Why are Mazda persisting with the Rotary Wankel engine?

[anonymous-user]

Mr2Mike said:

RayTay said:

The quietness, smoothness and lack of vibration of a wankel gives even more flexibility in locating accommodation near to machine rooms.

You didn't answer whether a wankel could be run on HFO, if not it would completely prevent it's adoption for ships. Are there any commercial diesel wankel engines in production?

Those huge, low revving two stroke diesels also top the charts on thermal efficiency as far as internal combustion engines go. Could a wankel engine hope to get even close to the efficiency of them?

One of the other advantage of large marine reciprocating engines is that they are highly modular, and highly servicable, with the ability to swap major parts (like rods, pistons, bores, valve heads etc) without having to remove and disassemble the engine. The architecture of a wankle, makes it pretty much a necessity to split the crankcase to change a "piston" (rotor).

[lostkiwi]

Mr2Mike said:

RayTay said:

The quietness, smoothness and lack of vibration of a wankel gives even more flexibility in locating accommodation near to machine rooms.

You didn't answer whether a wankel could be run on HFO, if not it would completely prevent it's adoption for ships. Are there any commercial diesel wankel engines in production?

Those huge, low revving two stroke diesels also top the charts on thermal efficiency as far as internal combustion engines go. Could a wankel engine hope to get even close to the efficiency of them?

Rolls Royce made a rotary engine (wankel design) with two rotors where the first rotor acted as a compressor to the second one. This was how they managed to get the effective compression ratio high enough.

If you deviate slightly from the wankel design take a look at the Liquid Piston design. Effectively they turned the wankel design inside out by putting the tip seals into the housings and the intakes and exhaust ports in the rotor.
They can be made in compression ignition or spark ignition variants and they claim better fuel economy than both.
http://liquidpiston.com/technology/engine-benefits...

[RayTay]

Mr2Mike said:

You didn't answer whether a wankel could be run on HFO, if not it would completely prevent it's adoption for ships. Are there any commercial diesel wankel engines in production?

Those huge, low revving two stroke diesels also top the charts on thermal efficiency as far as internal combustion engines go. Could a wankel engine hope to get even close to the efficiency of them?

Hi Mr2Mike, Yes they can run on heavy fuel oil. I did mention that in the rotaries for UAVs where the HFO is heated to 98C before injection and the fuel is ignited via spark ignition. All to standardise on a single fuel, HFO, for NATO.

Many tests and projections are pointing to an equal, or even higher thermal efficiency in rotaries when running at a constant speed in genset applications applying the newer technologies that iron out known faults.

Max_Torque said:

One of the other advantage of large marine reciprocating engines is that they are highly modular, and highly servicable, with the ability to swap major parts (like rods, pistons, bores, valve heads etc) without having to remove and disassemble the engine. The architecture of a wankle, makes it pretty much a necessity to split the crankcase to change a "piston" (rotor).

Hi Max_Torque, The large diesel marine engines are sort of easy to replace major parts in situ. Modular is not the right word for them. They cannot be swapped out as a whole being massive. The idea is to swap out a rotary and swap in another to keep the ship running. The rotaries will be small enough to swap out. One could be swapped out and one swapped in, in a matter of hours. The swapped out unit then can be split and re-conned in a machine shop. Bare in mind rotaries are one third of the weight and size of an equivalent output in power over a piston/crank engine, which has great advantages in many applications.

lostkiwi said:

Rolls Royce made a rotary engine (wankel design) with two rotors where the first rotor acted as a compressor to the second one. This was how they managed to get the effective compression ratio high enough.

If you deviate slightly from the wankel design take a look at the Liquid Piston design. Effectively they turned the wankel design inside out by putting the tip seals into the housings and the intakes and exhaust ports in the rotor.
They can be made in compression ignition or spark ignition variants and they claim better fuel economy than both.
http://liquidpiston.com/technology/engine-benefits...

