PerfectPitch prop from CDI
 

Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2. This looks like a potentially good
candidate replacement because they have already figured out which prop
works for a given boat and because they say they can put a larger prop
on with their "Extendo" system.
I am a little worried about the plastic of this prop not being able to
take my aggressive barnacle removal method. Is it easy enough to
remove that re-painting it every so-often works?
My old bronze prop has succumbed to corrosion and many impacts with
oyster beds and with a Laser mast in the water.

Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag. How does one do this? Do you simply
mark the prop shaft inside the boat and then rotate it till your mark
is in the right place? This really seems like a PITA considering the
gawdawful engine installation on most boats. Even on my boat it
requires removing an engine panel and peering down into a dark space.
Is there any other system? Would the prop left in neutral auto-rotate
to the lowest drag position (I have never had a two blade prop so I
dont know) and stay?
Could I attach a magnet to the shaft so that it engages a magnetic
reed switch (non-contact) to tell me when it is in correct position?
Can you get it in correct position by "bumping" the start switch?

PerfectPitch prop from CDI
 

Frogwatch brought forth on stone tablets:
Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2. This looks like a potentially good
candidate replacement because they have already figured out which prop
works for a given boat and because they say they can put a larger prop
on with their "Extendo" system.
I am a little worried about the plastic of this prop not being able to
take my aggressive barnacle removal method. Is it easy enough to
remove that re-painting it every so-often works?
My old bronze prop has succumbed to corrosion and many impacts with
oyster beds and with a Laser mast in the water.

Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag. How does one do this? Do you simply
mark the prop shaft inside the boat and then rotate it till your mark
is in the right place? This really seems like a PITA considering the
gawdawful engine installation on most boats. Even on my boat it
requires removing an engine panel and peering down into a dark space.
Is there any other system? Would the prop left in neutral auto-rotate
to the lowest drag position (I have never had a two blade prop so I
dont know) and stay?
Could I attach a magnet to the shaft so that it engages a magnetic
reed switch (non-contact) to tell me when it is in correct position?
Can you get it in correct position by "bumping" the start switch?


If you want the prop to *stay* lined up with the keel, you'll need a
shaft lock.

When you install the shaft lock, set it up so that the prop is properly
lined up with the lock engaged.

see http://www.shaftlok.com/

bob
s/v Eolian
Seattle

PerfectPitch prop from CDI
 

RW Salnick brought forth on stone tablets:
Frogwatch brought forth on stone tablets:

Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2. This looks like a potentially good
candidate replacement because they have already figured out which prop
works for a given boat and because they say they can put a larger prop
on with their "Extendo" system.
I am a little worried about the plastic of this prop not being able to
take my aggressive barnacle removal method. Is it easy enough to
remove that re-painting it every so-often works?
My old bronze prop has succumbed to corrosion and many impacts with
oyster beds and with a Laser mast in the water.

Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag. How does one do this? Do you simply
mark the prop shaft inside the boat and then rotate it till your mark
is in the right place? This really seems like a PITA considering the
gawdawful engine installation on most boats. Even on my boat it
requires removing an engine panel and peering down into a dark space.
Is there any other system? Would the prop left in neutral auto-rotate
to the lowest drag position (I have never had a two blade prop so I
dont know) and stay?
Could I attach a magnet to the shaft so that it engages a magnetic
reed switch (non-contact) to tell me when it is in correct position?
Can you get it in correct position by "bumping" the start switch?


If you want the prop to *stay* lined up with the keel, you'll need a
shaft lock.

When you install the shaft lock, set it up so that the prop is properly
lined up with the lock engaged.

see http://www.shaftlok.com/

bob
s/v Eolian
Seattle

(stupidly replying to my own message)

Well, maybe your transmission doesn't freewheel... (I have a Borg
Warner Velvet Drive, which is kind of like an automatic - regardless of
the shift lever position, the output shaft freewheels when the engine is
not running).

