Gas Turbines?

[pdf27]

Stuck at home with a broken collarbone and my inner engineering geek is screaming to be let out (not to mention I should be on a sailing holiday instead!), so I've started reading up on marine diesel engines and thinking about how they could be developed and replaced in future.

Starting with the HYMAR report coupled with a lot of reading on these forums, is seems that engines on sailing boats are primarily used for electrical power and low-speed manouvering, with a secondary use propelling the boat to hull speed for a few hundred miles, does that seem correct?

One of the bits of automotive technology that seems relevant here are range-extender engines. Being automotive, they are (eventually) going to be produced in huge volumes, and will be designed to be cheap, small, reliable and quiet.

In particular, the small gas turbines produced by Bladon Jets look pretty promising. 70lb for a 70kW (100 hp) unit including generator looks excellent to me - the equivalent Yanmar is ~480lb.
Fuel efficiency is not as good (340g/kWh for the turbine, 230g/kWh for the diesel at full power dropping to the same as the turbine at idle. Interestingly most small generators seem to be at about 350g/kWh).
Noise and vibration however should be incomparably better - like being in a jet .vs. a piston aircraft - and the noise is likely
Additionally, the weight and space saved should enable a much bigger house/manoeuvring battery bank. 410 lb translates into a ~20 kWh battery bank (~2000 Ah at 12v) - probably enough to run an anchored boat for a week with no air conditioning. They also quote a 6kW (10hp) unit as being capable of fitting in a biscuit tin.

The real difference to me is reliability. Current designs use air bearings and air cooling, so it would appear that only fuel, control and electrical connections are needed - and the unit would be largely maintenance free for it's design life since with 1 moving part and no lubrication there really is very little to work on beyond the fuel/control systems.

So does that seem a plausible option for the future - small gas turbine generators, big battery banks and electric drive? I'm very concious that I don't have the practical experience to spot likely practical prolems, but the theory looks pretty nice to me...

[David M]

Its a mixed bag. A turbine compared to a diesel is going to have more expensive fuel and the fuel is going to be more of a logistical problem to get to the boat. It is going to be more expensive for a given horsepower. You will have to figure out how to duct the gas so that there is very little back pressure, which means a very large duct and possibly a resonator to keep the noise down. A jet turbine also has a higher specific fuel consumption and is noisier. Not many cruisers are going to be happy with hearing a jet engine in the same anchorage. You might grow tired of the noise as well.

There are smaller boats with jet turbines but they are usually used for propulsion and for going high speed. Some cruise ships, ferries and military ships have jet turbines for generating electricity and for propulsion either through reduction gears or electric drive motors.

As you said, the upside is less weight and fewer moving parts.

For me figuring out how to obtain and deliver jet fuel (highly refined kerosene) to the boat would be the primary deal killer. Doing this might be even more difficult or impossible in some foreign ports. Many countries have environmental laws about transferring fuel near the water. They really don't want large volumes of fuel to be delivered to and transferred by non-professionals.

[dan360]

I just read the case study on their website - Bladon Jets | Micro Power Generator case study

It seems like they're promising fuel flexibility:

"The Bladon Jets micro generator is capable of running on a wide variety of common liquid or gaseous fuels, including more environmentally friendly options like CNG or biofuels – it can even be switched from one fuel to another, depending on what is available."

[pdf27]

Originally Posted by David M

Its a mixed bag. A turbine compared to a diesel is going to have more expensive fuel and the fuel is going to be more of a logistical problem to get to the boat.

Actually, that's one thing that will certainly not be a problem - if they're going for automotive applications then it MUST be capable of running on either diesel or gasoline, and the Jaguar prototype they used as a demonstrator for these was diesel fuelled. They're working on a multi-fuel version for power generation in remote areas, and conceptually it's a lot easier to deal with different fuels in a gas turbine engine than a piston one.

Originally Posted by David M

It is going to be more expensive for a given horsepower.

I'm not sure about that - there is a lot less to manufacture, and if it goes into automotive quantities the economies of scale could make it cheaper than dedicated marine diesels. I agree that cost is a concern, particularly as this uses relatively novel machining methods - essentially I can only see this as viable if a major automotive OEM gets involved.

Originally Posted by David M

It also has a higher specific fuel consumption and is noisier. Not many cruisers are going to be happy with hearing a jet engine in the same anchorage.

Fuel consumption is something I'm trying to understand the exact importance of. A back of envelope calculation (literally) gives fuel consumption about the same as most generators/engines at low power, and about 30% worse than typical diesel engines at full power.

