RE: {Beneteau Owners} Perkins Engines

[Dan....@carrier.utc.com]

Bill,

 

Perhaps we should not confuse "power" with "torque". Power is equal to torque times (angular) speed, so usually more speed will deliver more power unless the torque curve drops off sharply. In a high rpm mode, the engine will normally deliver more power, but the fuel economy will be shot. To get the most bang for your buck, the trick is to run the engine at the rpm at which the torque is at its maximum. For most marine diesels I've heard of, this happens to be at 70 - 80% of the max rpm, depending on the manufacturer and model.

 

I have the torque curves for my Prima M50 (max rpm 3000), which predictably show the sweet spot at about 2100 - 2200 rpm. When I cruise at that rpm (MaxProp, clean bottom, reasonable seas, wind and current), I get 6.5 - 7 kts and burn only 0.6 gallons per hour. I've never tested it properly, but believe that if I pushed it to say 2500 - 2600 rpm, I'd get a 10% increase in speed and 50% increase in fuel consumption, which does not make any sense to me unless conditions dictated it.

 

I'll just mention that since I dumped my old fixed 3-blade prop (21"x13") in favour of the 3-bladed MaxProp (20"x14"), I've lost about 0.3 kt when motoring at the same rpm, but have gained enormously when sailing and backing under power.

 

Regards,
Dan

'Babar' '94 OC440

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From: Benetea...@googlegroups.com [mailto:Benetea...@googlegroups.com] On Behalf Of bbigd...@aol.com
Sent: Wednesday, 7 November 2007 3:39
To: Benetea...@googlegroups.com
Subject: {Beneteau Owners} Perkins Engines

I just received the following note from Perkins:

"The engine was originally rated at

4500 RPM and would run happily at this speed in a vehicle application.



If the application has changed then you would need to run the engine speed

to suit, but at 2800 RPM you will not reach peak power."



Everything I have heard or read says run the engine at 2600-2800, 

but Perkins is saying that is below peak power?



That seems shocking to me.



Bill

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[Force Majeure]

I posted the M80T curves here on the site under the files section.
The file is VP-TMD22P-bulletin.pdf which is actually a Volvo document,
but it is the same engine rebadged, with identical curves. I have the
Perkins curves too, but not electronically. They are available for
viewing at boatdiesel.com for a fee. It looks like peak torque is
around 2,400 or so, but it is quite flat between 2,200 and 2,600.

Anyway, it is torque that is important. Per the curves I have, the
horsepower used at cruising speed is probably only in the 15hp range,
but torque is at its max. While it is an 80hp motor, like all
diesels, the torque is developed very early, and it is the torque that
is driving the boat. It is the same for cars incidentally, and if one
were designing an infinitely variable transmission for a diesel car or
truck, one would ignor the fact that peak power is at 4,500 rpm and
would instead take advantage of peak torque and the tachometer would
probably sit merrily somewhere in the "fat" part of torque band
regardless of the speed.

Jeff

> From: Benetea...@googlegroups.com
> [mailto:Benetea...@googlegroups.com] On Behalf Of bbigduke...@aol.com
> Sent: Wednesday, 7 November 2007 3:39
> To: Benetea...@googlegroups.com
> Subject: {Beneteau Owners} Perkins Engines
>
> I just received the following note from Perkins:
>
> "The engine was originally rated at
>
> 4500 RPM and would run happily at this speed in a vehicle application.
>
> If the application has changed then you would need to run the engine speed
>
> to suit, but at 2800 RPM you will not reach peak power."
>
> Everything I have heard or read says run the engine at 2600-2800,
>
> but Perkins is saying that is below peak power?
>
> That seems shocking to me.
>
> Bill
>
> _____
>

> Email and AIM finally together. You've gotta check out free AOL

> <http://o.aolcdn.com/cdn.webmail.aol.com/mailtour/aol/en-us/index.htm?...
> OLAOF00020000000970> Mail!

[bbigd...@aol.com]

How do I get to the file listed below?

Bill

---

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