engines comparing

[Aravind]

last night I posted a reply to this thread, but it seems to have disappeared for some reason.

I think I found a decent engine:

the Nanni 6.420TDI: 320bhp, 4.2L, 6inline, 19l/h @ 100hp, 2400rpm, 800nM, Toyota block. (same block as Yanmar 6LPA, but slightly better)

good transmission compatibility, will check for props later.

[NBs]

Originally Posted by Aravind

I acquired some new data, and it seems like 100hp @ prop is plenty.

I have been absorbing all of your info, and also found some new data about my current engines:
Cat 3208 data
According to this brochure, the current twin engines each (210hp, 722kg, 1592lb, bottom one in the folder), each do:

---- @ engine -------------------------------- / (+- @prop, read from graph)
2800rpm - 157bkw - 534Nm - 210bhp / 157kw - 210hp
2600rpm - 125bkw - 460Nm - 160bhp / 130kw - 160hp
2400rpm - 99lbkw - 392Nm - 125bhp / 95w - 130hp
2200rpm - 76bwk - 330Nm - 100bhp / 70kw - 100hp
2000rpm - 57bkw - 272Nm - 78bhp / 60kw - 78hp
1800rpm - 42bwk - 221Nm - 58bhp / 40kw - 62hp
1700rpm - 35bkw - 197Nm - 50bhp / 30kw - 50hp
1600rpm - 29bkw - 174Nm - 42bhp / 25kw - 40hp
1500rpm - 24bwk - 153Nm - 37bhp / 10kw - 35hp

The ship was able to cruise @ 2200rpm, 100hp net, 330Nm Torque, 10knots, using 2x 20Liters of Diesel.
The ship is a steel sailboat of 79 feet, weighing 75tonnes.

I'm still considering which engines to replace these fat 3208's with.
My priorities are:
1 - fuel economy
2 - easy maintenance, mechanical preferred over electrical
3 - engine size (I prefer smaller)
4 - cost price (bigger engines cost more)

Since the engines to be installed are auxiiairy engines (it's a sailyacht after all), would twin 4cylinders be good enough? Most boats of this size/weight have a solo 6cyl. so why would I put twin 6cyl in?
I will cross oceans, but sail 80%+ of the time. On top of that, there will be a 10kw+ parallel hybrid added, for when there is sun and no wind, and for maneuvering in harbors etc.(5+kw of solar panels and a small 3cyl generator to feed it if necessary, still way more economical then starting one of the big engines.

- Yanmar 4LHA-STP - 240bhp - 19l/h @ 100hp MECHANICAL
- Yanmar 4LV250 250bhp 20l/h @ 100hp
- Yanmar 6LPA-stp2 315bhp - 24l/h @ 100hp MECHANICAL
- Yanmar 8LV320 320bhp - 18l/h @ 100hp
- Yanmar 8LV350 350bhp - 17l/h @ 100hp
- Yanmar 8LV370 370bhp - 17l.5/h @ 100hp
- Yanmar 6LY2M-WTD 352bhp - 20l/h @ 100hp MECHANICAL
- Yanmar 6LY2A-UTP - 370bhp - 20l/h MECHANICAL
-
Nanni: French brand with toyota blocks:
-Z4.230, 230bhp - 20l/h
All the nanni engines seem to be using 20l/h at 100hp, whether it is a 4cyl 230 or a 6cyl 300

- Steyr SE266S36 258hp 6cyl - 18l/h @ 100hp

- Perkins M250C 250hp - 20l/h @ 100hp

- Cummins QSB 6.7 250bhp 658kg, heaviest engine, can't find the fuel consumption chart.


So far the Yanmar 8LV350 looks to hit the sweet spot with 17L/h


looking forward to your replies.

Hi,

Here is cummins 250hp qsb curves
https://www.sbmar.com/docs/performance-curves/QSB%206.7%20%5b250%2C2600%2C3887%2CHD%2CMay%2013%2 CM-93960%5d.pdf

Cummins is best diesel engine, my opion.

NBs

[Lee Jerry]

Originally Posted by Aravind

last night I posted a reply to this thread, but it seems to have disappeared for some reason.

I think I found a decent engine:

the Nanni 6.420TDI: 320bhp, 4.2L, 6inline, 19l/h @ 100hp, 2400rpm, 800nM, Toyota block. (same block as Yanmar 6LPA, but slightly better)

good transmission compatibility, will check for props later.

I think you are putting way too much stock (confidence) in the fuel consumption numbers based on the nominal prop curve. They just aren't that accurate; I'd guess they're +/- 10% at best (probably worse). That's +/- 2 l/hr at the nominal 20 l/hr rate your looking at. The nominal curve is provided for guidance, not as a design tool. They're not "real" curves. Further, there isn't standardization in that nominal prop curve: the 6-cyl Nanni referenced uses an exponent of 3, whereas many others use 2.5; the Yanmars you linked use both/either. It's possible "one" of your curves may hit one of these, but not too likely. (** More below for those who may care).

I'll repeat some earlier questions:

Your previous engine was 210 hp and the original post said you were targeting 200 hp. So why are you now looking at >50% more powerful engines?

Can you fit a prop large enough to absorb this extra power?