Hi lostkiwi, Yes RR did have a diesel rotary with one rotor as the compressor around 1970. This idea has been taken up again by Pratt & Whitney Rocketdyne who have received R&D funding from US agency DARPA. Again this is to use the single heavy fuel for NATO purposes. There has been no news of their results. Rotron of the UK approach using HFO from another angle. Yes, Liquid Piston do have a superior conceptual design and have had working models running, and they received funding for the R&D. I like the idea of apex seals in the housing, that can be easily swapped in and out, like on a periodic service. I can only see initially military UAV applications for the design. Military do not care about emissions for certain usages and they are prepared to spend on UAV R&D. Then it may be taken up by others for differing applications. The current wankel design is known and improvements are there to elevate the design. Then it is not that difficult to move over a new conceptual rotary design.

Edited by RayTay on Saturday 13th February 18:52

[Mr2Mike]

RayTay said:

Hi Mr2Mike, Yes they can run on heavy fuel oil. I did mention that in the rotaries for UAVs where the HFO is heated to 98C before injection and the fuel is ignited via spark ignition. All to standardise on a single fuel, HFO, for NATO.

That's not actually a diesel engine, and won't have the efficiency benefits of a diesel. Running spark engine on heated heavy fuel oils is hardly new, it goes back a very long time, probably as far back as the 1st World War.

UAVs use small displacement, high speed engines, a role quite well suited to a wankel engine. Ultra large, super low RPM doesn't seem like such a good fit.

RayTay said:

Many tests and projections are pointing to an equal, or even higher thermal efficiency in rotaries when running at a constant speed in genset applications applying the newer technologies that iron out known faults.

Higher thermal efficiency than the big two stroke diesel ship engines? Call me cyncial, but I find that extremely unlikely. A conventional wankel (i.e. tri-lobe rotor, epitroichoidal housing) has so many inherent deficiencies that I can't see it getting even close. Are you talking about one of the derivative rotary engines that isn't actual a wankel?

There have been numerous concept engines over the years whose inventors are claiming super high efficiency, but I've not seen any that have actually delivered yet, as in a practical design suitable for production.

[anonymous-user]

RayTay said:

Hi Max_Torque, The large diesel marine engines are sort of easy to replace major parts in situ. Modular is not the right word for them. They cannot be swapped out as a whole being massive. The idea is to swap out a rotary and swap in another to keep the ship running. The rotaries will be small enough to swap out. One could be swapped out and one swapped in, in a matter of hours. The swapped out unit then can be split and re-conned in a machine shop. Bare in mind rotaries are one third of the weight and size of an equivalent output in power over a piston/crank engine, which has great advantages in many applications.

Modular is exactly the right word for them, as the manufacturers prove a design for a single set of reciprocating parts and the engine just gets longer/has more cylinders as the power requirement increases. Really the only none modular part is the main crankcase, with everything else being cylinder specific (ie separate cylinder heads etc)


There is one fundamental flaw in using a small(er) power dense rotary engine for low cost large scale marine propulsion. And that flaw is that if you want to make the same power output as a larger engine, then you need to increase the speed of the small engine (Power = speed x torque). Unfortunately, large marine propellors have a small speed window for high efficiency operation. Hence, you'll either need to use a high speed prop, or use a gearbox (mechanical or electric) All of those things are EXPENSIVE on a large scale

[otolith]

I thought most large marine applications were diesel-electric these days?

[RayTay]

Mr2Mike said:

That's not actually a diesel engine, and won't have the efficiency benefits of a diesel. Running spark engine on heated heavy fuel oils is hardly new, it goes back a very long time, probably as far back as the 1st World War.

UAVs use small displacement, high speed engines, a role quite well suited to a wankel engine. Ultra large, super low RPM doesn't seem like such a good fit.

Higher thermal efficiency than the big two stroke diesel ship engines? Call me cyncial, but I find that extremely unlikely. A conventional wankel (i.e. tri-lobe rotor, epitroichoidal housing) has so many inherent deficiencies that I can't see it getting even close. Are you talking about one of the derivative rotary engines that isn't actual a wankel?

There have been numerous concept engines over the years whose inventors are claiming super high efficiency, but I've not seen any that have actually delivered yet, as in a practical design suitable for production.

