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12V vs. 8V...what runs smoother?

 
 
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Old 07-18-2007, 12:23 PM   #1 (permalink)
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12V vs. 8V...what runs smoother?

I am building a 92 feet motor yacht in the Maldives and I am looking both MAN and MTU engines for it. I have already been told that 10V is not as smooth as a 12V, which was the information given to me by MAN engineers. If so, is there any difference between 8V and 12V in terms of its running (smoothness)?

I would appreciate any opinions, advice and experience in this matter and thank you in advance.

Samih.
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Old 07-18-2007, 01:23 PM   #2 (permalink)
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It all depends on the performance you are looking to get out of the boat.
I would say go for the bigger engines. The bigger the engines, the less stress there is on them, given the size of your boat.
10v as well as 12v seem kind of small for such a big boat.
You should take your data to a professional, they will answer your question better.
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Old 07-19-2007, 09:08 AM   #3 (permalink)
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Smooth

This is a difficult question to answer without comparing specific engine models. The V12 layout is generally regarded the smoothest running .
From my experience if you are looking for smoothness then there are many other factors that can have have a significant effect :- method of engine mount, location of the engine,choice of propeller, gearbox mounting, type of hull etc etc.
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Old 07-19-2007, 02:05 PM   #4 (permalink)
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Quote:
Originally Posted by 32 degrees
The bigger the engines, the less stress there is on them given the size of your boat.
10v as well as 12v seem kind of small for such a big boat.
You should take your data to a professional, they will answer your question better.
Hi,

If bigger engines are used ( Higher Output) than really required and you do not load them up enough you will have a whole set of problems just from this.

There are 10V and 12V Engines made that would sink a 92' boat. There are plenty of 8V engines that will provide enough power for that size boat if it is a displacement craft.

Folks come here expecting to get professional advice from those with experience in the areas they are asking questions.

Straight out poor and or misleading advice is worse than no advice at all.
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Old 07-20-2007, 01:24 AM   #5 (permalink)
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Hi everyone

Thanks for your opinions based on your expertise, knowledge and experience.

I agree with K1W1 that if it is not properly loaded, then it can also create problems.

And I can also appreciate the fact that smaller engines will put too much stress on them.

And yes, its true that the way it is mounted and a whole lot of other factors will also contribute to a smoother running of the engine.

The engines that I am probably thinking to go for right now are twin MTU 12V2000M70 engines. Each gives around 1055 hp.

I know that this is much smaller than the standard engines used for yachts of this size (by the way, its a semi-planning, deep V hull). Then again, I am looking at achieve a top speed of around 18 to 20 knots. No more.

There is, however, an additional factor that comes into play here. Unlike standard dimensions of a yacht of this size, I wanted it to become wider so the beam is actually much larger than the 'standard' beam for such a yacht. This yacht has a beam of 23 feet (7 meters). The displacement is nearly 80 tonnes (fully loaded).

What do you guys think of it? Is this engine going to be too small? And can anyone give me an opinion on this engine itself? Anyone who has used it? Or would you recommend to go for equivalent MAN engine?

Thanks a lot in advance.
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Old 07-20-2007, 03:07 AM   #6 (permalink)
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Hi,

The info you are after would best be sought from the Naval Architect doing your boat.

There are many variables that come into play. It's not just a simple calculation of length x speed equals Horsepower.
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Old 07-20-2007, 09:10 AM   #7 (permalink)
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The MTUís you mentioned are very popular and my experience working with them was good- the only problems I had were related to the electronic controls.
My GUESS is that they are about the right size for what you are proposing. It is great that you asked these questions here and I would also recommend you try and talk to some service guys however I agree with K1W1 (who is a guru when it comes to this type of thing) you would be crazy to make this kind of decision without the professional assistance from a naval architect and the individual engine manufacturers.
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Old 07-20-2007, 11:46 AM   #8 (permalink)
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Thanks!!!!

Hi K1W1, The Reverend and everyone else who has contributed!!

Ofcourse, I am also having a Naval Architect in my team for this project. And as K1W1 has pointed out, it isn't such a simple formula and there are a number of factors involved.

And thanks for your input 'The Reverend' in highlighting your own experience.

Cheers,
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Old 07-20-2007, 11:55 AM   #9 (permalink)
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GF,
12's may run smoother than 8's or 10's, and that has been basically true for years. But with the advent of common rail fuel applications and computer technology, some of the issue of the past may not be significant any more. Talk to the engine manufacturers and get some references, either captains or owners of 8, 10, 12 V's and get their opinion, from a practical standpoint. But definitely go with a common rail setup (not even sure if standard fuel systems area available any more from MAN).
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Old 07-20-2007, 03:08 PM   #10 (permalink)
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golden_fox:

Something else you might consider is the addition of an AquaDrive to your drivelines.
Very simply, the propeller shaft is isolated from the engine movements and is connected via a universal joint which allows the engine to (if it wants) jump up & down & sideways on softer isolation mounts. The boat around it feels nothing when set up properly.

BTW, 1050 HP engines would seem to be insufficient for the speeds you are anticipating, IMHO.
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Old 07-20-2007, 04:15 PM   #11 (permalink)
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I agree with what Loren is saying 1050 HP seems to be insufficient for the performance you want out of the boat. Have a look at:

MTU 10V 2000 M93
MTU 12V 2000 M93
CAT C32 ACERT
MAN V12 1550- CRM

MTU are really good engines, as Reverend said there is the occasional electronic control problems.
If you go for the MTU's leave space in your dash for the displays. Any electrical problem you may have will show up on the displays, you can then take the reference number and report it to MTU. This will be easier than bringing a technician just for diagnostic tests.
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Old 07-21-2007, 12:14 AM   #12 (permalink)
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Quote:
Originally Posted by Loren Schweizer
golden_fox:

Something else you might consider is the addition of an AquaDrive to your drivelines.
Very simply, the propeller shaft is isolated from the engine movements and is connected via a universal joint which allows the engine to (if it wants) jump up & down & sideways on softer isolation mounts. The boat around it feels nothing when set up properly.

BTW, 1050 HP engines would seem to be insufficient for the speeds you are anticipating, IMHO.
Hi Loren,

Thanks for your input. Its funny you should mention AquaDrive, as I had just contacted them last night!!!

Does this mean that you have experienced and used AquaDrive and you were pleased with its performance?
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Old 07-21-2007, 12:24 AM   #13 (permalink)
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Quote:
Originally Posted by 32 degrees
I agree with what Loren is saying 1050 HP seems to be insufficient for the performance you want out of the boat. Have a look at:

MTU 10V 2000 M93
MTU 12V 2000 M93
CAT C32 ACERT
MAN V12 1550- CRM

MTU are really good engines, as Reverend said there is the occasional electronic control problems.
If you go for the MTU's leave space in your dash for the displays. Any electrical problem you may have will show up on the displays, you can then take the reference number and report it to MTU. This will be easier than bringing a technician just for diagnostic tests.

I believe you guys are right, 32 degrees & Loren, that the engines will not be sufficient to generate the speeds that I am mentioning. However, I also do not want to go for light duty, as its rated for only 1000 running hours per year. And i do not want to be running around that or pushing the engines beyond 1000 hours, wouldn't you say so?

Therefore, it has to be medium duty with running hours of a minimum 2000 hours.
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