If your transmission holds the shaft, then your suggestions seem like
good answers, if the shaft is inaccessible (doh! It's a SAILboat).

Beware of corrosion and salt spray from the stuffing box in whatever you
set up.

bob
s/v Eolian
Seattle

PerfectPitch prop from CDI
 

On Oct 15, 6:57 am, Frogwatch wrote:
...Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag....

Correct me if I am wrong but I believe the S2 8.5 is a fin keel, spade
rudder set-up with the prop just ahead of the rudder. In this case
there will seldom be any drag reduction advantage to aligning the
blades of the prop with the keel.

-- Tom.

PerfectPitch prop from CDI
 

On Oct 15, 3:45 pm, " wrote:
On Oct 15, 6:57 am, Frogwatch wrote:

...Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag....

Correct me if I am wrong but I believe the S2 8.5 is a fin keel, spade
rudder set-up with the prop just ahead of the rudder. In this case
there will seldom be any drag reduction advantage to aligning the
blades of the prop with the keel.

-- Tom.

why not?

PerfectPitch prop from CDI
 

On Oct 15, 10:10 am, Frogwatch wrote:
On Oct 15, 3:45 pm, " wrote:

On Oct 15, 6:57 am, Frogwatch wrote:

...Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag....

Correct me if I am wrong but I believe the S2 8.5 is a fin keel, spade
rudder set-up with the prop just ahead of the rudder. In this case
there will seldom be any drag reduction advantage to aligning the
blades of the prop with the keel.

-- Tom.

why not?

Because, unless the leeway angle is near zero the prop will not be in
the keel's wake. In cases where the prop is right behind the keel or
is in a cut-out in a two bladed prop can be hidden behind the keel or
skeg by aligning it. In your case the prop is a long way from the
keel and even a small amount of leeway will move it into the free
stream and in any case if the keel is well designed and in good
condition the wake two cord lengths back will be insignificant. So,
in your case alignment isn't likely to make a difference you can
measure most of the time. If you are concerned about drag I would
recommend a two bladed geared folding prop.

-- Tom.

PerfectPitch prop from CDI
 

On 2007-10-15 12:57:14 -0400, Frogwatch said:

Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2.

CDI really got my respect when they would NOT sell me one of those
blades because they hadn't yet gotten the numbers they advertise with
the blade they were developing for our engine.

Have you held one in your hand? A work of art.

I strongly believe that your experience with that prop will exceed
their promises. Take their recommendation of anti-growth system. And
get the biggest prop that will fit.

Don't bother trying to hide the prop behind the fin keel or strut. Just
stop it from turning some how.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

PerfectPitch prop from CDI
 

On Mon, 15 Oct 2007 21:20:57 -0000, "
wrote:

If you are concerned about drag I would
recommend a two bladed geared folding prop.

The earliest screw propellor equipped ships had props you could raise
out of the water to avoid drag while under sail, which was nearly all
the time.

Casady

PerfectPitch prop from CDI
 

Frogwatch wrote:
Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2. This looks like a potentially good
candidate replacement because they have already figured out which prop
works for a given boat and because they say they can put a larger prop
on with their "Extendo" system.
I am a little worried about the plastic of this prop not being able to
take my aggressive barnacle removal method. Is it easy enough to
remove that re-painting it every so-often works?
My old bronze prop has succumbed to corrosion and many impacts with
oyster beds and with a Laser mast in the water.

Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag. How does one do this? Do you simply
mark the prop shaft inside the boat and then rotate it till your mark
is in the right place? This really seems like a PITA considering the
gawdawful engine installation on most boats. Even on my boat it
requires removing an engine panel and peering down into a dark space.
Is there any other system? Would the prop left in neutral auto-rotate
to the lowest drag position (I have never had a two blade prop so I
dont know) and stay?
Could I attach a magnet to the shaft so that it engages a magnetic
reed switch (non-contact) to tell me when it is in correct position?
Can you get it in correct position by "bumping" the start switch?

