Fuel consumption

Hi Deleted User,
Confident mine is 150hp not 200 - believe this figure is for the TAMD41. My displacement boat [37 ft, 10 tons] makes 7 knots @ 3000 rpm on it's single engine. Hull is pretty clean & Linssen must know more about propping than I do! My analogue gauge is not precise and my figures are based upon only two fill ups. The graph on the volvo blurb show 150hp from 3100 rpm onwards and around 140+ at 3000 rpm. If you would not regard it as waste of time I would happily email it to you. May I underline that my figures are at best tentative but hope to get a third reading early next month when I fill up again.

Regards

John G
 
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........ Confident mine is 150hp not 200 - believe this figure is for the TAMD41. ......... The graph on the volvo blurb show 150hp from 3100 rpm onwards and around 140+ at 3000 rpm. If you would not regard it as waste of time I would happily email it to you. .....

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TMD41B = 158SHP
The graph is right, assuming you get 3800 RPM @ full load..., then 3000 RPM will take out approx 140 SHP.
140SHP = 98KW
98 KW @ 0.22Kg/hr = 21.56 KG
21.56KG @ 0.86 (diesel weight / L) = 25.1L/Hr

I would have thought that 5 L/hr, when taking out 140SHP, is pretty impossible, but if you said 5GPH, then it would make more sense.... Unless you spend a lot of time on idle, or on very low revs.... /forums/images/graemlins/smirk.gif
 
Divemaster, assuming 140hp is correct (seems v high to me considering max hp is only 150hp but I have'nt seen the curve) you've done the calc better than me. I could'nt remember the SG of diesel
25.1 lph = 5.5 gph which @ 7 knots = 1.3 mpg which sounds v high to me for a displacement boat of this size. I would expect nearer 2 mpg but maybe 7 knots is close to hull speed so could be JEG would save fuel by running at slower speed?
 
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Divemaster, assuming 140hp is correct (seems v high to me considering max hp is only 150hp but I have'nt seen the curve) you've done the calc better than me. I could'nt remember the SG of diesel
25.1 lph = 5.5 gph which @ 7 knots = 1.3 mpg which sounds v high to me for a displacement boat of this size. I would expect nearer 2 mpg but maybe 7 knots is close to hull speed so could be JEG would save fuel by running at slower speed?

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140HP, taken off the Propeller load curve at 3000 RPM on a TMD 41B ... actually the curve cross above 140... but assumed that 140 was good enough for approximation (strange curve though...). The engine is 158 Shaft HP @ max 3800, but of course if the boat is under propped, you'd get a better consumption than calculation states, as you would not take out the 140SHP that the calculation was based upon.

Just looked at the TMD41A (1988), which have a different rating @ max 150 Crankshaft HP and 143 SHP... at given 3000 RPM, it will burn approx 183gram/HP hour.... In turn 3000 RPM will one again give 140 crankshaft HP (No propeller Load data ... but still same kind of curve which is virtually flat the last 500RPM). Assuming the same, this will give 140 x 183g = 25.6KG/hr ... @ 0.86 = 32Lhr again very high, but older engine and even higher % load vs max .. so expect that...

All calculations are of course cool and based upon statistical evidence and not this specific hull and conditional scenarios. When you put the other variables in there such as hull shape, true hull speed, actual propellor load etc. into the picture, the results may of course vary significantly /forums/images/graemlins/confused.gif I would also expect a displacement boat with these engines to display a different load/fuel consumption characteristic than what appears to be the design intent on these rather high reving engines from this particular manufacturer....

on the A engine, by reducing the RPM to 2500, you will take out 120 HP @ 185g/hph, which gives approx 25L/hr, which is a significant difference from 32L/hr /forums/images/graemlins/shocked.gif... if speed difference is virtually non-existent, I'd rather keep at 2500 RPM in this case....
 
Gentlemen,
Please remember that in my posts I used the terms tentative & best guess; perhaps ignorant & ill informed would have been more appropriate.

With regard to my usage it would be true to say that revs are normally less than 3000 but surely even if they were only 1000 this could not explain a difference of roughly 5 gph to 1.

Deleted User has kindly agreed to view the volvo blurb & he may well elucidate but, based on my experience of cars it would seem unlikely that a variation of such magnitude is possible. Still ignorance is said to be bliss & I was pleasantly surprised when I guestimated the comsumption.

Thank you for your imformative discussion.

John G
 
John,
Don't know if this is of any interest but the consumption on our 74P's (440hp each?) over 5 hrs returning from Jersey the other weekend with a clean bottom , recently serviced and at 2200 revs (running ave 26knts, mainly due to following sea all the way and racing storm home, normally = 23knts) was 14.1 Gallons per hour, each. F43 fully loaded, 13+ tonne.
Just for info & comparison. Paul
 
Good morning,

One great thing about forums like this is that it spurs a great discussion, one of which several people are interested in ... and particulary one ot these where fuel consumptions is being discussed .... I have looked into this in quite some depth for my own boat .... which admittedly is a bit thirsty, and I am trying to assess what my boats fuel consumption actually is, based upon the performance curves from manufacturer vs. what actually happens when underway (currently more than 18% below manufacturers stats). So basically quite natural that this particular discussion takes off just a little bit.
With respect to the possible variations referred to, I have to say that these kind of variations are perfectly possible indeed... Assuming that you indeed do have a Volvo TMD41A machine, as illuded to above, you would actually at 1500RPM extract a mere 35 HP out of the engine, and would end up with a fuel consumption of > 8.75L/hr, which is just under 2Gph ... reducing the engine load even more will indeed get you down to, if not below 1Gph (but no figures available from the manufacturer on this). If your machine is more modern than this, I would actually expect better figures. /forums/images/graemlins/laugh.gif
 
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..........i can't find these data graphs anywhere. Any clues please?

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Not straight forwards;

Volvo Penta
Global
Marine Leisure
Older engines
Diesel
osv...

Or right in Here and on to your drive unit and engine..... Each engine have a PDF file and performance graphs....
 
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thanks
The first couple of engines (engines for shafts) I looked at didn't have the graphs. /forums/images/graemlins/tongue.gif

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You're welcome .... which engine(s) are you interested in?
 
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it would be true to say that revs are normally less than 3000 but surely even if they were only 1000 this could not explain a difference of roughly 5 gph to 1

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yep - quite easily if 3000 was working hard ie pushing the pure hull speed.
 
my current boat has twin ad31p on duoprops so was interested in this. But am also contemplating upgrading boat to a beneteau antares 980 or jeanneau prestige 32 both shaftdrives and was wondering how the fuel usage would compare.
 
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my current boat has twin ad31p on duoprops so was interested in this. But am also contemplating upgrading boat to a beneteau antares 980 or jeanneau prestige 32 both shaftdrives and was wondering how the fuel usage would compare.

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AQAD31P (With Graph ... page 2 Left hand side...

Most engines in there should have the performance curves, some have prop load... but fuel cuves differ from Grammes per HP hour and L/Hr .... to just load curves at RPM... where you'd need to calculate...
 
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