Awhile back, I asked if anyone knew about techniques to temporarily
increase the power of a diesel similar to using nitrous oxide in a gas
engine. Today I got a JC Whitney catalogue and in it was a kit for
doing just that. I guess you would have improved power until the
nitrous ran out or till your engine overheated.
I wonder if you could adapt it for a small sailboat diesel.

Now, i wonder if you could have a duel fuel/duel ignition system where
it ran on gasoline for acceleration and on diesel for constant speed.

wrote:
Awhile back, I asked if anyone knew about techniques to temporarily
increase the power of a diesel similar to using nitrous oxide in a gas
engine. Today I got a JC Whitney catalogue and in it was a kit for
doing just that. I guess you would have improved power until the
nitrous ran out or till your engine overheated.
I wonder if you could adapt it for a small sailboat diesel.

There are all sorts of tricks you can do to get more power out of a
diesel engine. One of the simplest is just changing the injectors to a
larger orfice. Under lower throttle, it won't run much different but
more power will be available for full throttle, and that sounds like
what you want.

Now, i wonder if you could have a duel fuel/duel ignition system where
it ran on gasoline for acceleration and on diesel for constant speed.

Don't do it.

Steve

If your propeller is properly matched to the boat, the additional
power won't do anything on a displacement boat. A particular prop can
only put so much horsepower in the water unless the boat is light
enough and shaped so that it can enter the planing mode and continue
increasing the speed of the prop through the water. The prop on your
displacement sailing boat hull should be sized so that this limit is
reached just at hull speed and results in the engine being loaded to
it's maximum RPM.

If you put on a prop with enough diameter and pitch to use the
horsepower from your temporary boost gadget, it will be running the
engine harder all the time. In normal operation and lower than full
RPM, all speed settings will be producing higher horsepower at that
RPM. It would be like always lugging a manual car around one gear
lower. It's hard on the engine and results in shorter engine life.

90% of sailboats and most power yachts actually have props that are
too small. The horsepower of the engine in the brochure sells the boat
but it is a very rare buyer who understands the significance of the
prop size. I've seen countless boats with engines up to three times
the horsepower that the prop can use.

If you need more power, you can probably get it on your boat if there
is sufficient propeller clearance but you will pay a price in sailing
performance unless you get an expensive folding or feathering wheel.
Check your engine specs and find the maximum "Continuous" RPM. In
smooth water, the boat should reach this RPM just at full throttle.
Ideally, the exhaust will smoke black just a bit and then be clear
when you back off 100 RPM but this is hard to see with wet exhaust.

There may also be an "Intermittent" rating on your engine or, as in
the case of our Yanmar, a note that a higher RPM can be used for up to
an hour at a time. If you have frequent occasions when you need higher
power, such as bucking strong headwinds into a harbor entrance, you
might want to have the prop matched to this point at the expense of
slightly shorter engine life. Note that this will not increase the
smooth water speed of the boat significantly because that is limited
by the hull dynamics. When the boat speed is reduced by strong drag
such as from headwinds, the extra horsepower that the prop can put
into the water will be useful.

Unless there is a problem with the cooling system, the one hour
limitation (or more typical 10% of operating hours) is a bit of a
figment. The engine will not overheat or be damaged at the higher RPM
and you could actually run at the full "intermittent" RPM all day
long. You will be shortening engine life but it's not going to result
in a tow home unless the engine has other problems. In the typical
sailboat duty cycle, you will probably never see the difference in
engine life. The boat will wear out or be sold first.

Engine manufacturers promise a certain number of hours before
overhaul. The intermittent limitations are crude guidelines to
operation that will give the engine a reasonable chance of running
that many hours before major work is needed. Hours are a very poor way
to do this but are used because they can be determined by an hour
counter on the engine. The primary determinant of engine life in the
real world is the total amount of fuel that flows through the
cylinders. Manufacturers assume that engines will be generally
operated at or near maximum power so the intermittent RPM ratings are
to indirectly limit the total fuel burned while balls to the wall to
an amount that will not result in too many complaints about engines
that wore out prematurely.