Ever heard of a thing called paint? You can even mark a prop shaft with it.
I won't charge for this piece of wisdom as I learned it about fifty years
ago. (and the piant is still there!) You could easily fit a small glass
spyhole in the cockpit floor. However, some sailors would argue that
allowing the shaft to rotate in neutral causes less drag than locking it in
the upright position, particularly on a modern fin/skeg design.

Dennis.

Dennis.

PerfectPitch prop from CDI
 

On Oct 16, 4:29 am, "Dennis Pogson"
wrote:
Frogwatch wrote:
Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2. This looks like a potentially good
candidate replacement because they have already figured out which prop
works for a given boat and because they say they can put a larger prop
on with their "Extendo" system.
I am a little worried about the plastic of this prop not being able to
take my aggressive barnacle removal method. Is it easy enough to
remove that re-painting it every so-often works?
My old bronze prop has succumbed to corrosion and many impacts with
oyster beds and with a Laser mast in the water.

Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag. How does one do this? Do you simply
mark the prop shaft inside the boat and then rotate it till your mark
is in the right place? This really seems like a PITA considering the
gawdawful engine installation on most boats. Even on my boat it
requires removing an engine panel and peering down into a dark space.
Is there any other system? Would the prop left in neutral auto-rotate
to the lowest drag position (I have never had a two blade prop so I
dont know) and stay?
Could I attach a magnet to the shaft so that it engages a magnetic
reed switch (non-contact) to tell me when it is in correct position?
Can you get it in correct position by "bumping" the start switch?

Ever heard of a thing called paint? You can even mark a prop shaft with it.
I won't charge for this piece of wisdom as I learned it about fifty years
ago. (and the piant is still there!) You could easily fit a small glass
spyhole in the cockpit floor. However, some sailors would argue that
allowing the shaft to rotate in neutral causes less drag than locking it in
the upright position, particularly on a modern fin/skeg design.

Dennis.

Dennis.

I appreciate y'alls advice, especially tsmwebb and Jere Lull. For
those who suggest a folding/feathering prop, I do not consider this to
really be an option due to the extreme fouling conditions I
encounter. A friend who works in a boat yard says most he sees are
too fouled to work around here. Cost is another issue for a boat that
is 27 yrs old.
tsmwebb points out that the flow is rarely directly fore and aft and I
admit this had never occurred to me, however, is he correct? If he is
correct, I would not expect a 3 bladed prop to cause much loss of
sailing speed.
As far as using paint and a sight glass as Pogson suggests, this was
my initial idea but drilling a hole in my cockpit floor for the sight
seems sacriligeous. I could easily rig up the magnet and reed switch
I described. However, how easy is it to stop a prop in a given
position unless you rotatre the shaft by hand? Can you "bump" it with
the starter to a given position? I cannot believe that most sailors
take off their engine cover to peer down at the prop shaft whenever
they sail to align the prop with the keel.

PerfectPitch prop from CDI
 

On Oct 16, 4:29 am, "Dennis Pogson"
wrote:
Frogwatch wrote:
Anybody have experience with these? I am about to replace my fixed 3
bladed prop on my 8.5M S2. This looks like a potentially good
candidate replacement because they have already figured out which prop
works for a given boat and because they say they can put a larger prop
on with their "Extendo" system.
I am a little worried about the plastic of this prop not being able to
take my aggressive barnacle removal method. Is it easy enough to
remove that re-painting it every so-often works?
My old bronze prop has succumbed to corrosion and many impacts with
oyster beds and with a Laser mast in the water.

Now, one of the advantages of a 2 blade prop is that you can align it
with the keel for lower drag. How does one do this? Do you simply
mark the prop shaft inside the boat and then rotate it till your mark
is in the right place? This really seems like a PITA considering the
gawdawful engine installation on most boats. Even on my boat it
requires removing an engine panel and peering down into a dark space.
Is there any other system? Would the prop left in neutral auto-rotate
to the lowest drag position (I have never had a two blade prop so I
dont know) and stay?
Could I attach a magnet to the shaft so that it engages a magnetic
reed switch (non-contact) to tell me when it is in correct position?
Can you get it in correct position by "bumping" the start switch?

