Fuel Consumption Again

[whisper]

As a 4693 post Newbie can I please ask for sensible and kindly replies to the following question. (That precludes hlb !!)

I want to see what consumption a KAD44 should have at various rev. settings. I've looked at VP's site but can't see anything of any use. Guidance please.

 

[PaulGooch]

As a 4693 post Newbie can I please ask for sensible and kindly replies to the following question. (That precludes hlb !!)

I want to see what consumption a KAD44 should have at various rev. settings. I've looked at VP's site but can't see anything of any use. Guidance please.

If you don't know the answer to that question, you shouldn't ask it.

 

[PaulGooch]

Ah, i see you asked for sensible answers, sorry about that

I'm not sure that the question can be answered, to be honest. It's going to depend a lot on the boat that the engine is fitted to, loading etc. Some details of your boat ?

 

[timbartlett]

As a 4693 post Newbie can I please ask for sensible and kindly replies to the following question. (That precludes hlb !!)

I want to see what consumption a KAD44 should have at various rev. settings. I've looked at VP's site but can't see anything of any use. Guidance please.

Crude rule of thumb: diesels burn about 1 gallon per hour for every 20hp they produce.
So a 260hp diesel will burn about 13 gallons when it is running flat out.
It varies a bit from engine to engine, and at different revs -- generally less efficient at very high revs and always less efficient at low revs.

But the power used by a propeller is (roughly) proportional to the cube of the shaft speed. This is often called the "propeller law".
*The prop law isn't strictly valid, because the propeller is less effective at certain speeds, so for planing boats the "prop law" tends to overstate the advantages of throttling back: it may be more accurate to use a different index (anything in the range 2.6-3.0 -- generally lower indexes for higher performance boats)

But if we stick with the basic "propeller law", then if you half the shaft speed you will use (roughly) one eighth as much fuel.
More usefully:-
Using the standard prop law
90% rpm = 73% fuel consumption
80% rpm = 51% fuel consumption
70% rpm = 34% fuel consumption

Using the prop law adapted for planing craft with an index of 2.7
90% rpm = 75% fuel consumption
80% rpm = 55% fuel consumption
70% rpm = 38% fuel consumption

 

[gjgm]

As a 4693 post Newbie can I please ask for sensible and kindly replies to the following question. (That precludes hlb !!)

I want to see what consumption a KAD44 should have at various rev. settings. I've looked at VP's site but can't see anything of any use. Guidance please.

John
you can get the Kad 300 from Windy here
http://www.windy.no/performance_tests.html

Guess any difference with the 44s will be linear. Of course this applies to extremely agile,slender performance boats, not garden sheds.

 

[ulyden]

KAD 44 uses 57l/h at full load! So if you use 2.5 curve

3800rpm 57l/h
3600rpm 50l/h
3400rpm 43l/h
3200rpm 37l/h
3000rpm 32l/h

Some numbers in Norwegian

 

[hlb]

As a 4693 post Newbie can I please ask for sensible and kindly replies to the following question. (That precludes hlb !!)

I want to see what consumption a KAD44 should have at various rev. settings. I've looked at VP's site but can't see anything of any use. Guidance please.

Aww.

 

[whisper]

Crude rule of thumb: diesels burn about 1 gallon per hour for every 20hp they produce.
So a 260hp diesel will burn about 13 gallons when it is running flat out.
It varies a bit from engine to engine, and at different revs -- generally less efficient at very high revs and always less efficient at low revs.

But the power used by a propeller is (roughly) proportional to the cube of the shaft speed. This is often called the "propeller law".
*The prop law isn't strictly valid, because the propeller is less effective at certain speeds, so for planing boats the "prop law" tends to overstate the advantages of throttling back: it may be more accurate to use a different index (anything in the range 2.6-3.0 -- generally lower indexes for higher performance boats)

But if we stick with the basic "propeller law", then if you half the shaft speed you will use (roughly) one eighth as much fuel.
More usefully:-
Using the standard prop law
90% rpm = 73% fuel consumption
80% rpm = 51% fuel consumption
70% rpm = 34% fuel consumption

Using the prop law adapted for planing craft with an index of 2.7
90% rpm = 75% fuel consumption
80% rpm = 55% fuel consumption
70% rpm = 38% fuel consumption

Thank you Tim - I didn't realise it was so simple

 

[whisper]

John
you can get the Kad 300 from Windy here
http://www.windy.no/performance_tests.html

Guess any difference with the 44s will be linear. Of course this applies to extremely agile,slender performance boats, not garden sheds.

PAH..... Summer boater. At least I keep warm & dry all year round.
Are your medallions polished for this Summer yet???

 

[whisper]

KAD 44 uses 57l/h at full load! So if you use 2.5 curve

3800rpm 57l/h
3600rpm 50l/h
3400rpm 43l/h
3200rpm 37l/h
3000rpm 32l/h

Some numbers in Norwegian

Thanks Ulyden , that's very useful.

 

[whisper]

Ah, i see you asked for sensible answers, sorry about that

I'm not sure that the question can be answered, to be honest. It's going to depend a lot on the boat that the engine is fitted to, loading etc. Some details of your boat ?

Dear Sir,
"Boat details ?" Botnia Targa 25 = 7.9m o'all , 3 tonnes of boat + 1/2 tonne of unneccessary junk. Hope that helps.
Your Humble Servant etc etc.

 

[strakeryrius]

I know that there is a Volvo Penta manual for the KAD44 which has graphs which predict the fuel consumption at various revs - just can't locate mine at the moment as I have put them in a safe place.

From my log book (Targa 34 with KAD44s) I can tell you that I did 126 hours in 2008 and averaged 36.6 litres per hour - with a couple of long trips.

In 2009 I did 113.7 hours and averaged 28.5 litres/hour as we didn't get further afield than the IoW from Poole due to various plans having to be cancelled.

I usually cruise at 2600 revs. Hope that this helps a bit.

 

[whisper]

I know that there is a Volvo Penta manual for the KAD44 which has graphs which predict the fuel consumption at various revs - just can't locate mine at the moment as I have put them in a safe place.

From my log book (Targa 34 with KAD44s) I can tell you that I did 126 hours in 2008 and averaged 36.6 litres per hour - with a couple of long trips.

In 2009 I did 113.7 hours and averaged 28.5 litres/hour as we didn't get further afield than the IoW from Poole due to various plans having to be cancelled.

I usually cruise at 2600 revs. Hope that this helps a bit.

Thanks, I'll have a look at the manual when I return to the boat. Didn't realise such info was in it. Like many men over a certain age, I'm not too good at reading instruction books!!