fuel consumption?

[duncan]

hmmmmm at the risk of death by bamboo I am going to agree with petem's post............

at any given speed for the same hull either 2 or three engines will be burning the same amount of fuel because they will have to generate the same amount of horsepower to drive the hull.

however, as already highlighted, there will be small adjustments for increased drag (more prevalent at higher speeds) and increased weight (the extra engine and drive but pretty much a constant factor at all planning speeds).

overall, as others have highlighted/concluded, any additional fuel costs will be relatively minor financial factors relative to servicing and maintenance ie don't worry too much about them.

 

[[2068]]

>As every 42 I've worked on only had 12 valves x 3 = 36. You are thinking of KAD 44's and 300's.

Ooops, you're right. It's still a lot of maintenance, though.

dv.

 

[[2068]]

>at any given speed for the same hull either 2 or three engines will be burning the same amount of fuel because they will have to generate the same amount of horsepower to drive the hull.

You're right IF the two boats had the same cruise speed. But say the triple engined monster did 36kts flat out, you might be happy to cruise at 30kts. If the sensible twin did 30kts flat out, you might be happy to cruise at 25kts. So multiplying up the figures to get a rough hourly estimate probably won't be far out, although it's not really comparing apples with apples because the boats are travelling at different speeds.

It's the same reasoning behind being able to provide "typical" fuel consumption curves. In reality the curve will match no boats whatsoever (exactly) but the assumption is that it's the prop selection that takes account of boat weight, hull shape, numbers of engines, form drag, appendage drag, size of skippers pot belly etc. Once you have chosen the correct prop and can reach rated rpms flat out, then the engine should be tracking along that curve, and the hourly consumption figures should be predictable(ish).

All the above goes out the window if you attach them to a non planing hull, cos you'll end up with a completely different curve, even if you get max rated rpms.

I'm probably not explaining this too well. Spannerman? Help?

dv.

 

[epervier]

Re: Daka

with referemce to mooring fees look at my location, we are less than half of the south coast of england prices for moorings and if we put into the canal network over winter it becomes even less, a year in the french canal network about 480 euros, that one of the reasons there's so many red ensigns over this side.

 

[KevB]

I'm probably talking bollox here but.... isn't average fuel consumption worked out on the amount of bhp being produced by each engine? (someone will have figures) therefore if the boat needs 300bhp worth of power to do say 25 knots does it matter how many engines are producing it??? If two are producing 150bhp each to make 25 knots surely 3 producing 100bhp each will running more economically but still making 25 knots. Therfore I submit that dividing by two the consumption of a twin engined boat and then multiplying it by 3 wont give an accurate average. it'll be too high.....

 

[[2068]]

That would be the case if the cruise speed were the same.

But if you have a boat with triples, you're likely to want to use the higher cruise speed, weather permitting, in which case the hourly figure will be consumption for the two divided by two times three. Otherwise why bother with the triples?

It's madness, anyway.

dv.