Hi Mr2Mike, you are right in that the Rotron engine is not compression ignition. It does burn heavy fuel oil like a compression ignition engine, which will become a NATO requirement of the single fuel. A mix of about 54% diesel and rest a form of kerosine. As you say heating fuel is nothing new, but new in a rotary. In battlefield conditions a UAV can use the fuel of trucks.

Yes, running at a constant speed in a genset application they predict a higher thermal efficiency than the large diesel engines. Let's say the improved rotaries are just under the big diesels, the small size, less weight, smoothness, less vibration, etc are clear advantage in a cruise ship that would generate more revenue for the ship. Any new wankel design rotaries will not be like the batch we saw 30 years ago. That is not using a new concept engine, just the reuleaux triangle wankel design we are familiar with. Although small scale and niche, R&D has been directed towards the wankel. UAVs and series-hybrids tend to be the focus for R&D. I mentioned the marine side as some are looking ahead and see clear advantage in some sectors once, and if, rotaries become widespread in series-hybrids. There are no large wankels currently under development.

Max_Torque said:

Modular is exactly the right word for them, as the manufacturers prove a design for a single set of reciprocating parts and the engine just gets longer/has more cylinders as the power requirement increases. Really the only none modular part is the main crankcase, with everything else being cylinder specific (ie separate cylinder heads etc)

There is one fundamental flaw in using a small(er) power dense rotary engine for low cost large scale marine propulsion. And that flaw is that if you want to make the same power output as a larger engine, then you need to increase the speed of the small engine (Power = speed x torque). Unfortunately, large marine propellors have a small speed window for high efficiency operation. Hence, you'll either need to use a high speed prop, or use a gearbox (mechanical or electric) All of those things are EXPENSIVE on a large scale

Hi Max_Torque, few would call an engine that has ease of parts replacement "modular". Modular is viewed by many as a whole engine/generator in a bank that can be swapped in and out, or isolated and worked on. The idea is to have one extra module (rotary genset) than needed, in case one needs to be worked on, fails or is swapped out. Then full power is always available. wankel rotaries are smaller enough to have in banks and a control system sequence them in to the power demands of the ship. They can all be up to temperature using waste heat from running engines and take full load immediately. Having them in banks reduces the risk of full or partial down time. Recall the "poop cruise" ship in the Caribbean a few years back, drifting with no power. Having an extra massive diesel engine for backup is not cost effective and importantly takes masses amount of revenue generating hull space and annoyingly vibrates. This modularisation is seen on some large commercial gas boilers that have a frame with many square boxes on it. These boxes have a burner inside and are brought in by sequence control to the heat demand of say a building. Any one of the burner boxes can be swapped in and out, or isolated, and the heat is still being generated and all up and running and no down time.

These marine applications of rotaries would only be for gensets. No direct driving of mechanical props or whatever. Modern cruisers use electric propellers. Rotaries are more efficient when running at higher revolutions. Higher speed alternators would then be used. It is the opposite of the slow revs big diesel engines. It is a matter of detaching our minds of what we currently do.

otolith said:

I thought most large marine applications were diesel-electric these days?

Hi otolith, the cruise liners clearly are commercial ships that require a high degree of manoeuvrability. An advantage is to move in and out of berths without expensive tugs. Individually controlled electric props put these behemoths in berths with cms to spare. Electric props are not new. I think the first to use one was a Russian vessel well over 100 years ago. I know some dredgers used them for manoeuvrability about 112 years ago. The 1930s French liner Normandie had electrically driven props. Electric motors these days are a fraction of the size of earlier motors, as are generators. The traction motors can be a part of the wheel hub saving space in a vehicle.

We have post Panamax ships; only a few of them. The giants cannot run through the Panama Canal, even after the recent locks were widened. These are ocean side to ocean side vessels, like trans-Pacific, or China to Europe. They need to be near full, or full, to be economical. Most container ships do not need to be massive depending on the routes they serve. Ship designers are attempting to pack more into a Panamax ship's hull; the largest through the Panama Canal. ACL containers have a new design which has just come on-line which packs in 40% more into the Panamax hull. This means they have far more flexibility if trade routes change, like from the US west coast to the east coat through Panama and across to Liverpool which has Panama Canal sized locks. Mechanicals get in the way of lucrative cargo space. Accommodation can be located way above the cargo spaces; with a crew of about 15 these days that is feasible.

