How does a Turbine Engine work in a yacht?

The gas turbine is mounted in an enclosure where the exhaust is directed over a separate free power turbine then through a volute casing up the funnel or out the stern.

The free power turbine is geared down and goes to either a reversing gearbox to conventional shafting or from the gearbox to a controllable pitch propeller.

This is a similar method to how a helicopter takes power from it's turbines and converts it to the rotor.

Clear as mud?

The turbines I have seen in larger yachts (100+ft) are used as booster engines after the vessel is already traveling at a set target speed. Placed center line connected to a gear box then to a water jet nozzle that has no steering capability, just fwd thrust.

The biggest issue with turbines in yachts is they need a gear box that can reduce the RPM ratio to be used as a conventional propulsion system which I do not believe can be done yet. Military uses turbines connected to generators and then to electric powered propulsion systems of what ever type.

The next biggest issue with turbines on yachts is exhausting the exhaust heat. That has been extremely challenging for build engineers. Some vessels I know of can only use there turbine for less than an hour. Some vessel have just removed the turbine completely as it just proved to be to problematic for the vessel.

See the basic flaw of faith based engineering? What you believe is more than likely to be very wrong.

Back to the books for you young man. Start with simply Googling marine gas turbine reduction gears for a start. Then spend some time curled up with GE's LM series turbines and the naval installations of those and similar engines.
-------------------------------------------------

Here's a link for you Robert, it shows what some of the gears look like without going into a lot of technical details : http://www.renk.newsfactory.de/cms_media/objekte/225-Yacht_Prospekt.pdf

turbines and boats

some years ago I looked for this ...

goto youtube

Running for home - YouTube

and see the other videos in the list ...

I am sorry. I was retelling the experience that I had where engineers for turbine manufactures at the Ft Lauderdale boat show where teaching me just a few years ago while I was trying to educate myself. Maybe I misunderstood them on there gear box ratio problems for conventional propulsion usage on yachts oppose to just booster engines. I will google it and use your link and see what said.....

As noted, gas turbines can be geared to run props or water jets. In most "booster" applications they drive water jets because the drag from a water jet is lower (or close to zero if a door is used to close off the water jet when it is not in use).

Turbines have a power to weight ratio that is, generally speaking, about an order of magnitude better than a diesel. This higher power to weight ratio is mitigated by higher fuel consumption in the smaller (less than 5,000 hp) engines. Larger than that, turbines are pretty much the way to go, with better power to weight ratio and fuel consumption that is very close to, if not better than a comparable diesel.

Part power fuel consumption of a turbine is also an issue. Diesel engines have a pretty flat fuel specific consumption curve. That is, the mass of fuel consumed per horsepower produced is pretty constant. With a turbine, at lower power you don't get as good a specific fuel consumption and that means that, even if you have a pretty efficient turbine, you are going to burn more fuel at low speeds.

For engines below 5,000 hp, the decision to go with turbines is much more mission related. If you want to putt putt up the ICW at 6 knots, you certainly don't want a turbine. The low power fuel consumption would break any bank.

I do have a problem with way CODAG (combined diesel and gas turbine) "booster" systems have been applied in the past. Most of these have been applied to large planing or semi-planing hulls and the basic diesel engines sized to provide planing performance of perhaps 25 to 30 kts. After that speed the turbine is started and a few knots of speed are gained for a very high fuel flow.

Part of this is becuase the "booster engine" is a rather inefficient turbine (there is wide range of turbine performance, with good as well as poor performing engines). The reason that the gain in speed isn't large is that the weight of the diesel system is so large that the ship ends up being so heavy that even a pretty big turbine can't push it that much faster.

We've run some numbers on this and it looks like a smaller diesel system, one that can push the craft to hull speed or even a bit less, would save a lot of weight. Above hull speed you would kick in an efficient turbine and that would push the much lighter boat at planing speeds faster and would require less overall power, and it would result in almost the same fuel burn (within about 3%). This type of system would be the best of both worlds, a smaller diesel for low speed work and a larger gas turbine for high speed.

Turbines are generally more expensive than similar sized diesels, but as you get above about 2,000 hp that starts to change, and above 3,000 hp (per engine) turbines start to look pretty good. When you consider the maintenance cost they actually get better than diesels.

Turbines do have a larger exhaust flow, and the exhaust gas temperature is 100 or 200 degrees F greater than a diesel. Also there is a lot more air coming into the turbine so there are design issues with turbines that have to be addressed.

Overall, properly used, a turbine can be very close or as good as a high speed diesel in fuel consumption, and the advantages of clean exhaust, and very quiet operation make turbines attractive if the user wants a higher performance yacht.

