HP question

Assuming that the horsepower delivered to the shaft is the same, and
assuming the prop is the same, and assuming the prop is in the same
location, I don't see where it would make a difference whether that power is
generated by 15,000 gerbils, a diesel inboard, or a gas outboard. I don't
recommend the gerbils, though. They're not so bad themselves, but installing
an MSD to deal with their exhaust is monumental.

--
Karin Conover-Lewis
klc dot lewis at gte dot net


"Habbi" <habbi.TakeThisOut@islandtelecom.com> wrote in message
news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
 > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be equal
 > to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
 > when it come to performance but is it significant? In the same boat would
 > the diesel carry more load/ weight before becoming lugged? I have a 31' X
 > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp johnson.
 > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
 > duoprop which outperformes me unloaded and loaded. With an extra 1000 lbs
my
 > boat will not plane where as the other boat will. It seems like extra
weight
 > affects the 2 stroke much more than the diesel. How does a gas sterndrive
 > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
 > blade) and unloaded it barely reaches the recommended WOT. Thanks
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

Dosen't the torque produced play into this.
"Larry" <Larry2.RemoveThis@NOSPAMisomedia.com> wrote in message
news:vfbki67khbss33@corp.supernews.com...
  > > Would a 250 hp turbodiesel sterndrive be equal
  > > to a 250 hp 2 stroke outboard. Hp is close, but it's the application you
 > need to look closer at.
 >
 > A diesel belongs on a slow displacement hull where overall speed remains
 > slow. The outboard runs well on a light, fast, planing hull where it is
 > allowed to get the rpms up into the range of useful HP. The outdrive is
 > in-between the other two with good lower end power and will also push a
 > planing hull fast.
 >
 > You need to look at what rpm each unit makes the best power as this is
where
 > it should be run at "cruise".
 >
 > --
 > Larry
 > Remove NOSPAM to reply
 >
 > "Webidence" is defined as: "Using unproven evidence
 > gathered from the Web to prove your silly point".
 >
 >
 > "Habbi" <habbi.RemoveThis@islandtelecom.com> wrote in message
 > news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
  > > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be
equal
  > > to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
  > > when it come to performance but is it significant? In the same boat
would
  > > the diesel carry more load/ weight before becoming lugged? I have a 31'
X
  > > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp
johnson.
  > > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
  > > duoprop which outperformes me unloaded and loaded. With an extra 1000
lbs
 > my
  > > boat will not plane where as the other boat will. It seems like extra
 > weight
  > > affects the 2 stroke much more than the diesel. How does a gas
sterndrive
  > > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
  > > blade) and unloaded it barely reaches the recommended WOT. Thanks
  > >
  > >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

Marvin Murphy wrote:
 > Dosen't the torque produced play into this.

Yeah, it does, and the torque curve of an IC engine isn't anything even
remotely resembing flat. If you need low-speed torque, then you can get
an IC engine rated about a third of normal and hook it to a generator
and electric motor (usually 100% of rated torque at 0 RPM). From your
specs I presume that;s not it.

So you need to look at how you're going to use the engine.

The short answer: 1 HP != 1 HP.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

A HP is an HP. It is equivalent to 33,000 lbs lifted 1 foot in one minute.
However, it is the test that is performed that may not make the numbers
comparable. The device that is used is called a dynometer. There are several
types in use, but they all do the same thing, put a load on the motor. The
variable load end floats on bearings and is anchored to the dyno frame by an
arm and lever arrangement. This is connected to a pressure gauge and
directly reads brake torque. When the torque, engine speed and air density
is known, horsepower can be computed. The problem is that these power tests
are usually not the same from tester to tester, dyno to dyno and engine
configuration. The very best you can do is to compare torque and power
charts across the power band as advertised. Certain assumptions can also be
made like two cycle engines have a narrower usable power band than four
strokes and diesel engines make more low speed torque than gasoline engines.
In your example where the Volvo outperforms your boat, it could be because
the Volvo has the enough midrange torque to reach maximum HP RPM and the
outboard never reaches its correct engine speed to develop its rated power.
However, it is more likely that the counter rotating props are simply more
efficient. An important factor that you did not mention is fuel efficiency.
It is technically termed Brake Mean Specific Fuel Consumption and is stated
in pounds (of fuel) per horsepower hour. Your outboard will be around .5 lbs
per hour and that diesel about .42. If you consider the weight difference by
volume of gasoline verses diesel, you are looking at 25% more gallons per
hour for the outboard. Some low speed diesels can achieve .37 pounds per
hour, but typically those engines power displacement type craft and are
rarely found in a recreational environment. Additionally, the diesel rig
will cost considerably more the outboard. You get what you pay for. You
would have to amortize the cost difference with hours of use, fuel cost and
resale value and only you can do that.
Steve

