To refresh. I've got an "85" OMC 1.6L seadrive with a 13 1/4 X 17 prop
on it that needs replacing.

The nice folks at West Marine were kind enough to send me a huge catalog
full of things I can't afford but, since replacing the prop is a
necessity that was one of the things that got some serious attention.

My question relates to the ProPulse composite material, adjustable pitch
prop. I'm figuring on dropping over there sometime next week to take a
look at one and the Michigan Wheel Vortex but until then.....

West lists the flex of the composite as about the same as the aluminum
prop so I figure that and the reduced weight over an aluminum prop is
going to be a plus. Don't bother with that little item, you won't change
my mind. I've been working on my own vehicles, cars and motorcycles,
since I was fourteen and it doesn't take a rocket scientist to know that
the less hardware you have to sling around the more the horses get
translated into power output.

So, anyone with any experience with these props?

Further, from the chart I will either have to sacrifice a 1/4" on the
diameter or gain 3/4" since the props appear to come, as far as my needs
go, in only 13" or 14". What can I expect in operation if I sacrifice
the 1/4" or go for the 3/4" gain? Assuming I keep the 17" pitch that is.


Here's a thanks up front.

--
Mike G.
Heirloom Woods

www.heirloom-woods.net

Mike G wrote:

To refresh. I've got an "85" OMC 1.6L seadrive with a 13 1/4 X 17 prop
on it that needs replacing.

The nice folks at West Marine were kind enough to send me a huge catalog
full of things I can't afford but, since replacing the prop is a
necessity that was one of the things that got some serious attention.

My question relates to the ProPulse composite material, adjustable pitch
prop. I'm figuring on dropping over there sometime next week to take a
look at one and the Michigan Wheel Vortex but until then.....

West lists the flex of the composite as about the same as the aluminum
prop so I figure that and the reduced weight over an aluminum prop is
going to be a plus. Don't bother with that little item, you won't change
my mind. I've been working on my own vehicles, cars and motorcycles,
since I was fourteen and it doesn't take a rocket scientist to know that
the less hardware you have to sling around the more the horses get
translated into power output.

So, anyone with any experience with these props?

Further, from the chart I will either have to sacrifice a 1/4" on the
diameter or gain 3/4" since the props appear to come, as far as my needs
go, in only 13" or 14". What can I expect in operation if I sacrifice
the 1/4" or go for the 3/4" gain? Assuming I keep the 17" pitch that is.


Here's a thanks up front.


You're not going to thank too many people.

Don't do it(composite).

They make fine lightweight spares, that won't ding up your stowage area,
but are a performance compromise.

Your weight arguement doesn't hold water, either(pun intended).

Best performance with the OMCDrive is achieved with the arguably
heavier, but much better design of a stainless prop similar to the
aluminum you have been using... much better bite, thinner blades, better
balance. You will achieve a better running attitude under way - faster
- with more boat out of the water properly trimmed.

Of course, if you like the prop you have now, why not just have it
reconditioned? Most experienced, reputable shops can often make them
better than new.


Rob

In article ,
says...
You're not going to thank too many people.

Don't do it(composite).

They make fine lightweight spares, that won't ding up your stowage area,
but are a performance compromise.

Your weight arguement doesn't hold water, either(pun intended).

Best performance with the OMCDrive is achieved with the arguably
heavier, but much better design of a stainless prop similar to the
aluminum you have been using... much better bite, thinner blades, better
balance. You will achieve a better running attitude under way - faster
- with more boat out of the water properly trimmed.

Of course, if you like the prop you have now, why not just have it
reconditioned? Most experienced, reputable shops can often make them
better than new.


Rob




Thanks for the reply Rob, I'll keep your points in mind.

A SS prop isn't a consideration for me. I fish a rocky coast and
sometimes in shallow water and I can't see the benefits of the stainless
being cost effective in my situation. It hasn't happened yet but one of
these days I know I'll probably ding up a prop and I'd just as soon it
be one easily and inexpensively repaired.

The old prop is pitted and with a chunk missing. I will get it repaired
and put it aside for a spare but will, if I replace it with an aluminum
prop, get a duplicate of the 13 1/4 X 17 I have now. Most likely a
Michigan wheel product. I'm 99% sure the existing prop is the original
"85" prop with no cup. I figure that even if I go with a straight
replacement the newer designs might be of some additional help.