Noise is going to be interesting. Most noise from diesels is transmitted vibration (on the boat) and monopole noise from the exhaust gas being above atmospheric coming out of the exhaust. For a gas turbine, as a steady state device you won't get any monopole noise (which travels much better than dipole noise such as something shaking side-to-side).
There will also be some harmonics from rotational speed (1 kHz and 1.5 kHz for the various shafts) for transmitted vibration, but with air bearings that will be minimal. I regularly work with electrical pumps running at the same speed as these turbines, and there is essentially zero transmitted vibration.
There will be aerodynamic noise from flow over the blades and through the unit. That will however be close to white noise, so less obtrusive, and given the size probably not very loud either. In rotational speed and air throughput terms, we're looking at something much like the turbocharger on an engine of about that size - so you would expect similar noise levels, probably a bit lower due to the better bearings...

[Group9]

It's amazing how much power a small turbine can make. I watched them change out one of the engines on a Seahawk (Coast Guard version of the Blackhawk) once, and was shocked at how small the thing was, and how light it was.

[55north]

I love out of the box thinking, but the points which occur to me are -

- total system weight including motor, battery bank, jet, fuel tank and electrical control system will be substantially higher than the equivalent diesel

- the cost of the jet alone is likely to exceed that of the equivalent diesel, as is the cost of the motor

- kerosene is much more inflammable than diesel

- the system will be highly complex and include many electrical and electronic components, reducing reliability compared to an all-mechanical diesel engine

Not being a big fan of diesels myself, I've given a lot of thought to various configurations of all-electric and hybrid electric systems. Although serial hybrid systems are the norm now in large passenger vessels, they use diesel generators except when weight is critical. For small sailing boats at least, the weight and cost increase of a system like this just doesn't justify the increase in motoring efficiency. All-electrical systems are similarly plagued by weight and cost in addition to low endurance and requirement for recharging. Just for 'fun', I've worked out a few example systems. They work on the assumption that 1kW produces as much propulsion as 3hp because of increased system efficiency (Propulsion Marine claim it's 4hp, but I've rationalised this a bit...).

35' sailing vessel, 15,000lb displacement.

Diesel system:

Beta 30, $12,900 139kg, plus 100l fuel 80kg.

Total 219kg.

Endurance 17hr full power running.

All electrical system:

Propulsion Marine 10kW, $9,495 68kg.
Battery bank 15.4kWh LiFePO4, $9,700 181kg.

Total system $19,195 249kg.

Endurance 1.5hr full power running.

Serial hybrid system with diesel generator:

Propulsion Marine 10kW, $9,495 68kg.
Battery bank 5kWh LiFePO4, $3,150 59kg.

5.5kW diesel DC generator, $14,000 112kg. 100l fuel 80kg.

Total system $26,645 319kg.

Endurance 0.5hr all electric at full power, 45 hr 5.5kW generator output, 25hr 10kW equivalent output.

Serial hybrid with (not yet existent) micro gas turbine generator:

Propulsion Marine 10kW, $9,495 68kg.
Battery bank 5kWh LiFePO4, $3,150 59kg.

Gas turbine DC generator, $20,000???, 10kg???. 100l fuel 80kg.

Total system $32,645, 217kg.

Endurance 0.5hr all electric at full power, 25hr 10kW equivalent turbine output (very optimistic for such a small turbine but hey).


In my mind, the standard diesel is by far the most attractive option because it is the lightest and cheapest of the currently available systems.

The range of the electrical system is execrable and it would require constant shore power recharging, and it is heavy and expensive.

The serial hybrid with diesel generator offers somewhat greater fuel efficiency than standard diesel, so might be attractive to a powerboater or committed motorsailer in spite of the cost/weight. I believe some larger motorboats are starting to use systems like these.

The serial hybrid with the magic not-yet-existent micro gas turbine might be lightweight (at least in comparison to the other electrical systems) but my fuel consumption is a real best-case scenario and would not I think be achievable in the real world with such a small turbine, by a long way.


There is a reason 99% of sailing vessels use diesel engines. They are fuel efficient, lightweight, reliable and relatively inexpensive. But where would we be if we didn't question these things!

[pdf27]

The PE article states 25% thermal efficiency for the Bladon Jets unit and describes it as including a generator, which translates to 340g/kWh. Assuming 1kW is equivalent to 3hp (your numbers) that's 110g/hp_equiv/hr.

The Beta 30 does 3.5 litres per hour at 3000 RPM and 27hp. That's 108 g/hp/hr.

So you've got a generator unit of equivalent weight and fuel economy to a current generation diesel.

At this point it comes down to cost and how well it fits in with the lifestyle. Cost right now will be astronomical, but should drop radically if widely adopted for automotive use.
How well it fits with the lifestyle is what I'm trying to understand.