If you have two RPM ratings for your engine, do this:

Find the TBO (expected time between overhauls) for your engine. Take
the GPH at the continuous RPM and multiply by that number of hours.
Then divide by the GPM at the intermittent power setting. That will be
the difference in engine life. Decide if it is worth it. In a
sailboat, you may well look at the lower figure on a new engine and
realize that you will be in a nursing home or dead long before you
could run that many hours. In that case, what the hell?

Before selecting a prop for that higher power setting or operating at
it consistently, you do need to insure that the cooling system and
engine room ventilation are set up so that the operating temperatures
of the oil, cylinder heads, etc., will remain in a steady state beyond
an hour. If the engine was installed properly, they should.

There is a downside aside from drag to installing a prop for more
power that you need to consider. Most props on sailboats are too small
for the engine. You have to increase the area of the blades to develop
more power. Most props have very limited clearance between the tips
and the hull. Ideally, it should be 20% for smooth running. On no
account should the clearance be less than 10% although this is very
common. To get more blade area, you will probably have to add blades.

A prop blade is just a rotating wing or foil developing lift. A
characteristic of any foil is a vortex at the tip that accounts for a
large part of the drag. In the case of a prop, this drag is sideways.
This drag is effected by the presence of something like a hull near
the tips which results in this force being very asymmetrical in a
boat. This is why the prop slews the stern to one side. The less
clearance between the hull and prop tips, the more pronounced this
effect will be. When you go from a two blade prop to a three blade in
order to get more area, you add a tip and increase this tip effect by
50%. The result may be that a boat which used to back up or stop with
reverse controllably becomes a bitch to handle. Converting from a two
blade to a three blade OF THE SAME BLADE AREA may improve reverse
handling but doing it to increase blade area and performance may
result in handling characteristics while docking that make you wish
for your old prop back. This can be a real disappointment after
spending a grand or more on a new wheel.


--

Roger Long




wrote in message
oups.com...
Awhile back, I asked if anyone knew about techniques to temporarily
increase the power of a diesel similar to using nitrous oxide in a
gas
engine. Today I got a JC Whitney catalogue and in it was a kit for
doing just that. I guess you would have improved power until the
nitrous ran out or till your engine overheated.
I wonder if you could adapt it for a small sailboat diesel.

Now, i wonder if you could have a duel fuel/duel ignition system
where
it ran on gasoline for acceleration and on diesel for constant
speed.

I have found your post educative.
I'll like to put in my two cents on the table.
My observation is get the pitch of your propeller verified by a prop. shop
before doing anything.
Usually the propellers are casted out of bronze alloy. The sand mold is
normally made to a certain diameter and pitch. When it comes out of the
mold no further fine turning is done on the propeller. On my prop. I had 12
X 12 stamped on the hub. Using the commercial fishermen language it means
one turn will move the boat 12 inches forward. One year I had my prop.
check by a specialist and found that it was not made to a 12 degrees pitch.
The actual pitch was two degrees less. My prop. was reset using the proper
dies and punches and three degrees were added to the pitch.
Like you have stated it did not had speed in calm water but getting into a
safe harbor appears to move a little faster with less vibration at lower
RPM's.


"Roger Long" wrote in message
...
If your propeller is properly matched to the boat, the additional
power won't do anything on a displacement boat. A particular prop can
only put so much horsepower in the water unless the boat is light
enough and shaped so that it can enter the planing mode and continue
increasing the speed of the prop through the water. The prop on your
displacement sailing boat hull should be sized so that this limit is
reached just at hull speed and results in the engine being loaded to
it's maximum RPM.

If you put on a prop with enough diameter and pitch to use the
horsepower from your temporary boost gadget, it will be running the
engine harder all the time. In normal operation and lower than full
RPM, all speed settings will be producing higher horsepower at that
RPM. It would be like always lugging a manual car around one gear
lower. It's hard on the engine and results in shorter engine life.

90% of sailboats and most power yachts actually have props that are
too small. The horsepower of the engine in the brochure sells the boat
but it is a very rare buyer who understands the significance of the
prop size. I've seen countless boats with engines up to three times
the horsepower that the prop can use.

If you need more power, you can probably get it on your boat if there
is sufficient propeller clearance but you will pay a price in sailing
performance unless you get an expensive folding or feathering wheel.
Check your engine specs and find the maximum "Continuous" RPM. In
smooth water, the boat should reach this RPM just at full throttle.
Ideally, the exhaust will smoke black just a bit and then be clear
when you back off 100 RPM but this is hard to see with wet exhaust.