As a side note, I once had a Triumph TR 650C. One winter I stripped the
engine down and quasi blue printed it. Mostly just cleaning up the
moving parts, polishing, removing flashings from the connecting rods and
rocker arm assembly, in general just taking off excess metal down close
to what the optimal specs said they should be. No new pistons, shaved
heads, etc. Come spring I ran it down to the shop and had it put on a
dyno. Picked up around 8 HP just for shaving off not too many ounces of
excess metal.

Wish I could say the same for the Lucas electrics though.

Thanks again and take care.
Mike

--
Mike G.
Heirloom Woods

www.heirloom-woods.net

I second the fact that composite props are good as a spare but provide poor
overall performance compared to other props.
Michigan Wheel props are ok in aluminum but don't waist your time or money
on a SS one. Poor design.
If you want the boat to run at optimum performance thru out the entire
operating range - go w/ a good 4 blade SS for your application. You won't
believe the difference. Yes it will cost more but you should be able to
find a good one on ebay.
As for your concern about hitting something w/ the SS prop - When the
aluminum will peal an ear off - the SS will have a very small nick if
anything. Yes - they can be tore up if you hit a rock at speed but just
bumping the bottom you probably will not even know it. And don't believe
the tale of tearing up a gearcase. The prop has the same hub in it as an
aluminum (rubber). This will give way long before the propshaft or gears
(SS). Lower units get tore up due to hitting the object w/ the gearcase as
well as the prop or hitting a rock at full speed. Not by hitting a rock
while easing along.

Bottom line - stay w/ the aluminum if you want to spend $100 or so and have
it tear up everytime you hit a twig in the water.
Go SS if you want optimum performance and the prop to last. Should be able
to find one used for around $200 or less.

Tony

"Mike G" wrote in message
ews.com...
In article ,
says...
You're not going to thank too many people.

Don't do it(composite).

They make fine lightweight spares, that won't ding up your stowage area,
but are a performance compromise.

Your weight arguement doesn't hold water, either(pun intended).

Best performance with the OMCDrive is achieved with the arguably
heavier, but much better design of a stainless prop similar to the
aluminum you have been using... much better bite, thinner blades, better
balance. You will achieve a better running attitude under way - faster
- with more boat out of the water properly trimmed.

Of course, if you like the prop you have now, why not just have it
reconditioned? Most experienced, reputable shops can often make them
better than new.


Rob




Thanks for the reply Rob, I'll keep your points in mind.

A SS prop isn't a consideration for me. I fish a rocky coast and
sometimes in shallow water and I can't see the benefits of the stainless
being cost effective in my situation. It hasn't happened yet but one of
these days I know I'll probably ding up a prop and I'd just as soon it
be one easily and inexpensively repaired.

The old prop is pitted and with a chunk missing. I will get it repaired
and put it aside for a spare but will, if I replace it with an aluminum
prop, get a duplicate of the 13 1/4 X 17 I have now. Most likely a
Michigan wheel product. I'm 99% sure the existing prop is the original
"85" prop with no cup. I figure that even if I go with a straight
replacement the newer designs might be of some additional help.

As a side note, I once had a Triumph TR 650C. One winter I stripped the
engine down and quasi blue printed it. Mostly just cleaning up the
moving parts, polishing, removing flashings from the connecting rods and
rocker arm assembly, in general just taking off excess metal down close
to what the optimal specs said they should be. No new pistons, shaved
heads, etc. Come spring I ran it down to the shop and had it put on a
dyno. Picked up around 8 HP just for shaving off not too many ounces of
excess metal.

Wish I could say the same for the Lucas electrics though.

Thanks again and take care.
Mike

--
Mike G.
Heirloom Woods

www.heirloom-woods.net

Mike G wrote:


As a side note, I once had a Triumph TR 650C. One winter I stripped the
engine down and quasi blue printed it. Mostly just cleaning up the
moving parts, polishing, removing flashings from the connecting rods and
rocker arm assembly, in general just taking off excess metal down close
to what the optimal specs said they should be. No new pistons, shaved
heads, etc. Come spring I ran it down to the shop and had it put on a
dyno. Picked up around 8 HP just for shaving off not too many ounces of
excess metal.

