which hull produce lower fuel consumption?

[sobo]

Hi everyone

I have a situation here. Can someone share with me on how can i calculate fuel consumption of a boat?.

I have designing two different boats' hull form which using the same outboard engine. how can i calculate its fuel consumption at design speed so that I can compare which hull produce lower fuel consumption.

Thank you for your kindness

[PAR]

And you say you've "designed" these two hulls, but can't tell which might be more efficient under power? So, how far along in the design process are you?

[sobo]

sorry for misunderstanding
actually, i am investigating a boat which currently operated. From my naked eyes, I found that the hull design produced a lot of resistance. Therefore, i am designing a new hull form.
My problem would be how can I measure the fuel consumption of the new boat so that I can make a comparison on how much fuel can the owner saved by using my hull design.

[sobo]

after modelling both design in Maxsurf, i can clearly said that the new hull form produced lower resistance at design speed.

for now, i want to know the VALUE of fuel consumption that the owner can saved.

maybe by some calculation or anything.

thanks

[michael pierzga]

Try http://www.solarnavigator.net/hull_drag.htm

[gonzo]

It depends on the design parameters. For example, a planing hull will have less fuel consumption at slightly above planing speed than slightly below. You are not providing enough information for a relevant answer.

[War Whoop]

Fuel consumption?? A properly designed cat is what you are looking for.

[sobo]

thanks for your answer
both designs are catamaran type which have the same Volume Displaced, LOA, Breadth. It only differ by hull shape.

hope that the info is enough. feel free to ask me if i did not provide enough info.

thanks

[sobo]

Fuel consumption?? A properly designed cat is what you are looking for.

hi,
thanks for answering my question. but, could you elaborate more on your answer. i can't understand what you mean by properly designed cat

[daiquiri]

hope that the info is enough. feel free to ask me if i did not provide enough info.

Well, to be honest I don't see any useful info until now. We only know by now that both boats are catamarans, that they are powered by an outboard and that one will consume more than the other. Period.

Anyways, if you have calculated the drag and effective power required by the two boats (for a desired cruise or max speed), one way of calculating their fuel consumption is to make a calculation (actually to estimate, and sometimes even to guesstimate) of power efficiencies of the whole propulsion chain - starting from the propeller (corrected for the wake effects), through the shaft, bearings, gears, all the way to the motor.
In this way you'll obtain the engine break power (Pb) necessary to obtain the required effective power (Pe). Then you have to divide the Pb by the thermal efficiency of your engine (which will depend on the engine type), in order to get the power input by the fuel. then divide this last number by the specific energy content of the fuel used (http://en.wikipedia.org/wiki/Fuel_efficiency#Energy_content_of_fuel) and you will get the required fuel flow.

Or use the engine performance data supplied by the manufacturer.

And don't forget to always use consistent units!

Cheers

[sobo]

thanks daiquiri for your answer

that would be the answer i am looking for.thank you very much.
sorry for not providing good enough information.

fyi,actually,i am already obtained the effective power of my boat.

thank mate!

[BATAAN]

Long, skinny, shallow, light with lots of power.

[daiquiri]

Long, skinny, shallow, light with lots of power.
Why lots of power?

[BATAAN]

Enough power to overcome resistance of hull and weather and give designed performance under all conditions. Also, is good if 70% throttle gives cruising speed as engine is not so stressed. Of course everything is a trade-off and soon becomes all engine and tanks and gets too heavy if not careful. WW2 S-Boote is great example of a very fast highly powered design with useful load and all-weather use. 40+ knots.

[daiquiri]

Enough power to overcome resistance of hull and weather and give designed performance under all conditions.
Ah, ok then.
So not "a lots of power" but just the power sufficient to ensure the desired seaworthiness and performance in a seaway. ;)

Cheers

[BATAAN]

Yes, I mis-spoke. Nat Herreshoff's many steam yachts of pre WW1 at 60 to 120 ft LOA with a beam of 9 to 11 feet usually got by with about 120 hp and were very fast and comfortable in a chop.