"Habbi" <habbi RemoveThis @islandtelecom.com> wrote in message
news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
 > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be equal
 > to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
 > when it come to performance but is it significant? In the same boat would
 > the diesel carry more load/ weight before becoming lugged? I have a 31' X
 > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp johnson.
 > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
 > duoprop which outperformes me unloaded and loaded. With an extra 1000 lbs
my
 > boat will not plane where as the other boat will. It seems like extra
weight
 > affects the 2 stroke much more than the diesel. How does a gas sterndrive
 > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
 > blade) and unloaded it barely reaches the recommended WOT. Thanks
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

On Sun, 22 Jun 2003 14:25:44 GMT, "Habbi" <habbi RemoveThis @islandtelecom.com>
wrote:
 >Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be equal
 >to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
 >when it come to performance but is it significant? In the same boat would
 >the diesel carry more load/ weight before becoming lugged? I have a 31' X
 >12' 9 degree V aluminum workboat which I outfitted with a 250 hp johnson.
 >There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
 >duoprop which outperformes me unloaded and loaded. With an extra 1000 lbs my
 >boat will not plane where as the other boat will. It seems like extra weight
 >affects the 2 stroke much more than the diesel. How does a gas sterndrive
 >compare as well. BTW I have the lowest pitch prop available (16 X 11 3
 >blade) and unloaded it barely reaches the recommended WOT. Thanks
========================================================
The diesel will produce it's rated horsepower at a lower RPM because
of higher torque. It will also usually produce it's rated power over
a broader RPM range as well. Other than that, a HP is a HP. There's
a possibility that you're not getting enough RPMs to reach rated
horsepower. It's also possible that the diesel is able to swing a
larger, more efficient prop because of it's higher torque.
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

There is a lot more in the equasion than horse power. The stern drive
will be carrying the engine weight a few feed forward of an outboard
which will in many cases help the boat plane easier. There can also be
a better mix of gear box ratio and prop on the stern drive. There could
also be some other subtle differences in hull shape other than dead rise.

Habbi wrote:
 > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be equal
 > to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
 > when it come to performance but is it significant? In the same boat would
 > the diesel carry more load/ weight before becoming lugged? I have a 31' X
 > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp johnson.
 > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
 > duoprop which outperformes me unloaded and loaded. With an extra 1000 lbs my
 > boat will not plane where as the other boat will. It seems like extra weight
 > affects the 2 stroke much more than the diesel. How does a gas sterndrive
 > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
 > blade) and unloaded it barely reaches the recommended WOT. Thanks
 >
 >


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: <a style='text-decoration: underline;' href="http://www.rutuonline.com" target="_blank">http://www.rutuonline.com</a>
Shameless Commercial Division: <a style='text-decoration: underline;' href="http://www.spade-anchor-us.com" target="_blank">http://www.spade-anchor-us.com</a><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

From what I have seen in my local harbours these Volvo duoprop diesels are
not slow moving by any means, some of the these workboat will achieve 50 mph
(radar checked) . The Volvo's turn up much higher than conventional diesels.
Many people around here are getting them out of X coast guard fast rescue
craft. In my case the similar boat to mine with a 230 hp Volvo outperforms
mine with the 250 Johnson in top speed unloaded and will remain on plane
with a much heavier load than mine. Unloaded mine turns up to the proper
6000 rpm. Put 1000 lbs in it and it will not plane.