Wish I could say the same for the Lucas electrics though.

Thanks again and take care.
Mike


Moving parts... that's reciprocating mass as you've described. That
will make a difference... but with a prop, in water, the extra
performance of a ss prop far outweighs the negligible additional
rotational mass of a 7.5" radius, partial wheel, with most of the mass
even closer to the center... especially comparing the difference from
alum to ss. Thrust into the water is the force you are dealing with
here. Heck, 4 blade props weighing 33%+ more than a 3 blade don't even
make a noticeable difference do to mass.

Rob

Mike G wrote:
To refresh. I've got an "85" OMC 1.6L seadrive with a 13 1/4 X 17 prop
on it that needs replacing.

The nice folks at West Marine were kind enough to send me a huge catalog
full of things I can't afford but, since replacing the prop is a
necessity that was one of the things that got some serious attention.

My question relates to the ProPulse composite material, adjustable pitch
prop. I'm figuring on dropping over there sometime next week to take a
look at one and the Michigan Wheel Vortex but until then.....

West lists the flex of the composite as about the same as the aluminum
prop so I figure that and the reduced weight over an aluminum prop is
going to be a plus. Don't bother with that little item, you won't change
my mind. I've been working on my own vehicles, cars and motorcycles,
since I was fourteen and it doesn't take a rocket scientist to know that
the less hardware you have to sling around the more the horses get
translated into power output.

So, anyone with any experience with these props?

Further, from the chart I will either have to sacrifice a 1/4" on the
diameter or gain 3/4" since the props appear to come, as far as my needs
go, in only 13" or 14". What can I expect in operation if I sacrifice
the 1/4" or go for the 3/4" gain? Assuming I keep the 17" pitch that is.


Here's a thanks up front.


The composite props probably do flex a little bit but aluminium boat
props don't "flex" to the extent commonly believed. Indeed anyone with
any experience of aluminium will know that aluminium props, particularly
the thinner tip areas, would have a very very short life if the blades
were "flexing" back & forth on every revolution, what?? 3000 times a
minute at WOT??? snap:-)

The major reason stainless props perform better than alloy ones is the
blades' profile is thinner for the same strength, i.e. much stronger
(yes, yes & heavier:-)) material for a given volume allows thinner &
better finished blades. The extra weight of the material is even
compensated a little by needing less volume to achieve the same or
better strength.

Composites are light for a given strength but not very dense (i.e. big
on volume, well under 2 tonne a m3) so they lend themselves to
applications where weight to strength is paramount & volume is not as
important; say aircraft, race car or yacht rig components.

Aluminium alloy is also light for it's strength but again not very
dense (i.e. big on volume, only around 2.7tonne a m3), as above, good
where weight is a priority or as in this case corrosion resistance vs
strength vs ease/cost to mass produce, volume comes a long last:-).

Steel, stainless or otherwise, is heavy for it's strength indeed
composites can easily exceed the strength of steel but always when
compared weight vs weight (mass actually before you yell at me Del:-))
but steel is very dense (i.e. low on volume, around 7 tonne a m3) so
despite is relatively low strength it can achieve a given strength
target in less volume, so when weight isn't as critical a consideration
but least volume for a given strength is; then steel can & oft does win.

A boat prop is like most things moving in a fluid & trying to achieve a
driving reaction by displacing the fluid beit a boat prop or an
aeroplane wing, in that they consume power in two ways;
(a) the first is the usual parasitic surface drag caused by the object
being forced through a fluid, beit a boat or aeroplane hull or a boat or
aeroplane propeller. Clearly anything that can be done to minimise this
primary "drag" saves power like; smooth surfaces (i.e. a shiny stainless
prop vs painted or pitted alloy surface) means lass surface drag. The
next thing to minimise primary drag is to use a shape that will least
resist flow over/around the surface (i.e. sharp entry, minimum
thickness, the faster the article is traveling through the fluid the
more critical this is) So seeing water is about 600 times more dense a
fluid than air & boat props are moving through is a huge blade speeds,
this primary drag is a very significant consumer of HP & it is totally
wasted HP because it doesn't contribute to thrust.
(b) the second drag is the drag created by the actual displacement of
the fluid the article is being forced through (i.e. the angle of attack)
the higher the angle of attack, up to a certain point, the greater the
displacement of fluid & therefore the greater the secondary "drag" or
consumption of HP. This is the drag that does create thrust & ensuring
the fluid is displaced at an even pressure over the entire surface is
important to efficiency, so propeller blades are twisted such that every
part of the blade sees the same pressure over most of the blade's surface.

