Fuel Burn

markc

markc

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Following on from the discussion earlier on fuel burn, got me looking into the specs for my boat and trying to understand a disparity in figures.

The data I have for the boat provided by Ferretti states that the figures are with full load (fuel & water), 9 people on board, all safety equipment plus 400kg for 'stuff'.

Max RPM 2400 - WOT 300 l/ph - speed recorded 33 knts

On the survey, with clean props, a cleanish hull, 5 PAX, not much stuff and half load fuel & water, calm seas and min wind, we reached max revs and speed of 32 knots on the gps but were burning only 262 l PH - (being measured by MTU man with all his kit bolted to the engines).

What would need to change for the engines to burn 300 l/ph or could that disparity be put down to initial overstatement of burn by Ferretti? That would seem a lot, nearly a 20% difference. Or would extra weight increase the burn whilst still reaching max revs?

Cheers!
 
Tricky question indeed, M.
When you mention the data provided by Ferretti for your boat, do you mean the specific commissioning report that MUST have been done by an MTU engineer for the warranty validation, when the boat was first seatrialed?
If so, you're lucky, because afaik Ferretti normally didn't hand it over to their clients (maybe Deleted User who is a serial Ferretti owner can confirm or correct as appropriate).
Otoh, if you are talking of the generic builder specs, well, caveat emptor... As discussed also in jrudge thread, two exactly identical boats are yet to be built.

Anyway, you might be interested to hear what I understood after a good hour spent with a very experienced MTU engineer, when I was considering an F175 powered by the earlier version (i.e. TE92 rather than TE93) of your engines. And also V12 rather than V8 actually, but this is irrelevant in this context.
First of all, it's worth mentioning that the TE92 is widely recognized as the most bullet proof marinization ever made of the M-B OM440 block - even from MAN engineers, at least the honest ones.
100% mechanical, raw water pump with maintenance free bronze impeller, titanium/bronze used for heat exchanger/intercooler whereas MAN (and also other builders actually, but I'm focusing on the Germans who back in those days marinized the very same block) used aluminum, and so on.
The TE93 you've got in your boat is the TE92 successor and the last MTU version of the same block, before they abandoned what they called the 183 series engine (based on its unitary displacement of 1.83 liters) in favour of their new 2000 series, which afaik only Hurricane has on his boat, here in the asylum.
Now, the evolution from TE92 to TE93 was driven by the need to keep up with the constant quest for higher power to weight ratios, pushed by P boats builders.
To do that, on one hand they cut weight wherever possible (e.g. alu rather than bronze intercooler, IIRC) and otoh they introduced for the first time a somewhat limited electronic control of the injection pump.
As a result, the power went up 100hp (from 657 to 756) in the V8, and 150hp (from 985 to 1135) in the V12 - in both cases, increasing also the rated rpm, from 2300 to 2400.
Otoh, in spite of these official specs, that chap told me that he commissioned several boats which in the early 90s were powered by the TE92 and a few years later, on the same hull/model, were built with the newly released TE93, and NONE of them showed any meaningful performance improvement.
Needless to say, this didn't go down very well with the builders, who in the meantime were paying more for the newer engine...
Allegedly, this has a lot to see with the fact that MTU afterwards abandoned the development of the 183 block, in spite of the fact that their product was still better than MAN's in most respects.
But this is now just history.

Bearing all this in mind and coming back to your question, these are my thoughts, fwiw:

Firstly, if your "Ferretti data" are specific of your boat, then someone must have fiddled with the propellers in the meantime.
I mean, forget the fuel burn: if the boat made 33 kts @ 2400 fully loaded, it doesn't make any sense that now, with a lower load, she still reaches the same rpm but makes one knot less. If anything, I could rather understand the opposite.
Hence my guess that the props might be slightly different - i.e. changed or repaired in the meantime.

Otoh, if as I would expect those Ferretti numbers were generic, well, we can only use them as guidelines, but surely not for an accurate comparison with your specific boat.
This means that there could be absolutely nothing wrong with your current 32kts @ 2400 half loaded, and this is good news.

But that leaves us with your doubt on fuel burn.
So, back to basics: 0,2lph for each hp as a rule of thumb, remember? If we consider the rated 756hp of your engines, that's 151 litres each side.
Which is remarkably aligned with the Ferretti 300lph... Almost makes me think that all Ferretti did was take the number from MTU specs! :rolleyes:
But let's be even more suspicious. What if that MTU guy was spot on, and in spite of the official claims, the 93 engine didn't actually deliver more power than the 92?
As I said, the 92 was rated for 657hp, which at 0,2lph counts for 131 liters. And your engineer measured 262 liters.
Now, if this is a coincidence, it gets my vote for the most amazing one I ever came across in my life - and I'm talking in absolute terms, not just in boating stuff... :D

Just one final note - which is actually the very first thought which popped to my mind while reading your post.
What your MTU engineer did is plug some sort of diagnostic system into the engines ECU, right?
I mean, he didn't install additional fuel flow sensors on all the four diesel lines (in+out, for each engine), or did he?
I am asking because I've never seen any TE93 powered boat with a dashboard display capable of showing fuel burn, load, etc. in real time - in fact, I don't think such instrument even existed.
This doesn't mean that MTU couldn't have their own diagnostic tool capable of getting these numbers from the engine ECU, of course.
But if back in those days they didn't trust the reliability of these early electronic controls enough to offer also dashboard instruments, maybe also the accuracy of their diagnostic system wasn't 100% kosher...
Then again, in view of the above coincidences, maybe it was! :p
 
First figures it’s underpropped - hence it reaches rpm with all that extra kg,s
What we don,t know yet is how far over 2400 it went on that trip .