There are a lot of turbines that are based on Viet Nam era helicopter engines that are expensive and very thirsty. Newer engines in the 2,000 - 2,500 hp class have much lower fuel burns, but they haven't been marinized in any numbers. I think this will change in time and we will see more turbines in high performance large yachts in the future.

In ships where you need big power (like destroyers and cruisers) turbines have displaced diesels for a number of reasons. In the future this will float down to smaller craft and I think you will see more yachts that want high speed equipped with turbines that will be used more than the "booster only" systems that we see now.

turbines

I wonder how many new mega yachts on order have turbines spec'd for any purpose and if I suspect very few, why if they are supposedly very close to the same cost etc.

as for ships that require "big horsepower like destroyers and cruisers" these are paid for by a government who do not have to answer to anybody about their costs and you will see that "ships" that need big horsepower run 12 cylinder slow speed Diesel engines. Obviously putting one of these into a 300 foot or above yacht is not feasible but if turbines are that efficient we would be seeing them in new builds.

What I see as happening is the introduction of turbines running generators that in turn supply electric pods for propulsion, bow & stern thrusters and also ships eelctrical power.

Saying that installing a number of fuel efficient liquified gas/diesel powered generators mimicking the way the commercial ships are heading will be alot more prevalent in the years ahead.

I think it was about the late 60's or early 70's that there was two turbine powered container ships in service and everybody talked of this was the way of the future. I actually qualified as a chief engineer for these ships but other than a few government sponsored commercial ships the idea never caught on.

A pity really as the concept was to have two turbines in service and one onboard as a spare. Every three or four months one would be easily lifted from the ship and another one slotted in. The removed one would be sent back to Rolls Royce for a major service.

I can not think of the name of the manufacturer at the moment but the boat was built down in North Miami on Thunder Boat Alley, it was about 100 feet LOA and came with two 12 or 16 V92's and a turbine in the center. This turbine could only be run for a few minutes and was eventually removed and another Diesel installed.

I believe that you are referring to a 70' Cary that I owned years ago which was equipped with two 12 cylinder Deutz's connected to water jets with a centerline turbine connected to an ASD8. The boat struggled to get on plane with the diesels but once on plane it picked up nicely with the turbine. Unfortunately the first iteneration of the turbines exhaust was not water cooled and quickly turned into a molten mess of stainless and aluminum after the first time it was fired up. Once that was repaired the boat ran only a handful of times with the turbine till the owner of the company died (Victor Posner) and the boat fell into disrepair culminating with the turbine seizing.

I can attest to the fact that these things don't belong in boats, I ended up removing the turbine, arneson and all associated hardware leaving the boat with the Deutz's and water jets. The boat actually ran and handled better with the exception of running WOT.

boat

No, I do not believe it was a Cary, it was about 100 foot motor yacht, white "shag carpets" in the salon and a cabin suspended on cables above the port & center engine supposedly for a nanny. It was a real funky looking "thing" and I believe it was built in the factory that was at the east end of Thunderboat Alley on the left. The same factory that built Balck Fins for a while. I think the name of the manufacturer started with an "I" but my mind is a blank.

I don't think that many of the owners of large yachts value speed that much. They go to their boats to relax and going fast simply isn't a requirement. Most of these ships cruise along at or below hull speed most of the time. If you aren't going fast then a tubine doesn't make sense.

Huge low speed diesels are very efficient, but the weight, volume and size make them appropriated only for low speed applicatoins (liker container ships). You really need to compare high speed diesels with turbines, and when you make that comparison in the 5,000 hp and greater size class turbines compare very favorably with diesels on fuel consumption, and are a lot more reliable, easier to maintain, don't cost any more. This is why diesels aren't really even considred for ships like destroyers and cruisers.

The advantage of a turbine in a electric drive is that a generator running at turbine shaft speed is much much lighter and smaller than a similar generator coupled to a diesel. Also remember that turbines can burn any fuel with equal efficiency. Natural gas engines have lower compression ratios and consequently lower efficiency.

It used to be that if you got 10,000 hours on an aero engine you were putting ads in the magazines that you did it. Nowadays, if you don't get 20,000 hours between overhauls (or a lot longer) your customers are screaming. In the larger sizes turbine efficiency is better than high speed diesels, and this is slowly filtering down to smaller engines.

As I said, turbines have come a long way in the last 30 years. Just because somebody put a 45 year old helicopter engine into a yacht and it wasn't that good doesn't mean that it's a bad idea. You have to look at more modern technology engines to make a fair comparison.