"Glenn Ashmore" <rutu DeleteThis @bellsouth.net> wrote in message
news:3EF677B6.2020907@bellsouth.net...
 > There is a lot more in the equasion than horse power. The stern drive
 > will be carrying the engine weight a few feed forward of an outboard
 > which will in many cases help the boat plane easier. There can also be
 > a better mix of gear box ratio and prop on the stern drive. There could
 > also be some other subtle differences in hull shape other than dead rise.
 >
 > Habbi wrote:
  > > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be
equal
  > > to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
  > > when it come to performance but is it significant? In the same boat
would
  > > the diesel carry more load/ weight before becoming lugged? I have a 31'
X
  > > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp
johnson.
  > > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
  > > duoprop which outperformes me unloaded and loaded. With an extra 1000
lbs my
  > > boat will not plane where as the other boat will. It seems like extra
weight
  > > affects the 2 stroke much more than the diesel. How does a gas
sterndrive
  > > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
  > > blade) and unloaded it barely reaches the recommended WOT. Thanks
  > >
  > >
 >
 >
 > --
 > Glenn Ashmore
 >
 > I'm building a 45' cutter in strip/composite. Watch my progress (or lack
<font color=purple> > there of) at: <a style='text-decoration: underline;' href="http://www.rutuonline.com</font" target="_blank">http://www.rutuonline.com</font</a>>
<font color=purple> > Shameless Commercial Division: <a style='text-decoration: underline;' href="http://www.spade-anchor-us.com</font" target="_blank">http://www.spade-anchor-us.com</font</a>>
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

This all sounds like the old automobile "avertized" and "actual" horse power
thing to me. The horse power avertized is what the marketing types wish
they had Plus I've read more than once that the actual horse power
derived at the rear wheels is only somewhere in the 25 horse power range,
due to all the losses associated with the driveline and accessories (A/C,
Alternator, water pump and etc.)

I suspect there is some amount of "avertized" horse power in marine engines
as well. Plus there are various driveline impelmentations, hull shapes and
conditions, and much more. I'd guess even more varibles than on land.

Remember how fast Mercury engines use to be? I always heard they underrated
their engines to impress us with their "equal" horse power performance.
Maybe they still do.

Also, IMHO, diesel and more so European manufactures tend to use more honest
horse power ratings. In the good 'ol USA it is marketing, marketing,
marketing...

And, everybody knows anything can beat a Johnrude

"Habbi" <habbi DeleteThis @islandtelecom.com> wrote in message
news:gdBJa.2014$ps6.280665@ursa-nb00s0.nbnet.nb.ca...
 > From what I have seen in my local harbours these Volvo duoprop diesels are
 > not slow moving by any means, some of the these workboat will achieve 50
mph
 > (radar checked) . The Volvo's turn up much higher than conventional
diesels.
 > Many people around here are getting them out of X coast guard fast rescue
 > craft. In my case the similar boat to mine with a 230 hp Volvo
outperforms
 > mine with the 250 Johnson in top speed unloaded and will remain on plane
 > with a much heavier load than mine. Unloaded mine turns up to the proper
 > 6000 rpm. Put 1000 lbs in it and it will not plane.
 >
 > "Glenn Ashmore" <rutu DeleteThis @bellsouth.net> wrote in message
 > news:3EF677B6.2020907@bellsouth.net...
  > > There is a lot more in the equasion than horse power. The stern drive
  > > will be carrying the engine weight a few feed forward of an outboard
  > > which will in many cases help the boat plane easier. There can also be
  > > a better mix of gear box ratio and prop on the stern drive. There could
  > > also be some other subtle differences in hull shape other than dead
rise.
  > >
  > > Habbi wrote:
   > > > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be
 > equal
   > > > to a 250 hp 2 stroke outboard. Obviously the OB has the weight
advantage
   > > > when it come to performance but is it significant? In the same boat
 > would
   > > > the diesel carry more load/ weight before becoming lugged? I have a
31'
 > X
   > > > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp
 > johnson.
   > > > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo
diesel
   > > > duoprop which outperformes me unloaded and loaded. With an extra 1000
 > lbs my
   > > > boat will not plane where as the other boat will. It seems like extra
 > weight
   > > > affects the 2 stroke much more than the diesel. How does a gas
 > sterndrive
   > > > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
   > > > blade) and unloaded it barely reaches the recommended WOT. Thanks
   > > >
   > > >
  > >
  > >
  > > --
  > > Glenn Ashmore
  > >
  > > I'm building a 45' cutter in strip/composite. Watch my progress (or lack
<font color=green>  > > there of) at: <a style='text-decoration: underline;' href="http://www.rutuonline.com</font" target="_blank">http://www.rutuonline.com</font</a>>
<font color=green>  > > Shameless Commercial Division: <a style='text-decoration: underline;' href="http://www.spade-anchor-us.com</font" target="_blank">http://www.spade-anchor-us.com</font</a>>
  > >
  > >
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