There may also be an "Intermittent" rating on your engine or, as in
the case of our Yanmar, a note that a higher RPM can be used for up to
an hour at a time. If you have frequent occasions when you need higher
power, such as bucking strong headwinds into a harbor entrance, you
might want to have the prop matched to this point at the expense of
slightly shorter engine life. Note that this will not increase the
smooth water speed of the boat significantly because that is limited
by the hull dynamics. When the boat speed is reduced by strong drag
such as from headwinds, the extra horsepower that the prop can put
into the water will be useful.

Unless there is a problem with the cooling system, the one hour
limitation (or more typical 10% of operating hours) is a bit of a
figment. The engine will not overheat or be damaged at the higher RPM
and you could actually run at the full "intermittent" RPM all day
long. You will be shortening engine life but it's not going to result
in a tow home unless the engine has other problems. In the typical
sailboat duty cycle, you will probably never see the difference in
engine life. The boat will wear out or be sold first.

Engine manufacturers promise a certain number of hours before
overhaul. The intermittent limitations are crude guidelines to
operation that will give the engine a reasonable chance of running
that many hours before major work is needed. Hours are a very poor way
to do this but are used because they can be determined by an hour
counter on the engine. The primary determinant of engine life in the
real world is the total amount of fuel that flows through the
cylinders. Manufacturers assume that engines will be generally
operated at or near maximum power so the intermittent RPM ratings are
to indirectly limit the total fuel burned while balls to the wall to
an amount that will not result in too many complaints about engines
that wore out prematurely.

If you have two RPM ratings for your engine, do this:

Find the TBO (expected time between overhauls) for your engine. Take
the GPH at the continuous RPM and multiply by that number of hours.
Then divide by the GPM at the intermittent power setting. That will be
the difference in engine life. Decide if it is worth it. In a
sailboat, you may well look at the lower figure on a new engine and
realize that you will be in a nursing home or dead long before you
could run that many hours. In that case, what the hell?

Before selecting a prop for that higher power setting or operating at
it consistently, you do need to insure that the cooling system and
engine room ventilation are set up so that the operating temperatures
of the oil, cylinder heads, etc., will remain in a steady state beyond
an hour. If the engine was installed properly, they should.

There is a downside aside from drag to installing a prop for more
power that you need to consider. Most props on sailboats are too small
for the engine. You have to increase the area of the blades to develop
more power. Most props have very limited clearance between the tips
and the hull. Ideally, it should be 20% for smooth running. On no
account should the clearance be less than 10% although this is very
common. To get more blade area, you will probably have to add blades.

A prop blade is just a rotating wing or foil developing lift. A
characteristic of any foil is a vortex at the tip that accounts for a
large part of the drag. In the case of a prop, this drag is sideways.
This drag is effected by the presence of something like a hull near
the tips which results in this force being very asymmetrical in a
boat. This is why the prop slews the stern to one side. The less
clearance between the hull and prop tips, the more pronounced this
effect will be. When you go from a two blade prop to a three blade in
order to get more area, you add a tip and increase this tip effect by
50%. The result may be that a boat which used to back up or stop with
reverse controllably becomes a bitch to handle. Converting from a two
blade to a three blade OF THE SAME BLADE AREA may improve reverse
handling but doing it to increase blade area and performance may
result in handling characteristics while docking that make you wish
for your old prop back. This can be a real disappointment after
spending a grand or more on a new wheel.


--

Roger Long




wrote in message
oups.com...
Awhile back, I asked if anyone knew about techniques to temporarily
increase the power of a diesel similar to using nitrous oxide in a
gas
engine. Today I got a JC Whitney catalogue and in it was a kit for
doing just that. I guess you would have improved power until the
nitrous ran out or till your engine overheated.
I wonder if you could adapt it for a small sailboat diesel.

Now, i wonder if you could have a duel fuel/duel ignition system
where
it ran on gasoline for acceleration and on diesel for constant
speed.

