods with people not even knowing what they are talking, let alone how to operate them. You obviously had to lookup what that means, how can you give recommendations?

 

Just post the last psv/ahts you were on and lets all look at the spec?

here's a fleet I am familiar with all but 3 have shaft gen sets
http://deepseasupply.no/fleet.html

All these vessels with their CPP's have a huge gearbox behind the engine.
It has to house the reduction gears for starters.
Where do you think the shaft gen set connects...
Do you think they crank the engine with a 4m propeller connected to it??
do you really know this business as you claim?


educate yourself here, I think you will find every single vessel has shaft gen's
http://www.maersksupplyservice.com/Fleet/AnchorHandlingTugSupplyVessels/Pages/AHTS.aspx

what more can I say its the norm in this area not the exception

 

Who said shaft gens are not common? But it is a nono to choose the main propulsion as a constant speed engine just because you like AC generation by the shaft.

Now leave me alone with your mad contradiction. This is not the "who is right" thread.

Mohamed gave us the choice between a few feasible (in his opinion) propulsion systems, and asked for our experience and recommendations about them. He did not ask for recommendations about systems completely out of his ballpark (like Azipods, you accidentially recommended), or setups which require more maintenance than they can stem easily.

And there again the simple, cheap, reliable and extremely efficient CPP, directly coupled to a medium speed engine, is the favourable for the given jobs. Aux. and thruster should be driven by hydraulic engine/s according to power demand.

 

good day all,
thanks for your valuable input on this. Your discussion was and is still very useful for some like me from a different disciplin (Electrical Engineering) to a marine superintendent in an oil company in Yemen. I need professional's opinion about these things to take correct decisions. I prefer staying away of hard debates as we lose truth in between the fights.

I feel that I got into this forum a bit too late. We have prepared outline specification of the tug we required and sent it out as part of a full package "tender documents" to many shipyards. we have stressed that we want conventinal propulsion (FPP, rufdder and bow thruster) and less sophisticated controls. reason for that was what I acould gather from our FSO Master, Chief Engineers, tug's Masters and pilots that CPP is good for manueverability but if you have a problem with the propulsion system then you must go to dry dock. That has repelled us from CPP. I also came to know from a friend of mine that gere in the gulf area another oil company with all its tugboats built with CPP is now going to change to ASD due to the too many problems they have with CPP.

Some of the offers we received from shipyards has offered conventioanl propulsion as first choice to meet our requirement but they recommended to order CPP for better control.

I am not sure whether they have priced the CPP options in their offer as we do not open Commercial proposals until we select the technically acceptable ones. If now we discover that really as APEX says the CPP is cheaper then we will only have to answer the question about maintenance and breakdowns and to get an answer why that other company in the gulf has decided to replace CPP with ASD!!!

Fuel oil consumption might not be the issue although it is important. the main engines are most of the time OFF when they have nothing to do which is good part of the week.

another issue I would like your opinion about is the cooling system: box cooler or plate cooler? what is better to take? what are advantages and disadvantages?

thanks and regards,

Mohamed

 

Hello Mohamed

There are definetively ZERO issues with CPP´s when you purchase a proven system from a well known manufacturer! Again: ZERO!
The average gearbox has ten times the failure rate than the CPP.
Choose a Helseth, or Wärtsilä prop, for example, and forget the meaning of trouble*. This is not a wild guess, this is experience. I am well aware that my recommendation can cost you a lot of money or the job! Not all here grasp that.

The price comparison has much to do with your engine choice! When you have already medium speed at the shaft, you need just a reduction box (if), and come probably out cheaper with a CPP. When you have high speed engines, the advantage is gone. Then the CPP may cost a bit more than the conventional drivetrain. But even then, the lower consumption and far better load conditions on the engines pay back very soon. The latter being a definite KO argument all the time.

I cannot comment on the cooling question, that is more a religious than a technical one. I assume you don´t operate in ice conditions.

Regards
Richard

* and don´t forget ZF, Piening, Korsør and Berg. All of outstanding quality!

 

Just spoke with guy who worked on a AHTS with box coolers and he had the show stopper issue of working in a field with an oil spill.
The thick goo when into the box coolers and they were unable to get it out so overheating engines.
Had to shutdown and get it towed to a dry dock

 

Interesting aspect! Have never thought about that.
You can see, we are all more or less bound to our heritage. For me ice was a issue, oil out of sight...........

Regards
Richard

 

Hi all.

My company is going to order two tugboats to use them in Russia. Ice conditions are very harsh. The maximum vessel we need to operate with is handysize one with DWT 30000 ton. I'm biased to ASD tugs with 2500HP and BP of 30t. Displacement - ~400 ton. Do I need to think about CPP with rudders?

I'm considering Dutch Damen and Canadian Ocean Group
Do I coorrectly understand that these manufacturers are leaders of the tugboat market? Please, advise me some other manufacturers I should see.