running one engine when you have two

This has been argued quite a bit here and elsewhere. The question is whether there is damage caused by the freewheeling of the one drive unit not being used. Temperature and force come into play. Some manufacturers have even said their unit is safe for freewheeling. And some people have installed temperature gauges or collars.

So you're likely to end up with those who say they do it all the time and those who say they never do it. Without a doubt it can save fuel, but is there a risk offsetting the benefit? That's the big question and I'd expect you to get some very conflicting opinions here. How much the benefit is depends a great deal on the boat as well.

I personally would never do it unless I had problems with one engine or found myself running very tight on fuel and was afraid I wasn't going to make it otherwise. But then many do it and say they never have a problem.

Hi,

The success or failure will depend very much on what engines you have and how loaded one will need to be to get 6-6.5 kts.

I have done a round the world run on a 55m Motor Yacht with mechanical injected CAT 3512's in it.

We had electric pumps fitted to circulate the oil when free wheeling the non running side.

In flat water we could generally do around 9kts pretty conformable with stable exhaust temps.

If we were encountering seas or needed a bit more we used to resort to two engines.

I have done a few Trans Atlantic with the same engine in a different arrangement and no pumps, we used to start the non runner every 12 hrs for approx 10 mins while doing the logs and swap duty engine daily.

For me the long and short of it is it can be done and done successfully as long as you are aware of where you are in regard to load and are sensible in what you try to ring out of them.

If you are not in a hurry then time is relatively cheap.

That's probably the key, having the right set up and running them in the right cycles to insure the free wheeling causes no harm.

I found a boat not too long ago with an interesting triple engine design. I'm not sure now who made it. It had triples but the purpose wasn't to run all three for added speed as the third added very little speed. It was a middle engine to be run for expedition cruising and fuel conservation and the two outside engines to be run when wanting to operate in a faster semi-displacement mode.

I would be interested to know which boat you are referring to. That is an interesting configuration.

I'll try to find it. I don't remember at the moment. Now I know some who have done triple engines but not with that intent. For instance, Marquis and Regal among several. But I will search through my notes and history to find this one.

Well, Delta has 3 on the 54. It's been done a lot with IPS it seems. But Hatteras also in the past had triple with several boats. However, I still haven't located the one that expressly set it up to use one for expedition cruising.

Triple engine yachts

How about this nice little yacht with 3 x MTU 16V 2000 M94 and 3 x surface props, the Pershing 108 . But the 3rd engine is most likely not for fuel economy, when going single engine. Most triple engine boats like the above or the Mangusta 165 with 3 WJ or equivalent, use the center engine as a booster. The center propulsion train has no steering, so its either twin or tripple for speed.

The boats with tripple engine via shaft, wheel and rudder are mostly PT boats or other official duty types like coast guard, fishery service or police / custom patrol boats or SAR vessels. If they are eqipped with 3 individual power trains, most of them can use any kind of combination, single, twin and or twin asymetrical.

The bigger German SAR vessels have 3 MTU used for high speed towards the scene and after arrival one or more engines can be geared to high performance water pumps either for fire fighting or assisting in pumping out sinking ships. Loitering or trolling can be done on any engine.

The decision whether to use 2 or 3 engines is mostly a calculation of weight and engine room space available. Typical example is the new Van der Valk 26 meter RP with tripple IPS 1200. 3 x IPS 1200 make a total engine powertrain weight of 6900 kg, whereas 4 x IPS 900 with same amount of 3600 total equivalent HP have a combined weight of more than 7200 kg and they occupy more space in the engine room. By using 3 x MTU 16V 2000 or 2 x 16V 4000 for a boat, the version with the 3 x 2000 engines is lower on weight but still using more space. On the Pershing 108, the reason for the triple engine setup was just the maximum size of surface props available. A SP, that can take the power of an 16V 4000 M93L does not excist.

Larger warships use CODAD or CODAG propulsion. Means, several diesel and / or gas turbines are connected via combining gears to one, two or more shafts. By this setup, any amount or type of engine can be used to drive one, two or more shafts for different modes of operation. This allows long range economy or high speed combat maneuvering. The only yacht with this setup, I know, is the Dutch built MY Predator with 2 x 2 diesel via combining gear on two shafts.

Triple engine for expedition cruising does not make sense. Taking two bigger engines and a special technical setup for single engine operation is more economical.

Something does not seem to be correct.

Where did I goof?