It would work, .... until you ripped the engine from its mounts or
burned a hole in the top of a piston.


n article .com,
wrote:

Awhile back, I asked if anyone knew about techniques to temporarily
increase the power of a diesel similar to using nitrous oxide in a gas
engine. Today I got a JC Whitney catalogue and in it was a kit for
doing just that. I guess you would have improved power until the
nitrous ran out or till your engine overheated.
I wonder if you could adapt it for a small sailboat diesel.

Now, i wonder if you could have a duel fuel/duel ignition system where
it ran on gasoline for acceleration and on diesel for constant speed.

wrote in
oups.com:

Now, i wonder if you could have a duel fuel/duel ignition system where
it ran on gasoline for acceleration and on diesel for constant speed.



NO NO NO! Never let a diesel breath gas fumes! 21:1 compression will
self-ignite any type of vapor. The resulting "knock" will push the piston
rod right through the piston....just like in a pre-igniting gas engine.
You cannot turn a high compression diesel engine into a low compression gas
engine. Put it out of your mind.....

If you want more diesel power...buy a diesel with more cylinders:
or one with bigger cylinders....(c;
http://www.bath.ac.uk/~ccsshb/12cyl/
is 108,000 HP enough? It runs on near crude oil, not diesel at
$2.25/USGallon

--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.

In article ,
"Roger Long" wrote:

Unless there is a problem with the cooling system, the one hour
limitation (or more typical 10% of operating hours) is a bit of a
figment. The engine will not overheat or be damaged at the higher RPM
and you could actually run at the full "intermittent" RPM all day
long.

Minor points:

I found that at 3400, our Yanmar overheats in just under an hour as
advertised. At 3200, I can run until the fuel runs out. We are propped
for 3400 max, so I'm happy.

In article ,
"Denis Marier" wrote:

My observation is get the pitch of your propeller verified by a prop.
shop before doing anything.

snip On my prop. I had 12 X 12 stamped on the hub. The actual
pitch was two degrees less.

Full agreement. Ours averaged the right pitch, but one blade was an inch
shy, the other an inch high. Fixing that got rid of a lot of vibration.

"Steven Shelikoff" wrote in message

So I completely disagree with your assertion that all the
engine/prop should
have to do is just reach hull speed when loaded to it's maximum RPM.
IMHO, that is an unsafe setup because you have no margin for bad
weather.

That's because you don't fully understand it after a very brief post
on a complex subject. I was not talking about the selection of total
horsepower for the vessel which is a different parameter. The
horsepower / speed curve is going pretty close to straight up at hull
speed so the difference between an engine with just enough power to
get to hull speed and one with power margin will not change the prop /
hull relationships that much.

99.98% of sailboats and most powerboats are going to have what is know
as a "free running" wheel which is optimized for the upper speed
range. There is a limit to how much power the prop can produce which
is dependent on the area of the blades. If this is exceeded, the
pressure differential that drives the boat becomes high enough that
the pressure on the front of the blades will be low enough to boil the
water at ambient temperature. The resulting bubbles drive the
efficiency of the blades way down, erode the metal when they collapse,
and causes vibration. Power increase is marginal and can even go
down.

Blade pressures also increase as the speed the prop is moving through
the water goes down as with an external drag such as a headwind or a
tow. This means that the prop has to get bigger. Just look at the
prop on a towboat and a regular powerboat of the same horsepower.
When designing a towing wheel you input a very low figure like 4 knots
into the propeller calculation instead of the vessel's potential
speed. The result is a very large prop and higher fuel consumption
when running free. It would also be a lot of drag for a sailboat.

--

Roger Long

And:

If your boat is marginally powered, you could reduce the pitch so that
the engine will reach maximum RPM slightly before hull speed. This
will optimize it for lower speed you make in a headwind but you may
have to be careful about over speed depending on your governor set up.

You will only gain from this if blade area is sufficient. In most
sailboats, it is not. This also means that the engine will be running
at a slightly higher RPM for all boat speeds which means more noise
and wear.

If you have the engine power you need in headwinds, and the prop area
for maximum efficiency free running, optimizing the prop as I
described will still leave you with the bucking power you need in all
but the worst conditions. Very few people would want to lug the prop
necessary to deal with those forces around all the time unless it is
feathering. Very few sailboats will have been built with sufficient
prop clearance to install such a prop even if it is feathering. You
would have to plan for this at the design stage.

--

Roger Long