Just for fun..here are the post Panamax cranes being delivered to Liverpool's new terminal. The ships berth in the tidal river, not in enclosed docks. All the way from China and it never capsized.

Edited by RayTay on Friday 12th February 22:59

Edited by RayTay on Sunday 7th August 10:30

[AW111]

RayTay said:

Just for fun..here are the post Panamax cranes being delivered to Liverpool's new terminal. The ships berth in the tidal river, not in enclosed docks. All the way from China and it never capsized.

Edited by RayTay on Thursday 11th February 11:48

That ship doesn't need a rotary, just a few acres of canvas.

[RayTay]

lostkiwi said:

If you deviate slightly from the wankel design take a look at the Liquid Piston design. Effectively they turned the wankel design inside out by putting the tip seals into the housings and the intakes and exhaust ports in the rotor.
They can be made in compression ignition or spark ignition variants and they claim better fuel economy than both.
http://liquidpiston.com/technology/engine-benefits...

Hi Lostkiwi, this thread does go into some of these advances. What is being currently developed are engines for genset application in series-hybrids and rotaries for UAV and hybrid applications. Free-piston designs using one and two opposed pistons with electric coils in the pistons and cylinders are being developed in Germany and by Toyota.

Once USA funding is given, which is usually from a military agency, the engines falls off the radar. No results of progress are given and all is silent. This is the case for Pratt & Whitney Rocketdyne in the compression ignition heavy fuel oil development of a wankel design rotary and as you pointed out, Liquid Piston in an entirely new concept of rotary. The US military are keen in advancing rotaries, for UAVs and general genset applications, whether used in a series-hybrid vehicle or general portable field gensets. The rotaries will make the portable gensets smaller and lighter.

Computer modelling, knowledge of how the wankel design performs, new advances in metals (even ceramics), ignition systems and engine management can make the likes of the Liquid Piston engine succeed. When it does it is curtains for the piston/crank design of engines. In the meantime the US military want an engine to meet a specific niche. Once the niche application is successful it can then fan out into the general civilian market.

It is encouraging seeing all this research and highly interesting seeing the new designs and results of any research. I have never seen so much all at once on the internal combustion engine.

Edited by RayTay on Friday 12th February 11:20

[RayTay]

Mazda have done promising research on HCCI ignition for its SkyActiv-R rotary engine project using research from its SkyActive 2 program. They have removed the need to locate the spark plug outside the combustion chamber to allow the rotor to sweep past. Mazda solved this in the SkyActiv-R rotary project. Rotaries generally have high compression ratios giving the design easy adoption of homogeneous charge compression ignition (HCCI).

It looks like the next Mazda rotary will not have a spark plug and be HCCI ignition. Fuel consumption will match piston engines and when used a constant speed gennny as in hybrid outperform piston engines with all the advantages of low weight, small size, super-smooth, simplicity, etc. The expectation will be that the engine will be introduced in 2020, the 100th anniversary of Mazda. Looking good.

Explanation of HCCI from wiki:
"Homogeneous charge compression ignition (HCCI) is where the fuel/air intake is a pre-mixed lean air-fuel mixture then compressed to the point of auto-ignition. Electronic spark ignition is eliminated. Gasoline engines combine homogeneous charge (HC) with spark ignition (SI), abbreviated as HCSI. Diesel engines combine stratified charge (SC) with compression ignition (CI), abbreviated as SCCI. HCCI engines achieve gasoline engine-like emissions with compression ignition engine-like efficiency. HCCI engines achieve low levels of nitrogen oxide emissions (NO x) without a catalytic converter. However, unburned hydrocarbon and carbon monoxide emissions still require treatment to reach automotive emission regulations."