So composite blades might flex a little but alloy blades do only a very
little, what does matter is the surface finish & thickness of the blades
for a given strength & this is why diam for diam, pitch for pitch the
stainless props perform better, because they waste less of the available
HP overcoming primary drag, this means more of the available HP left for
secondary drag which, if the blade wing or whatever is properly shaped,
is translated into thrust or lift.


K

If you want the boat to run at optimum performance thru out the entire
operating range - go w/ a good 4 blade SS for your application. You won't
believe the difference.

I've been talking to a prop shop about changing from a 14.5 X 19 X 3 alum.
to a 4 blade SS prop. The shop recommended a 14.5 X 17 X 4 but said that I
would loose 3-5 mph from the top end, I guess because of the drag of 4
blades. Is there any other size 4 blade that won't cut the top speed?

TIA
Rich

Rich wrote:

I've been talking to a prop shop about changing from a 14.5 X 19 X 3 alum.
to a 4 blade SS prop. The shop recommended a 14.5 X 17 X 4 but said that I
would loose 3-5 mph from the top end, I guess because of the drag of 4
blades. Is there any other size 4 blade that won't cut the top speed?

TIA
Rich




Not really, for the same reason that you give up some top speed going
from a 2 blade to a 3 blade. 1 blade props would give you best top
speed, but they are extremely difficult to balance.

4 & 5 blade props are very smooth and have good initial bite, but for
most applications the 3 blade is the best compromise. You are usually
better off going to a similar ss prop if you are going to make the step
from aluminum to ss. In ss grinds, there are so many different blade
designs, with different surface area, blade shapes, rakes, trailing and
leading edges, diameters, blade thicknesses, & so on, the better
question would be "which 3 blade?". A prop with larger surface area and
a double cup can be run higher on the transom.

Also, two apparently identical props out of the box will usually act
somewhat differently on the boat.

Rob

You should not go down in pitch from the 19 to a 17 by going to a 4 blade.
The 4 blade should be a smaller diameter (13.5 or so). This compensates for
the extra blade in terms of top end rpms. You will loose a couple mph on
top end w/ a 4 blade due to extra drag but the overall acceleration and
handling make up for it unless you are really into top speed.
You will notice a big drop going to a 17 from the 19. Sounds like the prop
shop has a 14.5 x 17 x 4 that they want to get rid of. You want a 13.5 x 19
x 4 SS in your application assuming your rpms are within 300 of max for your
engine.


--
Tony
My boats and autos - http://t.thomas.home.mchsi.com



"Rich" wrote in message
...
If you want the boat to run at optimum performance thru out the entire
operating range - go w/ a good 4 blade SS for your application. You
won't
believe the difference.

I've been talking to a prop shop about changing from a 14.5 X 19 X 3 alum.
to a 4 blade SS prop. The shop recommended a 14.5 X 17 X 4 but said that
I
would loose 3-5 mph from the top end, I guess because of the drag of 4
blades. Is there any other size 4 blade that won't cut the top speed?

TIA
Rich

You may be right on all your technical info but the true reason a SS prop
outperforms an aluminum one is due to blade design/shape. Not thickness.
SS props have a rake and can have bow lift and/or tail lift in them based on
the design. You can't achieve these kinds of shapes w/ aluminum and it hold
together.

--
Tony
My boats and autos - http://t.thomas.home.mchsi.com



"K. Smith" wrote in message
...
Mike G wrote:
To refresh. I've got an "85" OMC 1.6L seadrive with a 13 1/4 X 17 prop
on it that needs replacing.