[55north]

Rereading your first post, I see you're talking about the 100hp range. The micro turbine could be much more interesting in that case as it's likely to be more fuel efficient, your 340g/kWh isn't too implausible and, as you say, it is about the same as the equivalent diesel generator. The 32 kg weight is very attractive compared to around a tonne for the diesel generator! They certainly are truly beautiful pieces of engineering.

[55north]

Originally Posted by pdf27

The PE article states 25% thermal efficiency for the Bladon Jets unit and describes it as including a generator, which translates to 340g/kWh. Assuming 1kW is equivalent to 3hp (your numbers) that's 110g/hp_equiv/hr.

The Beta 30 does 3.5 litres per hour at 3000 RPM and 27hp. That's 108 g/hp/hr.

So you've got a generator unit of equivalent weight and fuel economy to a current generation diesel.

At this point it comes down to cost and how well it fits in with the lifestyle. Cost right now will be astronomical, but should drop radically if widely adopted for automotive use.
How well it fits with the lifestyle is what I'm trying to understand.

Didn't catch the above before my last post. OK, the numbers are good but I question whether such a minute turbine can achieve that sort of fuel economy. I would be more optimistic in the 100hp range.

[pdf27]

Bladon seem to think these are plausible options for small-mid range cars - they're talking about a target of 10kW and over 100,000 per year. Cars in that range sell for less than $20,000, so they clearly think they can build the engines for substantially sub-$5,000. what they would sell for is of course another matter entirely.
This of course also applies to the electric motors - automotive ones are about the right size for boats, although they would need a reduction gearbox to run the props efficiently.

Having said that, we don't seem to see man autoderivative marine engines nowadays. I'm wondering if the lack of cooling needed by these turbines might make adapting them easier and cheaper, particularly if they're already set up as gensets...

[pdf27]

Originally Posted by 55north

Didn't catch the above before my last post. OK, the numbers are good but I question whether such a minute turbine can achieve that sort of fuel economy. I would be more optimistic in the 100hp range.

I'm curious myself. They're being cagey about it, so I suspect it isn't quite as good. However, what they're doing at the moment was always assumed not to be possible so I'm keeping an open mind.

Having said that, modern batteries have very high charge acceptance rates and it is looking like in a few years time an almost unlimited number of recharges. It may be possible to run the turbine for say 20 minutes every couple of hours and use a much bigger unit than you would for a diesel.

[bauer965]

To address a few folk's concerns, marine turbines run on Commercial #2 (what you currently get at your nearest pump, whether dyed for non-highway or not). Diesel and kerosene and commercial aviation/military grades (Jet A, JP-4/5/8) are very similar fuels, each with properties tailored to their specific application.
I actually prefer diesel in shipboard turbines, more BTUs/lb, less mass flow rate at given power setting and a tad cooler. There is a slight long-term maintenance consequence, simply in shorter blade cleaning intervals.

Withstanding, they are the wrong application on non-commercial sailboats.

You might also want to also query Jay Leno on the pro/cons of his turbine motorcycle.

[Cheechako]

Dont turbines souk a lot of fuel, except in very appropriate situations?
anyway, I think your initial premise may be faulty; In my experience sailboats motor more than they sail. Sure there are salts out there who refuse to turn the "iron reacher " on and will try to sail at 2-3 knots and 45 dgrees off course forever, but many cruisers just want to get from point A to Point B comfortably, while charging the batteries and making water! Then there's the turbine noise......

[pdf27]

Originally Posted by Cheechako

Dont turbines souk a lot of fuel, except in very appropriate situations?

Not really - when operating at their design condition they tend to be pretty efficient. Indeed power stations tend to use turbines rather than diesel engines for that reason.
The problem they have is that they tend to be a LOT less efficient off their operating point, while diesels are still pretty good. However, if you can use batteries to keep it running at their ideal operating point by soaking up the excess power then that problem goes away.

Originally Posted by Cheechako

anyway, I think your initial premise may be faulty; In my experience sailboats motor more than they sail. Sure there are salts out there who refuse to turn the "iron reacher " on and will try to sail at 2-3 knots and 45 dgrees off course forever, but many cruisers just want to get from point A to Point B comfortably, while charging the batteries and making water!

That's one of the things I'm trying to understand. How far/how often they typically travel, how much electrical energy they'd like to use if possible, etc.

Originally Posted by Cheechako

Then there's the turbine noise......

Remember that the turbine will have a similar air flow rate and rotational speed as a turbocharger added to your existing engine. The military jet engines you're thinking of produce ~20,000 hp and have supersonic exhausts (the source of virtually all the noise) to let them get to design speeds.

[motion30]

a turbine engine generates a lot of heat how would you deal with that?