What we don,t know is how far over ,or what the max rpm was in both runs ,

Agree second figures ( large time gap poss diff set of props - even diff makers - some diff ? )
Just lighter so does not sink as much creating drag so should rise up and go faster in theory , but age takes its toll on and the bottom / sterngear will not be as new / smooth as the factory test so speeds leapfrogged down .
But the prop is pitched and it’s Dia enough to reach 2400.rpm too .
Bescause it’s carrying less Kg,s it burns less - simples

Wonder how far over 2400it could go in both tests or went .?

I understand it’s had a major rebuild too , so the block may be the same but if the guts are different then considerations should be given to acceptance of the idea that alltough the E numbers are the same , they are Infact different engines for the purpose of this comparison.
Perhaps M could elaborate ?
 
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Thanks both for your input.

To clarify a few things, although i didn't see what the MTU guy fixed to the engines, it took him about an hour to install, then the same again to de-rig, with a tool box, so I assume that he fixed fuel flow meters. He did give accurate figures across the rev range.

The Ferretti figures I have are indeed generic rather than from this particular boat and there are various consumption graphs in the handbook. I have hull #22 so there may well be changes from #1, inc equipment etc, which I presume the original figures were derived from.

Regarding the props, I know that they are 100% to spec because they were accurately measured.

MapisM's thought is intriguing although it would be quite a big deal if MTU misrepresented the power output of the 93 over the 92, although anything is indeed possible. The coincidence is compelling though.

I'm going to see if I have any data from bench testing my engines after the rebuild - I guess they dyno tested them before being put back in the boat?

Cheers
 
Not necessarily, because not many engine shops, even among the officially authorized ones, are equipped to dyno test engines.
But of course it would be very interesting to check such test numbers, if available.

Ref. Ferretti numbers, are you sure that the ones you've got are at least specific of your engines?
I'm asking because I am pretty sure (having seen two of them!) that the 165 was also available with the MAN 2840LE401, which was a different engine in many ways.
100% mechanical, 820hp @ 2300rpm, V10 rather than V8 (hence heavier).

Anyway, if your guy fitted fuel flow meters and his numbers are accurate, leaving aside all reasoning about number consistency, 260lph at 32 knots is an excellent result indeed, when compared to some similar forum boats. In fact, the 165 is bigger than her name suggests, and she's actually very close to my DP56, or the Sq58 and the Princess 57, for instance.
Tbh, sheer curiosity aside (which I do understand!), in your boots I would have zero concerns about the boat performance... :encouragement:
 
MapisM, I took your formula and applied it to my Cummins QSB 6.7
0.2 x 425 = 85 actual fuel burn 84 lph
Very good!
 
The figures I have are certainly from the MTU installation and I also have the MAN ones too. As you say it was curiosity rather than concern that prompted me to ask the question. TBH, when I'm not plodding along at displacement speed, I'll be travelling closer to 22knts rather than 32knts!
 
https://lookaside.fbsbx.com/file/te...cYjFAmJw-5pWLR7WiNhZLzbWD0AE_LUXS687QyYwenz5w

https://lookaside.fbsbx.com/file/te...C8u9qKMfz6CTOiSKBV8ATZRS9Q56Sg8qYyuetDANh7g_I

Sorry guys struggling with Facebook tech from the Itama owners group .
Here you can see
Different L/hr for pairs —- so,s it’s poss if you popped along to the engine factory and chucked a dart at a 2 crates packaged to go - they may be identical, one a guzzler one fugal etc .
Chances are each boat will have slight differences - hopefully with a pair there’s a chance of averaging it out or two high or two low !
Also with one they took the MAN s to 2400 - see the Speed change from WOT rated 2300 to 2407 rpm .

There’s too many variables in Marc’s data namely not even the same boat / engine s - for any meaningful comparison now we know the data is from diff boats .
 
Scales are all different .
Would be more useful if one was superimposed on t,others graph using identical X and Y scales .
So, as they are the gradient comparisons are meaningless.imho

Edit - looks like the type of thing an Italian accountant would do display financial info to Gardia Finanza :):):)
 
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Portofino said:
Scales are all different .
Would be more useful if one was superimposed on t,others graph using identical X and Y scales .
So, as they are the gradient comparisons are meaningless.imho

Edit - looks like the type of thing an Italian accountant would do display financial info to Gardia Finanza :):):)
Click to expand...

They are what they are I'm afraid. I'm sure they weren't created to compare each engine type, but to give info to specific users
 
markc said:
They are what they are I'm afraid. I'm sure they weren't created to compare each engine type, but to give info to specific users
Click to expand...

Sorry Marc not being critical ,but the if the author was asking me to check his PhD thesis and I was his / her mentor I would suggest those graphs are reformatted before it was published.

How ever here’s a few thoughts and thx for posting
So in a final viva here’s a few discussion points I would bring up on the “ research “

https://imgur.com/a/AXgxo
 
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