The nice folks at West Marine were kind enough to send me a huge catalog
full of things I can't afford but, since replacing the prop is a
necessity that was one of the things that got some serious attention.

My question relates to the ProPulse composite material, adjustable pitch
prop. I'm figuring on dropping over there sometime next week to take a
look at one and the Michigan Wheel Vortex but until then.....

West lists the flex of the composite as about the same as the aluminum
prop so I figure that and the reduced weight over an aluminum prop is
going to be a plus. Don't bother with that little item, you won't change
my mind. I've been working on my own vehicles, cars and motorcycles,
since I was fourteen and it doesn't take a rocket scientist to know that
the less hardware you have to sling around the more the horses get
translated into power output.

So, anyone with any experience with these props?

Further, from the chart I will either have to sacrifice a 1/4" on the
diameter or gain 3/4" since the props appear to come, as far as my needs
go, in only 13" or 14". What can I expect in operation if I sacrifice
the 1/4" or go for the 3/4" gain? Assuming I keep the 17" pitch that is.


Here's a thanks up front.


The composite props probably do flex a little bit but aluminium boat
props don't "flex" to the extent commonly believed. Indeed anyone with
any experience of aluminium will know that aluminium props, particularly
the thinner tip areas, would have a very very short life if the blades
were "flexing" back & forth on every revolution, what?? 3000 times a
minute at WOT??? snap:-)

The major reason stainless props perform better than alloy ones is the
blades' profile is thinner for the same strength, i.e. much stronger
(yes, yes & heavier:-)) material for a given volume allows thinner &
better finished blades. The extra weight of the material is even
compensated a little by needing less volume to achieve the same or
better strength.

Composites are light for a given strength but not very dense (i.e. big
on volume, well under 2 tonne a m3) so they lend themselves to
applications where weight to strength is paramount & volume is not as
important; say aircraft, race car or yacht rig components.

Aluminium alloy is also light for it's strength but again not very
dense (i.e. big on volume, only around 2.7tonne a m3), as above, good
where weight is a priority or as in this case corrosion resistance vs
strength vs ease/cost to mass produce, volume comes a long last:-).

Steel, stainless or otherwise, is heavy for it's strength indeed
composites can easily exceed the strength of steel but always when
compared weight vs weight (mass actually before you yell at me Del:-))
but steel is very dense (i.e. low on volume, around 7 tonne a m3) so
despite is relatively low strength it can achieve a given strength
target in less volume, so when weight isn't as critical a consideration
but least volume for a given strength is; then steel can & oft does win.

A boat prop is like most things moving in a fluid & trying to achieve a
driving reaction by displacing the fluid beit a boat prop or an
aeroplane wing, in that they consume power in two ways;
(a) the first is the usual parasitic surface drag caused by the object
being forced through a fluid, beit a boat or aeroplane hull or a boat or
aeroplane propeller. Clearly anything that can be done to minimise this
primary "drag" saves power like; smooth surfaces (i.e. a shiny stainless
prop vs painted or pitted alloy surface) means lass surface drag. The
next thing to minimise primary drag is to use a shape that will least
resist flow over/around the surface (i.e. sharp entry, minimum
thickness, the faster the article is traveling through the fluid the
more critical this is) So seeing water is about 600 times more dense a
fluid than air & boat props are moving through is a huge blade speeds,
this primary drag is a very significant consumer of HP & it is totally
wasted HP because it doesn't contribute to thrust.
(b) the second drag is the drag created by the actual displacement of
the fluid the article is being forced through (i.e. the angle of attack)
the higher the angle of attack, up to a certain point, the greater the
displacement of fluid & therefore the greater the secondary "drag" or
consumption of HP. This is the drag that does create thrust & ensuring
the fluid is displaced at an even pressure over the entire surface is
important to efficiency, so propeller blades are twisted such that every
part of the blade sees the same pressure over most of the blade's surface.

So composite blades might flex a little but alloy blades do only a very
little, what does matter is the surface finish & thickness of the blades
for a given strength & this is why diam for diam, pitch for pitch the
stainless props perform better, because they waste less of the available
HP overcoming primary drag, this means more of the available HP left for
secondary drag which, if the blade wing or whatever is properly shaped,
is translated into thrust or lift.


K