Ever heard of a thing called paint? You can even mark a prop shaft with it.
I won't charge for this piece of wisdom as I learned it about fifty years
ago. (and the piant is still there!) You could easily fit a small glass
spyhole in the cockpit floor. However, some sailors would argue that
allowing the shaft to rotate in neutral causes less drag than locking it in
the upright position, particularly on a modern fin/skeg design.

Dennis.

Dennis.

My primary motivations for being interested in CDI is that I hear so
many stories of ppl who get new props and they just are not right and
thye just live with it due to the cost of hauling to change them. CDI
seems to have gotten it right and their props are supposed to be easy
to change if not. They can be changed in the water .
Another reason for considering a two blade instead of simply replacing
my existing 3 blade is that I have been in a few races lately on
other boats and I might want to do club races in mine.

PerfectPitch prop from CDI
 

On Tue, 16 Oct 2007 08:07:09 -0700, Frogwatch
wrote:

I cannot believe that most sailors
take off their engine cover to peer down at the prop shaft whenever
they sail to align the prop with the keel.

I figure most sailors fart it off, and live with whatever drag it has.

Casady

PerfectPitch prop from CDI
 

On Oct 16, 5:07 am, Frogwatch wrote:
... tsmwebb points out that the flow is rarely directly fore and aft and I
admit this had never occurred to me, however, is he correct? If he is
correct, I would not expect a 3 bladed prop to cause much loss of
sailing speed. ...

Well, I think it's true. :) You can approximate the lateral
deflection of the keel wash by multiplying the distance from the
trailing edge of the keel to the prop by the tangent of you leeway
angle. My guess is that on your boat a degree of two of leeway angle
will send the wash wide of your two blader if it is locked up and
down. However, there is more to it than that. Your boat also has a
somewhat modern keel. The "standard" section on fin keels when your
S2 was designed was the NACA 63xxA. At small leeway angles this
section is very low drag. As a result, it has a very narrow and
relatively short wake. My recollection of the S2 8.5 is that the keel
is a couple of cord lengths ahead of the prop. At the speeds you are
likely to be going and if your keel is in good condition there really
shouldn't be a significant amount of keel wash left when it reaches
the prop even in the zero leeway angle case. So, I don't think your
prop will be in the keel wash in most cases regardless of leeway.
That's the bad news, because the speed of the water relative to the
prop in the keel wash is less than the free stream speed and drag is
primarily a function of that speed. But, that' still not the whole
story. The drag of the prop is proportional to its effective area
times the square of the speed of the water flowing over it.
Generally, two bladed props have less area than three blade props so
they have less drag. There are other complicating factors, but I
think it's a good bet that the two blade prop will be less draggy
under sail than the three blade one but it will not be as good as a
folding prop or a prop that is hidden behind the keel.

-- Tom.

PerfectPitch prop from CDI
 

On 2007-10-16 11:15:38 -0400, Frogwatch said:

Another reason for considering a two blade instead of simply replacing
my existing 3 blade is that I have been in a few races lately on other
boats and I might want to do club races in mine.

The 2-blade will probably be considerably less drag as I recall the CDI
blades being fairly high-aspect compared to the older 3-blade props.
They can afford to be because of the improved foil shape.

If you club race, you'll get a few seconds allowance for NOT having a
folding/feathering prop, but more important, in normal sailing, you'll
find yourself being able to sail in lighter air than you're used to.

We went from 2 blades to feathering 3-blade (to get rid of a harmonic
vibration) and move in amazingly light air. The only justification I
could give for getting that expen$ive prop was to amortize it over the
number of years we expected to have the boat, but it's proven to be
worth the investment -- to me.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/