Edited by RayTay on Sunday 7th August 10:41

[hidetheelephants]

RayTay said:

Because of pressure by cruise liner companies for economic running and utilising all space inside a ship for revenue gain, large rotary turned gensets are being looked at. The ships use electric motors to turn the propellers and azipods. The operators prefer them to run on LPG gas for many reasons and one is an eco image. Black diesel smoke from funnels in Venice and sunshine ports is not a good selling point and riles many people as these ports are permanently full of cruise liners with engines permanently running. Being about a third of the size of a diesel genset, and much, much smoother and quieter eliminating vibration (an important point with passenger accommodation), large rotary gensets would save considerable space in a ship. Space is money in these vessels.

The space argument doesn't stand up to much scrutiny; medium speed diesel generators are already compact enough to fit below the waterline and no cruise company wants or needs to put passengers somewhere they can't have a porthole. There are also prosaic things like stability to take into account, diesels are nice and heavy and having them at the bottom of the ship is good; getting rid of them and fitting smaller and lighter replacements just creates the need for ballast instead.

The engine in the picture you've used is a slow speed diesel, I'm not aware of any cruise liners which use these as they are very bulky and create a lot of vibration; they are used in cargo vessels where vibration is less of a concern and fuel economy is king. The medium speed units liners typically use are about the same size as the HGV pulling it.

RayTay said:

Sway, look at the height of this ship's diesel engine. It has a lot of top weight there and is the height of at least three decks for sure. Banks of rotaries with say twin rotors at 1.5 metres in diameter all mounted on the keel will be about 0,5 of the height of one deck including the engine housing. This will put all the weight at the bottom of the ship for even better stability and space saving. Rotaries could be fitted that could be slotted out for re-con, so no major engine overhauls keeping the ship in dock losing revenue. Large mechanical items can be swapped in and out in a day keeping the ship moving. A genset module at a time gets overhauled on land. They could all be connected to the same cooling system pipes. Just isolate the cooling pipe valves, disconnect from the bus bars and slot it out.

Like I said the picture you've used is a slow speed diesel, which do not go into cruise liners. When liners are in for drydock it isn't the servicing of prime movers which is blocking up the critical path, it's the hotel services and interior decor; you're seeking answers to problems no-one has.

[RayTay]

hidetheelephants, space is paramount in cruise ships to maximise revenues. Storage, kitchens, laundry, ancillaries, etc can all go below the water line if smaller engines are used. Also as I have emphasised revenue earning 'up time' is very important with small modular rotary gensets giving that. What I am am writing about is the way they view matters in future generations of liners viewing that R&D advances in engine design materialise. Which looks that way. Engineers/designers do look ahead and smaller engines is something they would be homing in on.

The best best way of envisaging the largest modern cruise ship design, is imagine the ships as having two parallel long blocks of flats on a flat topped hull. Each block has cabins on one side looking inwards into an open internal forecourt and those on the other side looking outwards onto the sea. Getting all engines, tanks, ancillaries, kitchen, etc below that flat topped hull gives over more space for passenger accommodation/dining/entertainment above the flat topped hull.

You jest of course when writing that a truck engine can power a 140,000 ton cruise liner.

One thing is clear is that rotaries are about a third of the size of a diesel engine. That matters in many applications.

There has been experiments using a fuel mixture of petrol and diesel for HCCI ignition. The spark plug hole in current rotaries loses some compression/gasses from one chamber to the next as the rotary's apex seals run over the hole. This disadvantage is eliminated using HCCI. The fuel is premixed before entering the engine chambers so there is no need for holes in the engine housing.

Mazda may or may not fit a turbo to improve efficiency further on their up and coming rotary.

Edited by RayTay on Monday 8th August 15:16

[RayTay]

hidetheelephants, when liners are in 'dry dock' it is for major hull problems. The hotel maintenance side they try to do as they sail along and when if in port for a turnaround for few days to do more larger tasks. They may work 24/7 to get it done when in port with teams of carpenters, plumbers, etc, flooding onto the ship. The hotel side of maintenance always needs 'continuous' upkeep with 4,000 passengers coming and going every 7 days and wear and tear of the 1,500 crew. They have this well organised and efficient. They like parts to screw off and on to keep the ship moving.

A cabin that needs serious work can be out of commission for say a 7 day cruise. That cannot be done with major large diesel engines. It has to work. When it does not it may mean major down time reducing revenues. Modularised rotary gensets will not impair the revenue earning of the ship.

