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Old 21-02-2019, 06:34   #76
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Engine reviews Yanmar or Volvo

Originally Posted by Dockhead View Post
Yeah, but I need to retract my previous remark about horsepower. A64 is right -- I now think he was talking about not how horsepower is MEASURED, but how it is RATED, which are two entirely different things.

Yes, the same engine might be RATED at very different horsepower levels based on the type of service. So the same engine rated 75hp for commercial use might be capable of producing real 100hp for pleasure, so, short-term, intermittent duty. The governor may simply be set to prevent achieving the revs needed to make the higher figure, or the maker may simply set an operational limit for the heavier duty, but the engine is otherwise the same.

I was speaking as to how it is measured or not surprisingly now days with computer modeling etc. itís often not even measured, itís calculated now.
I still maintain that there is plenty of room in how HP is derived so that a creative marketing dept. can play with the numbers quite a bit.

Rating is a similar but different animal, itís quite common even in aircraft turbines for the same engine to be rated differently, often this is done so that a particular engine can be fitted and stay within the airframes power limit, but often itís simply a matter of $$, engine manufacturers price engines based on power output, pay more and they turn the fuel up and the engine will make more HP, or often itís literally just the printing on the manual and data plate and nothing more, but as itís a violation of the FARís to operate an engine beyond itís rated limit, to be legal you stop at rated power, even though more is available at the push of a lever.
Mercury Verado outboard are just two engines, one 4 cyl and one 6 cyl, they cover 150 hp to 400 hp with just two engines, with different programming.
The new little Suzukiís from 9.9 to 20 hp are all the same identical engine, the computer limits power output to the level you pay for.

These arenít ratings, they are actual physical limits, just software controlled limits though.

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Old 21-02-2019, 06:42   #77
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Re: Engine reviews Yanmar or Volvo

So far as tractor motors, a great many tractors are Yanmar powered as well. Almost all if not all of the little John Deereís are Yanmar powered, the Diesel ones anyway, the gas motor John Deere I had was Kawasaki powered.

However they arenít the tractor motors your Grandfather had, they are still smaller lighter, higher RPM Diesels.

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Old 21-02-2019, 12:27   #78
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Re: Engine reviews Yanmar or Volvo

I read a lot here about the " horse power", but the true power of a diesel is the " torque" it can provide. And one should note that the torque can be measured at the flywheel or at the transmission, not to be confuse with each other.

One can think of " torque" as the power to get you going and " horsepower" to keep you going.
Like riding a bicycle. When you are standing still all the horsepower ( Think "lungs" ) in the world won't get you going, that requires the torque ( leg muscles), but lung power is what keeps you going.

In diesel speak, you get all the different power ratings.
Like a runner, you are likely to maintain an easy speed for hours at a time, but flat out speeds are usually short lived.
Hence you will find different power ratings on a diesel engine spec sheet.

Unlike a gasoline engine, maximum torque for a diesel is not at maximum revs or near maximum revs.

Your typical 10 hp gas outboard may produce 10 hp at 5,500 rpm.
That same engine can be made to spool up to 6,000 rpm and make 15 hp.

There is a 10 hp max power for some area lakes. Engine manufactures quickly determined that by lowering the rpm for some of their stock engines, that could market an engine as 9.9 hp.

But that is gas engines, let's get back to diesel.

Your typical yachtie diesel may spool up to 3,500 rpm, but max. torque is usually attained at substantially less rpm..say 2,800 rpm. This would be the ideal " cruise" rpm, where you get maximum" power" at optimum fuel burn.

But the plot thickens here. Your engine's transmission reduction and the propellor diameter, pitch and number of blades, type of blades, etc are all components of reaching optimum power from your diesel engine.

It s a very complicated science and I can recommend reading David Gerr's book, "The Propellor Handbook" which delves into deciphering diesel engine power curves, their power curves, propellor selection, ad infinitum.

Simple choosing an engine based on horse power only will not get you far.
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Old 21-02-2019, 15:03   #79
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Thumbs up Re: Engine reviews Yanmar or Volvo

I have a Nanni 3.30, 29HP in my Adams 35 purchased from Collins Marine in Sydney.
It pushes our steel 7 tone hull along at 6+ knots in calm conditions. It is based on a Kubota 3 cylinder motor and cost $12,500 in November 2010. The next size up is a Nanni 4 cylinder 40HP motor which would be overkill in a 33 ft Arends but if you have the room and the extra cash, by all means go the 40HP. The 40HP is also Kubota based.
You can get much cheaper oil filters for Nanni/Kubota motors.
Ours has now done 520 hours and uses around 2 liters per hour. We have been very happy with it.
Good luck with whatever motor you purchase.

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