As said previously, HP = HP but nature and human differs HP is a
definition of Work done and Torque is a definition of Force. They are
related in a formulae which is: HP = Torque * RPM / 5250

So in your example either:

-Engine A is not equal to engine B which is possible by a 10 % margin
-Stern drive is more efficient than outboard by a 15 % margin maybe
-Hull design, appendices can add a big % difference

You've not told us about the displacement of both boats. When you add 1000
pounds is it 1000 out of 10 000 or 20 000 ? Is the other boat you're
comparing exactly the same weight ?

All those differences add up to make a huge difference. In my own opinion
in your problem, the biggest factor is stern versus outboard. In boat
propulsion science, its not the engine but the way it translate its energy
to water that is the real problem.





"Habbi" <habbi RemoveThis @islandtelecom.com> wrote in message
news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
 > Is all horsepower the same? Would a 250 hp turbodiesel sterndrive be equal
 > to a 250 hp 2 stroke outboard. Obviously the OB has the weight advantage
 > when it come to performance but is it significant? In the same boat would
 > the diesel carry more load/ weight before becoming lugged? I have a 31' X
 > 12' 9 degree V aluminum workboat which I outfitted with a 250 hp johnson.
 > There is a similar boat 31' X 10' 13 degree V with a 230hp volvo diesel
 > duoprop which outperformes me unloaded and loaded. With an extra 1000 lbs
my
 > boat will not plane where as the other boat will. It seems like extra
weight
 > affects the 2 stroke much more than the diesel. How does a gas sterndrive
 > compare as well. BTW I have the lowest pitch prop available (16 X 11 3
 > blade) and unloaded it barely reaches the recommended WOT. Thanks
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

"Habbi" <habbi.RemoveThis@islandtelecom.com> wrote in message
news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
 > Is all horsepower the same?

No. There's SAE horsepower and DIN horsepower.

 > Would a 250 hp turbodiesel sterndrive be equal
 > to a 250 hp 2 stroke outboard.

No. Diesels are measured in DIN horsepower. That 250 DIN
horsepower turbodiesel will be about 400(?) SAE horsepower.
That outboard, a gas engine, is measured with a different
formula, called SAE horsepower.

It's wildly unrealistic to say that 2 stroke outboard, which
you can almost lift and hold in your arms, will do the work of
250 horses.

You can see the difference in the boating catalogues, in the
mufflers section. A certain muffler will be rated for a 25
HP diesel or a 40 HP gas engine. These engines put out the
same amount of exhaust, roughly meaning they will do the same
amount of work, which that size muffler can handle.

 > Obviously the OB has the weight advantage
 > when it come to performance but is it significant?

No, it's insignificant.

 > In the same boat would
 > the diesel carry more load/ weight before becoming lugged?

Sure. It's a lot more powerful.

 > I have a 31' X
 > 12' 9 degree V aluminum workboat which I outfitted with a
250 hp johnson.
 > There is a similar boat 31' X 10' 13 degree V with a 230hp
volvo diesel
 > duoprop which outperformes me unloaded and loaded. With an
extra 1000 lbs my
 > boat will not plane where as the other boat will. It seems
like extra weight
 > affects the 2 stroke much more than the diesel. How does a
gas sterndrive
 > compare as well.

A 250 horsepower gas sterndrive will perform exactly the same
as your present outboard. Since it's a US gasoline engine,
that'll be 250 SAE horsepower.

Now, there's nothing wrong with any of this. This is just how
the system has grown up. The trick is, you must specify
whether it's SAE or DIN horsepower and know what the terms
mean, that's all. Then you can know how strong the engine is,
which is what you want to do.

Yanmar sells two diesel outboards, a 28 and a 32 horsepower.
Someone in here pooh-poohed them because they're heavy and
expensive. They're really _very attractive, and here we start
to see why. Yanmar sells them as workboat engines.