4613 bhp @ 2100 rpm = 11536.8933 lbs-ft


Detail: MTU Online


Horsepower to Torque Calculator, Formula

or

HORSEPOWER TO TORQUE CALCULATOR



Arneson ASD 18 rated for max 30000 lbs-ft

http://www.twindisc.com/Downloads/p...dfs/marine_pdfs/Marine_Product_Guide_2012.pdf Note: Page 4

It is usually less efficient in most all yachts to run one engine in a twin engine installation and creates much higher load factors and wear and tear on the single engine running. If the motors are propped to achieve full RPM dependant on both engines running full RPM, then the single engine running is going to see extremely high load factors throughout the RPM range. Electronic CATS will limit RPM to around 1200rpms under these situations and so will MAN's (common rails, I think they limit either 1350 or 1600rpms). Diesels in general get excellent fuel burn under 1000 rpms, so running both under 1000 rpms, versus running one at 1400rpms would burn much less fuel to run both slower if you're maintaining the same speed as running 1 faster.

The more engines and drives/propellors in the water the more the diminishing returns are. I know on a large outboard center console or race boat. The third engine adds at best 13 mph, and the 4th adds only 7mph say for a boat with twins that does 45-65mph with twins. Extra engines and drives will help with getting a heavy boat or heavy load onto plane and out of the hole. That's why they rigged those 37' Midnight express drug boats back in the Miami Vice era with 5 outboards back in the day. They'd run 2 outboards to cruise over. Run 5 to get the heavily loaded boat on plane, then run 2-5 motors back depending on how much fuel they had and distance.

I wouldn't want to maintain more than two IPS type drives and engines.....3 would be about MAX...... with 4 engines/drives, they really aren't worth having as they're the same speed efficiency as twin inboards.......

Surface Drives

I do not know, that is, what I was told by the yard during our visit. Maybe at the time of design and construction of the 108, the ASD-18L did not exist. Looking in older versions of their production guide, the listing stops at the ASD-16. And to my knowledge, the ASD-16 was the biggest available at that time. Surface drives are not my favorite means of propulsion but from the briefing I had, is the composition of the larger power trains, consisting of engine, gear and surface drives a very delicate business and maybe the advice from the Naval architect, the ASD guys or MTU was to rather take 3 x ASD 16 with 16V 2000 ??? Or maybe the ASD-18L is better suited for use with gas turbines and not with big bangers like the 16V 4000 M93L.

Would be nice to have more inside knowledge from somebody with operational experience with big ASDs here on the forum.

But I can tell, the Pershing 108 makes a hell of a rooster tail with its 3 ASD-16 at full speed .

And it would be nice to see an actual example of a yacht with twin 16V4000 M93L and ASD-18L.

The ASD 16 shows 16500 ft-lbs, still greater than the required 11536.8933 lbs-ft necessary.

ASD16 - Twin Disc.


P.S.- Perhaps this article yields a reason for 3 vs 2 engines.

Scroll to: Benefits of Choosing the Smaller Engines

Maritime Propulsion | Superyacht Pershing 108 - Builders Opt for Three Prime Movers

Maybe the design of an engine / ASD match is more complicated than a simple rule of three. I still tend to believe the briefing of the yard was correct at that time, even if they were Italians .

Great find that article. Weight, costs and size would be for sure some reasons for the triple engine configuration.

Close; but no cigar.

Mangusta 130 with twin 16V4000 M93L ; but with waterjets.

Motor Yacht MAO - Mangusta 130

That is exactly what we learned during our Tour de Acquisition in Italy. Italian naval architects are very conservative and reluctant to push borders or enter new fields. All Yards using surface drives, change above certain sizes to waterjets.

Taking the plain numbers, the ASD-18L would be fully capable of taking the input power of those 16V 4000 M93L but the Italian yards change at that amount of power towards Waterjets. Mangusta and the Pershing 115 are just two examples. It would be really interesting to know whether the ASD-18L has come to service in a yacht or any other type of boat jet.

The Pershing 115 even comes with twin MTU and center gasturbine and water jets.

Would appear to be poor editing (typo).

Here 'tis from the horse's mouth.

Mangusta 130 | OVERMARINE GROUP Note: Click Technical Specifications

BAIA coupe 100

MTU 12V 4000 M93L (X2)
Power rating 3510 hp x 2

Propulsion ASD 18*


P.S.- Not having any luck with a pic or vid.

The website has video of the coupe 100; but the twin 2000 series is standard and the vid may be of it. The triple option is also of the 2000 series. Both use a smaller asd.