I think you're talking about the 82 or 88 tempest. Two 16v92's on surface drives with a centerline turbine. It couldn't get out of it's own way, the turnine ended up getting pulled and replaced with another 16v92. If memory serves me correctly, it never could get on plane.

boats

Tempest, that was the name. Yes it certainly could not get out of its own way and that engine in the middle did not help, nor did the starboard one letting go when I was onboard. An interesting day that was.

As for the turbines, maybe I am missing something but a 170,000 container ship with a Wartsila 109,000 HP diesel slow speed engine cruising at 25.5 knots fully loaded does not strike me as a "low speed application".

I just have to ask again though if the turbine is so good why are the mega rich owners not putting them into all of the new mega yachts on order.

Alot of the cruise ships are running high speed diesels but not what I think you are referring too, those diesels are turning about 600 RPM and can be up to about a Vee 32 and sometimes they also install a single turbine but all are coupled to generators. The diesels are low down for weight reasons but the turbine can be anywhere and I have seen one way up high in a sound proof room.

I still think the high cost of purchasing and running them is the major reason why they are only installed in naval vessels.

PS. If you were ever on that Tempest what did you think of the shag carpets ?

Perhaps I should have put it in terms of Froude number, but if you can afford the weight and volume big low speed diesels are fine. To live with the Wartsila you have to support 460,000 pounds of engine, as well as give up an engine room that is five stories high and over 90 feet long. In a cruise ship that's a lot of paying cabins. It's intersting, but 80 MW is about the same total power as is required for an Ageis Class Destroyer. Most destroyers can't give up that kind of space and weight. For that reason turbines are pretty much the accepted way of pushing ships like that.

Again, it goes back to the question "how fast do you want to go". If the idea is to get up on a plane and go quickly, you're taking turbines. If you are going up the ICW at 6 knots, forget it.

The Milenium is running all gas turbines and it appears to be a very successful application. What they did on that ship was capture the waste heat from the turbine in a steam bottoming cycle. This results in an efficieny that is better than an equivalent high speed diesel, and is still much smaller and lighter. In a reciprocating engine about 1/3 of the power comes out the shaft, one third comes out the exhaust and one third comes out a coolant as waste heat. The best you can do with a diesel is try to capture heat from the exhaust. The coolant temperature is too low to do you much good so it is simply lost. With a turbine twice as much heat is available for a bottoming cycle, so the overall system can be more efficient than a high speed diesel.

Here is a link to an article that describes the power system.

http://www.touchbriefings.com/pdf/858/jofs.pdf

As emission regulations get tougher expect to see more turbines. Diesels are efficient, but very dirty.

Until recently turbine engines suitable for all but the largest and fastest mega yachts were very thirsty. That pretty much relegated them to an oddity status. If the only engine that makes sense for your application burns almost twice as much fuel as a diesel it isn't going to be even a consideration. More efficient, smaller turbines can make sense in CODAG applications where most of the power is provided by an efficient turbine. I think we will see more of them in the future.

boats

I do not go with your arguement giving the Millenium class of cruise ships as an example as they were built in 2000 /2001 and the latest and much bigger cruise ships like the Oasis of the Seas are using 6 Wartsila Diesel engines.

That sounds like you are using old technologies as if the turbines are that good now why are they not installed in the latest cruise ships.

Alot of the cruise ships are built with the weight needed in the lower areas for stability reasons and these engines are not one large single unit as in say a container ship but are in fact a number of much smaller but higher revving Diesels. They can be placed around the lower hull areas, not affecting any cabins, and supply electrical power to the pods and services.

Many yachts get up and go using Marine Diesels and the yachts I thought we are talking about do not spend much time going up the ICW.

If you look at the new Marine Diesel installations on large vessels the exhaust gases are actually reused either re-cycled back into the engine or to produce steam to drive steam turbine generators (alternators).

Yes, if you look at the overall efficiency of turbines or steam plants they are actually more efficient than Diesels but there are many other factors that have kept them from being used these days and as for the turbines I will say again it is only the governments who can afford to pay for them and the running costs.

I started my marine life on a steam turbine powered ship with steam turbine alternators and steam reciprocating pumps plus steam turbine cargo discharge pumps and with twin Foster Wheeler boilers and have sailed as chief engineer on both steam and diesel type of ships.

I would love to see turbines in every day use and although I hate to see the waste of money spent on wind turbines I believe the future lies in water turbines for renewable power and technology will progress to allow mini gas turbines in yachts, cars and trucks.