Joe Kovacs
SV Sea Breeze
Cooper River Marina Charleston SC<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

Joe,
I hate to bust your bubble, but your reply here is full of wives tales.
Please refer to this reference:
<a style='text-decoration: underline;' href="http://neptune.spacebears.com/opine/horsepwr.html" target="_blank">http://neptune.spacebears.com/opine/horsepwr.html</a> You will see that for all
intent and purposes, DIN and SAE Net Horsepower are the same. I believe that
your performance comparisons and observations are due to torque curve
differences not horsepower.
Steve

"Joe Kovacs" <jak.DeleteThis@wuhal.mail.net> wrote in message
news:147Oa.39053$PD3.125131@nnrp1.uunet.ca...
 > "Habbi" <habbi.DeleteThis@islandtelecom.com> wrote in message
 > news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
  > > Is all horsepower the same?
 >
 > No. There's SAE horsepower and DIN horsepower.
 >
  > > Would a 250 hp turbodiesel sterndrive be equal
  > > to a 250 hp 2 stroke outboard.
 >
 > No. Diesels are measured in DIN horsepower. That 250 DIN
 > horsepower turbodiesel will be about 400(?) SAE horsepower.
 > That outboard, a gas engine, is measured with a different
 > formula, called SAE horsepower.
 >
 > It's wildly unrealistic to say that 2 stroke outboard, which
 > you can almost lift and hold in your arms, will do the work of
 > 250 horses.
 >
 > You can see the difference in the boating catalogues, in the
 > mufflers section. A certain muffler will be rated for a 25
 > HP diesel or a 40 HP gas engine. These engines put out the
 > same amount of exhaust, roughly meaning they will do the same
 > amount of work, which that size muffler can handle.
 >
  > > Obviously the OB has the weight advantage
  > > when it come to performance but is it significant?
 >
 > No, it's insignificant.
 >
  > > In the same boat would
  > > the diesel carry more load/ weight before becoming lugged?
 >
 > Sure. It's a lot more powerful.
 >
  > > I have a 31' X
  > > 12' 9 degree V aluminum workboat which I outfitted with a
 > 250 hp johnson.
  > > There is a similar boat 31' X 10' 13 degree V with a 230hp
 > volvo diesel
  > > duoprop which outperformes me unloaded and loaded. With an
 > extra 1000 lbs my
  > > boat will not plane where as the other boat will. It seems
 > like extra weight
  > > affects the 2 stroke much more than the diesel. How does a
 > gas sterndrive
  > > compare as well.
 >
 > A 250 horsepower gas sterndrive will perform exactly the same
 > as your present outboard. Since it's a US gasoline engine,
 > that'll be 250 SAE horsepower.
 >
 > Now, there's nothing wrong with any of this. This is just how
 > the system has grown up. The trick is, you must specify
 > whether it's SAE or DIN horsepower and know what the terms
 > mean, that's all. Then you can know how strong the engine is,
 > which is what you want to do.
 >
 > Yanmar sells two diesel outboards, a 28 and a 32 horsepower.
 > Someone in here pooh-poohed them because they're heavy and
 > expensive. They're really _very attractive, and here we start
 > to see why. Yanmar sells them as workboat engines.
 >
 > Joe Kovacs
 > SV Sea Breeze
 > Cooper River Marina Charleston SC
 >
 >
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

I extracted the only part of Joe's note that I felt almost comfortable
with.
I have pulled a 55HP 2-stroke, and it was not light.
I have installed an 85HP HP 2-stroke, and I could not hold it up.

So I agree that that any 2 stroke capable of putting out 250 HP would
be kinda hard/impossible to lift by hand, more so for a four stroke,
more so for a four stroke diesel.

Brian W

On Mon, 7 Jul 2003 01:00:09 -0400, "Joe Kovacs" <jak.DeleteThis@wuhal.mail.net>
wrote:

 >"Habbi" <habbi.DeleteThis@islandtelecom.com> wrote in message
 >news:I%iJa.1705$ps6.229286@ursa-nb00s0.nbnet.nb.ca...
  >> Is all horsepower the same?
 >
 >/snip/
 >It's wildly unrealistic to say that 2 stroke outboard, which
 >you can almost lift and hold in your arms, will do the work of
 >250 horses.
/snip/
 >Joe Kovacs
 >SV Sea Breeze
 >Cooper River Marina Charleston SC
 >
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: HP question 

Horsepower is horsepower is horsepower.................Steve hit it on the
money!

1 hp = 33,000 ft lb/min


There are indeed different aspects of horsepower :

Shaft Horsepower
Brake horsepower
Indicated Horsepower
Friction Horpower
etc.


Dave
 >> Stay informed about: HP question