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Old 01-07-2016, 06:33   #91
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Re: Why not electric engine powered boats

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Originally Posted by StuM View Post
Cruise ships are in a class of their own. They have massive non-propulsion electrical requirements compared to other vessels of a similar size. When most of your power requirements are non-propulsion, it makes economic and engineering sense to upsize your generating power to provide your propulsion as well from a single system.

It's a totally different situation compared to small pleasure craft.
I'm curious about your background, that you're able to come on here and opine with great apparent authority on such a wide variety of subjects. Of course, in this regard you're talking utter bollocks. In D/E cruise ships about 85% of the generating capacity is earmarked for propulsion. They also have smaller auxiliary generators to handle hotel loads, when alongside and not plugged in. When you consider the expense and complexity of the various means they employ to gain even meagre gains in fuel efficiency, it is clear that the prime motivation in employing D/E is the efficiency. If not, they would stick to the tried and true method of employing separate diesel propulsion and generators for electrical services.
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Old 01-07-2016, 06:39   #92
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Re: Why not electric engine powered boats

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But the biggest issue for cruise ships is that they need azipods in order to have maximum maneuverability. Because most of their ports of call do not have tug boats, and the azipod thrusters allow them to operate independently of outside support. This opens up a lot of ports that typically couldn't handle ships close to as large as modern cruise ships.
They don't "need" azipods; but they do offer manoeuvring (and other) benefits. Before azipods became available, cruise ships still got into and out of harbours without tugs - they were just fitted with a bunch of bow and stern thrusters. Most of them still have a battery of bow thrusters, even with azipods.
The 7-year old Norwegian Epic is D/E with a conventional shafting arrangement, 4 bowthrusters and 2 stern thrusters.
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Old 01-07-2016, 07:20   #93
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Re: Why not electric engine powered boats

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I'm curious about your background, that you're able to come on here and opine with great apparent authority on such a wide variety of subjects. Of course, in this regard you're talking utter bollocks. . . .
Keep up the borderline ad hominem attacks and we'll get a lot more attention from the mods and may get this thread shut down.



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Old 01-07-2016, 07:21   #94
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Re: Why not electric engine powered boats

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They don't "need" azipods; but they do offer manoeuvring (and other) benefits. Before azipods became available, cruise ships still got into and out of harbours without tugs - they were just fitted with a bunch of bow and stern thrusters. Most of them still have a battery of bow thrusters, even with azipods.
The 7-year old Norwegian Epic is D/E with a conventional shafting arrangement, 4 bowthrusters and 2 stern thrusters.
Sure cruise ships got along without them in the past, cruise ships were smaller (I took a cruise with my parents way back and the ship was only 500' long. New ones are more than twice that size) and went to fewer larger ports. With the proliferation of cruise ships, they need to squeeze into smaller ports.

Also unlike a freighter that may enter and leave port once a week, so lost time waiting on tugs is a minor issue. Cruise ships do it on almost a daily basis (QEII is the exception doing transatlantic crossings regularly).

Azipods eliminate all those stern thrusters along with the drag inducing holes in the side of the hull that come with them. They can also downsize the bow thrusters a bit because due to the greater thrust available with the azipods in the stern.

Forward propulsion efficiency is not the driving force in the switch to azipods and diesel/electric. If it was about efficiency, they would go with a single prop running at slower speeds. It's not.
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Old 01-07-2016, 07:43   #95
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Re: Why not electric engine powered boats

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Sure cruise ships got along without them in the past, cruise ships were smaller (I took a cruise with my parents way back and the ship was only 500' long. New ones are more than twice that size) and went to fewer larger ports. With the proliferation of cruise ships, they need to squeeze into smaller ports.

Norwegian Epic was the 3rd largest cruise ship in the world when it was laid down.

Azipods eliminate all those stern thrusters along with the drag inducing holes in the side of the hull that come with them. They can also downsize the bow thrusters a bit because due to the greater thrust available with the azipods in the stern.

Perhaps, but I wonder when they're fitted with 3 or 4 azipods, why they don't just stick one or two near the bow and obviate the thrusters altogether. No matter what form your thrust is at the stern, you can't use it to push the bow about. That's simply not how ships, or even boats manoeuvre.

Forward propulsion efficiency is not the driving force in the switch to azipods and diesel/electric. If it was about efficiency, they would go with a single prop running at slower speeds. It's not.
Never said it was; it's about overall efficiency while maintaining an expected set of performance parameters. Not sure where your argument is here?
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Old 01-07-2016, 07:48   #96
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Re: Why not electric engine powered boats

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Keep up the borderline ad hominem attacks and we'll get a lot more attention from the mods and may get this thread shut down.
Oh good, the niceness police are here. Where were you before?


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Reading comprehension may not be your strong suit, so lets try again...read closely mi amigo...
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I suggest you learn a little about diesel engine power curves before opining on how to replace them.
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Old 01-07-2016, 08:05   #97
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Re: Why not electric engine powered boats

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Never said it was; it's about overall efficiency while maintaining an expected set of performance parameters. Not sure where your argument is here?
Those big bow thrusters on your example ship need lots of electric power, unlike your typical freighter and still have the need to get in and out of ports far more frequently. Once they put in the big generators to handle that load, it was probably cheaper to keep everything on the same system as they could redirect the same generator power that drives the main propulsion to the bow thrusters.

If you've ever handled a twin engine boat, you would realize that you can spin the boat in place without bow thrusters. With independently steered azipods, they can do even better and negate much of the need for giant bow thrusters.

