fuel consumption VS speed change

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QAMER
Bilge Dweller
Posts: 9
Joined: Sun Oct 12, 2008 6:58 pm

fuel consumption VS speed change

Hi anyone know how to solve this type of question formula/calculation . THANKS

question: If your ship burns 8 tons of fuel per hour at 15 knots, how many tons per hour will it burn at 21 knots?
11.2 tons
22.0 tons
15.7 tons
12.9 tons
Wrong

The Dieselduck
Posts: 2817
Joined: Sun Jul 22, 2007 1:41 pm

Re: fuel consumption VS speed change

My head is not much into this kind of puzzle these days, but it seems to me the question is missing some information to be able to answer correctly. You would have to know more info to calculate, like coefficent of hull friction and such... I know, from experience that fuel consumption goes up dramatically but the exact formula I forget right this minute.
Martin Leduc
Certified Marine Engineer and Webmaster
Martin's Marine Engineering Page
http://www.dieselduck.net

JK
Enduring Contributor
Posts: 2706
Joined: Tue Sep 04, 2007 2:29 am

Re: fuel consumption VS speed change

I played around with it while I was suppose to be working on something else and like Martin says, there must be something missing. Then again, in my job we don't buy the fuel so I don't worry too much about it.

Sébastien
Engineering Mentor
Posts: 97
Joined: Mon Oct 01, 2007 5:06 am
Currently located: Québec

Re: fuel consumption VS speed change

Reed's volume 4 chapter 7
It can be assumed that a major portion of the designed operational speed range is proportional, and that for any two points within this range the specific fuel consumption is constant. On the same trip, it can be assumed that the ships' displacement is also constant. You are left with cons1/cons2=(v1/v2)3. In your example cons2= 8* (21/15)3 = 8*2.744 = 21.95 tons

QAMER
Bilge Dweller
Posts: 9
Joined: Sun Oct 12, 2008 6:58 pm

fuel consumption VS speed change

Thanks to all of you specially SEBASTIEN.

The Dieselduck
Posts: 2817
Joined: Sun Jul 22, 2007 1:41 pm

Re: fuel consumption VS speed change

very sharp indeed sebastien, thank you. Its so simple I feel stupid.. ehehehe
Martin Leduc
Certified Marine Engineer and Webmaster
Martin's Marine Engineering Page
http://www.dieselduck.net

KWOBGUS
First Time Poster
Posts: 1
Joined: Sat Sep 01, 2012 10:28 am

Re: fuel consumption VS speed change

Hey I was just curious where you got 3 as a multiplication factor. Thanks!

JollyJack
Fleet Engineer
Posts: 1140
Joined: Wed Mar 24, 2010 3:57 am

Re: fuel consumption VS speed change

3 is not a multiplication factor, it's cons1/cons2=(v1/v2) cubed
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