Power/Resistance Calculation for Planing V-Hull & Fuel/Engine Required

[Joakim]

Originally Posted by daiquiri

Assuming that Joakim's calcs for the power required are correct (and the numbers do seem huge enough at first glance), 20 MW engines (around 27000 HP) would consume an enormous ammount of diesel fuel. Joakim says it would be around 4000 kg/h or 1056 gal/h though I believe it would be something around 4500 l/h or 1200 gal/h.

The power is a very rough estimate and as I said it may be possible to halve it.

A big modern diesel consume less than 200 g/kW/h and even 160 g/kW/h is possible (over 50% efficiency). 4000 kg/h is about 4800 l/h.

Joakim

[daiquiri]

Originally Posted by Joakim

The power is a very rough estimate and as I said it may be possible to halve it.
A big modern diesel consume less than 200 g/kW and even 160 g/kW is possible (over 50% efficiency). 4000 kg/h is about 4800 l/h.
Joakim

Hmmmm.... It is becoming a big mess in this site with the units, indeed. I had read l/h instead of kg/h when reading your data.
No problem, it means that we both have used the same fuel consumption per HP.

[Guest625101138]

Originally Posted by Kapitan_Raider

assuming 100 waterjet efficiency i forgot to mention. Whats the best that waterjets can convert ?

I gave you the expected efficiency in post #3.

Rick W

[Stumble]

If this is for a fast attack boat I think you need to consider that it will actually operate in two modes. The first is long distance range at some optimal cruising speed, the second is in attack mode running at or near full speed. Since you really can't carry enough fuel to operate at high speed all of the time the trade off is to take longer getting to the expected operational location while keeping the ability to operate at high speeds when necessary. In addition if this is a proposed ship for the US fleet, then keep in mind that under way refueling is a possability as well.

I stole this from Trinity Yachts Concept page, but it is a semi-displacement jet yacht carrying a lot more ammenities than you would need with a max speed of 27.5 kn, and a max range of 4,000nm at 10kn. http://www.trinityyachts.com/168hssdwaterjetmy.asp The ship leaves the dock with 22,000 gallons of fuel, so that works out to be about 5.25 gallons per mile. Which is pretty much in line with what you can expect from such a large vessel.

[Casper]

guys I've found a savitsky spreadsheet, can any of have a look, I don't konw if it is a good one http://www.hawaii-marine.com/templat...escription.htm

Regards,
CAS

[Guest625101138]

Originally Posted by Casper

guys I've found a savitsky spreadsheet, can any of have a look, I don't konw if it is a good one http://www.hawaii-marine.com/templat...escription.htm

Regards,
CAS

Why not plug your numbers in here:
http://illustrations.marin.ntnu.no/h...ing/index.html
It is free.

Rick W

[Guest625101138]

Originally Posted by Joakim

The power is a very rough estimate and as I said it may be possible to halve it.

A big modern diesel consume less than 200 g/kW and even 160 g/kW is possible (over 50% efficiency). 4000 kg/h is about 4800 l/h.

Joakim

Joakim
I am being picky but they should be kWh not kW when you are referring to energy. I know you made a simple mistake but given the knowledge displayed by some here they may not realise what you meant.

A little Bukh diesel I had years ago was specified to get 186g/kWh and my estimates at the time indicated that this was close to what I achieved.

Rick W

[Joakim]

Originally Posted by Rick Willoughby

I am being picky but they should be kWh not kW when you are referring to energy.

You are right and I corrected that to my original post. I think it is very important to be careful about units, but wrote too fast.

Joakim

[timtap]

Have you heard of Project 305 , a boat built at Devonport Dockyard in Plymouth for the Aga Khan which must be a nightmare to build as the speed requirements for this craft have been extremely problematic .

http://www.telegraph.co.uk/news/uknews/1568954/Aga-Khan's-andpound100m-boat-after-Blue-Riband-title.html

[daiquiri]

Originally Posted by timtap

Have you heard of Project 305 , a boat built at Devonport Dockyard in Plymouth for the Aga Khan which must be a nightmare to build as the speed requirements for this craft have been extremely problematic .
http://www.telegraph.co.uk/news/uknews/1568954/Aga-Khan's-andpound100m-boat-after-Blue-Riband-title.html

Yeah, I've read about it few months ago, and that fire incident in the engine room during the trials had struck me. That accident, plus the subsequent change of propulsion type is not a good sign, imho. Applying patches (and this one is big) to a new project is never a good sign to me. They are stretching to the technological limits the structural and propulsive requirements of the ship and it looks to me that it's birth and future life will not be easy.

I have a headache and some fever so all glasses look half-empty to me today.