The argument is propulsion on the open sea is not the driving force in cruise ships using diesel electric. If efficiency was critical, they drop back to 15-20kt cruise speed and cut fuel consumption in half...which is exactly what your typical direct drive diesel powered freighter does.
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Old 01-07-2016, 08:30   #98
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Re: Why not electric engine powered boats

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Those big bow thrusters on your example ship need lots of electric power, unlike your typical freighter and still have the need to get in and out of ports far more frequently. Once they put in the big generators to handle that load, it was probably cheaper to keep everything on the same system as they could redirect the same generator power that drives the main propulsion to the bow thrusters.

How do you think conventionally-engine cruise ships powered their bow/stern thrusters? If conventional arrangement was more efficient, it would be cheaper to keep that and have another generator that is only run up when the thrusters are needed.

If you've ever handled a twin engine boat, you would realize that you can spin the boat in place without bow thrusters. With independently steered azipods, they can do even better and negate much of the need for giant bow thrusters.

Neophytes believe that the boat is like a door, where the engines are the hinge - and you can swing the bow around like a door opening. That is not the case. The vessel turns around the pivot point which is actually not fixed, but at rest in most classes of vessels, is somewhere nearer the bow, maybe 1/4 to 1/3 of LWL back from the bow. This is the same whether using shafted screws or azipods. Not only have I handled twin engine boats, I've driven ships with azipods - have you?

The argument is propulsion on the open sea is not the driving force in cruise ships using diesel electric. If efficiency was critical, they drop back to 15-20kt cruise speed and cut fuel consumption in half...which is exactly what your typical direct drive diesel powered freighter does.
Again I'm not sure what your argument is - the operators of cruise ships clearly want to keep operating their ships like cruise ships, not freighters. Given the average operating regime of a cruise ship, the more efficient propulsion arrangement is D/E.
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Old 01-07-2016, 09:06   #99
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Re: Why not electric engine powered boats

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Again I'm not sure what your argument is - the operators of cruise ships clearly want to keep operating their ships like cruise ships, not freighters. Given the average operating regime of a cruise ship, the more efficient propulsion arrangement is D/E.
Let's cut the clutter, since you seem not to be getting it.

Cruise ship owners care very little about fuel efficiency when cruising in open water. They just don't. Other issues unrelated to open water cruising efficiency control the design and operation and dictate the use of diesel/electric.
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Old 01-07-2016, 10:48   #100
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Re: Why not electric engine powered boats

Never worked in the cruise ship world but I have quite a few years dealing with ships with 360 degree azimuth thrusters.


I would think maneuverability and station keeping ability would rank high in the design decision.

Never heard of fuel efficiency not being a factor.
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Old 01-07-2016, 11:21   #101
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Re: Why not electric engine powered boats

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Never worked in the cruise ship world but I have quite a few years dealing with ships with 360 degree azimuth thrusters.


I would think maneuverability and station keeping ability would rank high in the design decision.

Never heard of fuel efficiency not being a factor.
I am with you, I have never heard any ship owner to say they aren't concerned with efficiency. A better way to put it would be that efficiency takes a secondary concern to our issues.

For cruise ships maneuverability is mission critical so it gets top billing, vibration for passenger comfort is another mission critical issue here D/E is a better option, even installed space is better with D/E. And they are relatively efficient after all, say witching 10% the efficency of a large mechanical drive diesel.

But then cruise ships aren't really using the same type of generators we would, a lot of them have started deploying diesel turbine generators which are much more efficient but more expensive.

When discussing all of the options out there it is difficult to draw direct comparisons with pleasure yachting. Simply because even the largest yachts are really small compared to commercial vessels. There are just a handful of yachts in the world over 100m, but a huge number of commercial ones are. Just because something works for a 1,000' ling cruise ship has very little bearing on if it will work on a 65' sailboat.

Even so, if you design a ship for maximum efficency at a given speed there is no better option than a mechanical low speed diesel pared to a Variable pitch prop. Which is why Wartzilla keeps making bigger and bigger prime movers.
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Old 01-07-2016, 11:58   #102
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Re: Why not electric engine powered boats

Can't quite make it through all of the above, but I thought it was interesting, just finished a month long drydocking and had a carnival boat come in at the end. Insane sh@tshow, several hundred yard workers going 24/7, 14 days total something like 4 thruster overhauls with new blades 2 azipods and replacing a stabilizer they broke off. Rumors were the fines for delay days were in the 7 figures. Sounds like the business model is billable rm's and propulsion etc, is 90% about crew comfort. Interestingly enough this boat was originally a gas turbine, talk about lack of efficiancy.

D/E only makes sense when variable load and directional applied thrust is the norm.
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Old 03-07-2016, 14:34   #103
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Re: Why not electric engine powered boats

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Never worked in the cruise ship world but I have quite a few years dealing with ships with 360 degree azimuth thrusters.


I would think maneuverability and station keeping ability would rank high in the design decision.

Never heard of fuel efficiency not being a factor.
Never said it wasn't a factor just way low on their priority.

If fuel efficiency was the priority, you wouldn't see cruise ships running at 25-30kts. They could probably double their fuel efficiency by dropping back to 15kts. The problem is much higher priorities control the design of cruise ship propulsion (maneuverability, passenger comfort, time in port, etc...).

There is also a reliability issue. With multiple generators and multiple azipods, they can generally keep going if one generator or azipod fails. Likewise if the house generator fails, they can use a propulsion generator to keep the house power going.

If a load of crude oil gets delayed by a non-redundant propulsion system, there are repercussions but eventually the oil will get there and the owner will get paid. If the cruise ship doesn't sail, the have to refund the customers money, figure out what to do with 3000 people waiting for a ship and probably lose a lot of repeat business.

I stand by my statement that fuel effiency is no a significant priority for cruise ships.
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