engines comparing

[TrentePieds]

No calculation required :-)

"2 x 200HP" simply means two engines each rated at 200 HP. "1 x 400HP" means one engine only, rated at 400HP.

Twin engine boats handle very differently from single engine boats.

"Power loss factor" is a concept belonging to entirely different branches of engineering. If you mean to ask if one engine is better than two (or thre or four), or vice versa, then just ask in plain vernacular English. Or, if you like, in French, but remember that while the odd French word or phrase is okay, we do require that posts be in English.

TrentePieds

[Aravind]

ok, let me rephrase this:


If I have 1 400hp engine, and I want to switch to 2 engines, how much hp will each need to have to be making way at the same speed? (at the same rpm)



What is the formula to calulcate this, and does the formula work the same way when going to 3 or 4 engines?

[Statistical]

Originally Posted by Aravind

ok, let me rephrase this:


If I have 1 400hp engine, and I want to switch to 2 engines, how much hp will each need to have to be making way at the same speed? (at the same rpm)



What is the formula to calulcate this, and does the formula work the same way when going to 3 or 4 engines?

There is no formula. With properly sized propellers two 200 HP engines will at peak output produce the same propulsive force as a single 400 HP engine.

To be clear 200 HP or 400 HP is simply the peak power. Different engines may produce different peak power at different rpms. If you want them to be at identical rpm you would need two 200 HP engines which produce peak power at the same rpm as the 400 HP engine or alternative to X HP engines that at the required RPM produce 200 HP ea.

The propellers have to be properly sized. You can't simply throw your existing propeller designed for 400 HP and a specific gear ratio on a 200 HP engine potentially with a different gear ratio it would be massively overpropped.

The prop is going to be the largest variable. Generally speaking larger slower spinning props are more efficient so with a pair of props you may be able to spin them slower and thus more efficiently given the hull geometry constraint but that assumes there is a transmission which can gear the output down far enough. Still even this is relatively small impact for rough aproximation two 200 HP engines is comparable to one 400 HP engine.

[TrentePieds]

Aravind:

You are asking questions devoid of context. No-one can give you a sensible answer to such questions, and if you persist in asking in that manner, any answers you may get will merely lead you astray.

I went back through your posts since you first joined us, and as far as a can gather you were hoping, originally, to cross oceans in a sailboat having accommodations that can only be found in boats that are far, far bigger than a novice sailor can handle.

I take it you do not yet have a boat, so perhaps you will do yourself a favour by addressing the fundamental aspects of sailboat design rather than thinking about 400HP engines.

There are two books I will recommend to you. Both are available through Amazon:

Skeene's Elements of Yacht Design, Francis Kinney.

The Proper Yacht, Arthur Beiser.

Read them so you will have the beginnings of an understanding of what yacht design is all about. When you have the broad overview, and you have selected a boat that meets all your desiderata in regard to living aboard and in regard to where you wish to sail her, we can use that boat as a foil for a discussion of relevant details such as determining power requirements.

Bonne chance :-)!

TrentePieds

[Aravind]

Originally Posted by TrentePieds

Aravind:

You are asking questions devoid of context. No-one can give you a sensible answer to such questions, and if you persist in asking in that manner, any answers you may get will merely lead you astray.

I went back through your posts since you first joined us, and as far as a can gather you were hoping, originally, to cross oceans in a sailboat having accommodations that can only be found in boats that are far, far bigger than a novice sailor can handle.

I take it you do not yet have a boat, so perhaps you will do yourself a favour by addressing the fundamental aspects of sailboat design rather than thinking about 400HP engines.

There are two books I will recommend to you. Both are available through Amazon:

Skeene's Elements of Yacht Design, Francis Kinney.

The Proper Yacht, Arthur Beiser.

Read them so you will have the beginnings of an understanding of what yacht design is all about. When you have the broad overview, and you have selected a boat that meets all your desiderata in regard to living aboard and in regard to where you wish to sail her, we can use that boat as a foil for a discussion of relevant details such as determining power requirements.

Bonne chance :-)!

TrentePieds

Strange post, on the one hand you seem to like to personally try to attack people, and on the other hand you like to give your allmighty guiding hand...




Anyways, although I like to endulge into books, I very much doubt that books from 1904 and 1978 will help me to calculate power distribution between electric and diesel engines in a parallel electric assisted hybrid system versus a system with seperated diesel and electric engines.



Looks like I'm better off asking my renovation questions towards manufactureres rather then on this very helpful forum. </sarc>








edit: this post is not ment towards everyone. many ppl have put good value on previous questions and I thanked them for this.

[newhaul]

Ok now I scratching my head how did we get from a report to a report with one diesel and one electric ? Only works on a cat better off doing the dual hybrid systems they have. Or go full a pod electric with diesel gensets

[AKA-None]

Ahh net new information has just been revealed

[newhaul]

Originally Posted by newhaul

Ok now I scratching my head how did we get from a report to a report with one diesel and one electric ? Only works on a cat better off doing the dual hybrid systems they have. Or go full a pod electric with diesel gensets

Must decipher
How did we get from a repower of 2 diesel to a repower with one diesel and one electric?
That only really works well on a cat. You are better off with the diesel electric hybrid systems they have or go full electric with a Z pod and a diesel generator.

[Wotname]

I think it is more complex than simply comparing 2, 3 or 4 engines be they diesel or electric or both.

15 months ago the OP acquired a 32 metre wooden ex-german navy ship complete 2 main engines and 2 generators. A month later he decided on 54' typical sailboat yet 2 weeks later the OP took an option on a beautiful 60' GRP sailboat.

I guess this didn't work out as intended because a couple of weeks ago he wanted information on painting a steel hull and also about installing install a nice 6cyl engine in a 55ft sailboat.

We are now comparing several engines to repower his 79' sailboat. Someone posted upthread the questions were devoid of context, on the contrary, I think there is too much context to answer the questions rationally.

[Tillikum]

Originally Posted by Morris Wilson

Go with an inline 6 cylinder. they will be longer but much more accessible ov er all. sixes are inherently smoother (V12s are the best) I'm a heavy truck mechanic and know the cat 3208s well. They were a good engine built by Mitsubishi but not rebuild friendly. You are moving into the new emissions controlled engines and all that entails. Be ware. Fuel mileage is still mostly in the throttle lever. My expertice is more in the over 400 hp so maybe not relavent.

International DT466 might be a good choice: tough, highly reliable and relatively cheap,

https://www.boatdesign.net/threads/u...-diesel.53990/

[racer1958]

In my opinion a NA 3208 is hard to beat.
It's a mechanical engine, no ECM'S to cause issues. Can be fixed anywhere in the world.
It has been out of production for some time , but original and aftermarket parts are available.
With lots of CAT experience, that is a 20,000 hour engine in commercial marine applications.