[hidetheelephants]

RayTay said:

hidetheelephants, when liners are in 'dry dock' it is for major hull problems. The hotel maintenance side they try to do as they sail along and when if in port for a turnaround for few days to do more larger tasks. They may work 24/7 to get it done when in port with teams of carpenters, plumbers, etc, flooding onto the ship. The hotel side of maintenance always needs 'continuous' upkeep with 4,000 passengers coming and going every 7 days and wear and tear of the 1,500 crew. They have this well organised and efficient. They like parts to screw off and on to keep the ship moving.

A cabin that needs serious work can be out of commission for say a 7 day cruise. That cannot be done with major large diesel engines. It has to work. When it does not it may mean major down time reducing revenues. Modularised rotary gensets will not impair the revenue earning of the ship.

They dock annually regardless of whether there's anything wrong as the class rules require it, although being as ships exist in the real world and float on salt water there's always something wrong. Service work on prime movers occurs continuously, depending on crew size it may be carried out by the ship's crew at port stops or by ride-on crews en-route, it does not have to wait for a docking as the ships typically have enough redundancy and surplus power to allow one to torn down and still meet power requirements.

RayTay said:

The best best way of envisaging the largest modern cruise ship design, is imagine the ships as having two parallel long blocks of flats on a flat topped hull. Each block has cabins on one side looking inwards into an open internal forecourt and those on the other side looking outwards onto the sea. Getting all engines, tanks, ancillaries, kitchen, etc below that flat topped hull gives over more space for passenger accommodation/dining/entertainment above the flat topped hull.

Provided the designer is prepared to ignore 200 years of evolution in ship design for stability, yes. None of the crew accommodation, galleys, stores, etc can contribute to stability as they are not dense enough so the lost GM has to be replaced by adding fixed ballast, so unless the lifecycle costs of rotaries are less than the currently used prime movers shipping companies will say thanks but no thanks.

RayTay said:

You jest of course when writing that a truck engine can power a 140,000 ton cruise liner.

I wrote 'The medium speed units liners typically use are about the same size as the HGV pulling it.', which seems pretty clear; but for total clarity I mean medium speed diesels in liners are typically about the same size as a HGV, not that they are the same size as HGV engines.

Edited by hidetheelephants on Sunday 7th August 13:46

[RayTay]

hidetheelephants, large cruisers do dry dock regularly, however designers want to reduce this expensive dry docking. Advanced thinking ship designer do not want to be impaired by 200 years of ship evolution. They always want a leap forward.

Engines, all liquid tanks, including fuel tanks (or LPG gas tanks), storage, kitchens and crew can provide enough below waterline weight to give stability. Modern ships tend to be wide to comply with the displacement and stability laws. The top of the superstructure tends to be lightweight materials, like aluminium.

What is driving designers is packing in more lucrative passenger cabins & entertainment space and reducing ship 'down time'. Hence why we see many older ships having a few hundred cabins built on. If the NCCI rotaries, at one third of the size of exiting piston engines, and the not to be forgotten smoothness are a reality and up-scaled, believe me they will seriously look at them for a moduled engine array. Your views that nothing will change is rather naive. I can hear men 80 years ago saying nothing will replace steam engines as they have been around in force since the 1840s.

The 51,000 ton Crystal Symphony is small by the rather common 140,000 ton cruisers we see today, and minute to the Harmony of the Seas at 227,000 tons - which has six engines (gensets) over 5 metres high. Crystal Symphony has six Wärtsilä-Sulzer diesel engines which gives 25,260 kW (33,880 hp) combined. That is to propel the ship and service all the ship's services and ancillaries. The Scania trucks are about 730 HP. A massive difference. Modern cruisers turn the props by electric motors. The engines are gensets.

Edited by RayTay on Monday 8th August 15:03

[AW111]

Ray, are you deliberately misunderstanding HTEs post?
The power of a HGV has nothing to do with what he wrote.
And AFAIK, most of the vibration in liners comes from the prop, not the engine itself.

I think there are some niches that suit rotaries, but they are not a magic bullet.