Diesels generally don't like running at light load, so why pick an engine and plan to operate it at light load (i.e. <30% of rating or only 100 hp) most of the time?

Further to this last item, it may be better to cruise on a single engine at ~200 hp rather than two at ~100 hp. But the prop system has to be designed for this. In other words, it's a very different prop demand curve on the engine map. (Plus blade loading and cavitation for the propeller.)



** The different engine manufacturers provide different fidelity to their data, in particular the fuel consumption. If you look at a "full" engine map, like the attached example (randomly pulled off the interweb), you will see concentric rings of specific fuel consumption. The prop demand curve will pass through changing spec consumption, and thus when converted to actual consumption you get a wobbly curve like shown in the Yanmar specs. But others, like the Nanni and Perkins, just take a single specific consumption (maybe the best or maybe something more nominal, who knows) and convert that, and you get the smooth curve shown in their specs. The latter is less accurate. Again, that's on top of the prop demand curve being a nominal curve too.

[gulfislandfred]

I would look at the engine that gives the horsepower you want at the propeller, at the lowest RPM. Heavier may be better, but not necessarily.

Higher RPM makes high pitched noise, that I find harder to live with. Higher RPM wears things out faster, including things in the engine room within range of the vibration.


I realize this is an old fart attitude.



I would only get Volvo engines if they're based on a common block that you can get other brand parts for. Stuck with Volvo for parts and service is not a happy place.

[Cheechako]

My only comment is compare them all at the same RPM. That's a more true comparison. One may make 175 hp at 2400 rpm, another may make 175 hp at 3000 rpm. A lower RPM rated engine will have better longevity.
Also look at rating type for comparison: Continuous duty, Recreational, Intermittent.

[Statistical]

Originally Posted by gulfislandfred

I would look at the engine that gives the horsepower you want at the propeller, at the lowest RPM. Heavier may be better, but not necessarily.

Higher RPM makes high pitched noise, that I find harder to live with. Higher RPM wears things out faster, including things in the engine room within range of the vibration.


I realize this is an old fart attitude.



I would only get Volvo engines if they're based on a common block that you can get other brand parts for. Stuck with Volvo for parts and service is not a happy place.

Just be careful you have the space to swing a propeller that large. Power is torque * rpms. Propeller produce torque by size and pitch (and to a significant lesser extent number of blades).

[rslifkin]

Originally Posted by Statistical

Just be careful you have the space to swing a propeller that large. Power is torque * rpms. Propeller produce torque by size and pitch (and to a significant lesser extent number of blades).

Different engine RPM won't change the ideal prop diameter. Ideal prop diameter is going to be a function of boat speed, total engine HP, etc. Different engines with different RPM ranges will need different reduction gearing to match up to the optimal prop diameter.

[Statistical]

Originally Posted by rslifkin

Different engine RPM won't change the ideal prop diameter. Ideal prop diameter is going to be a function of boat speed, total engine HP, etc. Different engines with different RPM ranges will need different reduction gearing to match up to the optimal prop diameter.

True I was speaking more RPM at the propshaft. There are limits on transmissions available at least readily available at decent price.

[rslifkin]

Originally Posted by Statistical

True I was speaking more RPM at the propshaft. There are limits on transmissions available at least readily available at decent price.

True, if you have a particularly unusual combination you may not be able to find a suitable reduction ratio. A very high revving engine and a big prop that needs a deep reduction would be most challenging to match up, I think. But when picking an engine and trans as a package, any engine that you can't get a suitable reduction ratio for would just be ruled out.

[Morris Wilson]

Go with an inline 6 cylinder. they will be longer but much more accessible ov er all. sixes are inherently smoother (V12s are the best) I'm a heavy truck mechanic and know the cat 3208s well. They were a good engine built by Mitsubishi but not rebuild friendly. You are moving into the new emissions controlled engines and all that entails. Be ware. Fuel mileage is still mostly in the throttle lever. My expertice is more in the over 400 hp so maybe not relavent.

[cottonsail]

In my experience I would not recommend Volvo Penta. First the new engine does not come with an installation manual. That can only be downloaded by a Volvo Tech and only from a secure site. There is no national tech support. You will be directed to a dealership. That is a mixed bag. I put my engine in 3 years ago and I still do not have a warranty. When the Tech did the sea trials there were several deficiencies. He said correct the problems and just send me pictures of the corrected issues. Did that. Still waiting for over 2 years and multiple unreturned phone calls! The engine is great but zero support.

[drdoyle]

3406 Caterpillar

[Aravind]

Originally Posted by NBs

Hi,

Here is cummins 250hp qsb curves
https://www.sbmar.com/docs/performan...M-93960%5d.pdf

Cummins is best diesel engine, my opion.

NBs

the qsb5.9 is a sleeveless block iirc.

[rslifkin]

Originally Posted by Aravind

the qsb5.9 is a sleeveless block iirc.

It is, but the B series Cummins has a particularly good reputation for durability compared to many other engines of similar displacement and power output. Anything that makes the same power and is more durable (or sleeved) is going to be bigger and heavier.

[Aravind]

I want to learn more about motorisations:


I think that 2x 200hp is not the same as 1x 400hp, am I correct here? How can I calculate this?
What about triple or quadruple engines? What is the power loss factor if you add an engine?