Fuel consumption

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adrianm

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Just seen a program about fast boats on the box. Some of these commercial ferries are getting through 8,000 litres of fuel per HOUR!

Surely reducing consumption of those things would do more for fossil fuel reserves and the environment than trying to stop leisure boat users?
 
You've never had a row with a tree hugger about your boat?

You're lucky if not.

Also one of the reasons given for the red diesel duty hike is enviromental.
 
Look at it from the point of view of litres per person, then think that for most people it's one trip per year (Well, two trips if you count the return separately!) and you'll come to a very different conclusion.
 
Nope, same conclusion. Why do tourists in the med need to get from island to island so quickly?

A more traditional style of ferry would get there using a tiny fraction of the fuel and a more leisurely trip would make for a better experience too.

I mus be getting old, I really can't understand why everyone is always in such a hurry!
 
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I really can't understand why everyone is always in such a hurry!

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You really should become a rag and stick man! /forums/images/graemlins/smile.gif
 
Lol, actually I probably would be if they weren't so wet and leant over all the time. I like my home comforts too much.
 
Because if the ferries were'nt fast enough, peeps would go by plane. Its not just tourists on those ferries, its locals as well
 
Well, Condor Express was only doing 25kt (capability 41kt) on its crossing to the Channel Islands yesterday PM, so perhaps they are trying to cut down on fuel usage?
 
Hi All,

A bit off-thread I suppose and I appreciate this is the MoBo forum, but could anyone tell me what sort of fuel consumption a Volve 36hp diesel engine in a 6.5 ton yacht could expect to achieve. A friend of mine asked me and I haven't a clue.

Sorry, don't know the Volvo type/nnumber, but it is original equipment in a 1984 boat.

FWIW my guess was about 1/2 gallon/hr at cruising speed!

Anyone know more accurately?

Cheers Jerry
 
Diesel engines consume roughly 0.22 kg of fuel per kilowatt hour. Assuming that 1 kg of diesel fuel = 1 litre which it does'nt quite because its lighter than water then your mate's engine should consume 0.22 x 36 = 7.9 litres per hour = 1.7 galls per hour at max rpm or whatever rpm max power of 36hp is developed . Presumably, the engine is not driven at max rpm so this figure would have to be pro rata'd to the actual cruising rpm that your mate uses but, again, this is only an approximation because the relationship is'nt linear. So, if your mate was using 80% of the normal max rpm, then he could expect to use 80% x 1.7 = 1.4 gall/hr
If you want to know more accurately engine suppliers can provide power v rpm curves or fuel consumption v rpm curves if you ask nicely but the info may not be available for a 20yr old engine. Dont forget also that any figures assume that the engine is in good condition. Any faults may affect the fuel consumption. Also incorrect propping or a fouled hull which didnt allow the engine to develop full rpm would also affect fuel consumption
 
sorry to be picky mike, especially to such a good explanation, but as you state early on it's a function of the power being generated rather than revs so later, when you use 80% revs, this may (and almost certainly will) produce less than 80% of the power and use less than 80% of the nominal consumption.
 
To be fair, duncan, I did say in my post that this was an approximation as the relationship was'nt linear. He's a yottie so you have to keep things simple /forums/images/graemlins/grin.gif
 
HEY!! I heard that!! /forums/images/graemlins/mad.gif /forums/images/graemlins/laugh.gif Seriously, thanks for the info chaps. It's enough to know I was miles out in my guess, and I've copied your thoughts to pass to my friend. /forums/images/graemlins/smile.gif

Cheers Jerry
 
is a kilowatt the same as a hp? if not then you surely need a conversion factor in your sum to get the right answer, as the guy stated his engine at 36 hp, not 36 kw.
 
Jerry,

My Volvo 2003 27hp diesel in my 6.5 tonne yacht gave me 2.5 hours to the gallon at 2250 rpm which equated to a 6knt cruising speed.

My Bukh DV36M (36hp) in my previous yacht (also c.6.5 tonnes) gave me about 2.1~2.25 hours to the gallon at 2,600 rpm which again equated to 6knts.

We didn't tend to push the engines much harder unless in a large sea or against the tide so it is difficult to say how much this reducd to for higher revs, but the figures quoted are averages.

It is the thought of 12 gph for a MoBo which I now worrying about!

Hope this helps.
 
Hah, spotted my deliberate error, he says /forums/images/graemlins/blush.gif. Yup, 1hp = roughly 0.7kw so all consumption figures should be multipled by 0.7
 
Deleted User are you sure? I have been endeavouring to work out the consumption on my tmd41 & the best guess so far is approx. 5 litres per hr @ 3000 rpm; max revs given as 3800 which using your method gives about 23 litres per hour.I did try to use the graph on the volvo site, but failed to understand it.
 
JEG, I believe that the TMD41 produces 200hp/147kw @ 3800 rpm so lets assume the engine produces 100kw @ 3000rpm (what does your power curve say?). Fuel consumption = 0.22 x 100 = 22 litres/hr or 4.8 galls/hr. Obviously if you have 2 engines, the consumption is twice that figure. What speed do you get from your boat @ 3000rpm?
All these calculations are very approximate as consumption is also very dependent on correct propping and fouling of the hull
 
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