[RayTay]

AW111, I am not deliberately misunderstanding HTEs post. He mentioned the power of a HGV engine to push a cruise liner. Engines do vibrate, especially diesels. Vibrations from props can be eliminated greatly by azipods. Cavitation around props does not help and that is being worked on.

Rotaries are not a magic bullet for sure, but in genset applications, as in vehicle hybrids and ships, the NCCI rotaries do promise a lot and seriously threaten to replace piston engines if the HCCI versions are introduced. This is only looking at R&D on rotaries being done right now which does look highly promising. People do look ahead. If HCCI rotaries come on the market, I would not expect to see any of them in cruisers for 10 years after.

Edited by RayTay on Monday 8th August 15:41

[hidetheelephants]

AW111 said:

Ray, are you deliberately misunderstanding HTEs post?
The power of a HGV has nothing to do with what he wrote.
And AFAIK, most of the vibration in liners comes from the prop, not the engine itself.

I think there are some niches that suit rotaries, but they are not a magic bullet.

Another important point I didn't mention, quite apart from rafting being an excellent and inexpensive way to isolate diesels from the ship's structure.

RayTay said:

hidetheelephants, large cruisers do dry dock regularly, however designers want to reduce this expensive dry docking. Advanced thinking ship designer do not want to be impaired by 200 years of ship evolution. They always want a leap forward.

Engines, all liquid tanks, including fuel tanks (or LPG gas tanks), storage, kitchens and crew can provide enough below waterline weight to give stability. Modern ships tend to be wide to comply with the displacement and stability laws. The top of the superstructure tends to be lightweight materials, like aluminium.

What is driving designers is packing in more lucrative passenger cabins & entertainment space and reducing ship 'down time'. Hence why we see many older ships having a few hundred cabins built on. If the NCCI rotaries, at one third of the size of exiting piston engines, and the not to be forgotten smoothness are a reality and up-scaled, believe me they will seriously look at them for a moduled engine array. Your views that nothing will change is rather naive. I can hear men 80 years ago saying nothing will replace steam engines as they have been around in force since the 1840s.

Where have I said nothing will change? I said economics will lead and the economics of vapourware engines do not appeal to shipowners. You need to read what I've written, ship stability is not amenable to persuasion, you need dense things in the bottom of the ship, ballast tanks are not enough on their own and the liners cannot reasonably be made significantly wider as they are already as big as canal, port and drydock/construction facilities(and arguably structural orthodoxy and class rules too) will allow. These rotaries(or indeed any novel prime mover) will be adopted only when they can rival conventional four stroke diesels in fuel economy, durability long term maintenance costs, at which point the bilges of liners will be filled with ballast weights to maintain GM where it needs to be.

[Super Slo Mo]

RayTay said:

AW111, I am not deliberately misunderstanding HTEs post. He mentioned the power of a HGV engine to push cruise liner. Engines do vibrate, especially diesels. Vibrations from props can be eliminated greatly by azipods. Cavitation around props does not help and that is being worked on.

Inadvertently misunderstanding it then. He didn't mention the power of an HGV engine at all, re-read his post. It's pretty clear.

[RayTay]

hidetheelephants, vapourware engines do not appeal to shipowners for sure, but those under R&D and look promising appeal to ship designers. You seem to think a ship cannot have below the waterline weight unless they have large diesel engines, so the ship designers will only ever stick to these large heavy lumps. These lumps are quite tall. Smaller modular engines can be right on the keel putting the weight where it is most needed.

Liners can be made significantly wider. Few liners run through canals, they operate in the sunshine seas mainly moving seas to the seasons. Dry docks can be made wider, which is not a difficult thing to do. Liverpool, with 32 foot tides, got over the width of liners by having a floating landing stage that rises and lowers with the tide.

You are right that any novel prime mover will only be adopted only when they can rival conventional four stroke diesels in fuel economy and maintenance costs. And also reduced down time due to modularisation - slide in and out smallish gensets. If they do have these attributes and they are vastly smaller, and infinitely smoother giving to modularisation, that will tip the balance in cruisers where space in the hull means money. That day looks to be closer.

Edited by RayTay on Monday 8th August 18:54